Collection of Fuji Inverter Repair and Fault Troubleshooting Techniques

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Compilation of Fuji Inverter Repair and Fault Handling: Common Faults and Diagnosis (1) OC Alarm – The LCD on the keyboard panel indicates overcurrent during acceleration, deceleration, or constant speed operation. For OC alarms caused by high currents over a short period of time, it is generally due to a problem with the current detection circuit on the drive board; the module may also have been damaged as a result of shock. The issue might persist even after reset. The main causes are as follows: an excessively long motor cable, excessive output leakage current resulting from an inappropriate cable selection, or loose connections in the output cables together with cable damage, which leads to an arc effect when the load current increases. A short circuit in the 24V fan power supply of inverters with a small capacity (7.5G11 and below) can also cause an OC3 alarm; in such cases, the 24V fan power supply on the motherboard gets damaged, while the other functions of the motherboard remain normal. If the \"1, OC2\" alarm appears and cannot be reset, or if the \"OC3\" alarm is displayed as soon as the power is turned on, there may be a problem with the motherboard; if the \"OC3\" alarm appears as soon as the RUN button is pressed, then the driver board is damaged. (2) OLU alarm: The LCD on the keyboard panel displays: Inverter overloaded. When this alarm occurs on G/P9 series frequency converters, it can be resolved in three ways: first, modify the parameter settings for \"torque boost,\" \"acceleration/deceleration time,\" and \"energy-saving mode\"; second, use a multimeter to check whether the output of the frequency converter is indeed too high; finally, use an oscilloscope to observe the output at the detection point in the upper left corner of the main board to determine whether the main board is damaged. (3) OU1 alarm: LCD on the keyboard panel displays: overvoltage during acceleration. When an “OU” alarm occurs on a general-purpose frequency converter, the first things to consider are whether the cable is too long, whether its insulation has aged, and whether the electrolytic capacitors in the DC link are damaged. For loads with high inertia, it may be advisable to carry out online self-tuning of the motor. Additionally, when starting up, use a multimeter to measure the voltage at the intermediate DC stage. If the voltage shown by the measuring instrument differs from the voltage displayed on the operation panel’s LCD, there is a fault in the motherboard’s detection circuit, and the motherboard needs to be replaced. When the DC bus voltage is higher than 780VDC, the inverter issues an OU alarm; when it is lower than 350VDC, the inverter issues a low voltage LU alarm. (4) LU alarm: LCD on the keyboard panel displays: under voltage. If the device frequently gives a \"LU under-voltage\" alarm, it may be advisable to initialize the parameters of the inverter (confirm this by setting H03 to 1), and then increase the carrier frequency of the inverter (parameter F26). If the E9 device emits a low voltage alarm for the LU and cannot be reset, there is a problem with the (power) drive board. (5) EF alarm: LCD on the keyboard panel displays: ground short circuit fault. When this alarm occurs on the G/P9 series inverters, it may be due to a fault in the main board or the Hall element. (6) Er1 alarm: LCD on the keyboard panel displays: Memory error. Regarding the handling of the “ER1 not resetting” fault in the G/P9 series inverters: remove the FWD—CD shorting piece, power on the device, hold down the RESET button while keeping it powered on, and release it only when the LED power indicator light goes out; then power on the device again to see if the “ER1 not resetting” fault is resolved. If this method does not work, it indicates that the internal code has been lost, and in such a case the main board must be replaced. (7) Er7 alarm: LCD on the keyboard panel displays: poor self-tuning. When this fault alarm appears on G/P11 series inverters, it is usually due to a damaged charging resistor (in inverters with low capacity). Additionally, check whether the internal contactor is engaged (this applies to high-capacity frequency converters, those of model 30G11 and above; an alarm is issued only when the frequency converter is operating under load) as well as whether the auxiliary contacts of the contactor are in good contact. If the internal contactor is not engaged, first check whether the 1A fuse on the drive board is damaged. It could also be a problem with the driver board—check whether the two-core signals sent to the motherboard are normal. (8) Er2 alarm: LCD on the keyboard panel displays: Panel communication error. This alarm (motherboard issue) occurs in inverters of 11kW and above when the 24V fan power supply is short-circuited. For E9 series machines, it is usually the DTG component of the display panel that is damaged; when this component fails, it can also cause damage to the motherboard, resulting in an OC alarm as soon as the device is powered on after the display panel is replaced. As for the G/P9 machine, which displays an “ER2” error as soon as it is powered on, it is due to a failed capacitor on the driver board. (9) OH1 overheat alarm: LCD on the keyboard panel displays: Cooling fan overheated. OH1 and OH3 are essentially the same signal, detected