Research On Model Predictive Control Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)uses rare earths as its permanent magnet material,which makes it has natural advantages in China.The PMSM is widely used in industry,agriculture and daily household electrical appliance with its merits such as high efficiency,small volume,simple structure,light weight,high power density and so on.As the control strategy is a key factor that affects the operation performance of the PMSM,the research on the PMSM's control strategy is of importance.Vector control(VC)and direct torque control(DTC)are the two traditional control strategies of PMSM that are commonly used.VC has the advantage of the fine steady-state performance with low torque ripple,but its current loop's dynamic performance can't be further improved because its current loop is often designed by using PI controller,which has the problems such as integral saturation,the interaction between d/q axes currents,and the difficulty of dealing with the restraints of the system.DTC uses hysteresis comparator and switching vector table to realize fast dynamic response,but the high torque ripple exists in the system,which doesn't meet the industry requirements of the stable torque control.Meanwhile,PMSM will produce significant harmonic currents under low carrier modulation ratio condition when using traditional control strategies,which is harmful to the system stability.Model predictive control(MPC)has better dynamic performance than VC while its steady-state performance is superior to DTC.In addition,as MPC is capable of considering the multiple control objectives and system constraints,it could improve the system performance when considering the converter efficiency in the strategy.In this paper,MPC is analyzed and researched to obtain better performance than the traditional control strategies.Firstly,the mathematical model of PMSM is established,and the principle of rotor flux oriented VC for PMSM is introduced.Furthermore,the principle of MPC is analyzed,and the predictive function is derived for the PMSM.The objective function of the model predictive torque control and model predictive current control are constructed respectively to compare their advantages and disadvantages.In order to perform better than the traditional strategies,a 3-vector low switching frequency model predictive control is proposed in this paper,the strategy has obtained a steady-state performance which is as good as the steady-state response provided by VC.In themeanwhile,to increase the efficiency of convertor is also considered to reduce losses of the convertor,which could make it perform better than VC.As a result,the proposed strategy permits the PMSM drive system can operate under low carrier modulation ratio situation.Finally,the simulations and experiments are conducted to make a comparison based on an experimental PMSM drive system among the traditional vector control,single vector MPC and 3-vector MPC with reduced switching frequency.The results are used to verify the feasibility and correctness of the proposed control strategy,which show that the investigated method is superior to the traditional vector control strategy.