Fault phenomenon:
The fault of the inverter with no output is relatively broad in terms of fault mechanism and circuit level. The inverter has no U, V, W phase voltage output, but there is normal voltage between P and N of the main circuit (both ends of the energy storage capacitor), the high voltage indicator light is on, the inverter has entered "normal working status", and the mainboard MCU has also made a Based on this judgment, no relevant fault codes or abnormal instructions will be reported. The fault is puzzling: the circuit is normal, but there is no output, and it is difficult to find the fault link!
Cause Analysis:
The DC voltage between the main circuit P and N is normal, indicating that the rectification, current limiting and energy storage circuits are basically normal, and there is no short circuit fault in the braking circuit and inverter circuit. The reason why the inverter has no output voltage is that the inverter circuit is not working, because the possibility of the three upper arms of the inverter circuit being open at the same time is very small, and the reason why the inverter circuit is not working is that there is no driving pulse.
According to the working flow of the inverter circuit, the driving pulse required by the inverter circuit is generated by the CPU and is amplified by the drive circuit. Therefore, the reason why the inverter circuit does not work may be that the CPU and drive circuit are faulty. In addition, if the inverter When the circuit's overcurrent, overheating and other detection circuits fail, the CPU will misidentify and stop outputting drive pulses. In addition, the operating voltage of these circuits is provided by the switching power supply, so the failure of the switching power supply will also cause the inverter circuit to not work. .
Maintenance method:
The fault may be caused by damage to the CPU, drive circuit, switching power supply or detection circuit. The maintenance process is as follows:
a. Check whether the switching power supply has output voltage. If there is no output voltage, check the switching power supply.
b. Run the frequency converter, and use an oscilloscope to measure whether the CPU's drive pulse output pin has pulse output. If the CPU has pulse output, the fault should be in the drive circuit, which cannot send the drive pulse generated by the CPU to the inverter circuit. If the CPU has no pulse output, check the CPU and detection circuit.
During the power-on period, it is prohibited to use a multimeter or oscilloscope to directly measure the G pole of the IGBT of the inverter circuit, because interference signals may be generated during the measurement, which may cause the IGBT to abnormally trigger and conduct and damage it.
In addition, it is strictly forbidden to energize the inverter circuit after disconnecting the drive circuit, because the G pole of each IGBT in the inverter circuit is easily disturbed and leads to conduction between the C and E poles. If the upper and lower bridge IGBTs are turned on at the same time, If the power supply of the inverter circuit is directly short-circuited, the IGBT and power supply circuit will be burned out.
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