Permanent Magnet Synchronous Motor (PMSM) can be classified according to different standards. The following are the main classification methods and their detailed descriptions, which are crucial for understanding and choosing the appropriate PMSM.

I. Classification according to the structure of the rotor permanent magnet (the most core classification method)

This is the most commonly used and important classification method, which directly determines the characteristics of the motor (such as convexity, weak magnetic capacity, torque density, etc.).

1. Surface-type permanent magnet synchronous motor

Structural features: The permanent magnet is directly attached to the surface of the rotor core, and the magnetic steel is usually tile-shaped. The rotor is usually cylindrical and simple in structure.

Working principle: Due to its physical structure, the magnetic resistance of the straight axis and cross-axis magnetic path of the rotor is basically the same, so its convex polarity is almost 1 (ρ = Lq/Ld ≈ 1). This means that the magnetic resistance torque is almost zero, and the total torque of the motor is completely provided by the permanent magnetic torque.

Advantages:

The structure is simple and the manufacturing cost is low.

The rotational inertia is small and the dynamic response is good.

The air gap magnetic field waveform is closer to the sine wave, and the torque pulsation is small.

Disadvantages:

The permanent magnet is directly exposed to the air gap, and the centrifugal force is large during high-speed operation. Bundling measures (such as carbon fiber straps) are required, which limits the maximum speed.

Weak magnetic speed regulation is difficult (because Ld is small, a large negative d-axis current is required to weaken the magnetic field).

Application: It is widely used in occasions where the speed regulation range is not wide and the pursuit of smooth operation, such as fans, water pumps, ordinary servo systems, etc.

2. Built-in permanent magnet synchronous motor

Structural features: The permanent magnet is embedded in the iron core of the rotor. According to the arrangement of magnetic steel, it can be divided into a variety of subcactories (such as I-shaped, V-shaped, U-shaped, double V-shaped, etc.).

Working principle: Because the magnetic conductivity of the permanent magnet is close to the air, after embedding the permanent magnet, the magnetic resistance of the straight axis and the cross-axis magnetic circuit of the rotor is not equal (Lq > Ld), and the convexity is ρ > 1. Therefore, the motor torque consists of two parts: permanent magnet torque + magnetic resistance torque.

Advantages:

The mechanical structure is solid and the permanent magnet is protected, which is suitable for high-speed operation.

The existence of magnetic resistance torque improves torque density and efficiency.

It is easy to expand the speed of weak magnetism (because Ld is large, a smaller negative d-axis current can effectively weaken the air gap magnetic field), and the constant power speed regulation range is wide.

Disadvantages:

The structure is complex and the manufacturing cost is high.

Due to the asymmetry of the magnetic circuit, the torque pulsation is usually greater than that of the table.

Application: This is the absolute mainstream choice for electric vehicle drive motors at present, because it perfectly balances high-speed performance, wide speed control range and efficiency. It is also used in high-end servo systems, aerospace and other fields.

3. Permanent magnet-assisted synchronous magnetic resistance motor

Structural features: It can be regarded as an extreme form of built-in PMSM. Its rotors have a large number of flux barriers, and permanent magnets are embedded in these barriers, and the proportion of magnetic flux provided by permanent magnets is relatively small.

Working principle: It mainly relies on the magnetic resistance torque (accounting for more than 70%), and the permanent magnetic torque plays an auxiliary role. Its convex polarity (ρ = Lq/Ld) is very high.

Advantages:

The dependence on and consumption of permanent magnet materials is reduced, the cost is lower and it is more resistant to the risk of demagnetization.

High efficiency, especially near the rated point.

The weak magnetic ability is extremely strong, and the speed regulation range is very wide.

Disadvantages: the power factor is relatively low (requirs a larger inverter capacity), and torque pulsation control is a technical difficulty.

Application: More and more applications are used in cost-sensitive occasions that require high efficiency and a wide range of speed regulation, such as household appliances (high-end air conditioning compressors), industrial drives, etc., and have also begun to enter the field of electric vehicles.

II. Classification according to the distribution of air gap magnetic field

1. Sine wave permanent magnet synchronous motor

Characteristics: The waveform of the anti-electroelectric potential is a sinusoidal wave.

Drive mode: Three-phase sine wave alternating current drive is required, and vector control (FOC) algorithm is usually used.

Advantages: smooth operation, small torque pulsation, low noise.

Application: Most high-performance servo systems, electric vehicles and precision control fields use this kind of motor. Usually, what we call PMSM refers to this kind of motor by default.

2. Trapezoidal wave permanent magnet synchronous motor (also known as brushless DC motor, BLDC)

Features: The waveform of the reverse electromotive potential is a trapezoidal wave (the width of the flat top is usually 120° electric angle).

Drive mode: square wave current drive, simple control.

Advantages: the control system is simple, low cost and high torque density.

Disadvantages: The torque pulsation is large, the noise and vibration are also large, and the current spike will occur when changing the phase.

Application: For cost-sensitive occasions with low stability requirements, such as household appliances (washing machines, vacuum cleaners), drones, low-cost fans, power tools, etc.

Note: Although BLDC also belongs to the "permanent magnet synchronous motor" family, in the academic and engineering fields, PMSM usually refers specifically to sine-wave permanent magnet synchronous motors to distinguish it from square-wave-driven BLDC.

III. Classification according to stator winding

1. Centralized winding motor

Features: The pitch of the winding is equal to 1 (a coil is wound on each tooth).

Advantages: short end, low copper consumption, high efficiency, easy to manufacture and automate winding.

Disadvantages: The torque and torque pulsation of the tooth groove are relatively large, and the harmonic content is high.

Application: In situations where there are requirements for volume and efficiency, and can accept certain vibrations.

2. Distributed winding motor

Features: The pitch of the winding is greater than 1 (one coil edge is distributed in multiple grooves).

Advantages: The air gap magnetic field has good sine nature, small torque pulsation, and stable operation.

Disadvantages: The winding end is long, the amount of copper is high, and the manufacturing cost is high.

Application: Most high-performance PMSMs use distributed windings, such as servo motors and electric vehicle drive motors.

Which type of PMSM to choose mainly depends on your application scenario, performance requirements (speed, torque, stability), cost budget and control complexity.

Pursuit of high performance and wide speed regulation: built-in (IPMSM) is preferred.

Pursuit of low cost and simple control: optional table adhesive (SPMSM) or brushless direct current (BLDC).

Pursuit of extremely high efficiency and ultra-wide speed regulation and cost-sensitive: permanent magnet-assisted synchronous magnetoresistance motor (PMa-SynRM) can be considered.