7 types of electric vehicle motors
Release time:
2022-12-19
There are seven types of motors used in electric vehicles, namely: brushless DC motor, brushless DC motor, permanent magnet synchronous motor, induction motor, switched reluctance motor, synchronous reluctance motor and axial flux coreless permanent magnet motor.
There are seven types of motors used in electric vehicles, namely: brushless DC motor, brushless DC motor, permanent magnet synchronous motor, induction motor, switched reluctance motor, synchronous reluctance motor and axial flux coreless permanent magnet motor.
Brushless DC motor is a simple DC motor. It uses the brush to transfer the current to the motor winding through mechanical commutation. The armature or rotor is an electromagnet, and the magnetic field is a permanent magnet. This motor does not need a controller to operate or change the speed, and can provide maximum torque at low speed. The disadvantages are bulky structure, low efficiency, heat generation of electric brush and low efficiency. The heat is in the center of rotor and difficult to be eliminated. Therefore, the brushless DC motor is no longer used in electric vehicles.
Brushless DC motor with permanent magnet is called brushless because it has no commutator and brush. It adopts electronic commutation, maintenance-free, has high starting torque, efficiency up to 95% - 98% traction characteristics, and is suitable for high power density design. This traction characteristic makes brushless DC motor widely used in electric vehicles, which is suitable for small vehicles with a maximum power of 60 kW. The disadvantages are that the constant power range is limited, the torque decreases with the increase of speed, and the cost of permanent magnet is high. Toyota Prius uses brushless DC motor.
The rotor of permanent magnet synchronous motor has permanent magnet, which has high power density and high efficiency traction characteristics, and can be used for higher rated power, so it is more expensive than other motors. This kind of motor can work in different speed range without gear system. It is efficient and compact, suitable for hub applications, and has high torque at low speed. The disadvantage is that the iron loss is serious when the hub is running at high speed. At present, permanent magnet synchronous motors are mostly used in hybrid and electric vehicles, such as Chevrolet Bolt, Ford Focus, Nissan Leaf and BMW i3.
Unlike DC motors, induction motors can produce high starting torque at fixed voltage and frequency. However, this can be changed by various control methods, such as vector control or field-oriented control. With these control methods, the maximum torque required for traction can be obtained when the motor is started. The squirrel-cage induction motor has less maintenance, long service life and design efficiency of 92% - 95%. The disadvantage is that complex inverter circuit is required and motor control is difficult. Due to its low cost, induction motors have become the choice of high-performance electric vehicles. Tesla Model S is a good example of the high performance of induction motors. Toyota RAV4 and GM EV1 also use this motor.
Switched reluctance motor is a kind of variable reluctance motor with double significance. Its structure is simple and firm. The rotor is a laminated steel sheet without winding or permanent magnet. This reduces the inertia of the rotor and helps to improve the acceleration. Robustness makes this motor suitable for high-speed applications and can provide high power density. Its disadvantage is that the control is complex, and the increase of switching circuit will also bring noise. Synchronous reluctance motor is a kind of synchronous motor with reluctance property. The torque is caused by the difference between the AC and DC axis reluctance of the rotor, without excitation winding or permanent magnet. This kind of motor is increasingly popular in electric and hybrid vehicles because of its simple and solid structure. It has the advantage of no rotor loss and can provide higher permanent torque than induction motors of the same size.
Axial flux coreless permanent magnet motor is an advanced motor for electric vehicles. The outer rotor has no slot, so no iron core is required. It also has no stator core, so it is light in weight. The radial component of the air-gap magnetic field provides a higher power density. The rotor of the motor can be installed on the wheel side and the stator winding on the shaft. The slotless design makes it less copper loss, high efficiency and more available space. Renault Coupe uses this motor.
