How to use a multimeter to locate the frequency converter
During the routine maintenance of the frequency converter, various problems are often encountered, such as peripheral circuit problems, parameter setting or mechanical failure. If the frequency converter fails, how to judge which part of the problem is, here is a brief introduction.
1. Static testing
1. Test the rectifier circuit. Find the P terminal and N terminal of the DC power supply inside the inverter, adjust the multimeter to the resistance X10 level, connect the red meter stick to P, and the black meter stick to R, S, T respectively. There should be about tens of European resistance, and basically balanced. On the contrary, connect the black meter lead to the P terminal, and the red meter lead to R, S, T in turn, and there is a resistance close to infinity. Connect the red meter stick to the N terminal, repeat the above steps, and you should get the same result. If there are the following results, it can be judged that the circuit has abnormality,
A. The three-phase resistance is unbalanced, which can indicate the failure of the rectifier bridge.
B. When the red meter stick is connected to the P terminal, the resistance is infinite, and it can be concluded that the rectifier bridge is faulty or the starting resistor is faulty.
2. Test the inverter circuit. Connect the red hand of the meter to the P terminal, and the black hand of the meter to U, V, and W respectively. There should be a resistance of tens of ohms, and the resistance of each phase is basically the same, and the reverse phase should be infinite. Connect the black meter lead to the N terminal, and repeat the above steps to get the same result, otherwise, it can be determined that the inverter module is faulty. 2. Dynamic test After the static test result is normal, the dynamic test can be performed, that is, the power-on test machine. The following points must be paid attention to before and after power-on:
1. Before powering on, it is necessary to confirm whether the input voltage is correct. When a 380V power supply is connected to a 220V inverter, there will be explosions (frying capacitors, varistors, modules, etc.).
2. Check whether the broadcast ports of the inverter are connected correctly and whether the connection is loose. Abnormal connections may sometimes cause the inverter to malfunction, and in severe cases, the machine may explode.
3. Check the fault display content after power-on, and preliminarily determine the fault and its cause.
4. If no fault is displayed, first check whether there is any abnormality in the parameters, and after resetting the parameters, start the inverter under the condition of no load (not connected to the motor), and test the U, V, W three-phase output voltage values. If there is a phase loss, three-phase unbalance, etc., the module or driver board is faulty
5. In the case of normal output voltage (no phase loss, three-phase balance), load test. When testing, it is best to test with full load.
3. Fault judgment
1. Damage to the rectifier module is generally caused by grid voltage or internal short circuit. If the internal short circuit is excluded, replace the rectifier bridge. When dealing with faults on site, focus on checking the user's power grid, such as grid voltage, presence of equipment that pollutes the grid, such as electric welding machines, etc.
2. Damage to the inverter module is generally caused by motor or cable damage and drive circuit failure. After the drive circuit is repaired and the drive waveform is in good condition, replace the module. After the driver board has been replaced in field service, care must also be taken to check the motor and the connecting cables. After confirming that there is no fault, run the inverter.
3. No display after power-on is generally caused by damage to the switching power supply or damage to the soft charging circuit that causes no DC power in the DC circuit. If the starting resistor is damaged, the panel may also be damaged.
4. The overvoltage or undervoltage displayed after power-on is generally caused by input phase loss, aging circuit and damp circuit board. Find out its voltage detection circuit and detection point, and replace the damaged device.
5. After power-on, it shows over-current or ground short-circuit, which is generally due to damage to the current detection circuit. Such as Hall elements, operational amplifiers, etc.
6. The start-up display overcurrent is generally caused by damage to the drive circuit or inverter module.
7. The no-load output voltage is normal, but it shows overload or overcurrent after loading. This situation is generally caused by improper parameter setting or aging of the drive circuit or module damage.
