In the daily maintenance process of frequency converters, various problems are often encountered, such as peripheral circuit problems, poor parameter settings, or mechanical failures. If there is a fault with the frequency converter, how to determine which part of the problem is, we will briefly introduce it here

1. Static test

1. Test the rectifier circuit and locate the P and N terminals of the internal DC power supply of the frequency converter. Set the multimeter to resistance X10, connect the red meter rod to P, and connect the black meter rod to R, S, and T, respectively. There should be a resistance value of about tens of ohms, and it should be basically balanced. On the contrary, connect the black watch rod to the P end, and the red watch rod to R, S, and T in sequence, with a resistance value close to a large value. Connect the red meter rod to the N-end and repeat the above steps to obtain the same result. If there are the following results, it can be determined that the circuit is abnormal. A. The three-phase imbalance of the resistance value can indicate a rectifier bridge fault. B. When the red meter rod is connected to the P terminal, the resistance is very high, which can determine the fault of the rectifier bridge or the fault of the starting resistor 2. Test the inverter circuit by connecting the red meter rod to the P terminal and the black meter rod to U, V, and W respectively. The resistance value should be several tens of ohms, and the resistance values of each phase should be basically the same. The reverse phase should be very large. Connect the black watch rod to the N-terminal and repeat the above steps to obtain the same result. Otherwise, it can be determined that the inverter module is faulty

Secondly, air compressors Dynamic testing can only be carried out after the static test results are normal, that is, power on and test machine. Before and after powering on, pay attention to the following points:

1. Before powering on, it is necessary to confirm whether there is an error in the input voltage. Connecting a 380V power supply to a 220V level frequency converter may cause the machine to explode (such as capacitors, varistors, modules, etc.) 2. Check whether the various broadcasting ports of the frequency converter are properly connected and whether the connections are loose. Abnormal connections may sometimes cause the frequency converter to malfunction, and in severe cases, it may lead to machine explosion 3. After powering on, detect the fault display content and preliminarily determine the fault and its cause If no fault is displayed, first check if there are any abnormalities in the parameters, reset the parameters, start the frequency converter under no load (without connecting the motor), and test the three-phase output voltage values of U, V, and W. If there is a lack of phase or three-phase imbalance, the module or drive board may have a fault

5. Under normal output voltage (no phase loss, three-phase balance), conduct load testing

Thirdly, fault diagnosis

1. Rectifier module damage is generally caused by grid voltage or internal short circuits. Replace the rectifier bridge after eliminating internal short circuits. When dealing with faults on site, it is important to focus on checking the user's power grid, such as the voltage of the power grid, the presence of welding machines and other equipment that may cause pollution to the power grid 2. Inverter module damage is generally caused by motor or cable damage and drive circuit failure. After repairing the driver circuit and testing that the driver waveform is in good condition, replace the module. After replacing the drive board during on-site service, pay attention to checking the motor and connecting cables. After confirming that there are no faults, run the frequency converter 3. Power on without display is generally caused by damage to the switching power supply or soft charging circuit, resulting in no DC power in the DC circuit. If the starting resistor is damaged, it may also be due to panel damage 4. After power on, the display of overvoltage or undervoltage is generally caused by input phase loss, circuit aging, and moisture on the circuit board. Identify its voltage detection circuit and detection points, and replace damaged components