1. They are all motors.
Seemingly nonsense, what I want to say is that the motor of electric vehicle is just a kind of motor, nothing special. The analysis method can't escape the common electromagnetic analysis method, the calculation tools are all finite element software, the simulation solvers are all based on transient solvers, and the electromagnetic equation can't escape Maxwell's equation. No big deal. This is a kind of motor with special load requirements.
2. Classification and control are the same.
Electric vehicles are also divided into induction motors and permanent magnet motors, and the control theory and methods are the same as those of industrial motors.
Difference:
1. Strict volume and weight requirements
Because it is a car, this requirement is more prominent. Ordinary industrial motors are not so strict about size and weight, because the industrial site is huge, and generally the industrial goals are reached first. The size and weight of different electric vehicles determine their dynamic performance and driving experience, and directly affect the product quality. Therefore, the difficulty of electric vehicle motor lies in improving power weight density and power volume density. The smaller the motor, the lighter it is, and the greater the power, the better.
2. Unique torque characteristics
Ultra-high torque is needed when starting or at low speed, so that the vehicle speed can be increased to the required speed in the fastest way. General industrial motors do not have such high starting speed requirements. At the same time, it is necessary to provide enough power at high speed to enable the car to cruise at high speed.
3. Wide speed range
The maximum speed can be four times or even higher than the basic speed of the motor. At present, the best solution for electric vehicles is to omit the multi-speed gearbox and only use the fixed gear set. Therefore, the wider the speed range of the motor, the better. Take Tesla's model S as an example, the maximum speed of the motor can reach 18000 rpm, which is quite terrible. This is a great test for the power electronic governor.
4. Comprehensive efficiency requirements
Unlike electric locomotives, electric locomotives are powered by pantographs, while electric vehicles are powered by batteries. The cruising range depends entirely on the efficiency of the motor. For every increase in motor efficiency of 1%, the cruising range can be increased by 1%. Therefore, the efficiency of the motor is very high. Higher is victory, and every bit of energy should be optimized.
5. Others
As for low noise, high stability, reasonable heat dissipation and cost performance, I won't mention it. These are the basic requirements.
Technical details:
1. Torque-speed efficiency distribution:
The efficiency distribution diagram of electric vehicle motors shall be as follows:
What are the similarities and differences between electric motors and industrial motors?
Electric vehicles mainly travel in the yellow area, and will not start frequently, nor will they run continuously at ultra-high speed, but will accelerate and decelerate in the middle. Therefore, for the efficiency range, it is better for the yellow area to have higher efficiency. Therefore, we hope that the yellow area can extend in three directions to meet the maximum utilization of energy.
2. Speed adjustment curve:
It is basically similar to ordinary motors, except that the constant power area is wider; The maximum speed can reach four times the basic speed.
3. The smaller the motor leakage, the better!
This is very different from industrial motors. This is mainly an induction motor. Taking the general industrial induction motor directly connected to the power grid as an example, the slot on the rotor side can be simply called "fancy slot". There are deep grooves, double grooves and inclined grooves. Some of them are designed to improve aerodynamic characteristics, some are designed to compromise low-speed and high-speed performance, and some are designed to reduce torque fluctuation. However, these fancy grooves increase the magnetic leakage. The motor of electric vehicle is precisely controlled by inverter, so all the starting characteristics are different from those of traditional motors. Because the controller can control the frequency and amplitude when starting, there will be no disadvantage of directly connecting the grid-connected motor. At this time, the less leakage flux, the better, and the shallower and wider the groove, the better! At the same time, the air gap width should be appropriately increased to reduce the impedance of high-frequency harmonic components. If possible, try to replace aluminum squirrel cage with copper squirrel cage (high resistance). Tesla Motors' induction motors vividly demonstrate these characteristics:
4. Permanent magnet motor
Permanent magnet motors are mainly used in hybrid electric vehicles. 100% motors in HEV are permanent magnet motors. Perfect market share. Why? Because of its small size, light weight and high power density. Permanent magnets are divided into BLAC (Brushless AC) and BLDC (Brushless DC). The structures of the two motors are basically the same, and the only difference is the control current waveform. BLAC is a sine wave and BLDC is a rectangular wave. Relatively speaking, the performance of BLAC is slightly better than that of BLDC, but the advantage is not obvious. The most famous permanent magnet motor is Toyota Prius motor;
At present, the design of the whole machine has basically reached the limit of motor design, which can be called handicraft.