Three Phase VFD Control Motor Forward and Reverse

Working process of VFD control three-phase asynchronous AC motor forward and reverse. When we talk about variable frequency drive, we know that it has a good effect on speed regulation. In fact, a good effect could also be obtained for controlling the forward and reverse of three-phase asynchronous AC motor with a three phase VFD. We will explain with an example, such as the figure below:


The figure above refers to the circuit diagram for VFD to control the forward and reverse of three-phase asynchronous AC motor. It can be seen from the figure that the circuit consists of two parts: main circuit of load working and control circuit. Main circuit of load working consists of power supply switch (breaker), main contact of AC contactor KM, VFD built-in AC-DC-AC converter circuit, and three-phase asynchronous AC motor M. The control circuit consists of VFD built-in auxiliary circuit, start button switch SB2, stop button switch SB1, electromagnetic coil of AC contactor KM, contactor frequently-opening auxiliary contacts and motor forward and reverse selector switch SA. RP refers to the frequency-given signal potentiometer.

Connect the power supply switch QF firstly and ensure the circuit is powered on. When pressing the start button SB2, the contactor KM coil is powered on to pull in and lock, the contactor’s movable contact KM between COM and SA connects. When the contactor’s main contact in main circuit is closed, input end R, S, T of VFD is powered, and the VFD is prepared to work. Operate the selector switch SA, when SA is connected with FWD, the motor rotates in a forward direction. When the SA is connected with REV, the motor rotates in a reverse direction. When stopping is required, place the selector switch SA in the middle position, and VFD stops working firstly. Press the stop button SB1, the contactor’s KM coil is powered off to reset, main contact of the contactor disconnects, the three-phase power supply is cut off. If the stop button SB1 is pressed firstly, the contactor’s coil is powered off to reset, main contact of the contactor disconnects, cut off the input power supply of VFD directly, then the motor stops working.