In recent years, switched reluctance motors have gradually entered the market, because the motor has the advantages of other motors do not have, so gradually become the main direction of the future development of the market, has been successfully used in various fields such as electric vehicle drive, general industry, household appliances and textile machinery. So what exactly are the advantages of switched reluctance motors? Let’s find out!
The switched reluctance motor speed control system is a mechatronic product based on modern power electronics and microcomputer control technology. It is composed of two parts: switching reluctance motor and microcomputer intelligent controller, which is characterized by high efficiency, good energy-saving effect, wide speed range, no inrush starting current, large starting torque, flexible control, etc. In 1998, China included the development of motor speed regulation and energy-saving power electronics technology into the “Energy Conservation Law of the People’s Republic of China”, and the National Development and Reform Commission “motor energy-saving plan” clearly put forward: to improve motor speed regulation and energy-saving technology. The “Energy Saving Plan” of the National Development and Reform Commission clearly proposes to improve the efficiency of electric motors by 15-20% and to achieve electricity savings of 100 billion kWh/year. Therefore, this type of motor is widely used in transport vehicle drives, gantry planes, forging equipment and other applications that require heavy-duty starting, frequent starting and forward and reverse rotation.
In recent years, with the gradual development of the concept of energy saving in motors, switched reluctance motors are being used in various applications due to their following characteristics Features of switched reluctance motor speed control systems.
First, high efficiency and good energy saving. After testing, its overall efficiency is at least 3% higher than the AC asynchronous motor frequency conversion speed control system, and can be increased by at least 10% at low speeds, compared with DC speed control, series speed control, electromagnetic speed control, etc., the power saving effect is more obvious.
Second, the starting torque is large, suitable for heavy-duty starting and load changes are obvious and frequent starting occasions. Tests have found that when the starting torque reaches 150% of the rated torque, the starting current is only 30% of the rated current, which is a very obvious advantage.
Third, a wide range of speed regulation. The switched reluctance motor can run at low speed for a long time, and due to the high efficiency, the temperature rise at low speed is lower than at rated working condition, which solves the problem of motor heating at low speed when the frequency-controlled motor is running, and the maximum speed can be set flexibly according to the actual situation.
Four, can be frequent forward and reverse start and stop, good system regulation and control, good braking, can achieve regenerative braking, significant power saving effect.
Five, the starting current is small, avoiding the impact on the power grid. Switching reluctance motor has soft starting characteristics, no ordinary AC motor starting current is greater than 5-7 times the rated current phenomenon.
Sixth, high power factor, no need to increase the reactive power compensation device, testing found that the power factor of the switched reluctance motor system at no load and full load are greater than 0.98.
Seven, the motor structure is simple, solid, simple manufacturing process, low cost, reliable work, can be applied to a variety of harsh high temperature and strong vibration environment
Eight, phase loss and overload can still work. When the power supply is out of phase, or the motor or controller is faulty in either phase, the motor output power is reduced, but it can still operate. When the system exceeds 120% of the load or more, the rotational speed will only drop without burning the motor and the control cabinet.
Nine, the controller in the power converter and motor winding in series, there will be no frequency conversion system power converter may appear through the fault, the reliability is greatly improved.
The current motors have both advantages and disadvantages, and no one motor can replace all other types of motors. The switched reluctance motor also has the following disadvantages.
1. Torque pulsation: Switched reluctance motors work in a pulse supply mode, with large transient torque pulsation, and a very low speed when the stepping state is obvious, and because of their own non-linearity, this leads to difficulties in torque control. Although there are many articles on SRD direct torque control technology, it is still difficult to achieve precise control of torque, and SRD does not have advantages over other types of motors in precision control situations such as servo.
2. Noise: Switching reluctance motor phase winding turn on, radial force leads to stator deformation, phase change is more obvious, motor noise, reduce vibration and noise is an important research topic, many researchers are from the electromagnetic parameters design and speed control methods and motor structure research to improve several aspects, but now compared with other motors, still noise is large.
3. Position detector: position detector makes the simple structure of the switched reluctance motor becomes inferior, reducing the reliability of the system, so it is necessary to explore the practical detection scheme without position detector. At present, more research at home and abroad is using transient inductance information of the stator winding to achieve a position detector-free scheme, but further in-depth research is needed before practical application.
