Static testing
Testing rectifier circuit
Locate the P and N terminals of the DC power supply inside the frequency converter . Set the multimeter to the resistance x10 range. Connect the red probe to P and the black probe to R, S, and T respectively. There should be a resistance of approximately tens of ohms, and the resistance should be roughly balanced. Conversely, connect the black probe to P and the red probe to R, S, and T in sequence; you should see a resistance close to infinity. Repeat the above steps with the red probe connected to N; you should get the same result each time. If the following results are found, it can be determined that the circuit is abnormal: A. Uneven resistance across the three phases indicates a rectifier bridge fault. B. Infinite resistance when the red probe is connected to P indicates a rectifier bridge fault or a faulty starting resistor.
Testing the inverter circuit
Connect the red probe to terminal P, and the black probe to terminals U, V, and W respectively. There should be resistance values of several tens of ohms, with each phase having roughly the same resistance. The reverse phase should have infinite resistance. Connect the black probe to terminal N and repeat the above steps; the same result should be obtained. Otherwise, the inverter module is faulty.
For IGBT modules, the simplest measurement method (not the professional method) is to use a pointer multimeter on the 10kΩ resistance range to trigger Gw and Ew (black probe to Gw, red probe to Ew). Then, P to W will conduct. When Gw and Ew are short-circuited, P to W will be off. The same logic applies to the other IGBT pins.
Dynamic testing
Oscilloscope
Dynamic testing, i.e., power-on testing, can only be performed after the static test results are normal. The following points must be noted before and after powering on:
Before powering on, you must confirm that the input voltage is correct. Connecting a 380V power supply to a 220V inverter will cause the inverter to explode (capacitors, varistors, modules, etc. to explode).
Check that all ports of the frequency converter are connected correctly and that the connections are not loose. Abnormal connections may cause the frequency converter to malfunction, and in severe cases, it may even cause the machine to explode.
After powering on, check the fault display content and make a preliminary determination of the fault and its cause.
If no fault is displayed, first check if the parameters are abnormal. After resetting the parameters, start the inverter under no-load (without connecting the motor) conditions and test the U, V, and W three-phase output voltage values. If a phase loss or three-phase imbalance occurs, the module or drive board is faulty.
Under normal output voltage conditions (no phase loss, three-phase balance), perform a load test. Ideally, the test should be performed under full load.
