Research Of Pedictive Control Method Based On Variable Control Period For PMSM

Model predictive control(MPC)is a high-performance motor control strategy with the advantages of simple structure and good dynamics.However,the existing MPC motor control system has a constant control period,single prediction algorithm architecture,and does not give full play to the advantages of MPC to achieve optimal control of the system under various working conditions.In view of this phenomenon,this paper takes the permanent magnet synchronous motor(PMSM)as the research object,and combined with the variable switching frequency PWM strategy(VSFPWM),proposes a predictive control method based on variable control period for PMSM.First,the mathematical model and predictive model of PMSM are established in a two-phase synchronous rotating coordinate system,and the specific control flow of the PMSM predictive torque control method is described.An improved method is proposed to solve the problem of large amount of calculation: drawing on the working principle of the direct torque control voltage vector lookup table,the number of predictions required for one step prediction of the control system is reduced from 7 to 3,which greatly reduces the calculation of the algorithm.The improved simulation model of PMSM predictive torque control system was established,and the correctness of the method was verified by analyzing simulation results.Secondly,the four differences between the PMSM predictive torque control system with variable control period and the PMSM predictive torque control system with fixed control period are analyzed:(1)The motor status discriminating link,based on the reasons that cause the motor running state to change,design a given speed change discriminant basis and load change discriminant basis.The reasonable cooperation of the two discriminative bases can accurately identify the operating status of system;(2)Variable switching frequency PWM strategy,according to the two motor state discrimination bases,the speed change control period setting formula and the load change control period setting formula are designed respectively,and the matching relationship between the system operating state and the control period is realized;(3)Variable step number predictive torque control method realizes the matching relationship between running state and the predicted step number of the system;(4)Variable parameter PI controller,adjusting PI parameters according to the operating status of the system to achieve the optimal control of the system.The simulation model of PMSM predictive torque control system with variable control period was established,and the correctness of the method was verified by analyzing simulation results.Finally,by analyzing the simulation results of the two control systems in the process under different speed and load,the superiority of the proposed method is verified.The comparison performance mainly includes four aspects: dynamic response time,torque ripple,stator flux ripple and switching frequency.The simulation results show that compared with the traditional predictive torque control method,the PMSM predictive torque control method with variable control period shortens the dynamic response time and reduces the torque ripple and stator flux ripple during transient operation of the system.