Understanding the difference between permanent magnet synchronous motors and conventional asynchronous motors in one article

Permanent magnet synchronous motor and AC asynchronous motor are two common types of motors, and they have some obvious differences in structure, working principle, and application. The following will provide a detailed introduction to the differences between these two types of motors.

1. Structural differences:

-The rotor of a permanent magnet synchronous motor is equipped with permanent magnets, usually rare earth permanent magnet materials. The magnetic field generated by these permanent magnets is synchronized with the magnetic field generated by the stator current and causes rotation.

-The rotor of an asynchronous motor is made of conductors, usually conductive materials such as copper and aluminum. When the motor is running, the alternating magnetic field of the stator current will induce the current in the rotor, resulting in rotation. Therefore, the rotor speed is always slightly slower than the rotating magnetic field, which is also why it is called "asynchronous".

2. Startup method:

-The starting torque of open-loop starting of permanent magnet synchronous motors is relatively small, and external auxiliary starting devices such as frequency converters or starters are usually required to assist in starting.

-AC asynchronous motors have self starting characteristics and can be started by simply connecting to a power source without the need for additional starting devices.

3. Torque characteristics:

Source of torque: The permanent magnet synchronous motor relies on the permanent magnet inherent in the rotor, which directly attracts the stator magnetic field to rotate; Asynchronous motors need to first "excite" the stator magnetic field to generate a temporary magnetic field in the rotor, and then drive the rotor, which is an additional step.

Stability: The permanent magnet synchronous motor maintains stable torque without significant fluctuations, regardless of speed; When asynchronous motors are operating at low speeds or with heavy loads, the torque is prone to "one stroke, one stroke" and instability.

Response speed: The permanent magnet synchronous motor generates force when powered on and responds quickly; Asynchronous motors have to wait for the rotor to "generate a magnetic field", and start and apply force half a beat slowly.

4. Control mode:

-Permanent magnet synchronous motors can achieve precise control of speed and torque by adjusting the stator voltage or frequency.

-AC asynchronous motors are usually controlled by frequency converters to achieve speed and torque regulation.

5. Efficiency:

-The efficiency of permanent magnet synchronous motors is relatively high, generally above 85%. This is because they have less loss on the stator coils and no rotor resistance or rotor losses.

-The efficiency of AC asynchronous motors is relatively low, usually between 80% and 90%, and their losses are mainly concentrated in the copper coil and rotor losses.

6. Application areas:

Due to their different performance characteristics, the two types of motors also have significant differences in their application fields:

Asynchronous motor is the most widely used type of electric motor, accounting for about 95% of electric drive machinery. It is suitable for driving various equipment such as machine tools, water pumps, air compressors, blowers, and large lifting equipment. Almost all situations that do not require precise speed control but require reliable operation of the motor under various load conditions will choose asynchronous motors.

Synchronous motors are mainly suitable for high-power production machinery that require constant speed, such as continuous rolling mills, ball mills, etc., due to their constant speed. In the power system, synchronous motors are also used to regulate the frequency and voltage of the grid. Due to its high cost and difficult maintenance, synchronous motors are relatively less commonly used.

6.1 Modern Applications: The Choice of New Energy Vehicles

In the field of modern new energy vehicles, the selection of these two types of motors also reflects their differences in characteristics.

Permanent magnet synchronous motors have the advantages of high energy conversion efficiency (up to 94%), small size, and light weight, but the cost is relatively high. Widely used in models such as BYD and Roewe.

Although asynchronous motors have low energy conversion efficiency (up to 90%), they are low-cost, structurally simple, and relatively easy to maintain. Used by models such as Tesla Model S, Model X, and NIO ES8.

6.2 How to choose: Determine based on needs

How to choose between two types of motors? This depends on the specific application requirements:

Choosing asynchronous motors may be more suitable for scenarios that are cost sensitive, do not require precise speed control, have limited maintenance conditions, and are not as demanding in application environments.

Choosing a synchronous motor may be more suitable for applications that require precise speed control, high efficiency requirements, power factor adjustment, and high power (over 2000KW).

It should be noted that each type of motor has its unique advantages and scope of application. When choosing the type of motor, it is necessary to comprehensively evaluate and select based on specific application requirements, performance requirements, and economic factors.