Common frequency converter repair and maintenance

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Common repairs and maintenance for frequency converters; common faults of ABB frequency converters and corresponding repair measures. For the ACS300 frequency converter, a fault that we often encounter is damage to the switching power supply. The switching power supply of the ACS300 uses a waveform generator integrated circuit called LT1244, which has functions similar to those of the UC3844 chip. Damage to this integrated circuit often occurs due to sudden changes in operating voltage or damage to the load connected to the switching power supply. As a result of years of use, the electrolytic capacitors also reach the end of their useful life, and thus these capacitors become the direct cause of damage to the switching power supply. During maintenance, we find that the rectifier bridges in ACS300 frequency converters often get damaged. Perhaps for economic reasons, a compact three-phase full-bridge rectifier from an international rectifier manufacturer was chosen; it has a small size and low current-carrying capacity, as well as poor heat dissipation, which is why it gets damaged after being used for some time. The ACS300 main control board also experiences a fairly high rate of failures; communication issues between the control panel and the main board, as well as CPU failures on the main board, occur from time to time. Such failures are usually difficult to resolve. The ACS300 uses Mitsubishi’s IPM module, which results in a relatively low failure rate. If the module is damaged, it must be replaced; however, it is essential to ensure that the drive circuit is fully functional before making such a replacement. For the ACS500 inverter, a common fault is damage to the drive thick film. This drive thick film includes not only the drive circuit but also functions such as short-circuit detection, IGBT module detection, and overcurrent detection. Thanks to its robust protection features, the high-power modules of the ACS500 rarely get damaged. During repairs, if the drive thick-film component is damaged and no replacement parts are available, we can only repair the thick film itself. Since these thick-film components are soldered onto ceramic substrates, heat dissipation occurs quite rapidly; it is important to be careful not to damage the components by keeping the soldering iron applied to them for too long. Due to limitations related to the amount of time it is used, the cooling fan of the ACS500 can also fail. A common symptom is that only a \"buzzing\" sound is heard after power is applied, but the fan does not rotate. Since it is an axial flow fan, the fan coils and bearings are usually in good condition; upon inspection, it was found that the deflection capacitor was faulty, and normal operation was restored after replacing it. For the ACS600 inverter, its performance and quality are quite reliable. However, it can be damaged due to the influence of the surrounding environment, improper parameter settings, or incorrect operation. Of course, natural wear and tear is also an inevitable factor for inverters of all brands. Unlike previous ABB inverters, the ACS600 inverter uses fiber optic communication, **which increases the communication time between the CPU board and the I/O board. However, this may also lead to faults such as “LINK OR HWC” and “PPCC LINK”; the occurrence of such faults is not necessarily due to damage to the fiber optics. “ The “PPCC LINK” fault is a relatively common fault in ACS600 drives; damage to the CPU board or I/O board can both lead to this fault occurring. Damaged switching power supplies are also a problem in ACS600 frequency converters; the faults mainly occur in the switching transistors. Short circuits in these transistors often cause the power resistor used for current limiting to burn out as well. “The “SHORT CIRCUIT” output short-circuit fault is the most common type of fault we encounter. The ACS600 uses intelligent modules, and faults in the load or various issues that arise during operation can lead to damage to these modules. Damage to the modules often results in damage to the drive board as well. Since spare parts are relatively expensive, the cost of repairing frequency converters is also high; therefore, higher standards are required of technicians when it comes to performing board-level repairs. Regarding the newly launched ACS550 and ACS800 frequency converters, since they have been on the market for only a short time, there are no prominent or typical faults to discuss, so we will not cover them here. It can be said that ABB frequency converters still encounter various types of faults during use. Especially when the cost of spare parts is high, the need for board-level repairs increases, which places higher demands on repair technicians. It is also hoped that more people working in the field of frequency conversion and speed control will join this field in order to help solve various problems for end-users. It can be designed according to customer requirements, products can be provided, and upgrade services are available for customers. Common faults and repair solutions for LENTE frequency converters: For earlier models such as the 8100 and 8300 series of frequency converters, common faults include damage to the switching power supply; in most cases, it is the pulse transformer that is damaged. The resulting symptom is that the machine shows no response upon power-up, with no voltage at the control terminals. Since the core of the pulse transformer is not easy to disassemble, this poses certain difficulties in repairing the transformer. Moreover, the parameters of the pulse transformers used by different inverter brands vary, which also creates challenges for winding them. In the absence of replacement parts, it is generally difficult to repair such transformers under these circumstances. Given that the market for such machines is relatively small, we will not discuss it in detail. The OC5 fault is likely a fault phenomenon that we often encounter in the 8220/8240 series of frequency converters. OC5 indicates an overload condition of the inverter. Overload detection is generally carried out using Hall sensors; by measuring the currents in the U and V phases, a COMOS circuit with two input gates is used to determine whether the inverter is overloaded. The failure points of OC5 are usually caused by damaged sensors and faulty gate circuits. Hall sensors are susceptible to environmental influences, which can lead to shifts in their operating points, while gate circuits often get damaged due to variations in operating voltage or impacts from input signals. Replacing the damaged component should resolve such faults. Output phase loss is also one of the faults we encounter frequently. We all know that it’s impossible to drive a three-phase AC induction motor under conditions of phase loss; moreover, an overcurrent alarm will be triggered when attempting to do so. After disconnecting the motor, when we measure the three-phase output voltages, we often find that there is a significant difference between them. In such cases, we should first check whether the power module is damaged and whether the drive waveforms are normal. With the LENTE 8240 series of frequency converters, we often encounter the issue of no voltage in the drive circuit. The switching power supply is a circuit that must be checked. What sets the 8240 series inverters apart from other inverters is that the drive power is not supplied directly by the switching power supply; there is isolation between the drive circuit and the switching power supply. So we must also check whether there is a problem with the isolation transformer. By ruling out the above faults, it should be possible to determine whether the power supply for the drive circuit is functioning properly. Switching power supply failures: In the repair of 8200 series general-purpose inverters, we often encounter damaged switching power supplies. The main failure points are the damage to the power switch transistors and the damage to the control circuit of the switching power supply. The damaged switching transistors can be replaced relatively easily; both the original model of transistors and replacement transistors are available. However, repairing faults in the control circuit is more complex. The components of the control circuit in this type of machine are integrated on insulating ceramic substrates, making them difficult to replace, and it requires certain experience as well as repair skills. Faults caused by heat dissipation in frequency converters: The technology of separating heat dissipation via heat sinks is also a major selling point of LENNZE frequency converters. As we all know, conventional frequency converters rely on cooling fans for heat dissipation; however, in some applications, the use of such fans often becomes a common source of malfunctions in frequency converters. This phenomenon is mainly common in textile factories. Cotton fluff and synthetic fibers in the air of textile factories often clog the fans, triggering fault alarms in the frequency converters. The separate cooling technology of the heat sink in LENTE frequency converters precisely solves this problem. However, we also encounter situations where customers experience problems with the frequency converter being unable to handle heavy loads after using it for a while. Based on our experience, this could be caused by issues related to the frequency converter’s cooling; inadequate cooling leads to faster aging of the components and quicker wear and tear. Generally, in such cases, replacing the aged components can solve this problem. Furthermore, in practical applications, we can also determine the status and any faults of the frequency converter by checking the status of its LEDs, especially this method is more convenient when there is no control panel available. Generally, it is in the operating mode of the control panel when the green light is on and the red light is off. A flashing green light and a red light indicate that control is prohibited via the operation panel. The green light goes out, and the red light flashes once per second; at this point, the inverter is in a faulty state. It can be said that LENZE frequency converters still encounter various types of faults during use. The above provides a rough overview of some common faults and their analysis. LENZE frequency converters have notable advantages in terms of performance; features such as position control and synchronous control are among their strengths, which makes them worth studying for practical applications. Furthermore, from a maintenance perspective, the wiring of LENTE frequency converters is relatively complex, and the PCB boards feature multiple layers of wiring, which places higher demands on maintenance personnel. It is also hoped that those working in frequency converter maintenance will engage in more exchanges in order to solve more practical problems. LG inverter repair 1. OC fault Similar to other inverters, overcurrent alarms are also a common issue with LG inverters. Apart from problems related to parameter settings such as acceleration and deceleration times, the main hardware-related causes include damage to the high-power modules. High-power inverters may experience OC alarms due to damaged modules; low-power, cost-effective inverters use PIM modules produced by TYCO, while medium-power inverters use PIM modules from Fuji and IGBT modules from Mitsubishi. High-power inverters, on the other hand, utilize IGBT modules from Siemens. The damage to high-power modules can be caused by the following reasons: (1) A short circuit or missing phase in the output load; (2) An excessive load that results in continuous high currents; (3) Large fluctuations in the load, leading to excessive surge currents. All of these can trigger an OC alarm and cause damage to the power module. 2. HW fault This fault may be specific to the LG-IG5 series of inverters, and its main causes include the following possibilities: (1) Damage to the cooling fan. Due to factors such as the operating environment, excessive friction occurs in the fan bearings, resulting in a high fan load and consequently a HW failure; (2) Damage to the temperature detection circuit built into the power module can also cause HW failures; (3) Additionally, motherboard malfunctions are prone to causing HW failures as well. 3. Ground fault
Ground faults are also common types of faults we encounter in practice. Apart from issues related to improper grounding of the motor, the component most likely to malfunction is the Hall sensor. Due to influences from environmental factors such as temperature and humidity, the operating point of the Hall sensor can easily drift, resulting in a GF alarm. 　　 4. No display fault 　　A no-display fault is usually caused by damage to the switching power supply. Unlike conventional self-oscillating or externally-driven switching power supplies, LG inverters use a controllable voltage regulator called TL431 to adjust the duty cycle of the switching transistors, thereby achieving stable output voltage. When there is a load short circuit, it often causes the switching power supply to block the output, resulting in no display on the panel. 　 Like other frequency converters, issues such as LV and OV faults, as well as damage to the drive circuit, can also occur in LG frequency converters; therefore, we need to keep summarizing our experiences and seeking solutions through practice. 