Working principle of permanent magnet synchronous motor

The starting and operation of a permanent magnet synchronous motor is formed by the interaction of the magnetic fields generated by the stator winding, the rotor squirrel cage winding and the permanent magnet. When the motor is stationary, a three-phase symmetrical current is passed through the stator winding to generate a stator rotating magnetic field. The stator rotating magnetic field generates a current in the cage winding relative to the rotation of the rotor, forming a rotor rotating magnetic field. The stator rotating magnetic field interacts with the rotor rotating magnetic field. Asynchronous torque causes the rotor to accelerate from standstill. In this process, the rotor permanent magnetic field and the stator rotating magnetic field rotate at different speeds, resulting in alternating torque. When the rotor accelerates to a speed close to the synchronous speed, the speed of the rotor's permanent magnetic field and the stator's rotating magnetic field are nearly equal. The speed of the stator's rotating magnetic field is slightly larger than the rotor's permanent magnetic field. They interact to generate torque and pull the rotor into a synchronous operating state. In synchronous operation, no current is generated in the rotor winding. At this time, only the permanent magnets on the rotor generate a magnetic field, which interacts with the rotating magnetic field of the stator to generate driving torque. It can be seen that the permanent magnet synchronous motor is started by the asynchronous torque of the rotor winding. After the start is completed, the rotor winding no longer plays a role, and the magnetic field generated by the permanent magnet and the stator winding interacts to generate the driving torque.