Research On Control Technique For SRM With 2(N+1)-Switches Convertor Topology

At present,switched reluctance motor(SRM)has been developed and applied in many fields,such as transportation industry,aviation industry,household appliances and other fields.It also puts forward higher requirements for the switched reluctance motor drive system.Especially in the application of small household appliances,the cost of the controller and the stability of the speed control system should be taken into account.The cost of power electronics devices greatly affects the economic efficiency of the whole drive system,so it is imperative to adopt a simpler convertor topology.However,the convertor topology with simple structure must have some limitations in control strategy,and the independence of each phase control will be affected.How to balance the cost and the performance of convertor topology has become a problem to be solved.Compared with the traditional asymmetric half-bridge convertor topology,the 2(N+1)-switches convertor topology reduces power devices by 1/4,which can effectively simplify the system and reduce costs.It also inherits the advantages of the asymmetric half-bridge power topology,such as inter-phase independence and flexible control strategy.In this paper,the convertor topology of 2(N+1)-switches circuit is studied.Based on the analysis of its operational modal,the traditional control strategy is realized,which uses current chopper control at low speed and angle position control at high speed.A SRM drive system based on 2(N+1)-switches convertor topology is built to achieve reliable operation in a wide speed range.According to the control technology characteristics of 2(N+1)-switches convertor topology,the difficulty of demagnetization under traditional control strategy is analyzed and summarized,and the limitation of safe demagnetization flux width is quantitatively analyzed.Under high speed angle position control(APC),the maximum allowable width is one third of the electrical period.At the same time,as the speed decreases,the allowable width increases gradually after entering the current chopper control(CCC),and the maximum allowable conduction width approaches half of the electrical period.On the basis of safe demagnetization and in order to improve the performance of the drive system,a new fast commutation control strategy is proposed.By adding PWM to the common upper switch drive signal to accelerate the demagnetization of the off phase,the fast commutation can be realized,and the restriction of the safe demagnetization flux width can be eliminated.The new control strategy not only eliminates the peak of the continuous current,but also increases the allowable width,increases the output torque of the motor,and effectively improves the performance and efficiency of the drive system.Aiming at the stability of speed control of SRM drive system,the traditional PID control and active disturbances rejection control are analyzed and compared.The principle of ADRC is discussed in modules,including tracking differentiator(TD),extended state observer(ESO)and non-linear state feedback(NLSEF).Finally,a first-order speed loop ADRC is built based on the characteristics and motion equation of SRM.The calculation method of some parameters is given in this paper.Under the same control parameter,the dynamic and steady-state performances of ADRC are compared with traditional PI control,which proves that ADRC has more advantages in speed control of SRM drive system and the correctness of parameter calculation method.