How to use a multimeter to detect inverters
During the daily maintenance of the inverter, various problems are often encountered, such as peripheral circuit problems, parameter settings or mechanical failures. If the inverter fails, how to determine which part of the problem is the problem is briefly introduced here.
static testing
1. Test the rectifier circuit and find the P and N terminals of the internal DC power supply of the frequency converter. Adjust the multimeter to the resistance Ohm resistance and basically balanced. On the contrary, connect the black meter rod to the P terminal, and the red meter rod to R, S, and T in sequence, and there will be a resistance value close to infinity. Connect the red meter rod to the N terminal and repeat the above steps, and you will get the same result. If there are the following results, it can be determined that the circuit is abnormal,
A. The three-phase resistance is unbalanced, which can indicate that the rectifier bridge is faulty.
B. When the red meter rod 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. To test the inverter circuit, connect the red meter rod to the P terminal, and connect the black meter rods to U, V, and W respectively. There should be a resistance of dozens of ohms, and the resistance of each phase is basically the same. The reverse phase should be infinite. Connect the black meter rod to the N terminal and repeat the above steps to get the same result. Otherwise, the inverter module fault can be determined. 2. Dynamic test Only after the static test result is normal can the dynamic test, that is, power on the test machine, be performed. The following points must be noted before and after powering on:
1) Before powering on, you must confirm whether the input voltage is correct. Connecting a 380V power supply to a 220V inverter will cause explosions (explosion of capacitors, varistors, modules, etc.).
2) Check whether each broadcast port of the frequency converter is connected correctly and whether the connection is loose. Abnormal connections may sometimes cause the frequency converter to malfunction, and in serious cases, it may cause a machine crash.
3) After powering on, detect the fault display content and initially 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 no load (without connecting the motor), and test the three-phase output voltage values of U, V, and W. If phase loss, three-phase unbalance, etc. occur, the module or driver board is faulty.
5). When the output voltage is normal (no phase loss, three-phase balance), perform a load test. When testing, it is best to test at full load.
Fault diagnosis
1. Damage to the rectifier module is generally caused by grid voltage or internal short circuit. After eliminating the internal short circuit, replace the rectifier bridge. When handling faults on site, you should focus on checking the user's power grid conditions, such as grid voltage, whether there are welding machines and other equipment that pollute the grid.
2. Damage to the inverter module is generally caused by damage to the motor or cable and failure of the drive circuit. After repairing the drive circuit and measuring the drive waveform in good condition, replace the module. After replacing the driver board during on-site service, attention must also be paid to checking the motor and 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, resulting in no DC power in the DC circuit. For example, the starting resistor is damaged, or the panel may be damaged.
4. Overvoltage or undervoltage displayed after power-on is generally caused by input phase loss, circuit aging and moisture on the circuit board. Find out its voltage detection circuit and detection points, and replace the damaged components.
5. If overcurrent or grounding short circuit is displayed after powering on, it is usually due to damage to the current detection circuit. Such as Hall elements, operational amplifiers, etc.
6. Overcurrent on the startup display is generally caused by damage to the drive circuit or inverter module.
7. The no-load output voltage is normal, but after loading, it displays overload or overcurrent. This situation is generally caused by improper parameter settings or aging of the drive circuit or module damage.
