Abstract: This paper introduces the causes and solutions of several common inverter faults (such as parameter setting errors, overvoltage, etc.) during use. Taking the application of Siemens inverters in resin sand regeneration equipment as an example, the causes and solutions of these faults are analyzed. English Abstract: This paper introduces the reasons and solutions for some common inverter faults such as parameter setting errors, overcurrent, and overvoltage. The analysis of the fault causes and solutions is presented using Siemens inverters as an example. 1 Introduction AC drives, with their superior characteristics compared to DC drives, are often the preferred drive solution in many applications. Modern inverters generally use 16-bit or 32-bit microcontrollers as their core, thus achieving fully digital control. Their speed regulation performance is similar to DC speed regulation. However, the maintenance of inverters is more complex than that of DC speed regulation. Once a fault occurs, it is difficult for ordinary technicians in industrial and mining enterprises to handle. This paper analyzes common inverter faults, their causes, and solutions. 2. Parameter Setting Faults During the use of a frequency converter, the parameter settings of the frequency converter are crucial to whether it can meet the control requirements of the drive system. If the parameters are not set correctly, the control effect may be poor, or the system may not be able to operate normally. 2.1 Parameter Setting For a newly purchased frequency converter, the manufacturer usually sets a default value for each parameter at the factory. Under these parameter values, the system can operate normally in the panel operation mode. However, this alone cannot meet the requirements of most drive systems. The frequency converter parameters are modified in the following ways: (1) Confirm motor parameters. For example, ABB frequency converters set the motor power, current, voltage, speed, and maximum power in 99 parameter groups. These parameters can be obtained directly from the electrode nameplate. (2) Set the starting mode of the frequency converter. Generally, frequency converters are set to panel start at the factory. For Siemens frequency converters, the starting mode can be set to panel, external terminal, communication, etc. The user can choose according to the actual situation. (3) Select the frequency setting mode. Generally, the frequency setting of frequency converters can also be in three ways, namely panel setting, external voltage or current setting, and communication setting. Of course, for some frequency converters, the frequency setting mode can also be one or a combination of these three modes. After correctly setting these three parameters, the frequency converter can basically operate normally. If better control effect is required, the relevant parameters can only be modified according to the actual situation. For details, please refer to its instruction manual. 2.2 Handling of parameter setting faults Once a parameter setting fault occurs, the frequency converter cannot operate normally. It is best to restore all parameters to the factory value and then reset the relevant parameters according to the above steps. The parameter restoration method is different for each company's frequency converter. For the second and third types of parameters, the factory value can be restored by changing the application macro. The AOP panel of the Siemens MM420/MM440 frequency converter can only store one set of parameters. The frequency converter selection manual introduces that the AOP panel can store 10 sets of parameters, but when using the AOP panel to back up the parameters of the second frequency converter, it displays "Insufficient storage capacity". The solution is as follows: (1) Select the "Language" item in the menu; (2) Select an unused language in the "Language" item; (3) Press Fn+△ key to select delete, and press P key to confirm after being prompted. In this way, the AOP panel can store 10 sets of parameters. The reason for this phenomenon may be that the memory in the AOP panel is insufficient during the design. 3. Overvoltage Faults Inverters have a normal operating voltage range. When the voltage exceeds this range, it can easily damage the inverter. There are two common types of overvoltage: 3.1 Input AC Overvoltage: This refers to the input AC power supply voltage exceeding the normal value. It usually occurs during holidays when the line load is light, causing voltage increases or line faults. I often encounter situations where the inverter's fault indicator alarms on Monday mornings, but disconnecting the power and then reconnecting it after a while resolves the issue. 3.2 Overvoltage During Generator Operation: This is more likely to occur when the motor's actual speed is higher than the synchronous speed, causing the motor to operate in generator mode, or when the induction furnace is feeding energy back to the grid, and the inverter lacks a braking unit. The following situations can cause this fault. (1) When the frequency converter drives a large inertia load, its deceleration time is set to be small. During the deceleration process, the frequency converter output frequency decreases quickly, while the load decelerates slowly due to its own resistance. This causes the speed of the motor driven by the load to be higher than the synchronous speed corresponding to the frequency converter output frequency. The motor is in the generator state, and the frequency converter does not have an energy feedback function. Therefore, the voltage of the frequency converter DC circuit rises and exceeds its protection value, resulting in a fault. (2) When the medium frequency furnace or medium frequency equipment feeds energy back to the grid, the input voltage will also be too high, resulting in a fault. (3) This fault may also occur when multiple motors drive the same load. This is mainly due to the lack of load distribution, that is, the speeds of multiple motors are not synchronized. Taking two motors driving the same 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 is equivalent to the prime mover, and the motor with the lower speed is in the generator state, which is prone to causing a fault. To deal with this type of fault, a load distributor can be added, or the frequency converter parameters can be modified. 