randomly by the CPU. The analog signals from OH1 (which detects the motherboard compartment) and OH3 (which detects the main board compartment) are connected in series before being sent to the CPU, which then reports either of these faults at random. When the “OH1” alarm appears, first check whether the ambient temperature is too high and whether the cooling fan is working properly; next, check whether the heat sinks are clogged (this type of alarm occurs in food processing and textile industries). In scenarios with constant-pressure water supply and analog setting, this fault often occurs when an 800Ω potentiometer is used; the capacitance of the setting potentiometer must not be too low, and it should be at least 1kΩ. An incorrect connection of the movable terminal of the potentiometer can also trigger this alarm. If the 220V fan of high-capacity inverters (30G11 and above) does not rotate, an overheat alarm will definitely be triggered; in such cases, check whether the fuse FUS2 (600V, 2A) on the power board is damaged. When an “OH3” alarm occurs, it is usually due to the failure of a small capacitor on the drive board as a result of overheating; the consequence of this failure is an unbalanced three-phase output from the inverter. Therefore, when the inverter displays “OH1” or “OH3”, one can first power it on to check whether the three-phase output of the inverter is balanced. For the OH overheat alarm, there is also a possibility of a fault in the motherboard or electronic thermometer. The electronic thermometers of the G/P11 series frequency converters produce analog signals, while those of the G/P9 series frequency converters generate switch signals. (10) 1、OH2 alarm: For G/P9 series machines, due to the existence of external alarm definitions (E function), if there is no shorting clip at the terminal for these external alarm definitions or if the shorting clip is not properly connected while in use, an OH2 alarm will be triggered. If, at the same time, the CN18 connector on the main board (the connector for the thermocouple that measures temperature) becomes loose, a “1、OH2” alarm will occur and it will not be possible to reset it. After the inspection is complete, power must be reapplied to reset it. (11) Low-frequency output oscillation fault: When the inverter operates at a low frequency (below 5Hz), the motor’s rotation direction fluctuates frequently; this is usually caused by a problem with the inverter’s main board. (12) Oscillation fault during a certain acceleration phase: When the inverter experiences low-frequency three-phase imbalance (resulting in motor oscillation) or oscillation during a specific acceleration phase, we can try modifying the inverter’s carrier frequency (by reducing it), which may resolve the issue. (13) No output during operation. This fault comes in two scenarios: First, if the LCD display shows an increase in output frequency and voltage after the inverter starts operating, but no voltage is detected at the output, then the drive board is damaged; second, if the LCD display continues to show zero values for both output frequency and voltage after the inverter starts operating, then there is a problem with the main board. (14) Fault of failure to increase operating frequency: That is, after the inverter is powered on and the operation button is pressed, the operation indicator light comes on (when operated via the keyboard), but the output frequency remains displayed as “0.00” and does not increase. This is usually due to a problem with the drive board; replacing it with a new one will resolve the issue. However, if the inverter is able to reach the set frequency when operating under no load, but remains around 1Hz when under load, it is due to an excessive load – the inverter’s \"instantaneous overcurrent protection function\" comes into effect. This issue can be resolved by modifying certain parameters; for example, setting F09 to 3, H10 to 0, and H12 to 0. Changing these three parameters usually restores normal operation. (15) No display fault on the operation panel. When this fault occurs in the G/P9 series, it may be due to a damaged charging resistor or the C19 capacitor in the power drive board; in the case of high-capacity G/P9 series inverters, this fault can also be caused by internal contactors failing to engage. For the G/P11 low-capacity frequency converters, in addition to problems with the power supply board, there may also be issues with the small circuit board on the IPM module. In machines with a capacity of 30G11 or higher, it is possible that the fuse FUS1, which supplies power to the main board from the power supply board, is damaged, resulting in no display when the machine is powered on. Problems with the motherboard can also cause no display when power is applied. 