Analysis of future technology trends and implementation methods of motor systems
As one of the three core components of new energy vehicles, the drive motor system directly determines the main performance indicators such as climbing, acceleration and maximum speed of electric vehicles, and its technology and manufacturing level directly affect the performance and cost of the whole vehicle. .
With the sharp decline in subsidies and the increase in mileage and safety, China's new energy vehicle drive motors need to be developed in the trend of small size, light weight, integration, higher power density, and wider speed range.
Below, the high-tech electric vehicle network will focus on the major technical trends of the drive motor, as well as the implementation, difficulty of implementation, etc., for the majority of the industry to read and understand.
01 low cost
At present, there are two main ways to achieve low-cost strategies for driving motors, including reducing the amount of rare earth materials used, reducing the waste of rare earth materials, and optimizing the structure of the motor.
(1) Reduce the amount of rare earth materials used
Huayu electric data shows that according to the existing rare earth price, a rare earth magnet of a motor only accounts for 2.5% to 4.5% of the weight of the whole machine, but the cost accounts for about 33% of the whole machine. When the price of rare earth is high, the magnetic steel accounts for The cost of the whole machine is over 60%. For this reason, reducing the amount of rare earth can effectively reduce the cost.
(2) Optimize the motor structure
Most motor companies use topology optimization design and increase the reluctance torque ratio to reduce the amount of rare earth materials used. Among them, Huayu Electric has reduced the magnetoresistance by increasing the reluctance torque ratio and introducing the fourth-generation rotor punching structure.
(3) Adopt automated production equipment
At present, most of China's motor enterprises follow the traditional manufacturing process, and the production equipment is relatively backward. As a result, the utilization rate of raw materials (including permanent magnets, silicon steel sheets, etc.) of permanent magnet motors in China's new energy vehicles is about 10% lower than that of foreign countries. In order to better achieve cost control, domestic motor companies should achieve automated production as soon as possible.
02 small lightweight
The drive system accounts for 30%-40% of the total quality of pure electric vehicles. With the improvement of the lightweight requirements of automobiles, the development of small and lightweight motors is also imperative.
Implementation: At present, the weight of the motor system is mainly achieved by using high-performance materials, reducing the number of components, reducing switching losses, capacitor volume, and adopting high-density packaging and water cooling.
(1) Material selection
In general, the use of a permanent magnet synchronous motor as a drive is much lighter than an asynchronous motor, which is also an important reason for permanent magnet synchronous motors as mainstream motors. At the same time, the use of high-performance permanent magnet materials and high-performance magnetic materials can help achieve the goal of lightweight motor.
(2) Optimize the motor structure
Industry experts believe that changing the thickness of the insulation, or optimizing the ventilation structure, motor winding method, etc. can effectively reduce the size of the motor and reduce the weight of the motor. It is common to have a rotor core to increase the weight reduction design, or to use a rotor bracket to reduce the rotor weight.
Among them, there is a large radius difference between the bottom of the permanent magnet slot of the permanent magnet synchronous motor and the surface of the motor shaft, and there is a large optimization space. Through the mechanical strength and magnetic circuit simulation test of the rotor of the motor, the structure and size of the weight reduction groove in the rotor can be improved, and the lightweight and high-strength alloy material can be used to realize the weight reduction and high power density of the motor.
03 high power density
At present, power density has become an important design indicator for motor design. By 2020, the electronically controlled power density of pure electric passenger cars in China needs to reach 35KW/L.
Implementation: Generally speaking, there are usually three methods to improve the power density of the motor: one is to optimize the electromagnetic design of the motor, including the optimization of the heat dissipation system, the forming winding, the concentrated winding, etc.; the second is to use high-performance electromagnetic materials; It is appropriate to increase the rated speed of the motor; the fourth is to improve the heat dissipation capability of the motor.
(1) Selection of permanent magnets:
In order to improve the torque density and power density of the motor, permanent magnet materials with permanent magnetic flux density, coercive force and maximum magnetic energy product should be selected when selecting permanent magnet materials, and the temperature resistance of permanent magnets should also be considered. Among them, a motor enterprise technical expert said that the use of 0.35 thick high magnetic properties ferromagnetic material can effectively reduce the iron loss of the motor in the high speed zone.
(2) Motor structure optimization:
First, it is necessary to establish a reliable model of iron loss to analyze magnetic field saturation, waveform distortion, iron loss of core material, and ideal model prediction based on sine, pulse and linear assumptions. The second is to optimize the structure of the motor system, including the optimization of the heat dissipation system, the forming winding or the centralized winding.
Realization of the problem: It is understood that the heat dissipation environment of the high power density motor is more severe, and the loss per unit volume during operation is also higher, which will bring serious temperature rise problems, thereby affecting the reliability and life of the motor. For this reason, it is necessary to improve the cooling system of the motor and optimize the heat dissipation capability of the winding, which is a major problem that needs to be solved in the current high-power density motor for electric vehicles. At present, most motor companies use air cooling and water cooling to dissipate heat.
04 wider speed range
The speed regulation range is an indicator to measure the transmission capacity of the system. At present, the speed regulation range has two performance modes: one is the ratio of the minimum speed and the maximum speed that can be achieved by the speed control system, such as 1:100; the second is the highest The ratio of the rotational speed to the minimum rotational speed (D value) indicates that, for example, D=100, etc., the essence of the two is the same.
Specific requirements: The drive motor is required to output large torque at low speed and high speed, and it needs to have constant power output characteristics during high speed cruise.