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1 Overview In modern industry, AC drive is used as the preferred drive solution in many occasions due to its superiority over DC drive. The motor system controlled by a frequency converter has the advantages of significant energy saving effect, convenient adjustment and control, simple maintenance, network centralization, remote control, and the ability to form an automatic control system with PLC. These characteristics of frequency converters make them increasingly widely used in power electronic systems, industrial automatic control and other fields. The installation, wiring, and debugging of different models and specifications of inverters on the market have their own characteristics, but the main methods and precautions are basically the same. However, when using frequency converters, once a fault occurs, it is difficult for ordinary operators in industrial and mining enterprises to deal with it. Frequency converter faults may be caused by product quality problems, operating environment problems, application method problems, or parameter setting problems of the frequency converter. This article introduces the common faults of frequency converters, their causes and treatment methods. 2 Analysis and treatment of causes of parameter setting faults When using the inverter, whether it can meet the control requirements of the transmission system, the parameter setting of the inverter is very important. If the parameter setting is incorrect, the control effect will be poor in the least, and the inverter will not operate normally in the worst case. For a newly purchased inverter, the manufacturer generally sets a default value for each parameter when it leaves the factory. In this case, the inverter can operate normally in the panel operation mode, but it cannot meet the requirements of most transmission systems. To obtain better control effects, the user must modify the parameters of the inverter according to the actual conditions of the transmission system and refer to its instruction manual. 2.1 Handling of parameter setting faults Once a parameter setting fault occurs, the inverter cannot operate normally. It is best to restore all parameters to factory values, and then reset the relevant parameters according to the parameter setting steps in the instruction manual. For different types of inverters, their parameter recovery methods are also different. Improper parameter setting. This problem often occurs on constant torque loads. At this time, you should focus on checking the acceleration and deceleration time settings or increasing the torque setting value. 2.2 Example introduction Example 1: A Fuji FRN280G11-4CX frequency converter tripped during operation and displayed undervoltage "LU". Analysis and repair: When starting high-power equipment such as the 2# nitrogen and hydrogen compressor (4000 kW synchronous motor), the other two Fuji FRN5.5G11-4CX inverters on the same power supply did not jump during operation. Only this inverter jumped during operation and displayed an undervoltage "LU" alarm. After the power is turned off, open the casing and check that the medium-voltage wiring of the primary and secondary circuits inside the inverter is not loose. ； Check that there is no contact in the motor terminal box. After powering on, check the setting parameters of the inverter. The setting value of F14 is "1" (momentary power failure and restart will not work). Modify the setting parameter F14 of the inverter and the setting value is "3" (momentary power failure and restart action). After the frequency converter detects undervoltage, the protection function does not work, stops output, and automatically restarts when the power is restored. After modifying the setting parameters of the inverter, when starting high-power equipment, the inverter no longer skips undervoltage "LU" during operation. Example 2: A FRN1.5G11-4CX inverter is newly put into use. The frequency setting is already very high, but the motor speed is obviously lower than other motors at the same frequency. Analysis and repair: Check the setting parameters of the frequency converter. Check the frequency gain F17, its setting range is 0.0~200%, the factory setting value is 100%, and the user's actual setting value is 200%. Since the frequency setting signal gain is the ratio of the set analog frequency signal to the output frequency, that is, if the set frequency is 40Hz, the actual output frequency is only 20Hz. After changing the set frequency gain setting value to the factory setting value (100%), the problem was solved. 3 Analysis and treatment of overvoltage fault causes 3.1 Overvoltage (OU) The overvoltage of the frequency converter is concentrated on the tributary voltage of the DC bus. Under normal circumstances, the DC power of the frequency converter is the average value after three-phase full-wave rectification. If calculated based on U=380V line voltage, the average DC voltage Ud=1.35 U=513V. When overvoltage occurs, the energy storage capacitor of the DC bus will be charged, and the overvoltage detection value is 800VDC. When the voltage rises to the overvoltage detection value, the inverter overvoltage protection will operate. Therefore, there is a normal operating voltage range for the frequency converter. When the voltage exceeds this range, the frequency converter is likely to be damaged. There are three types of common overvoltages in frequency converters:: OU1 acceleration overvoltage, OU2 deceleration overvoltage, OU3 constant speed overvoltage. Overvoltage alarm usually occurs when the vehicle is shut down. The main reason is that the deceleration time is too short or the braking resistor and braking unit are not installed. The specific time when an overvoltage fault occurs in the inverter is usually during a thunderstorm. As lightning enters the power supply of the inverter, the