3 Some parameter settings in the application: (1) When a frequency converter with a three-phase 220V output (50Hz) is required for on-site use, but only a frequency converter with 380V and the same power is available, we can, based on the basic principles of V/F frequency conversion, modify parameter F04 (basic frequency 1) to 90Hz, parameter F03 (maximum frequency 1) to 50Hz, and keep parameter F05 (rated voltage) at its factory setting; this will then meet the requirements of the on-site application. When applying this setting, make sure to turn off automatic energy-saving operation (parameter H10) and set torque enhancement (parameter F09) to 0. (2) When motor vibration problems (mild three-phase imbalance) occur in a certain frequency range with G/P9 series inverters, the parameter settings of the torque increase curve can be adjusted, which helps to reduce the vibration or change its frequency range. By further reducing the carrier frequency to 2 kHz, the problem can generally be resolved. (3) Low-voltage general-purpose frequency converters usually have an “instantaneous overcurrent limitation” function. That is, when the load is too heavy and the current flowing through the converter rises too rapidly, the converter automatically reduces (or limits) the output frequency. However, this automatic frequency reduction is not allowed in some applications, in which case this function must be disabled. To protect the motor and the converter, it is necessary to minimize sudden current changes through proper parameter settings; for example, set F09 to 0.0 (it can also be set to 2.0 first, after which the difference between the two settings can be compared). Turn off energy-saving mode by setting H10 to 0. To prevent overcurrents that occur when a constant-torque load starts under low voltage, it is also necessary to select an appropriate acceleration/deceleration curve, such as by setting H07 to 0. (4) When the inverter emits an “OL1” alarm, a direct solution is to adjust the overload action value (this is not recommended). To address the issue fundamentally while still providing overload protection, we can set parameter F09 to 2 (the appropriate value for fans is 0.1, and for water pumps it is 0.8; generally, setting it to 2 results in a lower current compared to setting it to 0.0). Additionally, turn off energy-saving mode by setting parameter H10 to 0. (5) When driving large-inertia loads, the G/P11 series inverters are prone to encountering the OU2 constant-speed overvoltage fault; adjusting the deceleration time parameter F08 accordingly, setting the braking torque parameter F41 to 0, and setting the energy-saving operation parameter H10 to 0 can help resolve this issue. (6) When you wish for the device to operate at the jog frequency, make sure to set JOG—CM to ON first; and before JOG—CM is turned OFF, set FWD—CM or REV—CM to ON so that the device can operate at the jog frequency specified by parameter C20. Its feature is that, during the jog operation of the equipment (whether at a constant speed, while accelerating, or while decelerating), even if the JOG—CM signal is OFF, the jog operation mode of the inverter is determined by the given Run and Stop signals. 4 Fault Diagnosis Examples: A FRN11P11S-4CX device fails by displaying an OC3 alarm immediately upon power-up (sometimes within a few seconds), and the reset function does not work properly (it works sometimes but not other times). After replacing the CPU board, which showed errors OH1 and OH3 while operating under load, with a new one, the device began to display the OC1 error as soon as it was powered on – this error could be reset, but after a few seconds the OL2 error appeared – and this error could not be reset. On the other hand, when the device’s main board was installed in the chassis (7.5P11), which showed errors OH1 and OH3 during operation, the device functioned normally without any errors. This indicates that it is not the motherboard of the device that is faulty, but rather the power supply driver board; as for the machines showing OH1 and OH3 error messages, it is the motherboard that has a problem, while the driver board is fine. 5 Issues related to the replacement of drive boards and motherboards: (1) For the 7.5G11–18.5P11 power rating series, the drive boards of P-type frequency converters can be swapped with those of G-type frequency converters with a capacity one level lower; (2) When replacing the motherboard of an E-type frequency converter with a different power rating, first enter the F00 function code, then hold down the Stop, Run, and Pro buttons simultaneously to access the U parameters (the THR and CM terminals must be shorted together while FWD is disconnected from CM), and select the control program parameters corresponding to the capacity of that frequency converter. Next, the F01–F06 parameters should also be modified or confirmed as required, following the same steps as for F00. After modifying the U parameters, be sure to reset them to their factory settings in order to save the changes. (3) G/P-type motherboards of different capacities can be interchanged within a certain capacity range (they have the same specifications and dimensions below 30kW, and the same specifications as well above 30kW); to make the changes, the C parameter in the control program needs to be adjusted, and the process is similar to that for E-type machines. 