When the power module is detected on the road (disconnected from the power grid), measure the collector and emitter of the six diodes of the rectifier bridge and the six IGBT tubes of the output bridge respectively with the pointer multimeter R×l to judge whether they have broken down. l and Table 2 are normal measurement results, otherwise there are breakdown components inside. Use the pointer multimeter Bx1k to measure the resistance between the gate and emitter of the six IGBT tubes (drive signal input terminals) and they should be the same. If there is a difference, the drive circuit or the IGBT tube is damaged. The above measurements can only measure the breakdown damage of the IGBT tube. No open circuit damage can be detected. After the power module is removed from the circuit board, each IGBT tube can be further measured. The method is shown in Figure 1. The needle on the left indicates no conduction. The needle on the right indicates continuity. If it cannot be turned on and off, the tube is damaged.

TLP251 is an optocoupler drive circuit commonly used in frequency converters. When the power module breaks down, it often affects the circuit. Its internal circuit and measurement method are shown in Figure 2. When the ② pin is disconnected or connected with the 10V power supply through a 3kΩ resistor. ⑥ The pin has high and low voltage changes of 0V or 9V.

Part of the internal package of the inverter power module is a single-phase or three-phase bridge rectifier circuit composed of diodes, and the other part is a three-phase bridge composed of six IGBT tubes (insulated gate bipolar transistors) and six damping diodes used together type output circuit.

P1 is the positive terminal of plus 300V rectification output, N1 is the negative terminal of rectification output, these two pins are externally connected with filter electrolytic capacitors, and are connected to P2 through mutual inductance coil P1, and N1 is connected to N2 to supply power to the output bridge composed of six IGBT tubes.

The collectors of the three IGBT tubes of the upper half of the three-phase output bridge are connected to the positive terminal of the power supply, and the emitters are the three-phase output terminals of U, V, and W respectively. The emitters and grids of the three tubes constitute the upper half of the three-phase Bridge drive signal input terminals GU-U, GV-V, GW-W. The collectors of the three IGBT tubes of the lower half of the three-phase output bridge are connected to U, V, and W respectively, and the emitters are connected to the negative terminal of the power supply. The grids of the three tubes and the negative terminal of the power supply form the drive signal of the three-phase lower half bridge. Input terminals GX, GY, GZ, B are brake control terminals.

There is no braking circuit inside this module. TH is the internal thermistor protection output. Although the pins of other types of general-purpose inverter power modules and the markings on the circuit board are different, it is not difficult to identify the main functional pin positions. High-end products use intelligent power modules, which contain driving circuits and braking circuits, and correspondingly more pins.