5. FU fault 　　Both the LG-IS5 and IH series of inverters are equipped with fast fuse protection. Since the breaking capacity of these fast fuses is around 5 ms, they can activate when a large current flows through the inverter, thereby protecting the high-power modules. However, the damage to the fast fuse also led to the occurrence of a FU fault. Replace the fast fuse. Common faults of frequency converters and their troubleshooting measures (Made in Taiwan). For Taian frequency converters, the N2 series is the one that we encounter most frequently in terms of faults. Common fault codes include overcurrent (OC). There are several possible causes for this: motor malfunctions, excessively short acceleration time, or damage to the detection CT; all of these can lead to overcurrent faults. In fact, the most common cause of overcurrent alarms during maintenance is damage to the PIM module. Sometimes, a short circuit in the drive circuit can lead to an overcurrent alarm as soon as the device is powered on; it’s also possible that damage to the high-power transistors can result in an imbalance in the three-phase output voltage, which in turn triggers an overcurrent alarm when the inverter is operating. The common method we use to determine the source of the fault is to run the inverter without moving the motor, and measure the output voltage to figure out whether there is a problem with the motor or with the inverter itself. If it is a frequency converter fault, we still need to determine whether the fault is caused by a damaged PIM module or by incorrect detections by the detection circuit. By making measurements, we can determine the quality of the PIM module; however, it is important to note that we cannot overlook the measurement of the waveforms in the drive circuit. The lower bridge drive of the Tai’an N2 series frequency converters uses PC929 driver optocouplers equipped with short-circuit protection; damage to the PIM module can also easily lead to damage of the driver optocouplers. Damage to the detection circuit is primarily caused by a faulty Hall sensor, which can also trigger an overcurrent alarm. The design of the switching power supply for the N2 series inverters represents a common approach used in current switching power supplies; an UC3842 chip is used as the waveform generator, and the duty cycle of the switching transistor K1317 is adjusted to achieve control over the output. The entire circuit design is simple and reliable, and it is widely used. However, a short circuit in the load connected to the switching power supply, or a sudden change in its operating voltage, can also cause damage to the switching power supply. The problem usually lies with the UC3842 chip, but if there is a sudden change in the external power supply, it may also cause damage to the pulse transformer. In the Tai’an N1 series frequency converters, pulse transformers suffer from quite a high rate of damage, but the reasons for this are different from those associated with damage to N2 series frequency converters. It is mostly related to the manufacturing process during the winding of pulse transformers. With Delta frequency converters, the most common issue we encounter is damage to the switching power supply. Such as Delta’s VFD-A series frequency converters. Its switching power supply features a symmetric design, with two switch transistors working together to regulate the output voltage; the problems usually arise in the drive circuit for these switch transistors. Furthermore, the pulse transformer of this switching power supply is also a vulnerable component. The 7200GA model from Dongyuan utilizes the technology of Yaskawa’s 616G3 series inverters. The faults we encounter most frequently are SC faults as well as CPF00–CPF04 faults. Of course, damage to the switching power supply is also one of the common faults. SC short-circuit faults are mostly caused by damage to the power modules, and a short circuit at the trigger terminal of the power module often results in a short-circuit fault being detected as soon as the device is powered on. Damage to the drive circuit can also cause SC failures. Often, as soon as it starts running, an SC failure occurs. Then we can only rule out faults by measuring the power module and checking the drive waveform. As for the faults CPF00–CPF04, they are mostly related to the control board, making them relatively difficult to detect. Generally speaking, Mitsubishi frequency converters were among the first to enter the Chinese market; as a result, some older models are still in use. Let’s first analyze the faults of these products. In the early days, the inverters we had access to mainly included those from the Z series and A200 series. For the low-power Z024 series inverters, common fault symptoms included OC, ERR, and no display. The main reasons for OC were as follows: 1. Aging of the drive circuit – prolonged use inevitably leads to the aging of components, which in turn causes distortion in the drive waveform and instability in the output voltage; as a result, an OC alarm often occurs as soon as the device starts operating. 2. Damage to the IPM module can also trigger an OC alarm. The power modules used in Z024 series machines not only contain detection circuits for overcurrent, undervoltage, etc., but also include amplification and drive circuits; therefore, damage to the detection circuits, the drive circuits, or the high-power transistors can all result in an OC alarm. The causes of no-display faults are mostly due to damage to the thick-film circuit of the switching power supply. The ERR fault is a low-voltage fault; it usually occurs due to problems with the resistance of the voltage detection circuit or its wiring, rather than an actual drop in the input voltage. Most OC failures in the A200 series are caused by damage to the drive circuit. This circuit uses a thick-film circuit packaged in ceramic, which poses certain difficulties for repairs; it is a circuit designed around a drive optocoupler. In addition, we may also encounter some LV faults; voltage deficiency faults usually occur due to problems with the busbar detection circuit. Mitsubishi frequency converters are equipped with a thick-film circuit designed for detecting voltage and current to address this issue. Damage to the pulse transformer in the switching power supply is also a common fault in A200 series frequency converters; the primary and secondary windings of the pulse transformer can be damaged due to a short circuit in the load connected to the switching power supply output, or due to sudden changes in the bus voltage. The series currently being promoted and used in the market are the A500 series, E500 series, F500 series, and S120 series. Next, we will analyze the common faults of the A500 and E500 series with you. For the A500 series, we sometimes encounter UV (under-voltage) faults; we can check the rectification circuit, model 7 of the A500 series. In inverter rectifier bridges with a power rating of 5 kW or less, there is a thyristor built in; during normal operation of the inverter, this thyristor serves to disconnect the charging resistor. Damage to this built-in thyristor can lead to undervoltage faults. Damaged switching power supplies are also a common fault in A500 series frequency converters, and the component that is often damaged is an M51996 waveform generator chip; damage to this chip is usually caused by sudden changes in operating voltage. Furthermore, during routine maintenance, we still often encounter damage to the CPU board. Common fault alarms include E6 and E7, while the damaged components are mainly found in the program storage chips on the CPU board, as well as in some interface chips. For the E500 series variable frequency drives, a common fault we encounter is the Fn fault, which is mainly caused by fan damage. However, the inverter does not block the output when there is an alarm. It can be said that there are a variety of faults that occur in Mitsubishi frequency converters during use. It is hoped that more people working in the field of frequency conversion and speed control will join forces to help solve various problems for end-users. Composition of frequency converters, common faults, and repair strategies. Frequency conversion speed control technology represents an important direction in the development of modern power transmission technologies. With the progress of power electronics technology, AC frequency conversion technology has gradually matured, moving from theory to practical application. Inverters not only provide smooth speed control over a wide range, with high efficiency and low starting current, ensuring stable operation, but they also offer significant energy-saving benefits. Therefore, AC variable-frequency speed control has gradually replaced traditional speed control systems such as slip speed control, pole-changing speed control, and DC speed control, and is being increasingly used in industries such as metallurgy, textiles, printing and dyeing, cigarette manufacturing lines, as well as in building and water supply sectors. However, due to factors such as the environment, service life, and human operation, the service life of frequency converters is significantly reduced, and various faults also occur during use. Next, we will discuss together the composition of frequency converters, as well as their common faults and solutions. It is generally divided into several main parts such as the rectifier circuit, smoothing circuit, control circuit, and inverter circuit. I. Rectifier circuit: The function of a rectifier circuit is to convert an alternating current power supply into a direct current power supply. A rectifier circuit is usually a separate rectifier module, but there are also many modules that combine both a rectifier circuit and an inverter circuit, such as the Fuji 7MBI series. A damaged rectifier module is a common fault in frequency converters. In a static state, one can determine whether the rectifier module is damaged by using a multimeter’s resistance setting to measure the resistance in both forward and reverse directions; of course, a voltage tester can also be used for this purpose. In some brand inverters, the rectifier circuit uses thyristors in the upper bridge and diodes in the lower bridge. Such as high-power brands like Danfoss and Delta. A simple way to determine the quality of a thyristor is to apply a DC voltage (around 10V) to the control terminal and check whether it can conduct in the forward direction. In this way, it is possible to roughly determine the quality of the thyristor. Additionally, the rectifier module of Fuji inverters G9S(P9S) 11kw and below features the integration of five functions in one module. Rectifier, pre-charge thyristor, brake tube, power switch transistor, thermistor. Such as the names of the pins and functions of the CVM40CD120 rectifier module, for reference by peers. Rectification: R, S, T, A(+) N-(-). Charging thyristors: A1, P1, G+n (trigger). Braking tubes: DB, N_, G7 (trigger); DB1. B+ is its freewheeling diode. Power switch transistors: D8, S8, G8. Thermistors: Th1, Th2, G9S (P9S). Power range: 15kw–22kw. The rectification module is VM100BB160; in addition to rectification, it also includes a pre-charging thyristor. Those with a power of over 30kw have a single rectification function for the rectifier module. For a power of 75 kW or more, multiple parallel rectifier modules are used. II. Smoothing Circuit: In a rectifier, the rectified DC voltage contains pulsating voltages at 6 times the frequency of the power supply. Additionally, the pulsating current generated by the inverter also causes fluctuations in the DC voltage. To suppress these voltage fluctuations, inductors and capacitors are used to absorb the pulsating voltages (currents). In general, in variable-frequency drive systems, there is a margin in the components constituting the DC section of the power supply, so a simple capacitor-based filtering smoothing circuit is used instead of an inductor. We test the filtering capacitor for capacitance and voltage tolerance, and we can also check whether the safety valve on the capacitor has ruptured. Is there any leakage as a way to determine its quality? III. Control circuit: Modern frequency conversion speed control systems generally use 16-bit or 32-bit microcontrollers or DSPs as the control core, thereby achieving fully digital control. An inverter is a speed control device that allows the voltage frequency to be adjusted. The circuit that provides the control signals is called the main control circuit. The control circuit consists of the following components: the \"operation circuit\" for frequency and voltage, the \"voltage and current detection circuit\" for the main circuit, and the \"speed detection circuit\" for the motor. The control signals of the operation circuit are sent to the amplifying \"drive circuit\" as well as the \"protection circuits\" for the inverter and motor; however, when using a frequency converter in practice, its maintenance work is also relatively complex. Here are some methods for dealing with the causes of fault alarms in the frequency converter control circuit. When using common frequency converters, it is crucial to set their parameters properly to ensure that they can meet the requirements of the drive system. Incorrect settings can cause the inverter to trigger an alarm and fail to operate properly. 1. Parameter settings: When the frequency converter leaves the factory, the manufacturer sets a value for each parameter; these values are known as the factory (default) values. Generally, the default values do not meet the requirements of most transmission systems. Therefore, before using the frequency converter correctly, it is necessary to set its parameters as follows: (1) Confirm the motor parameters by setting the motor’s power, current, voltage, speed, and maximum frequency. These parameters can be obtained directly from the motor nameplate. (2) The control method used by the inverter, namely speed control, torque control, PID, or other methods. After selecting the control method, it is generally necessary to perform static or dynamic discrimination based on the required control accuracy. (3) Set the startup mode of the frequency converter; generally, frequency converters are set to start from the panel at the time of manufacture, but users can choose the startup mode according to actual conditions. It can be done using panels, external terminals, communication methods, etc. (4) Regarding the selection of the input signal, there are generally also various ways to set the frequency of an inverter. Panel input, external input, external voltage or current input, communication method input. Of course, the frequency conversion setting can also be one of these methods or a combination of several of them. Once the above parameters are set correctly, the frequency converter will function properly; to achieve better control results, it is necessary to adjust the relevant parameters according to the actual conditions. Once the parameter setting issue occurs, the parameters can be modified according to the instructions. If that doesn’t work, the data can be initialized to restore the default values. Then, the settings should be adjusted again following the steps outlined above. The method for restoring the parameters to their factory settings varies depending on the brand of the inverter. 2. “OC” overcurrent alarm fault – This is the most common fault in frequency converters. We first rule out faults caused by parameter issues; for example, current limits or an excessively short acceleration time can lead to overcurrent. Then we must determine whether there is a problem with the current detection circuit. Taking the FVR-075G7S-4EX as an example, we sometimes observe that the panel shows a current value when the FVR-075G7S-4EX is running without a motor connected; where does this current come from? At this point, it is necessary to check whether there are any problems with its 3 Hall sensors. 3. “OV” overvoltage fault: First, it is necessary to rule out faults caused by parameter issues, such as an excessively short deceleration time, as well as overvoltage resulting from regenerative loads. Then we can check whether there is a fault in the voltage detection circuit. In a typical voltage detection circuit, the voltage is sampled from the intermediate DC bus (around 530V DC), then reduced in voltage through a resistor with a high resistance value, and isolation is achieved using an optocoupler. When the voltage exceeds a certain threshold, an “5” is displayed to indicate overvoltage (in this device, it is shown on a digital display). We can check whether the resistors have oxidized and changed their values, as well as whether there is any short circuit in the optocouplers. 