Fractional-order Terminal Sliding-mode Control Method For Speed Control System Of PMSM

Permanent magnet synchronous motors（PMSMs）are widely utilized in numerous industries such as electric vehicles,numerical control tools and robots due to the advantages of simple structure,high power density,and high dependability.The PMSM is a multivariable nonlinear system with strong coupling,which is difficult to control and the high performance of the control algorithms is required.Owing to the advantages of conceptual simplicity and strong anti-disturbance,sliding mode control（SMC）has been widely used in the control of the PMSM by the scholars.As one of the mainstream controller design methods for the PMSM,the SMC can improve the robustness and precision of the PMSM control system.However,the traditional SMC method cannot deal with the unmatched uncertainties in motor drive systems,which limits the application of the SMC.The integral sliding mode control and disturbance observer based control is able to suppress the unmatched uncertainties,but limited to the strict assumption that unmatched uncertainties should be constant or slow time-varying.Conventional sliding mode based controllers for speed-and current-loop are based on the reduced order model of PMSMs without considering the unmatched uncertainties and the fractional-order characteristics of the stator inductances.Therefore,the precision,the rapidness and the anti-disturbance of PMSM control systems still need to be improved.To deal with the above problems,this thesis proposes a fractional-order integral type sliding mode control for the fractional-order system with unmatched uncertainties.Firstly,considering the unmatched uncertainties in the PMSM system and the fractional-order characteristics of the stator inductances,the fractional-order mathematical model of PMSM is established.Furthermore,a full-order terminal sliding mode observer is designed to make the observer better than the traditional sliding mode observer in terms of the observation accuracy and the robustness to parameter perturbation.Meanwhile,the chattering in the output injection of the traditional sliding mode observer is eliminated,where the precision and dynamic performance of the observer can be further improved,and the reliability of the system can be enhanced.Finally,with fully analysis of the matched and unmatched uncertainties in the PMSM system,the thesis proposes a fractional-order sliding mode based speed-and current-controllers by using the virtual control technique to improve the dynamic response of PMSM control system according to the fractional-order model of PMSMs.The chattering is attenuated by virtue of the integral-type control law and the memory and genetic characteristics of fractional-order calculus.Thus,the continuous current and voltage reference signals can be generated.The correctness and superiority of the proposed method have been validated by the simulation and experimental results.