voltage detector on the DC side of the inverter operates and trips. In this case, it is usually only necessary to disconnect the power supply of the inverter for about 1 minute and then turn it on again to reset. Another situation is when the frequency converter drives a large inertia load, the deceleration time setting is small, because in this case the deceleration stop of the frequency converter belongs to regenerative braking. During the stop process, the output frequency of the frequency converter decreases linearly, and the frequency of the load motor is higher than the output frequency of the frequency converter, and the load motor is in the power generation state. state, mechanical energy is converted into electrical energy and is absorbed by the smoothing capacitor on the DC side of the frequency converter. When this energy is large enough, the so-called "pumping phenomenon" will occur. The voltage on the DC side of the frequency converter will exceed the maximum voltage of the DC bus and trip. For this kind of fault, first, set the deceleration time parameter longer ； The second is to install a braking unit and increase the braking resistance. ； The third is to set the stop mode of the frequency converter to "free stop". Another situation is that the frequency converter works normally when the motor is no-load, but cannot start with load. This problem often occurs with constant torque loads. At this time, you should focus on checking the acceleration and deceleration time settings or the torque boost function. The reason is that the DC link voltage of the frequency converter rises and exceeds its protection value, causing failure. 3.2 Example introduction Example 1: A Taian N2 series 3.7kW inverter jumps "OU" when shutting down. Analysis and maintenance: Before repairing this machine, you must first understand the cause of the "OU" alarm. This is because when the frequency converter decelerates, the motor rotor winding cuts the rotating magnetic field faster, and the electromotive force and current of the rotor increase, making the motor in a power generation state, and the feedback energy passes through the inverter link. The diode connected in parallel with the high-power switch tube flows to the DC link, causing the DC bus voltage to increase. Therefore, we focused on checking the brake circuit. There was no problem when measuring the discharge resistance. When measuring the brake tube (ET191), we found that it had broken down. After replacing it, it was powered on and ran, and then there was no problem with the quick stop. Example 2: A Fuji FRN110G9-4CX inverter tripped during operation and displayed constant speed overvoltage "OU3". Analysis and repair: First analyze the possible causes that cause the inverter to jump during operation and display the constant speed overvoltage (OU3) alarm, and then find and handle them one by one. 4 Analysis and treatment of causes of undervoltage faults 4.1 Undervoltage (LU) Undervoltage is also a problem often encountered in the use of inverters. Mainly because the main circuit voltage is too low (380V series is lower than 400V), one path of the rectifier bridge is damaged or one of the three thyristor paths is not working properly, which may lead to undervoltage faults. ； Secondly, the main circuit contactor is damaged, causing the DC bus voltage to be lost on the charging resistor, which may also lead to undervoltage. ； There is also the problem of undervoltage due to failure of the voltage detection circuit. The lower limit of the bus voltage of most frequency converters is 400V, that is, when the DC bus voltage drops below 400VDC, the frequency converter will report a DC bus low voltage fault. When two-phase input is used, the DC bus voltage is 380×1.2=452V>400V ； When the frequency converter is not running, the DC voltage can also reach the normal value due to the smoothing capacitor. New inverters all use PWM control technology. The voltage and frequency regulation work is completed on the inverter bridge, so it can still work normally if the input phase is missing in the low frequency band. However, due to the low input voltage and low output voltage, the asynchronous motor has low torque and the frequency cannot increase. 4.2 Example introduction Example 1: A Fuji FRN18.5G11-4CX inverter jumps "LU" when powered on. Analysis and repair: After checking that the rectifier bridge and charging resistor of this inverter are all good, but no contactor action is heard after powering on. Since the charging circuit of this inverter does not use a thyristor but relies on the pull-in of the contactor to complete the charging process, it is believed that the fault may be in the contactor or control circuit and power supply. Remove the contactor and apply 24V DC separately. The contactor works normally. ； Then I checked the 24V DC power supply and found that the voltage was output after being stabilized by the LM7824 voltage regulator tube. I measured that the voltage regulator tube was damaged. I found a new one and replaced it with a new one. After powering on, it worked normally. Example 2: A Danfoss VLT5004 2.2 kW inverter displays normally when powered on, but "DC LINK UNDERVOLT" (DC link voltage is low) jumps after adding load. Analysis and maintenance: This inverter failure appears to be rather special, but after careful analysis, the problem is not that complicated. The inverter also completes the charging process through the charging circuit and contactor. No abnormality was found when powering on. It is estimated that it is caused by the voltage drop of the DC circuit when the load is added. The voltage of the DC circuit is full-wave rectified by the rectifier bridge and then provided by the capacitor after smoothing, so the rectifier bridge should be checked carefully. After measurement, it was found that one bridge arm of the rectifier bridge was open, and the problem was solved after replacing it with a new one. This indicates that there is a problem with the power input circuit. It may be that the line is seriously overloaded or the line contact is poor. For another example, when the letter "E" is displayed on the PMU panel LCD of the Siemens 6SE70 series inverter, the inverter cannot work. Pressing the "P" key and re-stopping the power supply have no effect. There is no relevant introduction in the operation manual. When checking the external DC24V power supply, it is found that the voltage is low. After solving the problem, the inverter works normally. 