4 “UV” under-voltage fault: First, we can check whether the voltage at the input is too low or if there is a missing phase; then we examine the voltage detection circuit to determine if it matches the actual voltage level. 5. “OH” overheat fault: The temperature of the inverter is too high; check the ventilation of the inverter and whether the axial flow fan is operating properly. Some frequency converters are equipped with devices for monitoring the motor temperature, in order to check the motor’s cooling performance; we then examine whether all the components of the detection circuit are functioning properly. 6. “SC” short-circuit fault: We can check whether there is any short-circuit in the components inside the inverter. Using the Yaskawa 616G545P5 as the column module, if there are issues with the drive circuit or the optocoupler, it is usually a problem with the module or the drive. Replace the module to repair the drive circuit. “The “SC” fault will be eliminated. 7. “FU” rapid fuse fault: Most of the inverters currently available come equipped with a function for detecting rapid fuse faults. Especially high-power frequency converters, taking the LG SV030IH-4 frequency converter as an example. It mainly samples and monitors the voltages in front of and behind the fast fuse. When the fast fuse is damaged, voltage at one end of the fast fuse is inevitably lost; at this point the isolation optocoupler activates, triggering a FU alarm. Replacing the fast fuse should resolve the issue; it is particularly important to note that before replacing the fast fuse, it is necessary to determine whether there is a problem with the main circuit. IV. Inverter circuit: Unlike the rectifier circuit, the inverter circuit converts direct current voltage into alternating current voltage of the desired frequency, causing the 5 power switching devices in the upper bridge and the 6 power switching devices in the lower bridge to turn on and off at predetermined times. Thus, three-phase AC voltages with phases differing by 2/3π from each other can be obtained at the output terminals U, V, and W. An inverter circuit usually refers to an IGBT inverter module (early inverters used power modules such as GTRs); damage to the IGBT module is also a common fault in inverters. For IGBT modules, we introduce the simplest measurement method (this is not how professionals conduct measurements): use the 10k ohm setting on an analog multimeter, with one probe touching GwEw (the black probe touching Gw and the red probe touching Ew), so that conduction can occur from P to W. When Gw and Ew are short-circuited, P to W is turned off, and the same applies to the other transistor pins. The voltage withstand value can be measured using a transistor parameter tester, but to measure the C-E voltage withstand value, the G-E terminals must be shorted together. When an IGBT module is damaged, the driving components are usually also damaged. The most vulnerable components are voltage regulators and optocouplers. Conversely, if there are problems with the components of the drive circuit, such as capacitor leakage, breakdown, or aging of optocouplers, this can also lead to damage to the IGBT module or an unbalanced variable-frequency output voltage. Check if there is a problem with the drive circuit; you can compare the resistance of each trigger terminal when the circuit is not powered on to see if they are consistent. By powering on the device, it is possible to measure the voltage waveform at the trigger terminal. However, some inverters cannot be started without installing a module; in such cases, a dummy load is connected in series to the P terminal of the module to prevent accidental contact with the trigger terminal or other circuits during inspection, which could otherwise cause damage to the module. Common Faults of Variable Frequency Drives and Repair Strategies
AC variable frequency speed control technology represents an important direction in modern power transmission technology. With the application of power electronics, microelectronics, and modern control theory in AC speed control systems, variable frequency AC speed control has gradually replaced traditional speed control methods such as slip speed control, pole-changing speed control, and DC speed control. It is now used increasingly in various fields of industrial production and daily life. However, due to factors such as the operating environment, service life, and human operation, the service life of variable frequency drives is significantly reduced, and various faults occur during use. Below, we will discuss some common faults of variable frequency drives along with corresponding solutions. First, we can conduct a static test on the drive. A general-purpose variable frequency drive typically consists of the following components: 1) rectifier circuit, 2) DC intermediate circuit, 3) inverter circuit, and 4) control circuit. The static test mainly involves checking the high-power transistors (power modules) in the rectifier circuit, DC intermediate circuit, and inverter circuit, with a multimeter being the main testing tool. For the rectifier circuit, tests are carried out on the rectifier diodes to determine their quality, although a voltage tester can also be used for this purpose. In the DC intermediate circuit, the capacitance and voltage tolerance of the filter capacitors are measured; we can also check whether the safety valves on the capacitors have ruptured or if there is any leakage to assess their condition. To determine the quality of power modules, it is necessary to examine the freewheeling diodes within them. For IGBT modules, it is also important to check whether they can conduct and switch off when subjected to a trigger voltage. Secondly, we can determine the location of the fault using the display on the frequency converter. 1. OC. Overcurrent – this is probably the most common fault in frequency converters. We must first rule out failures caused by parameter issues. For example, current limiting and excessively short acceleration times can both lead to overcurrent. Then we must determine whether there is a problem with the current detection circuit. Taking FVR075G7S-4EX as an example: sometimes we observe that the panel still shows current readings when FVR075G7S-4EX is running without a motor connected. Where does the current come from? At this point, it is necessary to test its three Hall sensors; in order to determine which sensor is damaged, we can turn the device on each time a sensor is removed to check whether there is any current flow. Through such tests, the OC fault can generally be ruled out. 2. OV. Overvoltage: First, we need to rule out faults caused by parameter issues. For example, an excessively short deceleration time, or overvoltage caused by regenerative loads, etc. Then we can check whether there are any problems with the voltage on the input side, and finally we can examine whether there is a fault in the voltage detection circuit. Generally, the voltage sampling point for a voltage detection circuit is the voltage of the intermediate DC circuit. Taking the Sanken SVF303 as an example, it samples the voltage from the DC circuit (around 530V DC), reduces this voltage using a resistor with a high resistance value, and then isolates the signal through an optocoupler. When the voltage exceeds a certain threshold, the display shows “5” to indicate overvoltage (this device uses a digital display). We can check whether the resistors have oxidized and changed their values, as well as whether there is any short circuit in the optocouplers. 3. UV. Under-voltage. First, we can check whether there is a problem with the voltage on the input side, and then examine the voltage detection circuit; the fault diagnosis is the same as for overvoltage. 4. FU. Fast fuse failure. Most of the inverters currently available come equipped with a fast-blow fault detection function. (especially high-power frequency converters) Taking the LG030IH-4 frequency converter as an example. It mainly samples and monitors the voltages at both ends of the fast fuse; when the fast fuse is damaged, the voltage at one end of it will be absent, at which point the isolation optocoupler activates and a FU alarm is triggered. Replacing the fast fuse should solve the problem. It is particularly important to note that before replacing the fast fuse, it is necessary to determine whether there is a problem with the main circuit. 5. OH. Overheating is mainly caused by poor heat dissipation inside the inverter. We can check the cooling fans and ventilation channels. 6. SC. Short-circuit fault. We can check whether there is a short circuit inside the inverter. Taking the Yaskawa 616G5A45P5 as an example, we will check its internal circuits; there may not be a short circuit. In such cases, we can check whether the power module is faulty. If the drive circuit is functioning properly, replacing the power module should allow the machine to be repaired. Common drive circuit configurations of general-purpose frequency converters and their analysis. AC variable-frequency speed control technology represents an important development direction in modern power transmission technologies. With the application of power electronics, microelectronics, and modern control theory in AC speed control systems, variable-frequency AC speed control has gradually replaced traditional speed control methods such as slip speed control, pole-changing speed control, and DC speed control. It is now used increasingly in various fields of industrial production and everyday life. As variable-frequency speed controllers become more widely used, many engineering and technical personnel have gained a good understanding of them. A typical general-purpose frequency converter consists of the following components: 1. Rectifier circuit, 2. DC intermediate circuit, 3. Inverter circuit, 4. Control circuit. The inverter circuit, which generates adjustable voltage and frequency, is the core technology among all the components of a frequency converter. The inverter circuit mainly includes the inverter module and the drive circuit. Due to factors such as manufacturing processes, packaging techniques, and high-power transistor components, currently, inverter modules are mainly produced by a few manufacturers in Japan (Tokyo Electric, Mitsubishi, Mitsushiba, Fuji, Sanken) and in Europe and the United States (Siemens, Sick, Motorola, IR). As part of the inverter circuit, the drive circuit has a significant impact on the three-phase output of the frequency converter. There are several ways to design drive circuits: 1. Drive circuits composed of discrete components with pins. 2. Optocoupler-driven circuits. 3. Thick-film drive circuits. 4. Dedicated integrated circuit drive circuits. Drive circuits made up of discrete components with pins were widely used in frequency converters in Japan and Taiwan during the 1980s. These included frequency converters from companies such as Fuji in Japan (G2, G5; Sanken: SVS, SVF, MF, Kasuga; Mitsubishi’s Z series and K series), as well as those from Taiwan (Olin, Puchuan, Tai’an). With the development of large-scale integrated circuits and the advent of surface-mounting technology, such drive circuits, which are complex and have low integration levels, have gradually been phased out. Optocoupler-driven circuits are widely used in modern frequency converter designs. Thanks to their simple structure, high reliability, and good switching performance, they are adopted by many frequency converter manufacturers in Europe, the United States, and Japan. There are many types of optocouplers available, providing ample options for selection. Commonly used optocouplers include Tokyo Electric’s TLP series, Sharp’s PC series, and HP’s HCPL series. Taking Tokyo Electric’s TLP series as an example, the TLP250 and TLP251 models are commonly used to drive IGBT modules. For modules with a current level of around 15A, the TLP251 is usually used. The simplest drive circuit consists of these optocouplers along with a drive power supply and current-limiting resistors. For modules with a medium current level of around 50A, the TLP250 model is typically used. For modules with even higher currents, an additional amplification circuit is added after the optocoupler drive to ensure safe operation of the IGBT module. Thick-film drive circuits are a type of hybrid integrated circuit developed based on resistive-capacitive components and semiconductor technology. They utilize thick-film technology to create components and connecting wires on ceramic substrates, integrating all the elements of the drive circuit onto a single ceramic substrate, thus forming a single unit. The use of thick-film drives simplifies circuit design and wiring, improves the reliability of the entire device and the consistency of mass production, while also enhancing technical confidentiality. Modern thick-film drives often incorporate various protection and detection circuits, indicating that the technical complexity of these drives is increasing. Additionally, there are now dedicated integrated circuit drive circuits, such as IR’s IR2111, IR2112, IR2113, as well as Mitsubishi’s EXB series and M57956, M57959 series of thick-film drives. Some European and American frequency converters also incorporate high-frequency isolation transformers into their drive circuits (such as Danfoss’ VLT series). The use of high-frequency transformers to isolate the power supply and signals in the drive circuit enhances its reliability and prevents damage to the low-voltage circuits in case of failures in the high-voltage circuits. In actual maintenance work, it has been observed that these drive circuits have a very low failure rate, and high-power modules rarely experience problems. In everyday industrial applications, damage to high-power modules is a common issue, and the causes can vary widely. Motor short circuits, poor insulation from ground, motor stalling, and excessively high external power supply voltages can all lead to damage to the high-power modules in frequency converters. When replacing high-power modules during maintenance, it is essential to ensure that the drive circuit is functioning properly; otherwise, the module may be damaged again after replacement. It is also important to understand the differences between the drive circuits for GTR modules and IGBT modules—the former are driven by current, while the latter are driven by voltage. Various issues in the application of frequency converters Today, frequency converters have reached a high level of intelligence. Before using them, it is necessary to thoroughly understand their performance and operating methods. This greatly affects the proper operation of the inverter and the motor. Taking the common problem of motor burnout as an example: There are many parameters in a frequency