1. The IGBT module was damaged due to poor heat dissipation.
The frequency converter suddenly emitted an explosive sound during operation, and the external fuse blew. Disassembly revealed that the inverter's IGBT module was damaged. Testing of the relevant circuit boards showed that the IGBT trigger circuit was damaged, while other circuit boards tested normal. During disassembly, the power board and current detection board were found to be covered in oil and dust. Opening the inverter's heatsink fan revealed that the heatsink was also covered in oil and debris, completely blocking the airflow channels. Therefore, it was deduced that the inverter's IGBT module was damaged due to poor heat dissipation.
Repair Process: First, completely disassemble the inverter, remove the heat sink from the heat dissipation channel, and clean the heat sink with compressed air. Simultaneously, clean all internal structural components and circuit boards of the inverter. Install the IGBT module, following the module's requirements and installing it in the correct order with appropriate torque. Repair the trigger circuit, and then install the other components in sequence. After installation, perform a static test. If the static test results are satisfactory, perform a power-on test and a load test. If the load test is passed, the repair is successfully completed.
Experience Summary: Based on the repair experience of several frequency converters of different models and under different operating environments, the main cause of IGBT module failure in frequency converters is the harsh operating environment, which leads to damage to electronic components on the gate drive card and blockage of the frequency converter's heat dissipation channels. The most easily damaged components are the Zener diode and optocoupler. To check for problems in the drive circuit, compare the resistance of each trigger terminal when the power is off. Measure the voltage waveform at the trigger terminals when the power is on. However, some frequency converters cannot be powered on without the module installed. In this case, connect a dummy load in series with the module's P terminal to prevent accidental contact with the trigger terminals or other circuits during inspection, which could burn out the module.
2. Simple Measurement Methods for IGBT Modules
An imbalance in the inverter's output voltage manifests as motor vibration and unstable speed. Without experience, it's difficult to determine which drive circuit is faulty. In this case, start the inverter at 2Hz and use a multimeter in DC voltage mode to measure the voltage values of pu, PV, PW, and un, vn, and wn respectively. These six voltages will differ; the one with the higher voltage indicates a problem. You can draw a diagram to analyze the principle. For IGBT modules, we introduce the simplest measurement method (not the professional method): Set the digital multimeter to diode test mode and test the forward and reverse diode characteristics between C1, E1, C2, and E2 of the IGBT module, and between the gate g and E1 and E2, to determine if the IGBT module is intact. Take a six-phase module as an example. Disconnect the wires from phases u, v, and w on the load side. Using a diode tester, connect the black probe to phase p (collector C1) and measure u, v, and w sequentially with the red probe. The multimeter should display an infinite value. Reverse the probes, connecting the red probe to p and measuring u, v, and w with the black probe. The multimeter should display a value of approximately 400. Next, connect the black probe to phase n (emitter E2) and measure u, v, and w with the red probe. The multimeter should display a value of approximately 400. Connecting the red probe to p and measuring u, v, and w with the black probe should display an infinite value. The forward and reverse characteristics of each phase should be identical. If a difference occurs, it indicates a deterioration in the IGBT module's performance, and it should be replaced.
