How to choose the EV (electric vehicle) motor

Question

Accepted Answer

The performance of the drive motor directly determines the performance of the drive system. In electric vehicles, the selection principles of electric motors are as follers.

(1) High performance, low weight, and small size;

(2) Higher efficiency in a wider speed range;

(3) The electromagnetic radiation is as small as possible;

(4) Low cost.

In addition, the selection of the motor must also consider the characteristics of its control system, which can realize two-way control and recover braking regenerative energy. From the perspective of development trends, traditional DC motors will lose their competitiveness, and the application of switched reluctance motors and permanent magnet hybrid motors in electric vehicles has development potential.

The DC motor drive system has the advantages of low cost, easy smooth speed regulation, simple controller, mature technology, etc., and is widely used in electric vehicles. The disadvantages of DC motors are lower efficiency than asynchronous motors, large size and mass, inconvenient maintenance of brushes and commutators, and commutation limits the speed of the motor (the maximum speed is between 6000r/min and 8000r/min). It is only a three-phase AC motor. Half of the maximum speed, or even lower.

Compared with DC motors, asynchronous motors have the characteristics of high efficiency, simple structure, sturdy, maintenance-free, small size, and light weight, so they have broad application prospects. However, its control system is more complicated, the vector control technology requires high frequency conversion speed regulation, and the cost of using high-power semiconductor devices and microprocessors is relatively expensive. However, due to its light weight, high efficiency, and more effective realization of regenerative braking, it is The operating cost is lower than that of the DC motor drive system.

With the reduction of cost and the improvement of reliability, the permanent magnet synchronous motor drive system will be used in a certain range of electric vehicles. Its efficiency can reach 97%, the smallest volume, the lightest weight, and the commutator without DC motor. The shortcomings of electric brushes, but there are still shortcomings such as high cost, reliability and service life worse than asynchronous motors.

Switched reluctance motor is a new type of motor. Its structure is simpler than that of any kind of motor. Its efficiency can reach 85% to 93%. Its speed can reach 15000r/min. Its torque-speed characteristics are better. Within the range, the torque and speed can be flexibly controlled, and it has the characteristics of high starting torque and low starting power, but the torque ripple is large during operation, the noise is also large, and the volume is larger than the asynchronous motor of the same power.

As the power system of the three major parts of electric vehicles, the importance of electric motors is self-evident. With the development of motor research and development technology, motors that are more suitable for electric vehicles will appear in the future. Let's share it again at that time.