How to judge if VFD is good

The easiest way to judge if the VFD is good is Power-on detection.It is best to connect the inverter with a motor that the power is less than the inverter’s rated power.You will know if the inverter is good or not in this way, especially the inverter algorithm about low frequency and high torque.

First, you can modify the frequency within 5HZ after changing the parameters to check if the motor torque is weakened and whether the motor speed change accordingly.

Then you can check if the output waveform is perfect.  

Also, you can test the the peak value of current and voltage by starting and stopping frequently in short time.

Pls test the input terminals R,S,T and output terminals U,V,W resistance value by using a multimeter at 1KΩ before power-on.

Then disconnect the wiring of R,S,T and U,V,W to test the rectifier circuit and inverter circuit.

1. Testing the rectifier circuit

Set the multimeter to the resistance X1KΩ , connect the black pen to the P terminal and the red to the R, S, T terminals in turn. There should be a resistance of about tens of kilo-ohms and they should be basically the same. Connect the red pen to the P terminal and the black  to the R, S, T terminals in turn. There should be a resistance close.

Connect the black test lead to the N terminal and repeat the above steps. There should be the same result.

If the three-phase resistance is unbalanced or the resistance is infinite when the red test lead is connected to the P terminal, it can be determined that the circuit is abnormal and the rectifier bridge is faulty.

2. Testing inverter circuit

Connect the black pen to the P terminal and the red pen to U, V, W in turn. There should be a resistance of several tens of kilo-ohms and the resistance of each phase is basically the same.

Connect the red pen to the P terminal and the black pen to U, V, and W in turn. There is a resistance close to infinity. Connect the red pen to the N terminal and repeat the above process to get the same result. Otherwise, it can be determined that the inverter module is faulty.