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(1) the structure and performance of the motor
The drive motor system is one of the three core components of the new energy vehicle. The motor drive control system is the main execution structure of the new energy vehicle, and its driving characteristics determine the main performance index of the vehicle. It is an important component of the electric vehicle. The whole drive system of an electric vehicle consists of two parts: the motor drive system and the mechanical drive mechanism. The motor drive system is mainly composed of motor, power converter, controller, all kinds of sensors and power supply.
In brief, the motor drive system is mainly composed of two parts: the drive motor and the motor controller. From the industrial value chain of the motor drive system, the ratio of the cost of the drive motor and the motor controller is approximately the same.
The following: the structural components of the motor
The drive motors for new energy vehicles belong to the category of medium and low voltage motors. Because of its special application field, it has higher performance requirements than ordinary medium and low voltage products:
1) wide range of speed control: new energy vehicles have two types of scenarios, in the start, acceleration, climbing, requiring work in the constant torque interval; at high speed, the motor required to work in the constant power interval;
2) high power density, mainly in order to minimize the space within the car, the battery power, improve mileage;
3) safe and reliable, requiring the stability of the motor work and seismic performance, good heat dissipation;
4) lightweight, that is, the small size of the motor, to meet the requirements of lightweight vehicles;
5) overload ability: in the start, acceleration, climbing conditions, requiring the motor has 4-5 times overload capacity.
Below: performance requirements for new energy automotive drive motors
(1) there are differences in application scenarios for different motor types
Motors are generally required to have two functions of electric and power generation. Some types of motors, such as direct current, AC, permanent magnet, brushless or switched reluctance, can be used by type. According to the selected type of motor power converter, DC/DC power converter, DC/AC power converter, which is selected according to the motor drive current, the battery will convert DC to DC voltage, the corresponding AC or pulsed power supply.
The drive motors for new energy vehicles mainly include three types: permanent magnet synchronous, AC asynchronous and switched reluctance. Because of its different characteristics, each has its application.
Permanent magnet synchronous motor (PMSM) has the advantages of small size, light weight, large power density, high reliability, high speed regulation accuracy and fast response speed. But the maximum power is low and the cost is higher. The permanent magnet synchronous motor has the highest power density, its work efficiency is up to 97%, to output power and the maximum acceleration of the vehicle, it is mainly used in the energy requirements of the highest volume ratio of new energy passenger cars.
AC asynchronous motor has low price and reliable operation, but its power density is low, the control is complex, and the speed range is small, which is inherent limitation. Price advantage makes it widely used in new energy buses.
Switched reluctance motor (SRM) has low price, simple circuit and wide speed range. But the vibration and noise are large, the control system is complex, and the DC power supply will produce very large pulse current. Used of large buses.
Following: drive motor performance index comparison
The current development direction of new energy automobile drive motor is as follows: small size, light weight, high efficiency, better torque characteristics, long service life, high reliability, low noise and low price. As time goes on, the development of new energy driven motors presents the following trends:
Permanent magnet motor has the advantages of high torque density, high power density, high efficiency, high reliability and so on. China has the world's most abundant rare earth resources, so high-performance permanent magnet motor is the important direction of the development of automotive drive motors.
Digital control of motor: the appearance of special chip and digital signal processor promotes the digitalization of motor controller, improves the control precision of motor system and reduces the system volume effectively.
The motor system integrated by electromechanical integration (integrated motor and engine or motor and gearbox integrated) and controller integration, driving system to decrease the weight and volume of the system can effectively reduce the manufacturing cost.
(two) permanent magnet synchronous motor is the main trend
At this stage, AC asynchronous motor is mainly led by Tesla car companies in the United States and some European enterprises. On the one hand, the original path with the Tesla technology, AC induction motor at low prices, and the large volume of American car no Guaai; on the other hand, the high-speed road network developed, high performance AC motor good efficiency interval.
New energy vehicles, including China and Japan, are still the most widely used permanent magnet synchronous motors. The road condition is the main factor for the country. Permanent magnet synchronous motor can keep high efficiency when it starts and stops again and again. It is the best choice for the limited working condition of high-speed network. In addition, China's rare earth reserves are rich, rare earth permanent magnet industry in Japan has a supporting foundation, but also an important factor. At present, the use of permanent magnet synchronous motor in China's new energy vehicles accounted for more than 90%.
Japan's TOYOTA, Honda, Nissan and other car companies are basically using permanent magnet synchronous motor drive systems, such as Toyota Corporation's Prius, Honda Corporation's CIVIC. Because in Japan, the supply of permanent magnet motor using rare earth magnet more companies, while the majority of cars at medium and low speed, so the use of acceleration and deceleration