5 Cause analysis and treatment of over-current faults 5.1 Over-current (OC) Over-current is the most frequent alarm phenomenon in the inverter. When this kind of fault occurs, first check whether there is a short circuit between phases or a short circuit to ground in the circuits U, V, and W of the motor connection terminals. ； Secondly, check whether the load is too heavy and reduce the load. ； Finally, check whether the acceleration and deceleration time parameters are too short and whether the torque boost parameter is too large, thereby reducing the torque boost amount. If there are no such phenomena, you can disconnect the current transformer on the output side and the Hall current detection point on the DC side, and run after reset to see if overcurrent occurs. If so, it is likely that the 1PM module is faulty, because the 1PM module contains overvoltage, overcurrent, undervoltage, overload, and overcurrent. Thermal, phase loss, short circuit and other protection functions, and these fault signals are transmitted to the microcontroller through the output Fn pin of the module control pin. After receiving the fault information, the microcontroller blocks the pulse output on the one hand, and displays the fault information on the panel on the other. At this time, the 1PM module should generally be replaced. Overcurrent during acceleration or deceleration is often caused by excessive acceleration or deceleration, which can be solved by increasing the acceleration (deceleration) time or accurately presetting the speed increase (decrease) self-processing (anti-stall) function. Common overcurrents in frequency converters include the following three categories. (1) When restarting, it trips as soon as the speed increases. This is a very serious phenomenon in overcurrent faults. The main reasons are: load short circuit, mechanical parts are stuck ； The inverter module is damaged ； The torque of the motor is too small, etc. (2) It will jump when power is turned on. This phenomenon generally cannot be reset. The main reasons are: the module is bad. ； The drive circuit is broken ； The current detection circuit is broken. (3) The trip does not occur immediately upon restart but occurs during acceleration. The main reasons are: the acceleration time setting is too short ； Current upper limit setting is too small ； The torque compensation (V/F) setting is higher. 5.2 Example introduction Example 1: An LG-IS3-4 3.7 kW inverter jumps as soon as it is started and displays "OC". Analysis and repair: No signs of burnout were found when the machine cover was opened. The online measurement of the IGBT (7MBR25NF-120) basically determined that there was no problem. To further determine the problem, the IGBT was removed and the high-power transistors of the 7 units were measured and turned on and off. All were fine. Later, when measuring the drive circuit of the upper half bridge, I found that one circuit was obviously different from the other two circuits. After careful inspection, I found that the output pin of an optocoupler A3120 was short-circuited to the negative pole of the power supply. After replacement, the three circuits were basically the same. After the module is installed, power on and run, and everything is fine. Example 2: A BELTRO-VERT 2.2kW inverter jumps when powered on, displaying "OC", and "OC" cannot be reset. Analysis and repair: First check the inverter module, no problem found ； Secondly, I checked the drive circuit, and there was no abnormality. It is estimated that the problem is not in this area. It may be in the over-current signal processing part. After removing the circuit sensor and powering it on, it showed that everything was normal, so I thought the sensor was broken. I found a new one and replaced it with a load test. Everything was normal. 6 Analysis and Treatment of Overload Fault Causes 6.1 Overload (OLU) Overload is also one of the faults that cause the frequency converter to jump more frequently. When you see an overload phenomenon, you should first analyze whether it is the motor overload or the inverter itself. Due to the strong overload capability of the motor, as long as the motor parameters in the inverter parameter table are properly set, motor overload is generally unlikely to occur. ； The frequency converter itself is prone to overload alarm due to its poor overload capability. At this time we can detect the inverter output voltage. The possible reasons are that the acceleration time is too short, the grid voltage is too low, the load is too heavy, etc. Generally, it can be solved by extending the acceleration time, extending the braking time, checking the power grid voltage, etc. ； If the load is too heavy, reduce the load. Since the selected inverter cannot drag the load, the inverter capacity should be replaced or increased. ； It may also be caused by poor mechanical lubrication, and the production machinery should be inspected and repaired. 