Maintenance of common faults of frequency converter

Inverter is composed of circuit boards and various connectors of modules, each circuit board has many solder joints, and any virtual soldering and poor contact will lead to failure.

When a frequency converter fails, the LED displays "UV" (short for undervoltage). In the manual, the alarm is DC bus undervoltage.

Because the control loop power supply of this inverter is not taken from DC bus, but rectified separately from AC input through transformer.

Therefore, it is judged that the alarm should be true. So check from the power supply, the input power supply voltage is correct, and the filter capacitor voltage is 0 volts.

Because the short-circuit contactor of the charging resistor has no action, it has nothing to do with the rectifier bridge. The fault range is reduced to the charging resistance. After the power failure, use a multimeter to detect that the charging resistor is broken.