Permanent magnet synchronous motor

Permanent magnet synchronous motor is a new type of motor. Permanent magnet synchronous motor has the advantages of simple structure, small size, high efficiency, energy saving and environmental protection, high power factor and low failure rate. Permanent magnet synchronous motor uses permanent magnet instead of excitation winding for excitation. When the three-phase stator windings (each with an electrical angle difference of 120°) of a permanent magnet motor are supplied with a three-phase alternating current of frequency F, a rotating magnetic field moving at a synchronous speed is generated. In steady state, the main pole magnetic field rotates in synchronization with the rotating magnetic field and therefore the rotor speed is synchronized. The rotating magnetic field of the stator and the main pole magnetic field established by the permanent magnets remain relatively stationary, and they interact to produce an electromagnetic torque that drives the motor to rotate and perform energy conversion. Compared with AC asynchronous motors, permanent magnet motors have the following advantages. The external characteristic efficiency curve of a permanent magnet synchronous motor has a much higher efficiency value at light loads compared to an asynchronous motor, which is the biggest advantage of a permanent magnet synchronous motor over an asynchronous motor in terms of energy savings. Usually, when a motor drives a load, it rarely runs at full power. This is because:On the one hand, when the user selects the motor, the power of the motor is usually determined according to the extreme working conditions of the load, and there are few chances for extreme working conditions to occur. At the same time, in order to prevent the motor burned in asynchronous conditions, the user will also give the motor power to leave a margin; on the other hand, in the design of the motor, in order to ensure the reliability of the motor, the designer is usually in the user's requirements on the basis of the power to leave a certain amount of power margins, which leads to the actual operation of more than 90% of the motor working in the rated power of 70% or less, especially when driving a fan or a water pump. As a result, motors usually operate in the light load zone. For induction motors, the efficiency is very low under light load, while permanent magnet synchronous motors can still maintain high efficiency under light load.