What is the difference between AC asynchronous motor and permanent magnet synchronous motor carried by pure electric vehicle?

Whether we talk about the power system of Tesla or Weilai automobile, we can hear the two key words of asynchronous motor and permanent magnet synchronous motor. So what are the advantages and disadvantages of motors equipped with these two different technologies? Today, through the Tesla model? S model, let's talk together.

Of course, let's first understand the working principle of pure electric vehicles: the battery supplies power to the motor through the control system, and the electric energy is converted into mechanical energy in the motor and transmitted to the system. Finally, it is transmitted to the driving wheel to make it rotate, and the traction force for driving the car is generated through the interaction with the ground.

Knowing the working principle, we will go directly to today's topic, 20 19 Tesla model? The S-long battery life version is equipped with permanent magnet synchronous motor on the front axle and AC asynchronous motor on the rear axle. The biggest difference between synchronous motor and asynchronous motor lies in whether the rotor speed of the two motors is consistent with the magnetic field speed of the stator rotation. If the rotor speed is the same as the stator speed, it is called a synchronous motor. If not, it is called asynchronous motor. They are quite different in performance parameters and applications.

Permanent magnet synchronous motor is mainly composed of rotor, end cover and stator. Generally speaking, the biggest feature of permanent magnet synchronous motor is that its stator structure is very similar to that of ordinary induction motor, but it is mainly different from other motors in the unique structure of rotor. The biggest difference from the commonly used asynchronous AC motor is the unique structure of the rotor, which has high-quality permanent magnetic poles. When three-phase symmetrical alternating current is applied to the three-phase stator winding of the motor, it will generate a rotating magnetic field and cut the rotor winding, thus generating an induced current in the rotor winding (the rotor winding is a closed path), and the current-carrying rotor conductor will generate an electromagnetic force under the action of the stator rotating magnetic field, thus forming an electromagnetic torque on the motor rotating shaft to drive the motor to rotate, and the motor rotating direction is the same as that of the rotating magnetic field. When a conductor cuts magnetic lines in a magnetic field, an induced current is generated in the conductor, hence the name "induction motor". The combined action of induced current and magnetic field exerts driving force on the motor rotor.

The structure of asynchronous induction motor can be divided into stator and rotor, as well as end cover, fan and other accessories. The stator is the fixed part of the motor and the rotor is the rotating part of the motor. Because the stator of asynchronous motor generates exciting rotating magnetic field and absorbs electric energy from power supply, the rotating magnetic field generates electric energy on the rotor and converts it into mechanical energy, so unlike DC motor, the stator of AC motor is armature. In addition, there must be a certain gap (called air gap) between the stator and the rotor to ensure the free rotation of the rotor.

Advantages of synchronous motor:

1, the rotor has no excitation winding, so there is no copper consumption of the rotor, so the efficiency is higher;

2. High-performance permanent magnet materials provide excitation, and the given power is small and the volume can be reduced;

3, the rotor has small moment of inertia and good dynamic performance;

4. High power and torque output under low efficiency.

Disadvantages of synchronous motor:

The cost is high, the reliability is low, the processing technology is complex, the mechanical strength is poor, and the performance of electric vehicles is greatly affected by the environment.

Advantages of asynchronous motor:

1、? There is no demagnetization problem of permanent magnets at high temperature, and peak power, rated power and peak power working time can be prolonged.

2、? The motor characteristics are less affected by the environment;

3、? Have the ability to start high torque and high-speed torque adjustment;

Disadvantages of asynchronous motor:

Rotor magnetic field comes from stator excitation, which leads to copper consumption and lower energy conversion rate than permanent magnet synchronous motor.

Pure electric vehicle using AC asynchronous induction motor

From the characteristics of the motor, the electric vehicle equipped with AC asynchronous motor is more inclined to the performance strategy, making full use of the performance output and efficiency advantages of this motor at high speed, such as early models? S. Its characteristics are: when the car is driving at high speed, it can maintain high-speed operation and high efficiency of electric energy use, and reduce energy consumption while maintaining the maximum power output of the car.

Vehicles equipped with permanent magnet synchronous motor tend to adopt energy consumption strategy, and make full use of the performance output and efficient operation of this motor at low speed, which is suitable for small and medium-sized cars. Its characteristics are small size and light weight, which can greatly increase the cruising range of electric vehicles. And its speed regulation performance is particularly good, and it can still maintain high efficiency in the face of repeated start-stop, acceleration and deceleration. ?

Asynchronous induction motor and permanent magnet synchronous motor have their own advantages, so some main engine factories began to consider combining the characteristics of the two motors to match. For example, 20 19 Tesla model? The S-long battery life version is equipped with two motor technologies at the same time to meet the technical advantages of different motors under different working conditions. The front axle is equipped with optimized permanent magnet synchronous motor, which is low-speed and efficient. The maximum output power is 202kw(275Ps) and the maximum torque is 404 N m. When the vehicle speed is in the middle and low speed, the computer outputs instructions to the permanent magnet synchronous motor to work. The rear axle is equipped with a high-speed AC asynchronous motor, with the maximum output power of 285kw(387Ps) and the maximum torque of 440 N m. When high-speed operation is required, both motors work at the same time to provide strong acceleration performance. When slowing down, the motors are intelligently adjusted according to the braking requirements. For ordinary braking, permanent magnet synchronous motor is used to recover braking energy, while for sudden deceleration, when two motors provide braking torque at the same time, the energy is recovered.

Sure, 20 19? S adopting this strategy is also based on the development idea of changing small into big. If it is a replacement development, Tesla must be a model? S is equipped with permanent magnet switched reluctance motor. This new motor technology has the characteristics of small size, low cost and high power, and the conversion efficiency reaches 89%. Tesla put him on the latest model? Three up.

Comprehensive? condition

Asynchronous induction motor and permanent magnet synchronous motor have their own advantages and disadvantages. When the car is driving at high speed, the asynchronous induction motor can maintain high-speed operation and high-efficiency electric energy utilization. However, in the face of repeated start-stop, acceleration and deceleration, the permanent magnet synchronous motor with good speed regulation performance can still maintain high efficiency. The choice of motor depends on the final vehicle positioning and energy consumption strategy of the main engine factory. However, from the current development of motor technology, Tesla has been at the forefront of the industry.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.