A permanent magnet synchronous motor mainly consists of a rotor, stator, bearings, windings, end covers, and other structural components.
Structure and Cross-Section of a Permanent Magnet Synchronous Motor
As the stationary component of the motor, the stator consists of two major parts: the stator core and the windings. The stator core is generally constructed from laminated silicon steel sheets, which are designed to reduce eddy current losses and enhance magnetic permeability. The stator windings, on the other hand, are made of insulated copper wires wound in a specific pattern in the slots of the core to form a three-phase winding.
When three-phase alternating current is introduced into these three symmetrical windings, a varying magnetic flux is generated in the stator winding according to the laws of electromagnetic induction. Due to the phase differences and the spatial arrangement of the windings, these fluxes interact with each other, which in turn creates a rotating magnetic field rotating at synchronous speeds in the space between the stator and the rotor.
3 forms of permanent magnet synchronous motor rotor
1.Permanent magnet pole rotor
A rotor with a permanent magnet pole installed on the circumferential surface of the rotor core is called a surface-projected permanent magnet rotor.
2. Permanent magnet pole embedded in the iron core
When permanent magnets are partially embedded into the surface of the rotor core, the design is referred to as a surface-embedded permanent magnet rotor.
3. Embedded permanent magnet rotor
In larger motors used more is embedded in the rotor inside the permanent magnet, commonly known as an interior permanent magnet (IPM) rotor, also referred to as a built-in permanent magnet rotor.
magnet rotor), permanent magnets embedded in the rotor core inside the iron core is open to install the permanent magnet slot, the arrangement of the permanent magnets in the main way as shown in the figure, in each form there is the use of multi-layer permanent magnets in a combination of ways.
Strength analysis of high-speed permanent magnet rotors
Sintered neodymium-iron-boron (NdFeB) is a high-performance magnetic material widely used in PMSMs, is favored for its excellent magnetic properties, but its physical properties also raise a series of challenges. This material performs well in terms of compressive properties but is relatively poor in terms of tensile strength, especially under high-speed rotating conditions where the permanent magnets on the rotor are subjected to extreme centrifugal forces. In order to guarantee the reliable operation of the motor, effective fixing measures must be taken to meet the structural strength and dynamic requirements of the rotor.
In the rotor design of high-speed permanent magnet synchronous motors, there are three main design types: embedded, surface-mounted and surface-embedded. In the design of surface-embedded permanent magnet rotors, they can be further classified into non-conductive alloy steel sheathed rotors and carbon fiber composite sheathed rotors based on the sheathing material used.
Currently, the most common protections include the use of carbon fiber to bind the permanent magnet and the addition of a high-strength, non-conductive alloy sheath to the outer layer of the permanent magnet.
Cost Efficiency in Rotor Structure Design
Built-in permanent magnet synchronous motors are commonly used in new energy vehicles, a choice that is largely due to their excellent performance and unique structural advantages. In the design of built-in motors, they can be categorized into two forms, distributed and centralized, depending on the layout of the windings. New energy vehicles tend to choose distributed winding motors over centralized ones for a number of reasons:
Firstly, distributed winding motors can optimize the distribution of electromagnetic force waves, reduce the generation of harmonics, and effectively improve NVH (noise, vibration and harshness) performance through precise pole-slot coordination, which is highly compatible with the application requirements of new energy vehicles.
Secondly, the stator structure of distributed winding motors avoids the design of protruding pole palms, and instead consists of one or more coils arranged according to a specific pattern to form a coil pack. This design provides flexibility for the diverse design of the motor rotor, enabling it to meet diverse operating conditions.
The rotor construction of permanent magnet motors has a specific design and function. The rotor is mainly made of multiple silicon steel sheets stacked and fixed, and these silicon steel sheets not only form the main structure of the rotor, but also help to reduce the eddy current loss, thus improving the efficiency of the motor.
Inside the rotor, several slots are designed, each serving a different function. The outer V-shaped slots are primarily designed to secure the permanent magnets in place and ensure their stability when the motor is running at high speeds.
The design of the slots also takes into account the lightweight requirements of the rotor. While ensuring sufficient structural strength, the well-designed slots and material selection reduce the weight of the rotor and lower the moment of inertia, which in turn improves the responsiveness of the motor.
