Three-phase asynchronous motor is a kind of motor powered by 380V three-phase AC power supply (phase difference 120 degrees). Because the rotor of three-phase asynchronous motor rotates with the stator rotating magnetic field in the same direction and at different rotating speeds, there is slip rate, so it is called three-phase asynchronous motor.
Variable frequency speed regulation is a speed regulating method to change the frequency of motor stator power and change its synchronous speed. The main equipment of VVVF system is to provide frequency conversion.
This paper introduces seven kinds of speed regulating methods and their characteristics of three phase asynchronous motors, and indicates the applicable occasions and situations. The rotational speed formula of three-phase asynchronous motor is n=60f/p(1-s). It can be seen from the above formula that changing the power supply frequency f, the pole logarithm P and slip rate s of the motor can change the rotational speed too much.