Several commonly used drive motors
2.1 DC motor
In the early days of the development of electric vehicles, most electric vehicles used DC motors as the driving motor. These motor technologies are relatively mature, with easy control and excellent speed regulation. They have been the most widely used in the field of speed regulating motors. . However, due to the complicated mechanical structure of the DC motor, such as brushes and mechanical commutators, the instantaneous overload capability and the further improvement of the motor speed are limited, and the mechanical structure of the motor will be worked under long-term operation. Loss is generated and maintenance costs are increased. In addition, the spark generated by the brush during the operation of the motor causes the rotor to generate heat, wastes energy, and is difficult to dissipate heat, which also causes high-frequency electromagnetic interference and affects the performance of the vehicle. Due to the above shortcomings of DC motors, current electric vehicles have basically eliminated DC motors.
2.2 AC asynchronous motor
AC asynchronous motor is a kind of motor widely used in industry. It is characterized in that the stator and rotor are laminated by silicon steel sheets, and the two ends are covered by aluminum cover. There are no mechanical parts between the stator and the rotor, and the structure is simple. The operation is reliable and durable, and the maintenance is convenient. AC asynchronous motors are more efficient than DC motors of the same power, and the quality is about one-half lighter. If the vector control method is adopted, the controllability and the wider speed range comparable to those of the DC motor can be obtained. AC asynchronous machine is the most widely used motor in high-power electric vehicles due to its high efficiency, high specific power and high speed operation. At present, AC asynchronous motors have been mass-produced, and there are various types of mature products to choose from. However, in the case of high-speed operation, the rotor of the motor generates severe heat, and the motor must be cooled during operation. At the same time, the drive and control system of the asynchronous motor is complicated, and the cost of the motor body is also high, compared with the permanent magnet motor and the switched reluctance. In terms of motors, the efficiency and power density of asynchronous motors are low, which is unfavorable for increasing the maximum mileage of electric vehicles.
2.3 permanent magnet motor
The permanent magnet motor can be divided into two types according to the current waveform of the stator winding. One is a brushless DC motor, which has a rectangular pulse wave current; the other is a permanent magnet synchronous motor, which has a sine wave current. The two motors are basically the same in structure and working principle. The rotors are permanent magnets, which reduce the loss caused by excitation. The windings on the stator are driven by alternating current to generate torque, so cooling is relatively easy. Since this type of motor does not need to be equipped with a brush and a mechanical reversing structure, no commutation spark is generated during operation, the operation is safe and reliable, the maintenance is convenient, and the energy utilization rate is high.
The control system of a permanent magnet motor is simpler than the control system of an AC asynchronous motor. However, due to the limitation of the permanent magnet material process, the power range of the permanent magnet motor is small, and the general maximum power is only several tens of millions, which is the biggest disadvantage of the permanent magnet motor. At the same time, the permanent magnet material on the rotor will have magnetic decay under high temperature, vibration and overcurrent conditions, so the permanent magnet motor is prone to damage under relatively complicated working conditions. Moreover, the price of permanent magnet materials is relatively high, so the entire motor and its control system are costly.
2.4 Switched Reluctance Motor
Switched reluctance motor is a new type of motor. Compared with other types of drive motors, the structure of switched reluctance motor is the simplest. The stator and rotor are double salient pole structures made of ordinary silicon steel sheets. There is no rotor on the rotor. The winding and the stator are equipped with simple concentrated windings, and have many advantages such as simple and sturdy structure, high reliability, light weight, low cost, high efficiency, low temperature rise and easy maintenance. Moreover, it has the excellent controllability of the DC speed control system, and is suitable for harsh environments, and is very suitable for use as a drive motor for electric vehicles.
Considering the use of electric motor as the driving motor, DC motor and permanent magnet motor are too poorly adaptable in structure and complex working environment, and it is easy to cause mechanical and demagnetization failure. Therefore, this paper focuses on switched reluctance motor and AC asynchronous. Compared with the machine, it has obvious advantages in the following aspects.
