Comparison and introduction of different types of drive motors for new energy vehicles

As the power system of the three major components of electric vehicles, the position of the motor in electric vehicles is undoubtedly pivotal, and its performance also directly determines the performance of electric vehicles, so the choice of the drive motor is particularly important. At present, there are three main types of popular electric vehicle motors on the market, one is brushless DC motor, the second is AC asynchronous motor, the third is permanent magnet synchronous motor and so on. According to the driving principle of the motor, the following new energy gentleman introduces the four common drive motors.

One, once the mainstream: DC motor

Faraday and his invention of DC motor

With simple control device, low cost and other characteristics, in the early development of electric vehicles, DC motor has become the first choice of many electric car manufacturers. But at the same time, the shortcomings of the DC motor itself are also very prominent, first of all, brushes and mechanical commutator and other components of its own more complex mechanical structure, but also to limit its overload capacity and motor speed.

And when running under high speed and large load for a long time, there will also be sparks on the commutator surface, and all these factors will affect the performance of the whole car. With the wear and tear of carbon brushes, the reliability and life of the motor will be reduced if maintenance is not carried out in time, and the current electric vehicles have basically eliminated DC motors.

Second, mixed feelings: AC asynchronous motors

Tesla and its invention of induction motor

AC asynchronous motor is one of the mainstream motors in today's industry, it is also called induction motor, it also has the advantages of simple structure, durable and reliable, easy maintenance, etc.. When the stator winding is energized with three-phase AC, a synthetic spatially synchronized rotating magnetic field will be generated to cut the rotor winding, thus generating a current in the rotor cage winding, which in turn will be subjected to a magnetic field to generate an electromagnetic force to drive the rotor rotation. The current will in turn be subjected to the magnetic field to generate electromagnetic force to drive the rotor. Because there are no mechanical parts in contact with each other between the stator and rotor, the structure is simpler, and the operation is more reliable because it eliminates wear parts. Compared with DC motors, AC asynchronous motors are more powerful and about one-half lighter in mass.

 

However, the rotor of the motor will suffer from serious heating problems under high rotation conditions, and in order to ensure the cooling of the motor, the asynchronous motor also needs to be equipped with a cooling system, which also leads to high costs. In addition, additional reactive power needs to be provided by the inverter to establish the magnetic field, so the efficiency and power density of asynchronous motors are low compared with rare earth permanent magnet motors and switched reluctance motors. Therefore, the new Tesla Model 3 has switched to permanent magnet synchronous motor as the drive motor.

Three, excellent overall performance: permanent magnet synchronous motor

 

According to the difference of current waveform of motor stator winding, it can be divided into two types: brushless DC motor and permanent magnet synchronous motor. These two types of motors are largely the same in structure and working principle, the rotor is permanent magnet, which reduces the loss caused by excitation, and the stator is installed with winding to generate torque through AC, so the cooling is relatively easy. As these motors do not need to install brushes and mechanical commutation structure, they do not produce commutation sparks when working, safe and reliable operation, easy maintenance, and high energy utilization.

Compared with the control system of AC asynchronous motor, the control system of permanent magnet motor is more simple. However, due to the limitation of permanent magnet material, under extreme conditions such as high temperature, vibration and overcurrent, the rotor permanent magnet will produce demagnetization, so under relatively complex working conditions, the permanent magnet motor is prone to damage, and the high price of permanent magnet material and the scarcity of rare earth resources lead to the high cost of the whole motor and its control system.

Fourth, the general direction of future development: switched reluctance motor

Compared with other types of drive motors, switched reluctance motor is a new type of motor, which only has a simple centralized winding on the stator side and no winding on the rotor, so the structure is relatively simple. The stator and rotor are both silicon steel laminated biconvex structure, which has the advantages of simple and sturdy structure, high reliability, light weight, low cost, high efficiency, easy maintenance, etc. It is very suitable for use as a drive motor for electric vehicles.

The disadvantages of switched reluctance motor are large torque fluctuation, position detector required, complicated control system, and large pulse current to DC power supply. Secondly, the switched reluctance motor is a biconvex structure, which inevitably has problems such as torque fluctuation and noise.

Summary: China is the world's most abundant reserves of rare earth permanent magnet materials, and for the relatively small volume of new energy passenger cars, most domestic car companies are still using lower power consumption, higher manufacturing costs of permanent magnet synchronous motor. Only three of them have the ability to develop their own motors, namely Beiqi New Energy, BYD Auto and Weilai Auto, and many of them can only rely on the supplier model. However, with the explosive growth of new energy vehicles, the market demand for new high-performance, safe and reliable, low-cost motor products will continue to grow, the future with the ability to self-research motor companies will be more and more, let us wait and see it.

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