converter that need to be set correctly before use, such as the acceleration and deceleration methods, base frequency, voltage level, current level, protection level, and so on. Only when these parameters are set correctly and calculations are performed can the correct output be generated, enabling the motor to operate properly. It is well known that the torque of a motor is generated by the interaction between the magnetic field of the motor and the current flowing through the rotor. When the voltage remains constant, reducing the frequency alone leads to an excessive flux, which causes saturation of the magnetic circuit and can result in damage to the motor. Therefore, both frequency and voltage must be changed proportionally; by adjusting the frequency, the output voltage of the inverter is also controlled to keep the flux in the motor at a constant level, thereby preventing phenomena such as weak magnetism and magnetic saturation. Hence, there is a close relationship between frequency and voltage. If used improperly, it is the main cause of motor burnout. Some customers often ask what the advantages are of using inverters to drive motors. First, it is necessary to understand the working principle of the frequency converter. In fact, an inverter works by using power semiconductor devices to switch on and off, thereby converting the mains power supply or modifying a series of pulses with varying widths according to certain patterns, and thus generating an output waveform of a specific shape (such as linear or curved). The output voltage increases in proportion to the motor’s acceleration frequency and voltage; the current level remains below 15% of the rated value. The starting torque can range from 20% to 120%, allowing for full-load starting. This approach helps to save energy, reduce noise, and ensure a smooth start. If the equipment is started directly using a power supply at line frequency, the starting current will reach 6 to 7 times the rated value, and severe mechanical vibrations will occur, which can lead to phenomena such as \"runaway operation\" and \"stall\". Therefore, we believe that frequency converters are the ideal tools for driving motor starting equipment. With technological advancements, the market for frequency converters will continue to grow and they will be adopted by more and more industries. Common Problems and Solutions in Inverter Drive Circuits. Over the past decade or so, as power electronics technology, microelectronics technology, and modern control theory have been applied to the field of AC electric drives, variable-frequency AC speed control has gradually replaced traditional speed control methods such as slip speed control, pole-changing speed control, and DC speed control. It can almost be said that where electric motors are used, frequency converters are also employed. Its main features are high-efficiency driving performance and good control characteristics. Modern general-purpose frequency converters generally consist of the following components: a control circuit, a pre-charging circuit (including a rectifier bridge), an intermediate DC circuit, and a drive circuit. The drive circuit plays a crucial role in determining the quality of an inverter. Today, we will discuss the common problems associated with drive circuits and their solutions. The term \"drive circuit\" is a general designation; as technology has continued to develop, drive circuits have evolved from those using pin-based components to optocoupler-driven circuits, then to thick-film drive circuits, and finally to the more modern integrated drive circuits. The latter three types of drive circuits are still commonly encountered in repair work. Today, we will discuss the repair methods for these different types of drive circuits by using practical examples. There are various reasons why drive circuits may become damaged; generally, the problems that arise include no output from the U, V, and W phases, unbalanced output, balanced output but with fluctuations at low frequencies, as well as startup alarms and other issues. When the fast-acting fuse located after the large capacitor in a frequency converter opens, or when the IGBT inverter module is damaged, it is highly unlikely that the drive circuit remains undamaged. Under such circumstances, one must not replace the faulty fast-acting fuse or IGBT inverter module with new ones; doing so can easily result in the newly installed components being damaged as well. At this point, it is necessary to check carefully for any signs of arcing in the drive circuit. One can start by disconnecting the connection wires of the IGBT inverter module’s drive terminals, and then use a multimeter’s resistance setting to verify that all six drive circuits have the same resistance value (although some inverter drive circuits do not have all six circuits with identical resistance values; for example, Mitsubishi and Fuji models). Even if all six circuits have roughly the same resistance value, this does not necessarily mean that the drive circuit is intact. Next, an oscilloscope should be used to check whether the voltages across the six drive circuits are equal, as well as whether their waveforms are consistent when a start signal is applied ； If you don’t have an oscilloscope available, you can try using a digital multimeter to measure the DC voltage across the six channels of the drive circuit. Generally, when the device is not running, the DC voltage across each drive channel is around 10 volts; after it starts operating, this voltage drops to 2–3 volts. If the measurements show normal values, it can be concluded that the drive circuit of this inverter is functioning properly. Next, connect the IGBT inverter module to the drive circuit. But remember that when you’re not 100% sure, the safest approach is to disconnect the P terminal of the IGBT inverter module from the DC bus, and insert a series of light bulbs or a resistor with higher power in between. This helps to protect the IGBT inverter module from being damaged by the high voltage stored in large capacitors in case a large current flows through the circuit. Below are a few examples related to the drive circuit when repairing frequency converters: 1. A customer brought in an Yaskawa 616G5 frequency converter with a capacity of 3.7 KW. The problem was that the three-phase output was normal, but the motor vibrated at low speeds, preventing normal operation. Upon receiving the unit, it is likely that the drive circuit of the inverter is damaged. The correct solution is to identify the fault symptoms, open the inverter, remove the IGBT inverter module from the circuit board, and use an oscilloscope to check whether the waveforms of the six drive circuits are consistent when they are activated. Identify the drive circuit with inconsistent waveforms, and replace the optocoupler in that circuit; these are usually PC923 or PC929. If the inverter has been in use for more than 3 years, it is recommended to replace all the electrolytic capacitors in the drive circuit as well. After that, use the oscilloscope to verify that the waveforms of all six circuits are consistent, then reinstall the IGBT inverter module and conduct load tests to eliminate any oscillation issues. 2. The customer has sent a Fuji G9 inverter; the issue is that it shows no display when powered on. Upon receiving it, it was suspected that the switch power supply of the inverter might be damaged. The inverter was opened to check the wiring of the switch power supply, but no damage was found in those components; moreover, no voltage was detected at the DC positive and negative terminals. At this point, it was assumed that there could be a problem with the drive circuit. All the capacitors in the drive circuit were removed, and it was found that a few of them were leaking fluid. New electrolytic capacitors were installed, and after powering it up again, the device worked properly. A customer brought in a Delta frequency converter. The problem was arcing at the output terminal of the converter. Upon inspection, it was found that the IGBT inverter module had been damaged, and the circuit board associated with the drive circuit was severely damaged as well. The correct solution involved first removing the damaged IGBT inverter module, being careful to protect the circuit board from further damage during removal. The damaged electronic components in the drive circuit were replaced one by one, and any open circuits on the circuit board were connected using wires. It was important to clean up any burned areas to prevent further arcing. After ensuring that all six channels of the drive circuit had the same resistance and voltage, waveforms were measured using an oscilloscope. However, as soon as the converter was turned on, an OCC error occurred (Delta frequency converters emit an alarm when there is no IGBT inverter module). A light bulb was used to connect point P1 of the module to the circuit board, with the other connections made using wires; yet the OCC error still occurred upon restart, indicating that there was still a problem with the drive circuit. The optocouplers were replaced one by one, and it was discovered that one of the optocouplers in that drive circuit had a detection function that was damaged. After replacing it with a new one, the converter started working properly. Conclusion: As frequency converters continue to evolve, the technology related to their drive circuits is also advancing rapidly. What can be covered here is only a fraction of what exists; it is hoped that this information will be useful to technical professionals and those who are interested in frequency converters. It is also hoped that those working in this field will engage in more exchanges so that everyone’s skills can improve further. Common faults and maintenance measures for Hitachi inverters. Compared to leading brands such as Siemens, ABB, and Mitsubishi in the automation field, Hitachi remains a relatively unknown brand. In fact, Hitachi’s products are quite commonly seen in the industrial control industry. Examples include the MICRO EH series, as well as larger-scale PLCs like the EH-150 series, along with inverters from the L, SJ, and J series, plus AC servo products. These products are still widely used in China. In particular, Hitachi frequency converters are widely used in applications such as driving conveyor and mixing devices with high starting loads, lifting devices that require four-quadrant operation, as well as winding processes in the textile and fiber industry. Hitachi’s frequency converters are well categorized in terms of selection. The frequency converters currently available on the market include the economical L100 series, the SJ100 vector-type frequency converter that offers the same functions as the L100 series, the SJ300 series with sensorless vector control, the SJ-300EL series designed specifically for elevators, and the L300P series intended for use in fans and pumps. Currently, several Hitachi inverters available on the market offer stable performance. In particular, Hitachi’s speed-sensorless vector control technology, which is patented, results in excellent starting characteristics at low speeds for its inverters. In terms of functional applications, Hitachi inverters currently offer a wide range of options. Built-in functions that are commonly used in similar inverters, such as the PID function, RS485 communication function, 16-stage acceleration/deceleration function, motor parallel operation function, speed control function, parameter copying function, and three-wire operation function, are all available in Hitachi inverters. It is particularly worth mentioning that when two motors operate in parallel, vector control is applied to both of them at the same time; this is something that is difficult to achieve with ordinary frequency converters. As is well known, vector control requires very precise parameters for the motors. The power, current, voltage, and impedance of the stator and rotor must all be very accurate; however, this is particularly difficult to achieve when two motors operate in parallel. This might also be a highlight of Hitachi’s inverters. Hitachi frequency converters offer relatively few optional accessories; among the communication options, Profibus and Device Net are the main choices available. In terms of noise resistance, suppression of high and low harmonics, and RF interference, Hitachi inverters offer a variety of options available; AC/DC reactors, RFI filters, LCR output sine wave filters, and others all help to effectively minimize the interference generated by the inverter. Compared to the overall frequency converter market, Hitachi’s share may not be very high; as a result, users have fewer sources from which they can find solutions when encountering faults. Below, we will discuss some common faults associated with Hitachi frequency converters: In the past, the Hitachi frequency converter that was commonly seen in the domestic market was the HFC-VWS3 series. This is a frequency converter that uses V/F control, with power modules made up of high-power GTR transistors. Its maximum power output can reach 132 KW, and it features an LCD display, which made it considered a high-end inverter in Japan during that period. However, compared to frequency converters that use digital tubes for display, the lifespan and stability of LCDs are relatively inferior. We often encounter situations where an LCD display has brightness but no text appears on it. In most cases, this is caused by a decrease in the capacitance of surface-mounted ceramic capacitors on the drive power supply side of the LCD. Replacing these capacitors can resolve the issue. In addition, this series of inverters makes extensive use of thick-film circuits, including those for switching power supplies and those for the drive section. The use of thick-film circuits is mostly due to considerations of technical confidentiality. When encountering similar problems, the first thing we should consider is how to determine the quality of these thick-film circuits. For the repair of frequency converters, identifying the source of the fault is also a very important task. In the case of damage to a switching power supply, after ruling out damage to external components such as switch transistors, oscillation resistors, and pulse transformers, the most likely problem lies in the thick-film drive circuit of the switching power supply. In the absence of obvious signs of damage, we can apply a direct current voltage to test whether the thick-film circuit can output the drive waveform properly; the applied direct current voltage is usually around 15V. If the output waveform is normal, we can generally assume that this thick-film circuit is functioning properly. The absence of a waveform output generally indicates that the thick film component is damaged; replacing it will resolve this issue. The drive thick film of the HFC-VWS3 series inverters is also a prone-to-failure component, but since all components on the thick film circuit are already