What are the types of electric vehicle motors？

The six types of motors commonly used in electric vehicles are DC brushless motors, permanent magnet synchronous motors, induction motors, switched reluctance motors, synchronous reluctance motors, and axial flux coreless permanent magnet motors.

Ⅰ.DC brushless motor

DC brushless motor with permanent magnets is called brushless because it has no commutator and brushes. It is electronically commutated, maintenance-free, and has traction characteristics of high starting torque and efficiency up to 95%-98%, making it suitable for high power density designs. This traction characteristic makes brushless DC motors widely used in electric vehicles for small cars with a maximum power of 60 kW. Disadvantages are limited constant power range, torque decreases with speed, and permanent magnets result in high cost. Toyota Prius adopts a brushless DC motor.

Ⅱ.Permanent magnet synchronous motor

Permanent magnet synchronous motors have permanent magnets on the rotor. They have high power density and high-efficiency traction characteristics and can be used for higher power ratings, making them more expensive than other motors. This motor can operate in different speed ranges without the need for a gear system. It is efficient and compact for hub applications and has high torque at low speeds. The disadvantage is the severe iron consumption at high speeds in the hub. Currently, permanent magnet synchronous motors are mostly used in hybrid and electric vehicles, such as the Chevrolet Bolt, Ford Focus, Nissan Leaf, and BMW i3.

Ⅲ.Induction motor

Induction motors do not produce high starting torque at a fixed voltage and frequency like DC motors. However, this can be changed using various control methods such as vector control or magnetic field orientation control. Using these control methods, the maximum torque required to satisfy traction can be obtained when the motor is started. Squirrel cage induction motors are low maintenance, have a long service life, and are designed for efficiencies of 92% to 95%. The disadvantages are the need for complex inverter circuits and the difficulty of motor control. Due to their low cost, induction motors are the preferred choice for high-performance electric vehicles. The Tesla Model S is the best example of the high performance of induction motors. Toyota RAV4 and GM EV1 also use this type of motor.

Ⅳ.Switched reluctance motor

Switched Reluctance Motors are a class of variable reluctance motors with a doubly significant, simple, and robust structure, where the rotor is a piece of laminated steel with no windings or permanent magnets. This reduces rotor inertia and helps to increase acceleration. The robustness makes this motor suitable for high-speed applications and provides high power density. The disadvantages are complex control and noise from the addition of switching circuits. Synchronous reluctance motors are synchronous motors with reluctance properties, where the torque is caused by the difference between the rotor's alternating and direct axis reluctance, and there are no excitation windings or permanent magnets. This type of motor is becoming increasingly popular in electric and hybrid vehicles due to its simple and robust construction. The advantage is that there is no rotor loss and it can provide a higher permanent torque than an induction motor of the same size.

Ⅴ.Synchronous reluctance motor

Synchronous reluctance motor is a type of synchronous motor, the torque of this motor is due to the difference in permeability through the straight and orthogonal axes of the rotor, and it has no permanent magnet or excitation windings. Currently, this type of motor is becoming very popular as a wash option for electric and hybrid vehicles due to its simple and robust construction. The main advantage of the synchronous reluctance motor is mainly the absence of cage rotor losses as the motor allows higher permanent torque compared to an induction motor of the same size. Synchronous reluctance motors have simple magnetic field-based control algorithms compared to induction motor drives. The exact torque can be reasonably designed without affecting the temperature of the rotor compared to other motors such as induction motors and permanent magnets, so the rotor cost of synchronous reluctance motor motors is low.

Ⅵ.Axial flux coreless permanent magnet motor

Axial flux coreless permanent magnet motor is the most advanced motor for electric vehicles. Its outer rotor has no slot, so no iron core is needed. It also has no stator core and is therefore lightweight. The radial component of the air gap magnetic field provides higher power density. The rotor of this motor can be mounted on the wheel side and the stator windings are placed on the shaft. The slotless design results in low copper losses, high efficiency, and more space available. The Renault Coupe uses this type of motor.