Research On Multi-step Predictive Torque Control Strategy For Permanent Magnet Synchronous Motor Drive System

The multi-step predictive torque control strategy can effectively reduce the inverter switching frequency of PMSM drive system and improve the operating efficiency of the motor system.However,on the one hand,the prediction model adopted by conventional predictive torque control is difficult to iterate due to its high computational complexity.On the other hand,conventional predictive torque control adopts exhaustive optimization method,and the calculation amount will increase exponentially with the increase of the prediction steps,so the optimization efficiency is low.In view of these two problems,this paper has carried out the related research work.In order to solve the problem of high computational complexity of traditional prediction model,a discrete mathematical model of direct decoupling control of torque and stator flux amplitude of permanent magnet synchronous motor by voltage vector is derived in this paper.The time-varying characteristics of the parameters of the model are analyzed,and some time-varying parameters are found to be approximately constant in steady state.On this basis,a simplified multi-step prediction model for tracking errors is derived.In order to solve the problem of low efficiency of exhaustive optimization,this paper analyzes the effect of applied voltage vector on the control of torque and stator flux,presents a method of selecting switching sequences by using band constraints of torque and stator flux,and designs a fast optimization algorithm based on band constraints.In addition,the steady-state and transient-state control modes and the corresponding cost functions are designed respectively to ensure that the system still has good steady-state and dynamic performance under low switching frequency.The influence of hysteresis size and switch weight coefficient on the control effect is also analyzed by simulation,which provides a basis for the setting of relevant parameters.Based on a 6k W permanent magnet synchronous motor,the proposed strategy is experimentally verified.Compared with the conventional predictive torque control strategy,the computational complexity of the proposed strategy is significantly reduced,and the three-step prediction can be realized within a sampling period of 50 microseconds.The proposed strategy can maintain the transient and steady-state performance of the conventional predictive torque control strategy and reduce the switching frequency by over 37%.