packaged, repairs are relatively difficult. E9 alarm: In the J300 series of frequency converters, we often encounter the E9 alarm. We can check the power supply on the three-phase input side. The J300 frequency converter is equipped with a function for detecting the three-phase input voltage; this voltage is sent to the CPU for processing via voltage-dividing resistors. The E9 alarm can occur in cases of missing phases or too low input voltage. ――– Faults: Such faults generally occur when the inverter is powered on. Usually, this kind of fault is not due to pure hardware damage, but it still happens frequently. We should focus our inspection on various connectors, including those that connect the operation panel to the inverter, as well as those that connect the control board to the drive board. Furthermore, such faults can also occur due to undervoltage on the DC side. Another fault phenomenon we encounter with the SJ300 series inverters is the E30 alarm, which is related to IGBT failures. The possible causes of the E30 alarm are as follows: 1. Damage to the power module. The low-power models in the SJ300 series of inverters use PIM modules manufactured by Fuji in Japan; these are modules that integrate rectification and inversion functions, and they differ from the IPM intelligent modules used in the J300 series. Of course, damage to the module can cause the E30 alarm to appear. However, in many cases, the PIM module is not damaged; instead, there is a fault in the bridge drive circuit. The fault signal is transmitted to the main control board via optocoupling for alarm and lockout output. It can be said that there are a variety of faults that occur in Hitachi frequency converters during use. It is hoped that more people working in the field of frequency conversion and speed control will join forces to help solve various problems for end-users. Common faults of Mitsubishi frequency converters and repair strategies. Mitsubishi is undoubtedly a highly reputable brand in the field of automation. Its PLCs, human-machine interfaces, frequency converters, servo products, as well as automated measuring instruments are all its strong selling points, and it has earned a good reputation across various industries. Mitsubishi frequency converters hold an important position in the frequency converter market thanks to their stable performance, extensive functions, excellent torque characteristics, and high cost-performance ratio. Thanks to its strong brand influence, its market share in China is increasing year by year. After nearly 20 years of development, Mitsubishi frequency converters boast quite stable and advanced product quality and functions. Especially with the continuous improvements in power devices and IC chips, frequency converter products are also constantly being updated. Starting from the K series and Z series that used discrete components in earlier times, to the A series that now utilizes IPM and PIM modules, Mitsubishi’s frequency converters have reached a new level of sophistication. It should be noted that in terms of the use of high-power modules, Mitsubishi inverters may have an advantage, as Mitsubishi is itself a well-known semiconductor manufacturer that is at the forefront in the development of power devices. In particular, Mitsubishi’s IPM modules are adopted by many inverter manufacturers due to their excellent performance. In terms of applications, modern Mitsubishi frequency converters can be mainly divided into the following categories: 1. The general-purpose A series, which includes the earlier A200 series, as well as the more economical A024 and A044 series. 2. The F series, designed specifically for fans and water pumps, includes the earlier F400 series as well as the widely used F500 series today; 3. the economical E series, and the compact S series. To meet market demands, Mitsubishi inverters have also developed option cards for use in various applications. These include a PG feedback card that provides accurate speed control, a positioning control card for precise positioning, a PI control card for pressure regulation, as well as relay and transistor output cards for expanding the number of output points. The continuous enhancement of inverter functions, along with the development of optional cards, has enabled Mitsubishi inverters to better meet the needs of various users, and this has also been the driving force behind the rapid growth of Mitsubishi inverters. Here, we will discuss with users some of the common faults associated with Mitsubishi frequency converters. Since Mitsubishi frequency converters entered the Chinese market quite early on, some older models are still in use; we will first analyze the faults that occur with these products. In the early days, the inverters we had access to mainly included those from the Z series and A200 series. For the low-power Z024 series inverters, common fault symptoms included OC, ERR, and no display. The main reasons for OC were as follows: 1. Aging of the drive circuit – prolonged use inevitably leads to the aging of components, which in turn causes distortion in the drive waveform and instability in the output voltage; as a result, an OC alarm often occurs as soon as the device starts operating. 2. Damage to the IPM module can also trigger an OC alarm. The power modules used in Z024 series machines not only contain detection circuits for overcurrent, undervoltage, etc., but also include amplification and drive circuits; therefore, damage to the detection circuits, the drive circuits, or the high-power transistors can all result in an OC alarm. The causes of no-display faults are mostly due to damage to the thick-film circuit of the switching power supply. The ERR fault is a low-voltage fault; it usually occurs due to problems with the resistance of the voltage detection circuit or its wiring, rather than an actual drop in the input voltage. Most OC failures in the A200 series are caused by damage to the drive circuit. This circuit uses a thick-film circuit packaged in ceramic, which poses certain difficulties for repairs; it is a circuit designed around a drive optocoupler. In addition, we may also encounter some LV faults; voltage deficiency faults usually occur due to problems with the busbar detection circuit. Mitsubishi frequency converters are equipped with a thick-film circuit designed for detecting voltage and current to address this issue. Damage to the pulse transformer in the switching power supply is also a common fault in A200 series frequency converters; the primary and secondary windings of the pulse transformer can be damaged due to a short circuit in the load connected to the switching power supply output, or due to sudden changes in the bus voltage. The series currently being promoted and used in the market are the A500 series, E500 series, F500 series, and S120 series. Next, we will analyze the common faults of the A500 and E500 series with you. For the A500 series, we sometimes encounter UV (under-voltage) faults; we can check the rectification circuit, model 7 of the A500 series. In inverter rectifier bridges with a power rating of 5 kW or less, there is a thyristor built in; during normal operation of the inverter, this thyristor serves to disconnect the charging resistor. Damage to this built-in thyristor can lead to undervoltage faults. Damaged switching power supplies are also a common fault in A500 series frequency converters, and the component that is often damaged is an M51996 waveform generator chip; damage to this chip is usually caused by sudden changes in operating voltage. Furthermore, during routine maintenance, we still often encounter damage to the CPU board. Common fault alarms include E6 and E7, while the damaged components are mainly found in the program storage chips on the CPU board, as well as in some interface chips. For the E500 series variable frequency drives, a common fault we encounter is the Fn fault, which is mainly caused by fan damage. However, the inverter does not block the output when there is an alarm. Common Faults of Mitsubishi Inverters and Repair Strategies (Continued) Previous articles have provided some information on the development of Mitsubishi inverters as well as the analysis and handling of common faults. In the domestic market, Mitsubishi enjoys a wide range of applications across various fields due to its stable quality and strong brand reputation. For our users, the problems encountered are diverse. Below, we will discuss some new fault patterns encountered by the Shanghai Sixin Inverter Repair Center during the repair of Mitsubishi inverters, along with corresponding solutions, for the benefit of all users. The most widely used Mitsubishi inverter models in the market currently are the A500 series and the E500 series. The A500 series is a general-purpose inverter suitable for applications requiring high starting torque and rapid dynamic response, whereas the E500 series is better suited for applications with simpler functional requirements and lower demands for dynamic performance, offering better cost advantages. Here, we will provide a brief overview of some new faults associated with these two most commonly used Mitsubishi inverter models and the corresponding solutions: OC1 and OC3 Faults In previous discussions, we mentioned that OC (overcurrent) faults in Mitsubishi inverters are often caused by the following factors (taking the A500 series as an example): 1. Improper parameter settings, such as setting too short a time period. 2. External factors, such as short circuits in the motor windings, including inter-phase shorts and shorts to ground. 3. Hardware failures in the inverter, such as damaged Hall sensors or IGBT modules. In some repair cases, even after ruling out these possibilities, the OC fault may still persist; replacing the control board also does not resolve the issue. In such situations, we should consider whether there are problems with the drive circuit. The detection circuit of the Mitsubishi A500 inverter is quite sophisticated, and any issue with any of these detection points can result in an alarm and prevent normal operation. This includes not only the components typical of a drive circuit, such as the drive power supply, drive optocoupler isolation, and drive signal amplification circuits, but also the output signal feedback circuit. When the conventional detection methods fail to resolve the problem, we need to pay special attention to whether the drive circuit is functioning properly, focusing on the various components mentioned earlier. UVT Fault The UVT fault refers to a low voltage condition. Many customers encounter this issue during use. The common low voltage detection point is the voltage at the DC bus, which is sampled after being divided by a resistor of high value. This sampled voltage is then compared with a standard voltage value to determine whether a normal voltage signal, an overvoltage signal, or a low voltage signal should be generated. For Mitsubishi A500 series inverters, the voltage signal is sampled from the switch-mode power supply side and isolated using an optocoupler. During repairs, we have found that damaged optocouplers account for a significant proportion of cases causing low voltage faults. This phenomenon was less common in previous inverter repairs. E6 and E7 Faults These faults are certainly familiar to many users, as they represent typical issues with Mitsubishi inverters. There are various reasons for these faults: 1. Damage to the integrated circuit 1302 H02. This IC integrates functions such as drive waveform conversion and multiple detection signals, and it is connected to the CPU board via multiple signals. In many cases, any issue with one of these signals can trigger E6 or E7 alarms. 2. Damage to the signal isolation optocoupler. There are multiple high- and low-voltage signals that need to be isolated between the IC 1302 H02 and the CPU board. Damaged isolation optocouplers account for a relatively high proportion of component failures. Therefore, when E6 or E7 alarms occur, we should consider whether this could be the cause. 3. Damaged connectors or poor connector contacts. The connection cables between the CPU board and the power board can break or become poorly soldered after several bends. Improper handling of the connectors can also lead to bent or broken pins. All of these factors can cause E6 and E7 faults. Damaged Switch-Mode Power Supply Damaged switch-mode power supplies are also a common issue with A500 series inverters. Apart from the factors we’ve discussed earlier, such as damaged pulse transformers, switch-mode field-effect transistors, start-up resistors, and rectifier diodes, another common faulty component is the M51996 waveform generator chip. This is a control chip that incorporates features such as adjustable turn-on and turn-off times, output voltage regulation, and voltage feedback regulation. The most prone to problems are pin 14, which relates to the power supply, pin 7, which adjusts the voltage reference, pin 5, which handles feedback detection, and pin 2, which is responsible for waveform output. Damaged Power Modules Power module failures mainly occur in E500 series inverters. In low-power inverters, since the power devices and detection circuits are integrated into a single smart module, once the module is damaged, it must be replaced, resulting in high repair costs and rendering repair unnecessary. For 5.5KW and 7.5KW E500 series inverters, the 7MBR series PIM power modules are used, making replacement relatively cheaper, and thus allowing for some level of repair for such inverters. Common Faults of Panasonic Inverters and Repair Strategies Panasonic is a well-known brand in the home appliance industry, but it is less familiar in the industrial automation sector. Under Panasonic Electronics, the products we commonly see are inverters, while Panasonic Electric Works offers a wider range of products. In addition to inverters, servo drives are also among the products offered by Panasonic Electric Works. Panasonic Electric Works also produces a variety of PLC products: the FP1 series, which are small, integrated units; the FP10SH series, medium to large-sized PLCs with a slot-based design and powerful computing capabilities; the FPO series, ultra-small PLCs that boast the smallest installation footprint among their peers. In addition, industrial touchscreens are also among Panasonic Electric Works’ key products. Whether it is Panasonic Electric Works or Panasonic Industrial Equipment & Solutions, the inverters they produce are mainly of medium and low power; for example, the maximum power of the inverters produced by Panasonic Electric Works does not exceed 22 KW, while that of the inverters produced by Panasonic Industrial Equipment & Solutions does not exceed 37 KW. These inverters are used in applications where high performance levels are not required, including the food machinery manufacturing industry, the textile industry, the chemical industry, and so on. In terms of functional applications, Panasonic frequency converters mainly utilize some