The application market for domestic switched reluctance motors mainly includes
(1) Forging machinery: At present, this is one of the most successful applications for switched reluctance motors. This one fully meets the five conditions mentioned above. It has the advantages of overload requirements, forward and reverse rotation, wide speed range and energy saving, completely ignoring the disadvantages of switched reluctance motors: noise, vibration and torque pulsation. In the business world of switched reluctance motors, there is a saying that forging got the world. The fact that Shandong Kehui has taken a leading position in the country in recent years is inseparable from its early and accurate market development and positioning.
Figure 2 Forging machinery
(2) Textile machinery: First of all, we should thank foreigners for their applications. Mainstream imported textile machinery in China Bjarat was the first to use switched reluctance motors, which led to a natural acceptance of switched reluctance motors by domestic weaving machine manufacturers. Since 2009, switched reluctance motors have gradually taken their place on rapier and towel weaving machines. The textile applications fulfil the conditions 1, 3 and 5 above, are energy efficient, have a fast start (the motor can be brought from zero speed to rated speed by 3 revolutions) and have no vibration or noise requirements. The switched reluctance motors used in foreign weaving machines are four-phase 8/6-pole motors, whereas in our early days three-phase 12/8-pole motors were used. At present, four-phase motors are also being introduced in China, which may gradually eliminate the three-phase 12/8 structure from the textile industry. Strangely enough, Beijing Sinovel was born in the Textile Research Institute. However, Beijing Sinovel’s switched reluctance motors have never been promoted on textile machinery. On the contrary, companies such as Shandong, Shenzhen and Hangzhou have been better promoted in the textile industry.
(3) Oil fields and coal mines: Energy and environmental protection have always been the focus of the national strategic layout. The effect remains obvious after the use of switched reluctance motors in oil pumping machines and coal mine conveyor belts. In recent years, the Shengli oilfield, Zhongyuan oilfield and Changqing oilfield have all carried out renovation projects and generally met the renovation requirements, but the oilfield market is the position of state-owned enterprises and, as you know, it is difficult to achieve large-scale promotion at present. As for coal mines, it is difficult for BCHF to succeed or fail. These are slow years for coal and it’s hard to scale up.
Figure 4 Oilfield pumping
(4) Small appliances: In this regard, the main focus is on the application of high-speed switched reluctance motors. Foreign vacuum cleaners, cooking machines, wall breakers and washing machines use switched reluctance motors in large numbers, with significantly improved performance, large numbers and wide range. However, there are only a few news mentions of the development of prototypes in this area in China and they have yet to see large-scale application, perhaps with cost and price being the main bottleneck limiting the spread of these occasions.
ig. 5 Applications for small appliances
(5) Electric vehicles: For switched reluctance motors, the mention of electric vehicle applications can be a pain. The earliest prototypes of switched reluctance motors, both in China and abroad, were developed for electric vehicles. They were optimistic about the advantages of high starting torque and good acceleration performance of switched reluctance motors, which are well suited for electric vehicle applications. Huazhong University of Science and Technology and Beijing Zhongfeng Company jointly installed 20 Wuhan hybrid buses with switched reluctance motors and carried out long-term operational tests with good results. However, the electric vehicle market has largely been dominated by permanent magnet motors in recent years due to noise and power density issues, which are also related to the low price of permanent magnet motors in China. In the long run, permanent magnets are a non-renewable resource and cannot meet the huge market demand for electric vehicles. Practitioners of switched reluctance motors should continue to dig deeper and wait for the flowers to bloom.
RD-driven mining forklift
(6) Other occasions: In recent years, there has been a gradual increase in the number of companies producing switched reluctance motors, and companies have gone to sea to show their talents. They have tried their hand at different occasions. The simplest occasions for energy-saving renovation, such as fans and pumps, as well as ball mills, sliding doors, shears, starters/generators and injection moulding machines, have also achieved some results, but the scale of use on these occasions is still relatively small. It remains to be seen whether they can be rolled out industry-wide in the future.
Conclusion: The switched reluctance motor is a new type of speed control system developed in the last 30 years. It also has obvious advantages and disadvantages. It is unrealistic for individual manufacturers to try to replace normal asynchronous motors (or innovative schemes) with switched reluctance motors in order to attract investment. How to make full use of the advantages of switched reluctance motors in combination with the characteristics of field applications and to avoid or reduce the drawbacks caused by their disadvantages is a direction in which researchers should constantly strive!