1. School of Electrical Engineering China University of Mining and Technology Xuzhou 221116 China; 2. International Joint Research Center of Central and Eastern European Countries on New Energy Electric Vehicle Technology and Equipment Xuzhou 221008 China; 3. International Cooperation Joint Laboratory of New Energy Power Generation and Electric Vehicles of Jiangsu Province Colleges and Universities Xuzhou 221008 China; 4. Faculty of Control Systems and Robotics Engineer Saint-Petersburg National Research University of Information Technologies Mechanics and Optics St. Petersburg 197101 Russia; 5. Electric Drives Department Moscow Power Engineering Institute National Research University Moscow 111250 Russia; 6. Department of Automation of Mining Production University of Mining and Geology "St. Ivan Rilski" Sofia 1700 Bulgaria
Abstract：Control variables are usually measured by sensors. However, sensors can increase system costs, cause interference, and reduce reliability. Thus, the sensorless technique is widely studied. For switch reluctance motor (SRM) systems, according to present control methods, current information is necessary to torque control. A new control variable is toned to replace the current and have a simple relation with electromagnetic torque to achieve good control performance without current sensors. Rotor position and speed are necessary for any SRM control methods, usually measured by a position sensor. The first derivative of position is speed, the second derivative of position is acceleration, and the third and more derivatives of position have no physical meaning. When only a position sensor is used in the SRM system, besides the speed, the acceleration is the unique possible feedback variable. Therefore, a current sensorless control method of SRMs using double closed loops of speed and acceleration is proposed. Firstly, the feasibility of the proposed method is analyzed in two points. ① Its convergence is proven; ② The approximate linear relation between electromagnetic torque and acceleration in a steady state is proven, and the equivalence of torque control and acceleration control is analyzed further. Subsequently, a hysteresis control method with three bounds is proposed to track reference acceleration. According to flux features of the SRM, there is a position where inductance increase sharply, and if the phase current cannot be reduced timely, the electromagnetic torque will also increase sharply, leading to a large torque ripple. Thus, an extra upper bound is set, and a negative voltage is used to quickly reduce the phase current when the acceleration is beyond the upper bound. Finally, Given both motor efficiency and torque ripple, turn-on and turn-off angle are appropriately selected. Angle position control (APC) and voltage pulse width modulation (VPWM) are two existing current sensorless control methods of SRMs. VPWM has better control performance than APC. Therefore, taking VPWM as a comparison object, the improvement of the proposed method is verified by experiments. The direct torque control (DTC) method is another comparison object to demonstrate the equivalence of torque control and acceleration control. The experiments are carried out under four conditions: low speed and light load, high speed and heavy load, speed change, and load change. Under (600r/min, 0.2N·m), the torque ripple of VPMM is about 0.32N·m, and those of DTC and the proposed method are about 0.2N·m. Under (1 500r/min, 0.7N·m), the torque ripple of VPMM is about 1.6N·m, and those of DTC and the proposed method are about 0.5N·m. If the initial condition is set to (600r/min, 0.2N·m), during speed change, the max torque of VPMM is about 4N·m, and those of DTC and the proposed method are about 0.2N·m. If the initial condition is set to (600r/min, 0.2N·m), during load change, the torque ripple of VPMM is about 2N·m, and those of DTC and the proposed method are about 0.5N·m. The experimental results show that the proposed method is comparable to the DTC and better than the VPWM in control performance. In addition, the relationship between the current and the electromagnetic torque is complex and nonlinear, but the conversion between them is needed in DTC. Due to the approximately linear relationship between electromagnetic torque and acceleration, the proposed method is independent of the electromagnetic torque, thus having a lower computational cost.
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2023, Vol. 38 