basic functions, including start/stop, forward/reverse operation, and multi-speed control. In Panasonic Electric’s VF—8X series of inverters, the RS485 communication function is available as an optional feature, which is different from the current practice of having this communication function built in. The positioning of Panasonic frequency converters should also be simple, practical, and cost-effective. This has enabled the brand’s frequency converters to secure a place in a highly competitive market. In terms of their internal structure, Panasonic Electric and Panasonic Industrial actually use completely different designs for inverters. In terms of product classification, Panasonic’s inverters, those produced by Panasonic Electric Works, are not categorized in as great detail based on function and industry as inverters from other brands. Panasonic Electric Works mainly offers the compact 220V, low-power VF0 series, as well as the cost-effective VF-7F series. For the medium-power VF-8X/8Z series, Panasonic offers models such as the DV700 series, M1D series, M1X series, and MIS series. Panasonic inverters are also positioned in the medium and low power range; thanks to their brand reputation and relatively low prices, they have managed to gain a certain share of the market. However, compared to the several leading brands in the inverter market such as ABB, SIEMENS, MITSUBISHI, FUJI, etc., Panasonic inverters may still have a lot of work to do. It is precisely due to the limited scope of use that there are relatively few summaries available regarding the repair of Panasonic inverters. Below, we will discuss some common faults associated with Panasonic inverters: no display when powered on. In the repair of DV707 series inverters, a frequent issue we encounter is the absence of a display when the device is powered on. After ruling out factors such as the external power supply and the monitor, it is usually the switching power supply that is damaged. During repairs, we find that the pulse transformer in the DV707 series inverters is a component that tends to get damaged easily. Due to factors such as high-frequency magnetic materials, load-bearing capacity, and the design of the short-circuit and overcurrent protection circuits in the switching power supply, the primary winding side of the pulse transformer is prone to damage. Since the design of the pulse transformer’s core differs from that of ordinary step-up/step-down transformers, it is difficult to disassemble it; even after disassembly, the magnetic materials may crack, and gaps may appear in the magnetic fields at the connection points, preventing the pulse transformer from functioning properly. In general, the pulse transformer is replaced. Furthermore, the design of the switching power supply in the DV707 series inverters also differs from that of other inverters. It uses an integrated circuit of model MA2810, which integrates components such as switch-mode power transistors and clamping voltage regulators into one unit, thereby reducing the number of external components required for the switching power supply. However, during maintenance, the MA2810 is prone to damage. Damage to the inverter module: In VF—7F series frequency converters, we sometimes encounter damage to the inverter module as well. A common phenomenon is that the inverter loses power suddenly during normal operation, which prevents it from starting the motor once power is restored. Upon inspection, it was found that the inverter module was damaged. The main reason for this was that after a power outage, the inverter continued to operate under command signals; at that time, the intermediate DC voltage dropped sharply due to the load drawn by the motor and the energy consumption of the inverter itself. This led to changes in the PWM modulation signal, resulting in damage to the power module. Under such circumstances, the drive circuit is generally not prone to damage. Replacing the inverter module allows the frequency converter to return to normal operation. In such situations, it is best to take measures in the control circuit to block the inverter’s output at the moment of a power outage. Damaged drive circuit: When repairing DV707 series frequency converters, we often encounter situations where the inverter module is damaged along with the drive circuit as well. No negative pressure in the drive circuit is a common phenomenon resulting from damage to the drive circuit. The DV707 series of inverters use Fuji’s PIM modules as their power devices, which are of the IGBT type. We know that IGBT high-power transistors are voltage-driven; in the absence of negative voltage, this prevents the IGBT from being turned off effectively, resulting in continuous conduction. Negative voltage is generally generated by the voltage-stabilizing diode, which is also the most common part to fail; by replacing it, the drive waveform should return to normal. LV failure is also one of the phenomena we often encounter during repairs. Especially in the DV700 series of inverters. After ruling out issues related to the external power supply, the problem is most likely a fault in the detection circuit; sampling is done through a voltage-reducing resistor, and after isolation via an optocoupler, the signal from the optocoupler is sent to the main control board for processing. The voltage-reducing resistor and isolation optocoupler may both get damaged. After replacement, the machine should return to normal operation. Maintenance methods for general-purpose frequency converters I. Precautions Operators must be familiar with the basic working principles and functional features of frequency converters, as well as possess basic knowledge of electrical work. Before inspecting and maintaining the inverter, it is necessary to completely cut off the main power supply to the equipment ； And it should be done once the Chang light of the inverter has completely gone out. II. Routine inspection items: Before powering on the inverter, it is necessary to check the temperature and humidity of the surrounding environment. Excessively high temperatures can cause the inverter to trigger an overheat alarm; in severe cases, this can lead to damage to the inverter’s power components and circuit short circuits ； Excessively high humidity can cause a direct short circuit inside the inverter. When the inverter is in operation, it is necessary to check whether its cooling system is functioning properly, such as whether the air flow in the air ducts is smooth and whether there are any abnormal noises from the fans. Frequency converters with a higher level of protection, such as those with an IP rating of IP20 or higher, can be installed in an open manner; whereas frequency converters with an IP rating below IP20 should generally be installed in enclosures. Therefore, the cooling efficiency of the frequency converter enclosure has a direct impact on its proper operation. Factors such as whether the fans in the ventilation system rotate smoothly, and whether there is dust or obstructions in the air inlets, are all aspects that must be checked regularly. Are the motor reactors, transformers, etc. overheating, and is there any unusual odor? ； Are there any abnormal noises from the inverter and motor? ； Check whether the current display on the inverter panel is too high or the range of current fluctuations is excessive, and whether the UVW three-phase voltages and currents are balanced. III. Regular maintenance: Clean the air filter, cooling ducts, and internal dust. Check whether screws, bolts, and connectors are loose, and whether there is any short circuit in the resistance between the input/output reactors and ground or between different phases; the value should be above several dozen megohms under normal conditions. Check whether there is any corrosion on the conductors and insulators; if so, clean them immediately with alcohol. If conditions permit, an oscilloscope should be used to measure the stability of the voltages output by the switching power supply at various levels, such as 5V, 12V, 15V, 24V, etc. Measure whether the square waves of each circuit in the drive circuit are distorted. Whether the UVW alternating waveform is a sine wave. Check whether there are any signs of arcing on the contacts of the contactor; in severe cases, replace them with new ones of the same model or with a capacity greater than the original ； Verify the correctness of the control voltage and conduct sequential protection operation tests ； Confirm that there are no abnormalities in the protection display circuit ； Verify the balance of the output voltage when the inverter is operating alone. It is recommended to conduct regular inspections, once a year. IV. Replacement of spare parts The frequency converter is composed of various components, some of which experience a gradual decline in performance and aging over time as a result of prolonged use; this is one of the main causes of failures in frequency converters. To ensure the long-term proper operation of the equipment, the following components should be replaced regularly: 1. Cooling fan The power modules of the frequency converter are the components that generate the most heat, and the heat produced by their continuous operation must be dissipated promptly. The typical lifespan of a fan is around 10K–40K hours. Based on the continuous operation of the inverter, the fan needs to be replaced every 2–3 years. There are two-wire and three-wire types of direct cooling fans; in a two-wire fan, one wire is the positive pole and the other is the negative pole. Be careful not to connect them incorrectly when replacing the fan ； In addition to the positive and negative terminals, a third wire is present in three-wire fans; be sure to pay attention to this when replacing them, otherwise it may cause an overheat alarm in the inverter. AC fans are generally available in 220V and 380V versions; be careful not to get the voltage level wrong when replacing them. 2. Filtering capacitors: The filtering capacitors in the intermediate circuit are also known as electrolytic capacitors. Their main function is to smooth the DC voltage and absorb the low-frequency harmonics present in the DC current. The heat generated by their continuous operation, combined with the heat produced by the inverter itself, accelerates the evaporation of the electrolyte, which directly affects the capacity of these capacitors. Under normal conditions, the service life of a capacitor is 5 years. It is recommended to check the capacitance value regularly on an annual basis; generally, it should be replaced when its capacity decreases by more than 20%. Common faults of Siemens frequency converters and repair strategies. Siemens is undoubtedly a renowned brand in the field of automation; its products include PLCs, human-machine interfaces, frequency converters, servo systems, and automated instruments – covering virtually all aspects of automated control. It has also earned a good reputation across various industries. Siemens inverters hold an important position in the inverter market thanks to their stable performance, a wide range of functional options, and excellent torque characteristics. Thanks to its strong brand presence, it has broken the monopoly held by Japanese-brand frequency converters in the Chinese market. According to statistics from relevant market research firms, Siemens’ high- and low-voltage frequency converters now rank first in the Chinese market. The use of Siemens frequency converters in the Chinese market began in the steel industry. At that time, motor speed control relied mainly on DC methods, and the application of frequency converters was still a nascent market. However, with the continuous development of electronic components and the advancement of control theory, frequency-controlled speed regulation gradually replaced DC speed control and became the mainstream method for driving equipment. Thanks to its strong brand presence, Siemens frequency converters achieved significant success in this vast Chinese market. Siemens’ success in this field can be attributed to the perfect combination of its brand and its technical capabilities. In the Chinese market, the early Siemens frequency converters we can find are mainly the current-source type SIMOVERT A and the voltage-source type SIMOVERT P. These converters entered the Chinese market primarily along with the introduction of related equipment; to this day, they are still used in limited quantities. Later on, the models that gained widespread popularity in the Chinese market were MICRO MASTER and MIDI MASTER. Additionally, the most successful series of Siemens frequency converters is the SIMOVERT MASTERDRIVE, which is commonly referred to as the 6SE70 series. It not only provides AC-AC frequency converters for general use, but also offers DC bus systems with multi-motor drive suitable for the requirements of special industries such as papermaking and chemical fibers. Of course, Siemens also introduced the ECO drive, which, in my opinion, was a technical failure yet was quite successful in the market. The technical failure was mainly due to its high failure rate, while its success in the market was attributed to it overtaking Fuji drives to become the leading brand in the Chinese market. At present, Siemens’ main models in the Chinese market are the MM420, MM440, and 6SE70 series. Due to the large volume of Siemens inverters sold in the Chinese market, many problems are bound to arise during their use. Here, we would like to discuss with users some of the common faults associated with Siemens inverters: Siemens is likely one of the brands that entered the Chinese market early on, so some older models such as MICRO MASTER and MIDI MASTER still have a large number of users. We will first analyze the common faults of these two series of products. For the MICRO MASTER series of inverters, the most common fault is no display when powered on. The switching power supply in these inverters uses a UC2842 chip as the waveform generator; damage to this chip can prevent the switching power supply from functioning, which in turn results in no display. Additionally, problems with the power supply for this chip can also cause the switching power supply to not work properly. For MIDI MASTER series inverters, the most common faults are damage to the drive circuit and damage to the IGBT module. The drive circuit of the MIDI MASTER is designed to use a pair of transistors to drive the IGBT module; this pair of transistors is also the component most prone to damage. The cause of such damage is often the failure of the IGBT module, which allows high-voltage, high-current electricity to flow into the drive circuit, thereby damaging its components. For the 6SE70 series of frequency converters, their superior quality results in a significantly lower failure rate. Common fault phenomena we encounter include F008 (low DC voltage). Since the sampling signal is obtained by reducing the voltage through resistors, fault F008 occurs mainly due to damage to the sampling resistors. In