What is the difference between permanent magnet synchronous and AC asynchronous motors
Different car companies have different motors. What is the difference between permanent magnet synchronous and AC asynchronous motors? What are the pros and cons?
According to the global new energy brand sales data released by the CleanTechnica website:
In 2021, the cumulative global sales of new energy vehicles will be nearly 6.5 million , an increase of 108% over the same period last year . Tesla is far ahead with nearly a million figures. BYD ranked second with sales of 593,900 units, a year-on-year increase of more than 220%, and its global market share reached 9.1 % .
The most important part of the current new energy models must be the three-electric system, and among them, the motor that drives the vehicle forward is obviously extremely important, and the two champions and runners-up of Tesla and BYD are represented, and there are also choices of motors. the difference. European and American car companies are mainly equipped with AC asynchronous motors , and representative car companies are Tesla, Mercedes-Benz, etc.; Chinese car companies are mainly equipped with permanent magnet synchronous motors , and representative car companies are BYD and Ideal Motors. What are the differences between the two types of motors, which prompts car companies to choose differently?
The two motor technologies can be clearly distinguished from the internal structure of an asynchronous induction motor and a permanent magnet synchronous motor. The rotor of the permanent magnet synchronous motor is a permanent magnet, abbreviated as PMSM in English. The rotor of the asynchronous induction motor is not a magnet but a closed coil, which is commonly known as a squirrel cage structure, or ACIM for short. We will not go into detail about the principle.
Characteristics of Asynchronous Induction Motors and Permanent Magnet Synchronous Motors
Synchronous motor advantages:
1. The rotor has no excitation winding, so there is no rotor copper loss, so the efficiency is high; 2. The high-performance permanent magnet material provides excitation, the given power is small, and the volume can be reduced; 3. The rotor rotational inertia is small, so the dynamic performance is good; 4. Greater power and torque output at low efficiency.
Synchronous motor disadvantages:
High cost, low reliability, complex processing technology and poor mechanical strength.
Advantages of asynchronous motors:
1. There is no permanent magnet high temperature demagnetization problem, which can prolong the working time of peak power, rated power and peak power. 2. The motor characteristics are less affected by the environment; 3. It has the ability to start high torque and high-speed torque adjustment;
Disadvantages of asynchronous motors:
The rotor magnetic field comes from the stator excitation, there is copper loss, and the energy conversion rate is lower than that of the permanent magnet synchronous motor.
Advantages and disadvantages of electric motors for new energy vehicles
Advantages of AC asynchronous motor : good reliability; good performance at high speed; easy to control the cost. Disadvantages: low power density ( larger volume at the same power level); low energy conversion efficiency (85%-90%); high energy consumption.
Models that choose AC asynchronous motors tend to give priority to performance. Taking advantage of the performance output and efficiency advantages of AC asynchronous motors at high speeds, the representative model is the early Model S. Main features: When the car is running at high speed, it can maintain high-speed operation and efficient electrical energy use efficiency, and reduce energy consumption while maintaining the maximum power output.
The advantages of permanent magnet synchronous motor: high power density; high energy conversion efficiency (90%-95%); low energy consumption. Disadvantages: Due to the addition of permanent magnets, the cost is increased; the permanent magnets have the risk of demagnetization in high temperature and vibration environments.
Models that choose a permanent magnet synchronous motor tend to give priority to energy consumption, and use the performance output and efficient operation of the permanent magnet synchronous motor in the low-speed stage, which is suitable for small and medium-sized vehicles. The characteristics are small size and light weight, which can increase the battery life. At the same time, it has good speed regulation performance, and can maintain high efficiency in the face of repeated start and stop, acceleration and deceleration.
Asynchronous induction motors and permanent magnet synchronous motors have their own advantages, so some OEMs consider combining the characteristics of the two motors for matching. For example, the front axle is equipped with a low-speed and high-efficiency permanent magnet synchronous motor, and the rear axle is equipped with an AC asynchronous motor that favors high-speed performance.
Although the power system barrier of electric vehicles is not as high as that of fuel vehicles, and the types are relatively single, both of these two motors require electronic control systems with very powerful algorithms to control them in order to achieve excellent power consumption and linear acceleration of vehicles. Sufficient battery power is required behind the system, so the three-electricity level of an electric vehicle is the essence of a pure electric vehicle.
Summarize
Permanent magnet synchronous motor and AC asynchronous motor are different in principle, so the characteristics of the two are also different. AC asynchronous motor has good reliability, high speed performance and easy cost control. Permanent magnet synchronous motors have high power density, high energy conversion efficiency and low energy consumption. At present, the permanent magnet synchronous motor will still be more suitable for subsequent development, and the combination of the two is also a good choice.
XINDA