4 Other faults 4.1 Overload Overload faults include frequency converter overload and motor overload. This could be caused by factors such as excessively short acceleration time, low grid voltage, or excessive load. It can generally be addressed by extending the acceleration time, extending the braking time, and checking the grid voltage. Excessive load may indicate that the selected motor and inverter cannot drive the load, or it could be due to poor mechanical lubrication. In the former case, a higher-power motor and inverter must be replaced; in the latter case, the production machinery needs to be inspected. 4.2 Overcurrent may be caused by a short circuit in the inverter's output. This requires checking the wiring and motor. If the inverter still experiences overcurrent after disconnecting the load, it indicates that the inverter's inverter circuit is damaged and should be repaired or replaced. If you disassemble the machine, you'll find a serious short circuit. The rectifier module and IGBT module are burst, and black carbon deposits from the short circuit are everywhere. Two relays in the main circuit have also burst. The main control board doesn't seem to have any problems yet, but several parts of the drive section are burned. In addition, part of the large energy storage capacitor is swollen, and the contact points of the two large screws on the capacitor board are completely charred. This is a common problem with Siemens ECO frequency inverters, because all electrical power passes through these two iron screws. Once the iron screws rust, it can easily cause poor charging and discharging of the capacitor. This leads to the capacitor overheating, leakage, and swelling, eventually damaging important components. To prevent poor contact and arcing again, it's best to solder several strands of thick copper wire when tightening the screws. If you don't know the parameters when repairing the trigger board, you can compare the intact components on the control board with the damaged ones. The voltages for repairing this board are -4.7V and -4.44V. After replacing the damaged components, you can power on the device for testing. The test procedure is to run the main circuit to the control board under no-load and load conditions for inspection. Before the power-on test, to ensure device safety and prevent further damage to critical components, the large-capacity capacitor should not be installed temporarily; instead, two small-capacity capacitors should be used. To protect the IGBT, the power supply circuit from the capacitor to the IGBT should ideally be connected in series with an incandescent light bulb (i.e., a dummy load). After powering on, if the display is normal, the inverter can be started, and six trigger pulses should be measured. If the signal is normal, the light bulb between the capacitor and the IGBT can be removed, and the large capacitor can be installed for no-load operation. After normal operation, a load can be connected for operation. After debugging, the machine should generally return to normal. 4.3 Undervoltage indicates a problem with the power input circuit, possibly due to severe overload or poor wiring contact. When the Siemens 6SE70 series inverter displays the letter "E" on the PMU panel LCD screen, the inverter cannot work. Pressing the P key and restarting the power cycle are ineffective. The operation manual does not provide relevant information. Upon checking the external DC 24V power supply, a low voltage was found. After resolving this issue, the inverter worked normally. 4.4 Overheating Another issue with the inverter is overheating. If an overheating alarm occurs and the temperature sensor is found to be normal, the problem may be caused by interference. This can be mitigated by shielding the fault. Additionally, check the inverter's fan and ventilation. For other types of faults, it's best to contact the manufacturer for a quick and feasible solution. 4.5 Other Issues Finally, it should be noted that if the inverter experiences a hardware failure, such as in the rectifier or inverter circuits, the IGBT module may be damaged, often resulting in damage to the drive components. The most easily damaged components are the Zener diode and optocoupler. Conversely, problems with drive circuit components, such as capacitor leakage, breakdown, or aging optocouplers, can also lead to IGBT module burnout or unbalanced inverter output voltage. To check for problems in the drive circuit, compare the resistance at the trigger terminals of each circuit when power is off. When powered on, measure the voltage waveform at the trigger terminals. However, some inverters cannot be powered on without the module installed. In this case, connect a dummy load in series with the module's P terminal to prevent accidental contact with the trigger terminal or other circuits during inspection, which could damage the module. If the inverter is severely damaged at this point (which can be checked by measuring for short circuits at the input and output terminals), it must be repaired by specialized technicians. Generally, it should not be powered on again to avoid expanding the scope of the fault. 5. Conclusion Inverters are technologically advanced devices that combine high-voltage and low-voltage circuits; therefore, their faults are diverse. Only through continuous summarization and exploration in practice can a set of quick and effective methods for handling inverter faults be developed. The above are just some of the author's practical experience. We hope to discuss this with everyone, and we also hope to better serve our customers.