Repairing the frequency converter is a combination of theoretical knowledge, practical experience and operation level, and its technical level determines the maintenance quality of the frequency converter.
Common fault detection methods
Static test
1, test rectifier circuit
Find the P terminal and N terminal of the internal DC power supply of the inverter, adjust the multimeter to the resistance X10 file, the red indicator bar to P, and the black indicator bar to R, S, and T respectively. Normally, there are several tens of euros of resistance. And basically balanced. Instead, the black bar is connected to the P terminal. The red bar receives R, S, and T in turn and has a resistance close to infinity. Bring the red bar to the N-side and repeat the above steps to get the same result. If there are the following results, it can be determined that the circuit has abnormality. A. The three-phase impedance is unbalanced, indicating that the rectifier bridge is faulty. B. When the red bar is connected to the P terminal, the resistance is infinite, and it can be concluded that the rectifier bridge has failed or the starting resistor has failed.
2, test inverter circuit
The red table rod is connected to the P terminal, and the black table rod is connected to U, V, W, respectively. There should be several tens of euros of resistance, and the resistance of each phase is basically the same, and the opposite phase should be infinite. N-end the black bar, repeat the above steps should get the same results, otherwise it can be determined that the inverter module is faulty.
Dynamic Testing
After the test result is normal, the dynamic test can be performed, that is, the power on test machine. Before and after power on, you must pay attention to the following points:
1. Before powering on, make sure whether the input voltage is incorrect or not. If the 380V power supply is connected to a 220V inverter, there will be explosions (fried capacitors, varistors, modules, etc.).
2. Check whether the frequency converter’s receiving ports are properly connected and whether the connection is loose. If the connection is abnormal, it may cause the inverter to malfunction. In severe cases, it will cause explosives and other situations.
3. Detect the fault display content after power-on, and preliminarily determine the fault and cause.
4. If the fault is not displayed, first check whether the parameters are abnormal. If no problem is found, record the original parameters first, and then restore the parameters to the original factory. Start the inverter under no load (without connecting the motor) and test. U, V, W three-phase output voltage. If there is a lack of phase, three-phase imbalance, etc., the module or the driver board is faulty.
5. In the case of normal output voltage (no phase loss, three-phase balance), the load test is as full load test as possible.
Fault judgment
1, rectifier module damage
Usually due to grid voltage or internal short circuit. Replace the rectifier bridge with the exception of internal short circuits. When dealing with faults at the site, it is important to check the user’s power grid conditions, such as grid voltage, presence of equipment such as welders that are contaminated by the power grid, and so on.
2. Inverter module is damaged
It is usually caused by damage to the motor or cable and malfunction of the drive circuit. After repairing the driver circuit, replace the module with a good drive waveform. After replacing the driver board in field service, check the motor and connecting cable. The frequency converter can only be operated without any fault.
3, no display on power
It is usually caused by the switching power supply being damaged or the soft charging circuit being damaged that the DC circuit is not caused by the direct current. If the starting resistor is damaged, the operation panel may also be damaged.
4, show over-voltage or under-voltage
Usually due to the lack of input phase, aging of the circuit and moisture in the circuit board. The solution is to find out its voltage detection circuit and detection point and replace the damaged device.
5, display over-current or short circuit to ground
This is usually due to damage to the current detection circuit. Such as Hall elements, op amp circuits.
6, the power and driver board start to show over-current
Usually caused by damage to the driver circuit or inverter module.
7, no-load output voltage is normal, with overload display or over-current
This is usually caused by incorrect parameter settings or aging of the drive circuit and damage to the module.
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