Basic Knowledge of Electric Motors- Switched Reluctance Motor
Date：2023-03-06 Author：XINDA MOTOR
Switched Reluctance Motor
Switched reluctance motor ( SR for short ) was born 160 years ago, but it has been considered as a motor with low performance for a long period of time, so it is only used in a few small power places. In the early 1970s, Ford Motor Company of the United States developed the earliest SR speed control system. It was first used by Americans to drive torpedoes, and it only entered industrial use in the 1980s, and gradually attracted widespread attention in the 1990s.
At present, it is mainly used for aviation , locomotive traction , driving of mining boring machines , and driving of electric vehicles. After entering this century, the switched reluctance motor speed control system has been further applied in other fields, and has begun to develop in the direction of civilian household appliances, such as washing machines and air-conditioning compressors. Just as the evaluation of the speed control system of the switched reluctance motor by foreign experts, the speed control system of the switched reluctance motor has become a new milestone of the speed control system. Hefei University of Technology was the first to engage in SR research in China, which began in the 1970s in response to the needs of the Navy. Up to now, Tsinghua University, China Southern Airlines, Shanghai Jiaotong University, Huazhong University of Science and Technology, Haihe University, etc. have trained a large number of SR doctoral students. Although China's SR started later than foreign countries, the overall performance of domestic KC , H series (1-55KW ) and SR71 series ( 0.25-0.75KW ) products has reached the level of foreign countries in the early 1990s. Metallurgy, machinery, mining, transportation, petroleum and other industries began to apply.
With the development of modern computer control technology, the performance of the AC speed control system is getting higher and higher, and the AC speed control system is gradually replacing the DC speed control system in the industrial field. As a rising star of the AC speed control system, the switched reluctance motor speed control system has the high performance of the sub-servo system and the price of the ordinary speed control system, and is very cost-effective, which is simply unmatched by brushless or brushed DC motors .
Features of switched reluctance motors
1. The starting current is small. The switched reluctance motor only needs 0.2 to 0.3 times the rated current to generate 1.5 to 2 times the rated starting torque. Regardless of whether it is a brushed or brushless DC motor, 1.5 to 2 times the rated current is required to obtain 1.5 to 2 times the rated starting torque. In other words, to achieve the same starting torque for a motor with the same power, the starting current of the DC motor will be 5 to 10 times that of the switched reluctance motor.
2. High operating efficiency. The switched reluctance motor can guarantee high efficiency in the range of speed regulation of 1:50 and the range of torque variation of 1 : 5 ; while the DC motor can only guarantee high efficiency at high speed and light load, and the high efficiency area is very narrow. For variable speed and variable torque conditions such as electric bicycles , the average efficiency of switched reluctance motors will be 15 to 30% higher than that of brushed and brushless DC motors .
3. The system is safe and reliable , and has a long service life. The switched reluctance motor has neither a fragile commutator mechanical structure nor a permanent magnet with unstable performance. Whether it is life or operation stability, the switched reluctance motor is much higher than the brushed and brushless DC motor. The switched reluctance motor has the characteristic of four-quadrant operation symmetry, and can realize the energy regenerative braking of the electric bicycle without adding any hardware, which not only increases the driving safety of the electric bicycle, but also improves the battery life. Utilization efficiency rate.
4. Strong overload capacity. Since the working magnetic field of the switched reluctance motor is different from that of brushed and brushless DC motors, it does not alternate, so the heat is very small, that is, the so-called cold rotor, and there is no permanent magnet with poor thermal performance, therefore, the switched reluctance motor With the unparalleled overload capacity of brushed and brushless DC motors, in a short period of time, switched reluctance motors are allowed to be overloaded by 2 to 3 times, making their performance close to that of gasoline engines. One of the main reasons for electric vehicles.
5. The system is cost-effective. The switched reluctance motor system is a mechatronic product, and its control performance is mainly realized by computer software. Therefore, the price of its controller is only about 30% higher than that of the brushless DC motor controller, and the switched reluctance motor saves the expensive Rare earth permanent magnets, and the manufacturing process is simpler than brushless DC motors. The price of switched reluctance motors should be about 15% lower than that of brushless motors . Therefore, the price of the switched reluctance in-wheel motor system ( the price of the in-wheel motor plus the controller ) should be comparable to the price of the brushless DC in-wheel motor system, that is, the switched reluctance motor system has a high cost performance.
XINDA