Our factory has a frequency converter (MM3-30KW) that was frequently shutting down without warning, significantly impacting the production line. We investigated all possible causes but couldn't find the problem. Later, the frequency converter manufacturer suggested it might be a power supply issue and recommended that we check that first.
The basic principle of a frequency converter is to provide a voltage and frequency adjustable power supply to an asynchronous motor to meet energy-saving or process requirements. It has three parts: rectification, DC, and inverter. If the external voltage is unstable, the DC voltage will drop, causing the inverter to be unable to continuously output the set voltage level, thus triggering the frequency converter's protection shutdown.
During our investigation, we used a Fluke 435II power quality analyzer to monitor the inverter's input power supply for approximately two weeks. This proved that power supply quality truly affects the inverter's normal operation. The recorded trend graphs showed significant voltage sags and dips, as well as transient processes, providing detailed data for power supply upgrades and remediation. Below are some of the recorded and analyzed results (including waveforms):
On the sixth day of monitoring, the frequency converter experienced another sudden shutdown. Reviewing the data recorded by the power quality analyzer clearly showed a very severe voltage dip occurring at the same time as the shutdown, with a drop of nearly 80%. Therefore, we can determine that this shutdown was caused by a voltage dip.
Finally, I'd like to share some common reasons that may cause inverters to shut down:
1. Check if the power supply voltage is normal; both too high and too low voltage can cause the machine to shut down.
2. Are the parameter settings correct? In some cases, such as constant pressure water supply, the machine will automatically stop after reaching the target pressure and restart when the pressure drops below the target pressure. This is normal.
3. To check for a large number of harmonics in the power supply, a power quality analyzer or a handheld oscilloscope is required.
4. Inverter hardware failure. For example, hardware failures such as contactor failures.
