| With simple structure,low cost and high reliability,switched reluctance motors are widely used in the fields of aerospace,oil extraction and power tools.Permanent Magnet assisted-Switched Reluctance Motors(PMa-SRM)add permanent magnets to the stator poles of switched reluctance motors to increase the power density,but similar to switched reluctance motors,the unique biconvex pole structure and nonlinear electromagnetic characteristics cause large torque ripple.To address this problem,this paper takes a 6/20-pole PMa-SRM as the object to suppress torque ripple from the control method,and studies the torque ripple suppression method with adaptive selection of PWM duty cycle according to speed and load,and performs simulation analysis and experimental verification,including the following aspects.Firstly,the structure of the PMa-assisted switched reluctance motor is described and the working principle is analyzed.The electromechanical energy conversion process of PMa-SRM is described from the voltage equation,mechanical equation and electromechanical linkage equation,and the linear,quasi-linear and nonlinear mathematical models of the motor are established.The torque and magnetic chain data of motor nonlinearity are obtained from finite element analysis(FEA)software,and the current is calculated by quadratic interpolation inversion to obtain a twodimensional look-up table to establish a high-precision nonlinear simulation model.Secondly,an adaptive PWM duty cycle torque ripple suppression method on three intervals is given for the problem of large torque ripple under wide speed and large load conditions of the motor.We analyze the reasons for the large torque ripple of the torque hysteresis loop control,divide one electrical cycle into three intervals based on the inductance and current characteristics of PMa-SRM,and select the corresponding PWM duty cycle adaptively according to the speed and torque error to stabilize the torque hysteresis loop interval and reduce the torque ripple.The simulation results show that the torque ripple is effectively reduced from 66% to 24% under the adaptive PWM duty cycle method at 1500r/min and 2N·m load.Thirdly,a PWM duty cycle resolution method based on current chopper control is given for the problems of high peak current and large torque ripple of PMa-SRM current chopper control.An electrical cycle is divided into a small inductance zone and an inductance rise zone,and the corresponding equivalent winding voltage is derived from the rate of change of current in each zone to derive the real-time PWM duty cycle analytic equation.In the current chopper control,the real-time winding voltage in each interval is controlled with the help of the analytical formula to achieve high dynamic tracking characteristics of the current and reduce current peaks and torque ripple.The simulation results show that the current peak is reduced from 10.5A to 10 A and the torque ripple is reduced from 35% to 18.75% under 750r/min and 4N·m load with PWM duty cycle resolution method.The peak current and torque ripple are effectively reduced.Finally,in order to further verify the effectiveness of the control strategy,the PMa-SRM prototype experimental platform is built for experimental verification.System hardware such as power converter,drive circuit,current and position detection,and system software such as speed detection,CAN communication and meter checking algorithm were designed and fabricated.The adaptive PWM duty cycle control strategy with three intervals and the PWM duty cycle resolution method with current chopper control are experimentally verified to validate the effectiveness of the proposed control strategy. |
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