Research And Implementation Of Control Strategy For Switched Reluctance Motor Drive System

With the rapid development of power electronics technology,switched reluctance motors have received extensive attention in the field of transmission with their excellent performance.Due to the special working principle of SRM,it has the advantages of simple structure,low cost and high operating efficiency in a wide speed range,which makes switched reluctance motor widely used in the textile industry and the aerospace industry.With the rise of the electric vehicle industry,switched reluctance motor has also begun to emerge in the field of electric vehicles.Since the current chopping control has the advantages of achieving simple implementation and high reliability,it is the most commonly used control method for switched reluctance motor in actual use.However,the current chopping control is a hysteresis control.When the motor is operated at light load,a large current ripple will occur.In particular,the peak value of the pulse current generated in the small inductance region may reach about twice the reference current.This will increase the line loss and torque ripple of the switched reluctance drive system and will also shorten the life of the switching device.In order to solve the problem of large current ripple in the traditional current chopping control,this paper proposes current prediction control based on current chopping control,PWM duty cycle analytical calculation method based on based on inductance characteristics and PWM duty cycle iterative learning control based on current chopping control.In order to solve the problem that the overshoot current and current ripple are large in during start-up and acceleration/deceleration of the switched reluctance motor,the current predictive control of the switching state of power devices in the next cycle is determined by measuring the amount of winding current variation in a PWM interrupt period.According to the switched reluctance motor voltage balance equation,it is concluded that the variation of the winding current is approximately equal when the switching states of the power devices are the same in the two adjacent PWM interrupt periods.Finally,the corresponding program is written in DSP,and the experimental prototype is compared with the traditional current chopping control method to verify the correctness of the proposed method.Since the current prediction control does not adjust the PWM duty cycle,the current waveform improvement during the stable operation of the motor is limited.To this end,a PWM duty cycle analytical calculation method based on the inductance characteristic is proposed.Firstly,according to the electromagnetic relationship of switched reluctance motor,the PWM duty ratio calculation formula that makes the winding current monotonically rise in the small inductance region and just reaches the given reference current,and the winding current is kept substantially constant in the inductor rising region is obtained.Secondly,in order to solve the problems of switched reluctance motor inductance parameter measurement,a method for determining the SRM inductance parameters by experiment is adopted,and the slope of different winding current conditions is fitted to the curve.This curve is used for online calculation of the PWM duty cycle.Finally,a comparative experiment with the traditional current chopper control method is carried out.The experimental results show that the PWM duty cycle analytical calculation method effectively reduces the current ripple and improves the control performance of the motor.Since the control effect of the PWM duty cycle analytical calculation method based on the inductance characteristic is affected by the accuracy of the motor model,when the motor resistance or inductance parameter changes due to heat or wear,it will directly affect the control effect.To this end,a PWM duty cycle iterative learning control based on current chopping control is proposed.The proposed control method only needs to know the geometry of the motor.Firstly,according to the switched reluctance motor electromagnetic relationship,an iterative learning law suitable for SRM is proposed in the small inductance region and the inductance rising region respectively.Compared with the P-type or P-type iterative learning law,the proposed iterative learning law eliminates the trial of the proportional and integral constants.Finally,a comparative experiment with the traditional current chopping control method is carried out on the experimental prototype.The experimental results show that the iterative learning control method based on current chopping control can effectively reduce the current pulsation of the motor during stable operation.Among them,the current prediction control is applied to the motor starting and acceleration/deceleration phase,the PWM duty cycle analytical calculation method is applied to the steady-state operation phase of the known motor inductance model,and The PWM duty cycle iterative learning control is applied to the steady-state operation phase of the unknown motor inductance model.