In the maintenance of frequency converter, we often hear over-voltage fault, but under voltage fault is often encountered in the use of frequency converter. The reason is the protection action caused by the main circuit voltage lower than the lower limit, the damage of a rectifier bridge, the power grid instantaneous power failure, and the input lack of equality. The after-sales personnel of frequency converter summarized the ways and methods of under voltage alarm and voltage detection in the process of dealing with inverter undervoltage fault. The details are as follows:

1. Comparator detection

The voltage at one end of the comparator is fixed by a voltage stabilizing tube. The detected voltage is sampled and compared with it, and the result is output through the comparator.

2. ADC detection (analog to digital converter)

The voltage to be detected falls within the detection range of ADC after the voltage is sampled by resistor step-down. The alarm range of voltage can be set by program.

The energy storage capacitor in the main circuit has great influence on the overvoltage and undervoltage of the frequency converter in operation. And all kinds of components of the inverter circuit have a certain service life, so once the inverter components reach the service life, they will bring the occurrence of faults. For example, the energy storage capacitor or other parts in the main circuit may affect the main circuit, so that the whole inverter failure. In general, if the frequency converter is out of service for a long time and reaches more than one year, a comprehensive physical examination should be conducted for the energy storage capacitor.

How to avoid this kind of phenomenon for a long time?

According to the requirements, the out of service frequency converter should be powered on once every two or three months for 30 minutes each time. For a long time not used electrolyzers, when electrified, first add about 50% of the rated voltage. As long as the pressurization time is more than half an hour, its leakage current will drop and it can be used normally.

In addition, for the frequency converter with long service life (more than five years), the capacity of energy storage capacitor must be tested. Most of the faults are caused by insufficient capacitor capacity, capacity drop or loss of capacity in DC circuit.