The structure and working principle of
permanent magnet synchronous motor
1. The structure of permanent magnet synchronous motor
Permanent magnet synchronous motor (PMSM) mainly comprises rotor, end cover and stator. The main structure is: shaft, rotor, stator core, stator winding, base and cooling fan.
The permanent magnet synchronous motor consists of stator core and winding, generating a synchronous rotating magnetic field. The function of the stator is to generate magnetic field during the operation of the motor. After the symmetrical three-phase alternating current is passed into the three-phase stator winding, a rotating magnetic field is generated that rotates along the inner circle space of the stator and rotor at a synchronous speed. The stator of the three-phase permanent magnet synchronous motor is not much different from that of the three-phase AC asynchronous motor in structure.
The first form: a rotor with a permanent magnet pole installed on the circumferential surface of the rotor core is called a surface protruding permanent magnet rotor.
The second form: the permanent magnet pole is embedded on the surface of the rotor core, which is called a surface embedded permanent magnet rotor.
The third form: It is more commonly used in larger motors to embed permanent magnets inside the rotor, which is called an embedded permanent magnet rotor (or built-in permanent magnet rotor or embedded permanent magnet rotor). The permanent magnet is embedded inside the rotor core, and there are slots for installing permanent magnets in the core. The main arrangement of permanent magnets is shown in the figure. In each form, there is a combination of multiple layers of permanent magnets.
2. Working principle of permanent magnet synchronous motor
Permanent magnet synchronous motors are generally equipped with a rotary transformer (resolver), as shown in the figure. It is an electromagnetic sensor used to detect the position and speed of the rotor. The principle of the resolver is basically the same as that of the transformer.
The resolver of the permanent magnet synchronous motor adopts a reluctance resolver, and its rotor is a rotor core without rotor windings. The rotor is made of a special shape with an iron core, and the output voltage changes in amplitude according to the gap between the rotor core and the stator core (amplitude modulation type).
The permanent magnet synchronous motor is a device in which the magnetic field of the electromagnet and the magnetic field of the permanent magnet pull each other to generate force and motion, as shown in the figure.
The three-phase symmetrical alternating current is connected to the three-phase winding of the motor stator to generate a rotating magnetic field. According to the principle that opposite poles attract each other and like poles repel each other, no matter what the initial relative position of the stator rotating poles and the permanent magnetic poles is, the stator rotating poles will always drag the rotor to rotate synchronously due to the magnetic force.
Characteristics of permanent magnet synchronous motor
Small size, light weight, and high power density. The application of high-performance ultra-strong permanent magnetic materials has greatly reduced the size and weight of permanent magnet motors, and the power density is at least 1.5 times that of ordinary three-phase asynchronous motors.
High efficiency and energy saving. Because the excitation magnetic field is provided by permanent magnets, the permanent magnet rotor does not need excitation, and the efficiency can be as high as 90%. Compared with asynchronous motors, the high-efficiency operation speed range is wide and the energy saving is significant. Especially when running at low speed, the advantage is more obvious.
Low temperature rise. Due to the high efficiency of permanent magnet motors, there is no resistance loss in the rotor winding, and there is little or almost no reactive current in the stator winding, which makes the motor temperature rise low and prolongs the service life of the motor
Fast response, wide speed regulation range, high reliability, low noise and smooth operation, suitable for medium and high power occasions. At present, electric passenger cars generally use permanent magnet synchronous motors.
A certain amount of permanent magnets are required, which is more expensive than three-phase asynchronous motors. In addition, permanent magnets are prone to irreversible demagnetization at high temperatures, and their reliability is lower than that of three-phase asynchronous motors.
