When maintaining an inverter, overvoltage faults are commonly encountered. However, undervoltage faults are also a frequent issue during inverter operation. This typically occurs when the main circuit voltage drops below the lower limit, triggering a protection mechanism, or when the rectifier bridge is damaged, or when there's a sudden power cut from the grid, causing an imbalance in input voltage.
During the troubleshooting of undervoltage faults, inverter service technicians have developed several effective methods for detecting low voltage alarms. Here are some common approaches:
Comparator Detection
This method involves using a comparator where one end is set to a fixed voltage via a Zener diode. The detected voltage is then sampled and compared with this reference value. The result is output through the comparator, allowing for quick detection of voltage deviations.
ADC Detection (Analog-to-Digital Converter)
In this approach, the voltage is first sampled using resistors to step it down to a level that can be processed by the ADC. Once converted to digital, the system can be programmed to set specific alarm thresholds for under-voltage conditions.
The storage capacitors in the main circuit play a critical role in both overvoltage and undervoltage events. Over time, all components in an inverter circuit degrade, and once they reach their service life, they may cause failures. For example, aging storage capacitors or other key components in the main circuit can lead to malfunctions in the entire inverter system.
If an inverter is not used for an extended period—typically more than one year—it’s recommended to perform a full physical inspection, especially on the storage capacitors. These components can deteriorate if left unused for too long, leading to performance issues or even failure upon reactivation.
To prevent such issues in long-dormant inverters, it's advisable to power them up every two to three months for about 20 to 30 minutes. For electrolytic capacitors that have been idle for a long time, applying a voltage at around 50% of the rated voltage for over half an hour can help reduce leakage current and restore normal function.
Additionally, inverters that have been in use for more than five years should undergo capacity testing on their energy storage capacitors. Frequent voltage fluctuations during operation often point to issues with the DC capacitors, such as reduced capacitance or complete loss of capacity. Regular maintenance and component checks can significantly extend the lifespan and reliability of the inverter system.
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