6.2 Example introduction example: A Fuji FRN11G11-4CX inverter drives a Y132S-6 7.5 kW motor. When it is put into operation, it jumps and stops frequently and displays (OLU). Analysis and maintenance: On-site inspection of the machinery, the mechanical part can be turned easily and there is no stalling phenomenon ； Refer to its instruction manual to check the parameters of the inverter. After inspection, the bias frequency was originally set to 3Hz. Before the inverter receives the operating command but does not give the frequency modulation signal, the motor will always receive a low-frequency operating command of 3Hz and cannot start. It has been measured that the motor's locked-rotor current reaches 50A, which is about three times the rated current of the motor. ； The overload protection action of the frequency converter is normal. Modify the parameters of the inverter, restore the bias frequency to the factory value, and modify the bias frequency to 0Hz, so that the motor can start normally. 7 Cause Analysis and Treatment of External Condition Fault 7.1 External Condition Fault External condition fault is also a relatively common fault. This fault has no alarm code display, and the fault is relatively hidden and difficult to find. For example, after the inverter is running, when using the "potentiometer" external analog input voltage command value, the frequency adjustment is normal. ； When using the "DC4~20mA" external analog input current command value, the frequency cannot be adjusted. The reason may be that the "DC4~20mA" external analog input current command signal is weak and cannot meet the working requirements. ； Or "DC4～20mA" external analog input current command signal "+, - pole" is reversed. 7.2 Example introduction example: For an Emerson TD1000-4T0037P 3.7 kW inverter, the craftsman reported that the speed could be adjusted normally using the "potentiometer" on site, but the speed could not be adjusted automatically using the DCS "DC4~20mA" in the control room. Analysis and maintenance: After checking according to the inverter fault phenomenon described by the craftsman, it was found that the setting parameters of the inverter had not changed. After disassembly and replacement, an inverter of the same model was replaced. After the parameter settings were completed, the fault was the same as above after starting up, but it was not eliminated. After the power is turned off, open the inverter shell and use a digital multimeter to measure the "analog current" signals of the inverter control terminals CCI and GND. The digital multimeter displays -10 mA. It can be judged from this that the cause of the fault was that when the maintenance personnel replaced the inverter and restored the secondary line, they mistakenly connected the two lines of the inverter control terminals CCI and GND to the wrong position. Remove the two wires of the inverter control terminals CCI and GND and replace them. After the processing is completed, power on and test run. The fault will be eliminated. 8 Cause Analysis and Treatment of Overheating Faults in the Frequency Converter 8.1 Overheating in the Frequency Converter (OH3) OH3 is also a relatively common fault. The main reason is that the load is too large or the temperature of the frequency converter is too high. If an overtemperature alarm occurs and the temperature sensor is checked to be normal, it may be caused by interference and the fault can be shielded. In addition, the ventilation condition of the cooling fan and heat sink of the frequency converter should also be checked, the stalled cooling fan should be replaced, the frequency converter should be cleaned, and the heat sink should be eliminated ； If the ambient temperature is too high, the ambient temperature should be lowered. For overheating faults in the inverter caused by other reasons, it is best to contact the manufacturer to obtain a quick and feasible solution. 8.2 Example introduction example: A customer reported that an ABB ACS500 22 kW frequency converter would jump and display "OH" after about half an hour of operation. Analysis and maintenance: Because the fault occurred after running for a period of time, it is unlikely that the temperature sensor is broken. Maybe the temperature of the inverter is indeed too high. After powering on, it was found that the fan rotates slowly ； After the power is cut off, check that the protective cover of the inverter is filled with a lot of cotton wool. After cleaning, turn on the fan and find that the fan is running well. 9 Cause analysis and treatment of heat sink overheating fault 9.1 Heat sink overheating (OH1) OH1 is also a relatively common fault. You should mainly check whether there is a short circuit between the inverter control terminals (13, 12, 11). ； Is the temperature sensor detection circuit normal? ； Is the cooling fan of the frequency converter running normally? ； Check the ventilation condition of the heat sink and whether the heat sink is blocked. ； Is the ambient temperature too high? 9.2 Example introduction example: A Fuji FRN15G11-4CX inverter shows that the heat sink is overheated (OH1) when it is powered on. Analysis and repair: Because the inverter was newly installed and it malfunctioned as soon as power was supplied, the possibility of the inverter being broken is unlikely. ； There is no clogging of the heat sink ； The cooling fan also operates normally. After the power was cut off, a multimeter was used to test the analog input circuit, and it was found that there was a short circuit between the control terminals (13, 12, 11) of the inverter. The reason was that the resistance value of the external frequency setting "potentiometer" in the analog input circuit was too small. It was replaced with a WXWXX0.25-1, 0.25W 47~4.7k potentiometer. After powering on, the inverter ran well and this fault did not occur again during operation. 10 Conclusion The inverter has a high technological content and is a device that combines strong current and weak current applications, so its faults are various. Only by constantly summarizing in practice can we explore a set of quick and effective solutions. The above is just my experience in practice, and I hope to discuss it with my colleagues.