6 Some points to note when configuring external hardware (1) DC reactors and AC incoming line reactors. DC reactors cannot completely replace AC incoming line reactors. The main function of a DC reactor is to improve the power factor and to provide protection for the capacitance in the intermediate DC link; however, in situations where the three-phase input voltage is severely unbalanced or there are thyristor loads in the electrical network, the advantages of the input reactor become evident: it primarily protects the rectifier bridge and charging resistors from voltage surges from the power supply. For low power levels (below 7.5 kW), using a line reactor alone is much more effective than using a DC reactor. (2) Output reactor and OFL filter: In practical applications, many customers install an output reactor when choosing inverters, mainly to suppress the leakage current on the output side, especially in cases where the output cables are long, such as in the use of submersible pumps. The OFL filter is not a simple output reactor; it contains an LC circuit that not only helps to suppress the leakage current on the output side but also stabilizes the terminal voltage of the motor and reduces external interference from the output side. Due to the high cost of OFL filters and the need to order them from abroad, in applications where the output wiring is very long and external interference must be avoided, it is recommended that users use an output reactor in combination with an ACL reactor (the ACL reactor should be installed on the output side of the inverter). 7 Multi-motor drive issue: The term multi-motor drive referred to here means that one inverter is used to drive multiple motors simultaneously, such as the winding rollers in textile industries. When multiple motors are driven simultaneously by one frequency converter, certain conditions must be met: for example, the motors must be of the same model, and the process requirements for the same load driven by each motor must be identical at any given time. For frequency converters, it is necessary to select a model with appropriate specifications based on current considerations (increasing capacity and changing from P-type to G-type), as well as to extend the acceleration and deceleration times to prevent the activation of the instantaneous overcurrent protection function or OC alarms. In terms of peripheral hardware, an output reactor should be added to reduce leakage current during operation. Detailed explanation of overvoltage faults in frequency converters: Overvoltage in frequency converters is primarily manifested in the voltage of the branches of the DC bus. Under normal conditions, the DC voltage of the inverter is the average value after three-phase full-wave rectification. If calculated using a line voltage of 380V, the average DC voltage Ud = 1.35 × U_line = 513V. When an overvoltage occurs, the energy storage capacitor of the DC bus is charged; when the voltage rises to around 760 V, the inverter’s overvoltage protection mechanism activates. Therefore, inverters all have a normal operating voltage range; when the voltage exceeds this range, the inverter is likely to be damaged. There are two common types of overvoltage. 1. Excessive input AC voltage: This situation occurs when the input voltage exceeds the normal range; it generally happens during holidays when the load is light, causing the voltage to rise or fall and leading to circuit failures. In such cases, it is best to disconnect the power supply and conduct inspections and repairs. 2. Overvoltage during power generation: This situation occurs quite frequently. It happens mainly when the synchronous speed of the motor is higher than its actual speed, causing the motor to operate in power-generation mode. Since the frequency converter does not have a braking unit, two scenarios can lead to this fault. (1) When the inverter drives a load with high inertia, the deceleration time is set to be relatively short. During the deceleration process, the speed output by the inverter is high, while the load slows down more slowly due to its own resistance, resulting in the speed of the motor driven by the load being higher than the speed corresponding to the frequency output by the inverter. In this case, the motor operates in a power-generation mode. Since the inverter does not have an energy feedback unit, the voltage in its DC circuit rises above the protective threshold, causing a fault. This type of fault often occurs in the drying section of paper machines. To address it, a regenerative braking unit can be added, or the inverter’s parameters can be modified to increase the deceleration time. Functions added to the regenerative braking unit include energy-consuming type, parallel DC bus absorption type, and energy feedback type. In the energy-consuming type, a braking resistor is connected in parallel to the DC circuit of the inverter, and the on/off state of the power transistor is controlled by monitoring the DC bus voltage. The parallel DC bus absorption type is used in multi-motor drive systems, where one or several motors are often operating in a power-generation mode, generating regenerative energy; this energy is absorbed by the motors that are in electric drive mode through the parallel bus. The grid-side converter of an energy-feedback inverter is reversible; when regenerative energy is generated, the reversible converter feeds this energy back into the power grid. (2) This fault may also occur when multiple electric actuators drive the same load, mainly due to a lack of load distribution. Taking two motors driving a load as an example, when the actual speed of one motor is greater than the synchronous speed of the other motor, the motor with the higher speed acts as the prime mover, while the motor with the lower speed enters a generating mode, which can lead to failures. In paper machines, this often occurs in the press section and wire section, and load distribution control is required during handling. The characteristics of the inverter, which is part of the drive speed chain of the paper machine, can be adjusted to be more flexible.