addition, we may also encounter errors F025, F026, and F027 related to the absence of input phases. One possible cause of these errors is that the 6SE70 series has an input phase detection function; damage to the input detection circuit can lead to alerts indicating the absence of input phases. If this cause is ruled out and the alert signals still persist, then it is likely that the CU board is damaged. In addition, the F011 (overcurrent) fault is also a common one; damage to the current sensor is one of the causes of this fault. Moreover, during repairs we often find that damaged surface-mounted filter capacitors in the drive circuit and switching power supply can also trigger the F011 alarm. We need to pay special attention to fault alarms caused by such reasons. For ECO inverters, the most common issues we encounter are burned-out power boards and damaged power modules. The main cause is the lack of an isolation circuit between the high-voltage side (power modules) and the low-voltage side (drive circuits); this allows high-voltage current to reach the control circuits, resulting in widespread damage to both the drive circuits and the switching power supplies. Additionally, damage to the pre-charge circuit is also a frequent fault (especially in units above 30 kW). Since the current-limiting circuit is located on the AC input side, any timing discrepancies—whether leading or lagging—between any one of the three-phase AC power sources can cause excessive current during the charging process for that phase or the other two phases, thereby burning out the current-limiting resistor and the cut-in relay. The F231 fault is also a common fault of the ECO inverter, caused by damage to the sampling resistor. As for the fault symptoms of the MM420 and MM440 frequency converters, they fall within the scope we discussed earlier; the only change is that the internal structure of these converters has been modified – integrated power modules from Siemens, a well-known manufacturer of power semiconductors, are now used, which reduces the size of the equipment and minimizes the number of internal connections, as the connections between circuits are made through direct contact. It can be said that the MM440 and MM420 series of frequency converters experience quite a number of failures, especially those with lower power ratings. Installation, commissioning, and fault detection of the SD-5L inverter (I) Installation environment, basic configuration, and interference resistance I. Installation of the inverter 1. Installation environment of the inverter (1) Ambient temperature –10℃ to 50℃. The interior of the inverter contains high-power electronic components that are highly sensitive to operating temperatures. However, to ensure safe and reliable operation, it is necessary to allow for some margin; it is best to keep the temperature below 40℃. When the ambient temperature is too high and there are large temperature fluctuations, the insulation properties of the inverter **degrade**. (2) Environmental humidity: Relative humidity should not exceed 90% (no condensation). If necessary, desiccants and heaters can be added to the frequency conversion cabinet. (3) Vibration and shock. When a control cabinet equipped with an inverter is subjected to mechanical vibration and shock, it can lead to poor electrical contacts. At this time, in addition to enhancing the mechanical strength of the control cabinet and keeping it away from vibration and shock sources, anti-vibration rubber pads should be used to secure vibrating components such as external and internal electromagnetic switches within the control cabinet. After the equipment has been in operation for a period of time, it should be inspected and maintained. (4) Electrical environment 1) Prevent electromagnetic interference. 2) Prevent overvoltage at the input. (5) Other conditions: Factors such as no direct sunlight, absence of corrosive and flammable gases, low dust levels, and an altitude below 1,000 meters must all be taken into consideration. 2. Installation methods: (1) Wall-mounted installation: The distance between the frequency converter and surrounding objects should meet the following requirements: at least 10 cm on each side, and at least 15 cm above and below. (2) Cabinet-mounted installation: A. This is currently the best installation method, as it provides effective shielding while also protecting against dust, moisture, and light exposure. B. For single frequency converters, external cooling should be used whenever possible (when the environment is clean and free of dust) ； 　C. When a single inverter uses internal cooling, an exhaust-type cooling fan should be installed at the top of the inverter cabinet, preferably directly above the inverter (to facilitate air circulation) ； 　Multiple inverters should be installed side by side whenever possible. If vertical installation is necessary, a partition must be installed between two inverters. 　In any case, the frequency converter should be installed vertically (which is also the most appropriate installation method). II. Wiring of the frequency converter 　　1. Main circuit wiring 　　(1) The input terminals (R, S, T) and output terminals (U, V, W) of the frequency converter must not be connected incorrectly. 　　(2) Ensure that the grounding terminal of the frequency converter is properly grounded; if the factory’s electrical system shares a common ground line, it is necessary to provide a separate ground wire. When multiple frequency converters are used, each one should be connected to the ground separately – it is not allowed to connect the grounding terminals of different frequency converters together before grounding them. (3) Connect the power input terminals of the inverter to the power supply through a leakage protection switch (it is important to choose reputable manufacturers for such switches and circuit breakers). 2. Wiring of the control circuit: (1) Analog control wires should be shielded wires; one end of the shield should be connected to the COM terminal of the inverter’s control circuit, not to the E terminal or the ground, while the other end should remain unconnected. (2) For digital control lines, it is permissible not to use shielded wires, but the two wires for the same signal must be twisted together, with the twisting pitch of the twisted pair being as small as possible. 　　III. Improving the power factor of the inverter: To improve the power factor or when the installation site is located very close to a high-capacity power source, it is necessary to install DC reactors and AC reactors. In addition to improving the power factor, it also has the following effects: (1) Suppressing inrush currents in the input; (2) Reducing the impact of voltage imbalance in the power supply. Selection of reactance: (1) The voltage drop across the reactor should not exceed 3% of the rated voltage. (2) When the transformer capacity exceeds 500 KVA, or when the transformer capacity is more than 10 times that of the inverter, a reactor should be installed. IV. Interference Resistance of Inverters 1. External interference to inverters mainly comes from the power supply lines. When the power supply system is connected to other devices (such as capacitors) or due to the operation of other devices (such as commutation devices like thyristors), it can easily cause distortion in the power supply, thereby damaging the switching transistors of the inverter. Inserting an AC reactor in the input circuit of the inverter can effectively suppress interference originating from the incoming line. 2. Interference from external sources on the inverter (1) Ways in which interference signals are transmitted: Air radiation – transmission via electromagnetic waves; Electromagnetic induction – induction through inductance between wires; Electrostatic induction – induction through capacitance between communication wires; Line transmission – transmission through wire networks. (2) Anti-interference measures: A. On the inverter side, interference signals transmitted by induction can be reduced through proper wiring and the use of shielded cables. For interference signals transmitted along lines, small inductors can be inserted into those lines to reduce their impact. Interference signals transmitted through radiation can be mitigated using absorption methods (radio interference filters). By inserting filter reactors between the inverter’s output and the motor, not only can interference be reduced, but additional torque caused by high harmonics can also be diminished, thereby improving the motor’s operating characteristics. On the output side of the inverter, it is absolutely not allowed to use capacitors to absorb harmonic currents. B. Power isolation on the instrument side: An isolation transformer is connected to the power supply side of the instrument. Signal isolation: Optocouplers are used to isolate the signal side. V. Lightning protection for frequency converters: Lightning protection systems are generally installed in frequency converters to prevent sudden lightning strikes from causing damage to the devices. However, in practical applications, especially when the power supply cables are introduced overhead, the absorption network of the inverter alone is not sufficient to meet the requirements. This issue is particularly important in areas with frequent lightning strikes; if the power supply is supplied via overhead lines, a dedicated lightning arrester for frequency converters should be installed at the connection point (as an option), or steel pipes should be buried at a distance of 20 meters from the frequency converter to provide proper grounding protection as required by regulations. If the power supply is supplied via a cable, the lightning protection system in the control room should be properly installed to prevent lightning from intruding and damaging the equipment. Practice has shown that this method can basically effectively solve the problem of lightning strikes. VI. Selection of braking components for frequency converters. 1 Brake unit (optional component) When the controlled equipment driven by the inverter requires rapid braking, a brake unit must be used to dissipate the energy fed back to the DC bus during motor braking. 2 Braking resistors (optional components): The braking resistors suitable for inverters of different power levels are as follows. Voltage level V, Motor power in kW, Resistance value in ohms/number in parallel, Resistance power in kW, Motor power in kW, Resistance value in ohms/number in parallel, Resistance power in kW: 380, 0.75; 400, 0.25; 37, 16; 9, 1.5; 400, 0.25; 45, 13.6; 9, 2.2; 250, 0.25; 55, 20/2; 12, 3.7; 150, 0.4; 75, 13.6/2; 18, 5.5; 100, 0.5; 90, 20/3; 18, 7.5; 75, 0.8; 110, 20/3; 18, 11; 50, 1.0; 132, 20/4; 24, 15; 40, 1.5; 160, 13.6/4; 36, 18.5; 30, 4.0; 200, 13.6/5; 45, 22; 30, 4.0; 220, 13.6/5; 45, 30; 20, 6.0; 280, 13.6/6; 54. Connection of braking components (example), Installation of braking resistors, Installation of braking control units. (II) Commissioning of the frequency converter and precautions: The basic steps to be taken during the commissioning of a frequency converter include testing with power supply but no load, operating without a motor but with load, trial operation under load, and coordinated adjustment in conjunction with a higher-level computer ； Points to note when completing these steps: 1. Before powering on the inverter, check whether its input and output terminals meet the requirements specified in the manual ； 2. Pay special attention to whether any new content has been added; read the precautions carefully ； 3. Check whether the wiring is correct and secure.        Typical frequency converters have 6 buttons: RUN, STOP, PROG, DATA/ENTER, UP (▲), and DOWN (▼); the functions of these buttons are generally the same across different frequency converters. In addition, some frequency converters also have function keys such as monitoring (MONITOR/DISPLAY), resetting (RESET), jogging (JOG), and shifting (SHIFT). I. Test run of the inverter with power connected (without connecting the motor). After powering it on, press the RUN button to operate the inverter at 50HZ; use a multimeter to check that the output phase voltages (U, V, W) of the inverter are balanced (370V–400V). After pressing the stop button, reconnect the motor cable.  II. Operation of the inverter with the motor under no-load conditions 1. Set the motor’s power and number of poles, taking into account the inverter’s operating current as well.  2. Set the maximum output frequency and base frequency of the inverter, as well as the torque characteristics.  3. Set the inverter to its built-in keyboard operation mode, press the step movement button, the start button, and the stop button, and observe whether the motor reverses direction and can start and stop properly.  4. Be familiar with the protection codes that activate when malfunctions occur during the operation of the inverter. Observe the factory settings of the thermal protection relay and the set values for overload protection; these can be modified if necessary.  III. Operational test under load 1. Manually operate the start/stop buttons on the inverter panel, observe the process of stopping the motor as well as the display on the inverter, to check for any abnormal phenomena. If any phenomenon occurs, adjust the relevant preset parameters and then run again.     2. If the inverter triggers overcurrent protection during the start-up or stop-up of the motor, the acceleration and deceleration times should be reset. The acceleration of the motor during acceleration and deceleration depends on the acceleration torque, whereas the rate of frequency change of the inverter during startup and braking is set by the user. If the motor’s moment of inertia or load changes, and acceleration or deceleration occurs at a preset frequency change rate, there may not be sufficient acceleration torque, which can lead to motor stall. In other words, the motor’s speed does not match the output frequency of the inverter, resulting in overcurrent or overvoltage. Therefore, it is necessary to set the acceleration and deceleration times appropriately based on the motor’s moment of inertia and the load, so that the frequency change rate of the inverter can be coordinated with the motor’s speed change rate. A way to check whether this setting is reasonable is to first set the acceleration and deceleration times based on experience; if overcurrent occurs during startup, the acceleration time can be appropriately increased ； If overcurrent occurs during braking, appropriately extend the deceleration time. On the other hand, the acceleration and deceleration times should not be set too long, as excessive time will affect production efficiency, especially during frequent starts and stops.     3. If the inverter continues to engage its protection mechanism within a specified time, the start/stop operation curve should be changed, from a straight line to an S-shaped, U-shaped, inverted S-shaped, or inverted U-shaped curve. When the motor load has high inertia, longer start and stop times should be used, and the type of operating curve should be set according to the load characteristics.     