The method of using a multimeter to detect the power module of a frequency converter
When the power module is in circuit detection (disconnected from the power grid), use a multimeter to measure the six diodes of the rectifier bridge and the collector and emitter of the six IGBT tubes of the output bridge in both positive and negative directions, respectively, to determine whether they are broken down. Tables 1 and 2 are normal measurement results, otherwise there are internal breakdown components. Measure the resistance between the gate and emitter of six IGBT tubes using a pointer multimeter in the Bx1k range. The resistance (at the input end of the driving signal) should be the same. If it is different, it indicates damage to the driving circuit or IGBT tube. The above measurements can only measure the breakdown damage of IGBT tubes. No open circuit damage detected. After removing the power module from the circuit board, further measurements can be made on each IGBT tube, as shown in Figure 1. The left hand side of the meter indicates no conduction. The watch needle on the right indicates continuity. If it cannot be conducted and cut off, it is due to damage to the tube.
The structure of the frequency converter power module:
The internal packaging of the inverter power module consists of a single-phase or three-phase bridge rectifier circuit composed of diodes, and a three-phase bridge output circuit composed of six IGBT transistors (insulated gate bipolar transistors) and six damping diodes used in combination.
The three IGBT tube collectors of the upper half bridge of the three-phase output bridge are connected to the positive end of the power supply, and the emitters are U, V, and W three-phase output terminals. The emitters and gates of the three tubes form the input terminals GU-U, GV-V, and GW-W for the driving signal of the three-phase upper half bridge. The lower half of the three-phase output bridge consists of three IGBT tube collectors connected to U, V, and W respectively, with the emitter connected to the negative end of the power supply. The gate of the three tubes and the negative end of the power supply form the input terminals GX, GY, and GZ for the driving signal of the three-phase lower half bridge. B is the braking control terminal.
There is no braking circuit inside this module. TH is the output terminal protected by an internal thermistor. Although the pins and markings on the circuit board of other models of universal frequency converter power modules may vary, it is not difficult to identify the main functional pin positions. High end products adopt intelligent power modules, which contain driving and braking circuits internally, with corresponding more pins.
The power module of a frequency converter, as the name suggests, is a module that encapsulates the power electronic and power components of the frequency converter according to a certain functional combination. The frequency converter itself is composed of a control unit and a power module. In general, the power module of a frequency converter is constructed by integrating the outer shell and external electrode terminals to reduce the number of components and the inductance of internal wiring.
