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Causes and measurement methods of IGBT damage of frequency converter

Oct 19, 2020

1. The IGBT module is damaged due to poor heat dissipation

    The frequency converter suddenly made an explosion sound during operation, and the external fuse was burned out. Disassembly of the machine found that the igbt module of the frequency converter was damaged. After testing the related boards, it was found that the igbt trigger circuit was damaged, and the other boards were normal. When removing the inverter board, it was found that there was a lot of oil and dust on the power supply board and current detection board. Turn on the heat sink fan of the inverter, and see that the heat sink is also covered with oil and debris, which completely blocks the heat dissipation channel of the inverter. It is concluded that the IGBT module of the inverter is damaged due to poor heat dissipation.

    Maintenance process: First, completely disassemble the inverter, remove the heat sink of the heat dissipation channel, clean the heat sink with compressed air, and clean the internal structure and boards of the inverter. Install the igbt module. When installing the igbt module, install it in order according to the requirements of the module, with a moderate torque. Repair the trigger circuit, and then install other devices in turn. After the installation is completed, a static test is performed. After the static test results are good, a power-on test and a load test are performed. The load test was qualified and the repair was successfully completed.

    Experience summary: Integrating the maintenance of several inverters in different models and different use environments, it is concluded that the main reason for the damage of the inverter igbt module is the harsh use environment, which causes damage to the electronic components on the gate drive card and the heat dissipation of the inverter. The channel is blocked. The most easily damaged devices are Zener tubes and optocouplers. Check whether there is any problem with the drive circuit, and compare whether the resistance of each trigger terminal is consistent when the power is off. The voltage waveform of the trigger terminal can be measured after power on. However, some inverters cannot be turned on without the module installed. At this time, a dummy load is inserted in the module p end to prevent accidentally touching the trigger terminal or other lines during inspection to cause the module to burn out.

    2. Simple measurement method of IGBT module

    The unbalanced output voltage of the inverter is manifested as motor jitter and unstable speed. Generally, it is difficult to determine which drive has the problem without experience. At this time, the inverter can be started at 2hz, and the DC voltage files of the multimeter can be measured: pu, pv, pw And the voltage values of un, vn, and wn, the voltages of these 6 routes will also be different at this time. If the one route is too high, there is a problem with this route. You can draw and analyze the principle by yourself. For IGBT modules, we introduce the simplest measurement method (this is not the case for professional measurement). Set the digital multimeter to the diode test file to test IGBT modules c1, e1, c2, e2 and between the gate g and e1, e2. To determine whether the IGBT module is in good condition according to the diode characteristics. Take the six-phase module as an example. Remove the wires of the u, v, and w phases on the load side, use the diode test file, connect the black test lead to p (collector c1), and then test the u, v, and w with the red test lead. The multimeter displays the value as infinity; Connect the test lead to p, measure u, v, w with the black test lead, and the multimeter displays a value of about 400. Then connect the black test lead to n (emitter e2), the red test lead to measure u, v, w, the multimeter displays the value of about 400; the red test lead to p, the black test lead to measure u, v, w, and the multimeter displays the value of infinity. The forward and reverse characteristics of each phase should be the same. If there is a difference, the performance of the igbt module has deteriorated and should be replaced.