Methods of Using a Multimeter to Detect the Power Module of an Inverter
When detecting the power module on the circuit (isolated from the power grid), use the R×1 range of a pointer multimeter to measure the six diodes of the rectifier bridge and the collector and emitter of the six IGBT transistors of the output bridge in both forward and reverse directions respectively to determine whether they are broken down. Table 1 and Table 2 show the normal measurement results. Otherwise, there are broken-down components inside. Use the B×1k range of the pointer multimeter to measure the resistance between the gate and the emitter of each of the six IGBT transistors (the input terminal of the driving signal) respectively, and they should be the same. If there are differences, it indicates that the driving circuit or the IGBT transistor is damaged. The above measurements can only detect the breakdown damage of the IGBT transistors and cannot detect the open-circuit damage. After removing the power module from the circuit board, each IGBT transistor can be further measured. The method is shown in Figure 1. The pointer on the left indicates non-conduction, and the pointer on the right indicates conduction. If it cannot be made to conduct and cut off, then the transistor is damaged.
The Structure of the Power Module of the Inverter:
Inside the power module of the inverter, one part is a single-phase or three-phase bridge rectifier circuit composed of diodes, and the other part is a three-phase bridge output circuit composed of six IGBT transistors (Insulated Gate Bipolar Transistors) and six damping diodes used in cooperation.
P1 is the positive terminal of the +300V rectified output, and N1 is the negative terminal of the rectified output. These two pins are externally connected to a filter electrolytic capacitor, and are connected through the mutual inductor coil, where P1 is connected to P2, and N1 is connected to N2, supplying power to the output bridge composed of six IGBT transistors.
The collectors of the three IGBT transistors in the upper half-bridge of the three-phase output bridge are all connected to the positive terminal of the power supply, and the emitters are the U, V, and W three-phase output terminals respectively. The emitters and gates of the three transistors form the input terminals of the driving signals for the three-phase upper half-bridge, namely GU-U, GV-V, and GW-W. The collectors of the three IGBT transistors in the lower half-bridge of the three-phase output bridge are respectively connected to U, V, and W, and the emitters are all connected to the negative terminal of the power supply. The gates of the three transistors and the negative terminal of the power supply form the input terminals of the driving signals for the three-phase lower half-bridge, namely GX, GY, and GZ. B is the braking control terminal.