4. If the inverter still has operational faults, try increasing the protection value for the maximum current; however, the protection should not be disabled, and at least a 10%-20% protection margin should be maintained.     5. If operational faults of the inverter still occur, an inverter with a higher power rating should be replaced.     6. If the frequency converter-driven motor fails to reach the preset speed during startup, there may be two possible scenarios: (1) Mechanical resonance occurs in the system, which can be determined by listening to the sound of the motor’s operation. By setting a frequency hopping value, it is possible to avoid resonance points. Generally, a frequency converter can have three level jump points set. When an inverter controlled by V/f control drives an asynchronous motor, at certain frequency ranges, the motor’s current and speed may oscillate; in severe cases, the system fails to operate. Overcurrent protection can also occur during acceleration, preventing the motor from starting properly, and this problem is more pronounced when the motor is operating under light load or has a low moment of inertia. Standard frequency converters are equipped with a frequency skipping function, allowing users to set the skipping points and the width of the skip on the V/f curve based on the frequency at which oscillations occur in the system. When the motor accelerates, it can automatically skip these frequency ranges to ensure the normal operation of the system.    (2) The motor’s torque output capacity is insufficient. Different brands of frequency converters have different default parameter settings, which results in varying load-carrying capacities under the same conditions. Additionally, differences in the control methods used by the frequency converters can also lead to variations in the motor’s load-carrying capacity ； Or, due to differences in the system’s output efficiency, the load-carrying capacity may vary. For this situation, the value of the torque increase amount can be increased. If this target cannot be achieved, the manual torque increase function can be used; however, do not set it too high, as this will increase the motor’s temperature rise. If that still doesn’t work, a new control method should be adopted. For example, Hitachi inverters use a method that maintains a constant V/f ratio; when startup does not meet the requirements, a sensorless space vector control method can be used, as it offers greater torque output capacity. For fan and pump loads, the torque reduction curve values should be reduced.  IV. Connecting the inverter to a host computer for system debugging After the basic manual settings are completed, if there is a host computer in the system, connect the control wires of the inverter directly to those of the host computer; it is also necessary to change the operation mode of the inverter to terminal control. According to the requirements of the host system, set the range of the frequency signal input terminal of the inverter to 0-5V or 0-10V, as well as the response speed of the inverter to analog frequency signals. If additional monitoring headers are required, select the monitoring quantity for analog output and adjust the range of the inverter’s output monitoring terminal. This situation may occur during debugging: for example, the inverter does not respond after a signal is sent from the host computer. Since some host computers only accept AC signals and not DC signals, whereas the control signals of frequency converters are mostly DC signals, an external relay can be considered in such cases. (III) Maintenance and upkeep: Changes in the operating environment of the frequency converter, such as effects from temperature, humidity, smoke, etc., along with the aging of the internal components of the frequency converter, can all lead to various faults in it. Therefore, during storage and use, the frequency converter must be subject to regular inspections as well as periodic maintenance. I. Routine Maintenance When the frequency converter is running normally, please check the following: 1. Whether the motor is making any abnormal noises or experiencing vibrations. 2. Are the inverter and motor overheating abnormally, and is the ambient temperature too high? 3. Is the load current reading the same as usual? 4. Is the cooling fan of the inverter operating properly? II. Regular Maintenance: When performing regular maintenance checks on the inverter, it is essential to cut off the power supply. Inspection can only be carried out after the monitor shows no display and the power indicator light for the main circuit goes out. The inspection items are shown in the table. Inspection Items, Inspection Contents, Countermeasures for Abnormalities: Main circuit terminals, control circuit terminal screws – Check whether the screws are loose; tighten them using a screwdriver. Heat sinks – Check for dust; blow it away using dry compressed air at a pressure of 4–6 kg/cm2. PCB printed circuit boards – Check for dust; blow it away using dry compressed air at a pressure of 4–6 kg/cm2. Cooling fans – Check for abnormal noises or vibrations; replace the cooling fan if necessary. Power components – Check for dust; blow it away using dry compressed air at a pressure of 4–6 kg/cm2. Aluminum electrolytic capacitors – Check for discoloration, unusual odors, or bulging; replace the aluminum electrolytic capacitors if these issues are present. IV. Fault Detection: OH: Overheating – Overheating is a fault that often occurs. When encountering this situation, the first things to consider are whether the cooling fan is running, whether it is stuck, whether the ambient temperature is too high, whether there is poor ventilation of the inverter, and whether there is a fault in the temperature detection circuit.   POFF: Under-voltage – The input power supply may be missing a phase, the connection terminals of the input power supply may be loose, or the voltage of the input power supply may be highly unstable. Check whether there are any issues with the rectification, and whether the DC voltage is below 380V. In the case of overvoltage, we must first rule out faults caused by parameter problems. For example, if the deceleration time is too short, overvoltage may occur due to the regenerative load (braking unit); then we can check whether there is a problem with the voltage on the input side, and finally we can examine whether there is a fault in the voltage detection circuit. Generally, the voltage sampling point for a voltage detection circuit is the voltage of the intermediate DC circuit. OCU, OCS: Overcurrent. This is probably the most common fault in frequency converters. We must first rule out failures caused by parameter issues. For example, current limiting and excessively short acceleration times can both lead to overcurrent. Then we must determine whether there is a problem with the current detection circuit, such as a fault with the Hall sensor or the Hall wires. Is there a short circuit on the output side of the inverter? OL: Overload – the acceleration time is too short, the motor is under excessive load, and the motor is sticking. HE: Current sensor failure – the Hall wire is not properly connected, the sensor is damaged, and there is a problem with the current detection circuit. OCU1: Hardware protection. This is the most common fault. There is a short circuit in the UVW phases of the inverter’s three-phase output; external electrical devices cause interference, resulting in damage to the IGBT and IPM modules. The following is a simple test for faults in the main circuit of the frequency converter: Technicians can use a digital multimeter to determine whether the components in the main circuit are damaged, based on the diagram shown above. (Mainly rectifier bridges, IGBTs, IPMs) For personal safety, it is necessary to ensure that the machine is powered off, and the input wires R, S, T as well as the output wires U, V, W must be removed before it can be operated! First, set the multimeter to the \"diode\" mode. Then, using the red and black probes of the multimeter, follow these steps for testing: 1. Connect the black probe to the negative terminal P(+) of the DC bus, and connect the red probe to R, S, and T in sequence, recording the values displayed on the multimeter ； Then touch the red test lead to N(-), and touch the black test lead to R, S, T in sequence, while recording the reading displayed on the multimeter ； If the six display values are roughly balanced, it indicates that there is no problem with the diode rectification in the inverter or the soft-start resistors; otherwise, the rectification module or soft-start resistor at the corresponding location is damaged, resulting in no display. 2. Touch the red test lead to the negative pole P(+) of the DC bus, and sequentially touch the black test lead to U, V, and W. Record the values displayed on the multimeter ； Then touch the black test lead to N(-), and touch the red test lead to U, V, and W in sequence, recording the values displayed on the multimeter ； If the six display values are roughly balanced, it indicates that there is no problem with the IGBT inverter module of the frequency converter; otherwise, the IGBT inverter module at the corresponding position is damaged, resulting in no output or a fault alarm. The above are merely static judgments. The actual judgment is based on the motor-equipped test, but it can serve as a simple reference for on-site assessment. I hope this can serve as a reference for everyone. If there are any errors or inaccuracies, your criticism and corrections are welcome; I would be very grateful. Suggestions and Solutions for Common Issues Faced by Typical Customers Using Puchuan Frequency Converters

I. Installation and Maintenance of Frequency Converters
1. Proper Grounding
Issue: The “E” terminal of the frequency converter is not properly connected to ground, which can cause the converter to be affected by interference or experience malfunctions. This may also result in the casing becoming electrified or being damaged due to sudden high voltages (such as those caused by power grid fluctuations or lightning strikes).
Suggestion: Customers must ensure that the “E” terminal is connected to an independent ground source, thereby reducing the impact of high voltages on the equipment and protecting both personnel and devices.

2. Tightening Bolts
Issue: The wiring terminals R, S, T, U, V, and W of the frequency converter are not tightened properly, leading to high contact resistance at these connections. This can cause the terminals to overheat, and over time, they may get damaged or even cause the device to explode.
Suggestion: Customers should make sure that the wiring screws are tightened properly. If the screws become loose, they should be replaced.

3. Keeping Away from Heat Sources
Issue: Installing the frequency converter in a location with heat sources can cause the device to overheat, deform, and even explode.
Suggestion: The frequency converter should be installed away from heat sources and other sources of radiation.

4. Regular Cleaning
In environments with a lot of cotton fibers or similar materials (such as in textile industries), these materials can block the air vents, causing the fans to stop working. This can lead to overheating of the frequency converter and even its explosion.
Suggestion: The frequency converter should be placed in a protective enclosure, and the ventilation channels of both the enclosure and the converter itself should be cleaned regularly to ensure proper cooling.

5. Protecting Against Dust
In environments with a lot of dust (such as in cement plants or flour mills), dust, which may contain conductive substances, can accumulate on the surfaces of electronic components, affecting their cooling capabilities. This can lead to abnormal functioning of the frequency converter and even short circuits that cause explosions. Recommendation: Install the inverter in a protective cabinet, add a dust cover, regularly clean the ventilation channels, and remove dust from inside the inverter. 6. Remember to prevent moisture. Issues related to humidity, oil, or other liquids (e.g., in chemical plants, water treatment facilities, outdoor equipment, etc.). Problems: Moist air, oil, or other liquids entering the machine leave visible traces; metal parts may rust, leading to machine failure after a short or slightly longer period of operation. Recommendations: Install the inverter in a protective cabinet, keep it away from oily areas, and place it in a dry environment. Use a dedicated control cabinet for the inverter to provide heating and dehumidification. Add waterproof barriers and regularly clean the inverter, etc.

II. Common causes of malfunctions and their solutions
Malfunction symptoms | Causes | Improvement measures
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OC-P during operation | 1. Excessive load on the inverter
a. Increase the inverter’s capacity
b. Check whether mechanical connections in the system are normal
c. Conduct insulation tests on the motor | 2. Improper parameter settings of the inverter
a. Extend acceleration/deceleration times
b. Set the V/F ramp-up method appropriately | 3. Unsuitable manufacturing process
a. Modify the process to reduce load fluctuations | 4. Poor grounding of the E-ground wire
a. Ensure proper grounding of the inverter to earth |
OL during operation | 1. Overly heavy load
a. Reduce the load
b. Enable the current limit function effectively |
LU during operation | 1. Input voltage is too low
a. Raise the supply voltage to the inverter
2. Insufficient grid capacity
a. Upgrade the power supply system
3. Large inrush currents in the grid
a. Minimize instances where high-power equipment startup causes voltage drops in the grid |
OH during operation | 1. Ambient temperature is excessively high
a. Install ventilation systems or air conditioning
2. Damaged inverter fan
a. Replace the fan
3. Blocked airflow paths in the inverter
a. Clear any obstructions in the inverter’s cooling channels |
OU during operation | 1. Excessive load inertia
a. Prolong deceleration time; add a braking unit and resistor
2. Input voltage is too high
a. Lower the input supply voltage |
Motor fails to rotate | 1. Loose motor wiring
a. Tighten the motor wires
2. Overly heavy motor load
a. Reduce the motor load
3. Inverter not operating
a. Configure startup and speed regulation settings before operating the inverter |
Motor overheating | 1. Poor-quality silicon steel sheets inside the motor
a. Replace the motor
2. Insufficient insulation resistance of motor windings
a. Replace or repair the motor
3. Excessive distance between inverter and motor (≥50 meters)
a. Shorten this distance; install an output reactor
4. Inadequate motor heat dissipation
a. Enhance the motor’s cooling capacity
5. Improper carrier frequency setting of the inverter
a. Set the carrier frequency according to the manual instructions