Research On High Speed Flux-weakening Control Strategy For Permanent Magnet Synchronus Motor Based On Model Prediction

The advantages of permanent magnet synchronous motor are large power density and high efficiency advantages.It has been widely used in some areas such as aerospace,deep ocean exploration and high-end equipment.Permanent magnet synchronous motor needs wide speed range and high dynamic response ability to satisfy these applictions.For example,automobile engine accelerates from zero to high speed and high-end CNC’s mainshaft high speed operation.For this reason,the high speed flux-weakening control mechanism and model predictive control of permanent magnet synchronous motor is deeply explored in this paper,which can be used to widen the speed range and ensure the high dynamic performance.For widening the permanent magnet synchronous motor’s speed range,its mathematical model is firstly studied in this paper.Then the voltage and current constraints of permanent magnet synchronous motor are put forward.According to the constraints of motor,the speed range are divided into the base area,weak magnetic area No.Ⅰ,and weak magnetic area No.Ⅱ.According to the respective constraints of different areas,the maximum torque trajectory control theory of permanent magnet synchronous motor which includes the maximum torque per ampere(MTPA)theory,the current constraint circle trajectory in the weak magnetic area No.Ⅰ and the maximum torque per voltage(MTPV)theory in the weak magnetic area No.Ⅱ is proposed.The simulation results show that the maximum torque trajectory control theory can greatly improves the performance of the motor in the full speed range.For improving the dynamic performance ascension of permanent magnet synchronous motor,the model predictive control strategy is studied in this paper.This strategy has the advantage of no modulators,variable switching frequency,rolling optimization and no astrict of certain restrictions,compared with the traditional vector control and other control strategies.The model predictive control strategy has the ability of strongly resisting load disturbance and without overshoot in current control.Firstly,the principle of single-step finite set model prediction control strategy is introduced.Then the model prediction equation is proposed,the evaluation function of model prediction control strategy is designed,and the implementation is given.Then,aiming at the problem of control delay in the single-step finite set model prediction control strategy,a two-step model prediction delay compensation control strategy is proposed,and the implementation is given.Finally,the speed range of the finite set model prediction control is extended to the flux-weakening field.The voltage feedback flux-weakening control strategy,the improved closed-loop 1/ω flux-weakening control strategy and the current error feedback flux-weakening control strategy are studied deeply.The implementations and the simulations are respectively carried out.The advantages and disadvantages of various model predictive flux-weakening control strategies are analyzed in detail.For improving the disadvantages of model predictive flux-weakening control strategies,the flux-weakening control strategy based on implicit function is put forward in this paper.combined with the permanent magnet synchronous motor speed range division and peak torque trajectory planning scheme,put forward the whole speed range of weak magnetic control strategy based on implicit function attract area,and puts forward the regional expression,Combining with the characteristics of finite set model predictive evaluation function operation,the implementation of model predictive control strategy based on implicit function weak magnetic field is presented.In addition,a constrained set multi-step model prediction strategy is proposed to solve the current error and torque ripple problems of single-step and two-step delay compensation prediction strategies.Finally,the above method is simulated and verified in detail,and its feasibility,advantages and disadvantages are analyzed.Respective experiments of flux-weakening control strategy of permanent magnet synchronous motor,single-step and two-step model prediction delay compensation control strategies,and based on implicit function prediction and weak magnetic multistep model predictive control strategy are conducted,which prove the feasibility of the proposed peak torque current control schemes and the performance in the full speed range operation.Then the paper analyzes the limitations of single step model predictive control and the two-step delay compensation model predictive control strategy is verified to reduce the control delay,and the feasibility of the multi-step model predictive control strategy based on implicit function magnetic weakening is proved.Finally,the improvement of the dynamic performance and the full speed range operation are reflected by method proposed.