Fault 1: Inverter charging and starting circuit failure. General-purpose inverters are typically voltage-type inverters, operating in an AC-DC-AC mode. When the inverter is first powered on, the charging current is very large due to the very large capacitance of the smoothing capacitor on the DC side. A starting resistor is usually used to limit the charging current. Two common inverter starting circuits are shown in the figure.
After charging is complete, the control circuit short-circuits the resistor through the relay contacts or thyristor. Starting circuit faults typically manifest as a burnt-out starting resistor, with the inverter alarm displaying a DC line voltage fault. Generally, inverters are designed with smaller starting resistors (10-50Ω, 10-50W) to reduce size. Frequent switching on of the inverter's AC input power or poor contact of the bypass contactor can cause the starting resistor to burn out. Therefore, when replacing the resistor, the cause must be identified. If the fault is caused by a change in the input power frequency, this phenomenon must be eliminated before the inverter can be put into use. If the fault is only caused by bypass contact components, these components must be replaced.
Fault 2: The frequency converter has no fault display but cannot operate at high speed. Inspection revealed that the frequency converter parameters were set correctly and the speed control input signal was normal. Upon power-on testing, the DC bus voltage was only around 450V (normally it should be between 580V and 600V). Further testing on the input side revealed a missing phase. The fault was caused by poor contact in one phase of an air switch on the input side. The reason the frequency converter can still operate at low frequencies without alarming due to a missing phase is that most frequency converters have a lower limit of 400V for the bus voltage. The frequency converter only reports a fault when the bus voltage drops below 400V. However, with two phases input, the DC bus voltage is 380V × 1.2 = 452V > 400V. When the inverter is not running, the DC voltage can still reach the normal value due to the effect of the smoothing capacitor. New inverters all use PWM control technology, and the voltage and frequency regulation is completed in the inverter bridge. Therefore, it can still work normally when the input phase is missing in the low frequency range. However, due to the low input voltage and low output voltage, the asynchronous motor speed is low and the frequency cannot be increased.
The inverter displays an overcurrent warning. When this occurs, first check if the acceleration time parameter is too short and the torque boost parameter is too large, then check if the load is too heavy. If none of these issues are present, disconnect the current transformer on the output side and the Hall current detection point on the DC side, reset, and run the inverter to see if the overcurrent occurs. If it does, the IPM module is likely faulty. The IPM module contains overvoltage, overcurrent, undervoltage, overload, overheat, phase loss, and short circuit protection functions, and these fault signals are transmitted to the controller via the Fn pin of the module's control pin. Upon receiving the fault information, the microcontroller blocks the pulse output and displays the fault information on the panel. The IPM module should be replaced.
Fault 4: The frequency converter displays an overvoltage fault. Overvoltage faults in frequency converters typically occur during thunderstorms. Lightning strikes the frequency converter's power supply, causing the DC-side voltage detector to trip. In this case, simply disconnecting the frequency converter's power supply for about one minute and then reconnecting it usually resolves the issue. Another possibility is that the frequency converter is driving a large inertia load, leading to overvoltage. In this case, one solution is to either increase the deceleration time parameter or increase the braking resistor (braking unit); or set the frequency converter's stopping mode to free-stop mode.
Fault 5
If the motor overheats and the frequency converter displays an overload warning, for frequency converters already in operation, the load condition must be checked. For newly installed frequency converters, this fault is likely due to improper V/F curve settings or problems with motor parameter settings. In this case, all parameters must be set correctly. In addition, this situation can also occur when the motor's heat dissipation performance deteriorates at low frequencies, in which case a cooling device needs to be installed.
While frequency converters are highly reliable as asynchronous motor drives, they can still be damaged if used improperly or by accidental events. To use frequency converters effectively in production, it is especially important for technicians to be familiar with their structure and principles and understand common faults.
