Vibration Suppression Of Switched Reluctance Motor Based On Digital-PWM Control

Switched reluctance motor?SRM?has been applied in many fields due to its advantages of simple structure,large starting torque,reliable operation and low cost.Many performances SRM has can compete with permanent magnet synchronous motor?PMSM?,and even surpassed it in some aspects.However,the larger vibration noise of SRM when operating is still an important reason limiting its development.In this paper,the vibration of SRM stator,which contributes the most to SRM vibration,are studied.Radial force is the fundamental cause of SRM stator radial vibration.By using analytical expression of radial electromagnetic force,analysis of SRM stator vibration characteristics are implemented.Three-dimensional finite element modal analysis of SRM stator is also carried out.The Simulink model of SRM control system is built,which aims to figure out the advantages of Two-stage Commutation under negative voltage PWM commutation when compared with negative bus-voltage commutation.The severe trail current of Two-stage Commutation under negative voltage PWM commutation will generate negative torque which will reduce the motor output.An adaptive turn-off strategy under negative PWM is proposed,which combine the advantages of the negative bus-voltage commutation and negative PWM commutation.After the phase winding chops the negative voltage for a while,the chopping turn-off signal is generated,leading to the sharp descending of the winding current.To find chopping turn-off angle?_offPWM,which corresponds to the chopping turn-off signal,linear inductance model of the SRM is used to deduce the relationship of i-?with constraint condition.When it is drawn together with the function of winding current-rotor position under negative voltage PWM,the abscissa of the crossover point is the?_offPWM.The accuracy of the Two-stage Commutation delay time is the precondition of the insurance of the effect of Two-stage Commutation.Under PWM control,using timer to realize the delay time will lead to error.In this paper,using the combination of driving signals upper and lower of the power circuit to accurately realize the freewheeling time of phase winding voltage,i.e.,Two-stage Commutation delay time.And discussing the calculating rule of the duty ratio of driving signals under different conditions.Control system for experiment is built with a controlled object of a 18/12 pole SRM with a rated power 5.5 kW,rated speed 1500 r/min.The experiment states that the strategy proposed can effectively solve the problem of inaccuracy time delaying and trail current of Two-stage commutation under negative voltage PWM.The t_on of IGBT is shorter than t_off,which leads to spike voltage in phase winding at the freewheeling commutation point of power circuit when using accurate delay time strategy.This problem is solved by turning off the IGBT about to turn off early.Noise testing verifies that the proposed strategy can effectively suppress the vibration of SRM stator.