Generally, the general-purpose inverter roughly includes the following parts: (1) rectifier circuit; (2) DC central circuit; (3) Inverter circuit; (4) Control circuit. The static test is mainly a test of the high-power transistors (power modules) of the rectifier circuit, DC center circuit and inverter circuit. The rectifier circuit is mainly a forward and reverse test of the rectifier diode to judge its good or bad. The DC central circuit is mainly to measure the capacity and withstand voltage of the filter capacitor, and we can also observe whether the safety valve on the capacitor bursts open, whether there is leakage, etc., to judge its quality or bad. The judgment of the quality of the power module is mainly the judgment of the freewheeling diode in the power module. For IGBT modules, we also need to determine whether they can be turned on and off when there is a trigger voltage.
1. Test the rectifier circuit
Find the P and N ends of the DC power supply inside the inverter, adjust the multimeter to the resistance X10 gear, connect the red watch rod to P, and separate the black watch rod to R, S, T, there should be about tens of ohms of resistance, and the fundamental balance. Instead, connect the black watch rod to the P terminal, and the red watch rod to R, S, and T in turn, with a resistance value close to infinity. Connect the red watch stick to the N-end and repeat the above process, and you should get the same result. If there are the following results, it can be concluded that the circuit has been abnormal, A. The resistance value of the three-phase is unbalanced, which can indicate the rectifier bridge fault. B. When the red watch rod is connected to the P terminal, the resistance is infinite, and it can be concluded that there is a problem with the rectifier bridge or a problem with the starting resistance.
Rectifier module damage is generally caused by grid voltage or internal short circuits. In the case of sweeping the internal short circuit, replace the rectifier bridge. When dealing with faults on site, it is necessary to focus on checking the status of the user's power grid, such as the grid voltage, whether there is equipment that pollutes the power grid such as welding machines, etc.
2. Test the inverter circuit
Connect the red watch rod to the P terminal, and the black watch rod separate from the U, V, and W, there should be a resistance value of tens of ohms, and the resistance value of each phase is fundamentally the same, and the reverse phase should be infinity. Connect the black watch rod to the N terminal, and repeat the above process to get the same result, otherwise the inverter module can be confirmed. At this time, it is not possible to blindly power on, especially when the rectifier bridge is damaged or there are significant traces of burning on the circuit board, so as not to form a greater loss.
The damage of the inverter module is generally caused by damage to the motor or cable and the drive circuit. After correcting the drive circuit, the module is replaced when the driving waveform is in excellent condition. After replacing the driver board in field service, care must also be taken to check the motor and connecting cables. After confirming that there is no problem, the converter is operated.
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