At the 2021 China International Motor Industry chain Annual meeting hosted by SMM (SMM), Yu Kehao, founder / general manager of Shandong Ai Magnetic Drive Technology Co., Ltd., introduced the characteristics, rise and application of switched reluctance motors. He said that in the past five years, China's switched reluctance motor products have become increasingly mature, especially in the industrial field, the application is growing rapidly. Great progress has been made in research and industrialization. But the advanced algorithm and accurate electromagnetic calculation still lag behind.
Understanding of switched reluctance Motor-distinctive characteristics can be called excellent
The rotation of switched reluctance motor is called reluctance motor because of the minimum magnetoresistance principle that "the magnetic flux is always closed by the minimum path of ampere reluctance, and the magnetic pull pulls the rotation of the motor rotor". It is also called switched reluctance motor because its coil current is turned on and off and the flux state is directly controlled by the electronic switch of the controller (such as IGBT). It can be seen that switched reluctance motor is a kind of control motor system, and its speed regulation is not carried out by changing the frequency of power supply, so it does not belong to the motor of variable frequency speed regulation system.
Technical characteristics: full speed zone, low speed zone (ultra-low speed zone), high system efficiency under different loads.
Technical features: wide peak torque, rated and peak torque can be obtained at any speed point within rated speed
Technical characteristics-small no-load and light-load current and low loss
Technical characteristics: there is a good relationship between current and load (torque) under different loads in full speed zone.
The peak torque output capacity of the switched reluctance motor is obviously better than that of the permanent magnet motor system in the ultra-low speed zone: the switched reluctance motor exceeds the brushless by about 10%.
Technical features: several other very important features
Excellent characteristics of high speed and ultra-high speed, excellent expansibility of constant power zone, tens of thousands of revolutions, tens of thousands of revolutions;
Under load, the soft start with low current and high torque starts completely without starting current shock.
Can start and stop direction quickly and frequently at any speed point;
Without the use of rare earth materials, no attenuation, the motor is easy to achieve more than 10 years of life maintenance cost is very low;
Good adaptability to bad working conditions, field, outdoor, high temperature resistance, shock resistance, continuous operation ability, strong overload capacity;
The supply chain is getting better and the market is expanding and the cost is getting lower and lower.
Comparative shortcomings of switched reluctance Motor
The position accuracy of An is low, and the position control is difficult.
B power density is low, volume control is difficult.
C torque pulsation is large, so it is difficult to control noise.
D technology is complex, the development is difficult, and the barrier to entry is high.
Technical complexity description-1
1. Integrated design
The SRD system is an inseparable whole composed of the motor and its control device. The design must proceed from the point of view of the system, comprehensively consider the motor model and control strategy, and carry out the global optimization design. A single motor and controller can not be done well.
two。 Switched reluctance motor is a highly nonlinear time-varying system, and the relationship between current and torque is very complex.
The working principle and structure of SRD are very simple, but because of the doubly salient structure, magnetic circuit saturation, eddy current and hysteresis effect of the motor, as well as the switching and controllability of the motor during operation, each physical quantity of the motor changes with the rotor position, and the current and flux waveforms of the stator winding are extremely irregular, so it is difficult to analyze and model by the traditional motor method.
Technical complexity description-2
3. Low Speed Vibration and noise of switched reluctance Motor
The SRM rotor torque is composed of a series of impulse torques, coupled with the influence of biconvex stage and magnetic circuit saturation, the composite torque is not constant.
SRD is nonlinear, and the traditional average torque control, such as current chopping and angle position control, do not take into account the problem of nonlinear and smooth torque transition during commutation, so there is a large ripple in the instantaneous output torque, especially the speed oscillation at low speed. As a result, it has become the main source of noise.
Technical complexity description-3
4. Switched reluctance motor has strong specificity.
Switched reluctance motor is a kind of control motor, which has many control parameters and is flexible. It is necessary (convenient) to design and develop products with different characteristics according to the requirements of different working conditions. Therefore, the versatility of the product is poor, which increases the difficulty of popularization. (also an advantage)
The rise of switched reluctance Motor
