There are four main categories currently used in electric hub motors, namely permanent magnet motors (PM), asynchronous motors (IM), switched reluctance motors (SRM) and transverse flux motors (TFM). Among them, the application of permanent magnet motors is the most common, while transverse flux motors are a very competitive new type of low-speed and high-torque motors.

Asynchronous motors have the longest development history among the 4 types of motors. The design, manufacture and control of the motor are relatively mature, with the advantages of simple structure, easy manufacture, low cost, high reliability, and mature control technology, and are favored by European and American countries. But the disadvantage of asynchronous motors is their low efficiency, especially at low speeds, their power density is low. Asynchronous motor is a strongly coupled, multivariable, non-linear system, which requires vector control and direct torque and other control methods, and the control cost is relatively high.

Permanent magnet brushless motors can be divided into two types: driven by square waves and driven by sine waves. Compared with other motors, permanent magnet brushless motors have a series of advantages such as high power density, high efficiency, small size, simple structure, large output torque, good controllability, high reliability, and low noise. Quite popular. Most electric vehicles in Japan use permanent magnet brushless motor drive systems. Of course, permanent magnet brushless motors also have some disadvantages. First of all, it is limited by permanent magnet materials, and the current maximum power is only tens of kilowatts. Secondly, the excitation of the permanent magnet rotor cannot be adjusted, which makes the motor speed adjustment difficult and the speed adjustment range is not wide.

Switched reluctance motor is a new type of speed-regulating motor developed in the past 20 years. It has the advantages of simple and reliable, high-efficiency operation in a wide speed and speed range, four-quadrant operation, fast response speed and lower cost. But its shortcomings are also many: large torque fluctuations, large vibration, large noise; system nonlinearity, difficult modeling, high control cost, low power density, and so on.

Transverse field motor was first proposed by the famous German motor expert H. Weh in the late 1980s and used it on electric ships and electric vehicles. Compared with other motors, the transverse magnetic field motor has some advantages: the circuit and the magnetic circuit are decoupled, and the design freedom is greatly improved; the high torque density is about 5 to 10 times that of the standard industrial asynchronous motor, and it is especially suitable for application Low-speed, high-torque and other occasions are required; the winding type is simple, there is no end of the traditional motor, the winding utilization is high; each phase is independent of each other; the efficiency is high; the control circuit is the same as the permanent magnet brushless motor, and the controllability is good. At present, many transverse magnetic field motors for electric vehicles have been successfully developed abroad, and preliminary research is also being actively carried out in China. Of course, transverse magnetic field motors also have many shortcomings: the number of permanent magnets is large, the amount is large, the structure is complex, the process requirements are high, the cost is high, the magnetic leakage is serious, the power factor is low, the self-positioning torque is large, and so on.