In inverter repair, we often hear about overvoltage faults, but undervoltage faults are also a common problem encountered in inverter use. The causes include protection activation due to the main circuit voltage falling below the lower limit, damage to a rectifier bridge circuit, momentary power outages, or input phase loss.
In the process of troubleshooting undervoltage faults in frequency converters, after-sales personnel summarized the methods for detecting undervoltage alarm voltage, as follows:
1. Comparator detection
The voltage at one end of the comparator is fixed by a Zener diode. The voltage to be detected is sampled and compared with the Zener diode, and the result is output through the comparator.
2. ADC detection (Analog-to-Digital Converter)
The voltage being detected is sampled by reducing the voltage through a resistor and falls within the detectable range of the ADC. The alarm range of the voltage can be set through the program.
The energy storage capacitor in the main circuit has a significant impact on overvoltage and undervoltage conditions of the frequency converter during operation. Since various components in the frequency converter circuit have a limited lifespan, failures will occur once these components reach their end of life. Issues with the energy storage capacitor or other components in the main circuit can affect the main circuit, leading to a malfunction of the entire frequency converter. Generally, if the frequency converter has been out of service for more than a year, a comprehensive inspection of the energy storage capacitor should be performed.
How can this phenomenon be prevented from occurring with frequency converters that have not been used for a long time?
As required, inactive frequency converters should be powered on once every two to three months for 20 to 30 minutes each time. For electrolytic capacitors that have not been used for a long time, when powering on, apply about 50% of the rated voltage first. As long as the voltage application time is more than half an hour, the leakage current will decrease, and it can be used normally.
In addition, for frequency converters with a long service life (more than five years), the capacity of the energy storage capacitors must be tested. Frequent undervoltage faults during operation are mostly due to insufficient capacity, decreased capacity, or loss of capacitance in the DC circuit capacitors.
