How to Run a 3 Phase Motor with PLC & VFD
Can PLCs and VFDs control three-phase motors? The answer is yes. We need to prepare these basic materials: ATO PLC, VFD, 3-phase motor, relay, contactor, DC power supply, circuit breaker, button box, cable.
The PLC program interlocks the forward and reverses the rotation of the motor to prevent the wrong touch of the motor's reverse rotation button. PLC and the VFD are powered on for 2s time control. After the motor stops, it needs to wait for 10s before the motor can be restarted. This is very practical in practical applications (there is a good buffer process for motor inertial motion).
- The button box gives a signal to the PLC.
- PLC control relay.
- The relay controls the contactor to close the VFD power supply and enable the motor to rotate forward and reverse.
The left is the simulation wiring diagram. On the right is the circuit diagram.
- Power on, the VFD will be powered in 2s.
- Press SB1, the motor rotates forward, SB2 is invalid.
- Press SB3 to stop the motor, and SB1 and SB2 are invalid within 5s.
- Press SB2, the motor reverses, SB1 is invalid.
PLC program explanation
After power on, the timer T00O starts to count for 2s. After 2s, KA1 (relay) is turned on, and the contactor KM is turned on. The VFD is powered.
- Press forward button SB1, KA2 is turned on. The VFD gets a forward signal.
- Press SB2, KA3 is connected. The VFD gets the reverse signal.
- Press SB3, T001 time 10s. The forward and reverse signals are invalid within 10s. KA4 is connected, X3 is disconnected, and VFD stops running.
2s after power-on, KA1 is powered (VFD powered). When SB1 is set to 1, KA2 has output. When SB3 is set to 1, the forward and reverse signals are invalid within 10s.
- P0.03=1 (Terminal control mode)
- P4.02=9 (Input terminal X3 function selection, 3-wire control)
- P4.08=2 (3-wire control mode 1, When X3 is disconnected from COM, VFD stops running.)
- Press the forward button, the motor starts to rotate forward. Because the forward and reverse rotations are interlocked in the PLC program, the reverse button is invalid at this time.
- Press the stop button, the forward and reverse buttons are invalid within 10s.
- Start to reverse, the forward button is invalid at this time. This is the working state of the intermediate relay.
If you want to know more details, please check the video below.