Research On Control Strategy Of Permanent Magnet Synchronous Motor Based On Fractional Sliding Mode

Permanent Magnet Synchronous Motor(PMSM)has simple structure and excellent performance.As a motion executive component,it has been more and more widely used in the control field.Especially with the vigorous development of new energy vehicle industry,the application prospect of PMSM is further widened.Sliding mode control is widely used in the design of motor control system because it is not sensitive to temperature change and parameter change caused by device aging in the process of electric operation for a long time,and has good anti-interference ability when external torque fluctuation.Fractional calculus has memory and genetic characteristics,which can weaken the chattering in sliding mode control system.This paper will mainly discuss the role of fractional sliding mode in improving the performance of PMSM control system.Firstly,the mathematical model of PMSM in natural coordinate system is established.Because there is coupling relationship between parameters,the voltage and current equations after decoupling are obtained through coordinate transformation.On this basis,the principle of vector control is introduced and the system simulation model is built.The speed-current loop of the vector control system are designed by using the PI control algorithm,the classical control system is reproduced,and the limitations of the cascade PI controller are analyzed.Then aiming at the problems of PI speed controller,a speed controller is designed on the basis of sliding mode variable structure control theory.The speed regulation performance is verified by the motor speed simulation response curve.However,by analyzing the phase trajectory curve,it is concluded that the system state will make high-frequency oscillation near the sliding mode surface,thus causing the chattering of the system.After the theoretical analysis of the principle of reducing chattering by fractional calculus theory,a speed controller based on fractional calculus is designed.In order to further improve the anti-interference ability,a sliding mode disturbance observer is designed to compensate the output of the speed controller.Through simulation and comparative analysis,it is proved that the speed controller based on fractional order can speed up the adjustment speed of the motor speed and reduce the overshoot,and at the same time has better anti-interference ability against external torque fluctuations.Next,a sliding mode rotor position observer is designed based on the back electromotive force to realize the sensorless control of the permanent magnet synchronous motor,and the phase lag and chattering problems are analyzed through simulation.Thus,the sliding mode surface was redesigned by using fractional calculus and terminal sliding mode operator,the approach law was optimized by using hyperbolic function,and a fractional nomalized phaselocked loop is designed to extract the rotor information.The simulation results show that the optimized sliding mode rotor position observer not only improves the rotor position observation accuracy,but also reduces the speed fluctuation caused by system chattering.Finally,the hardware circuit of the PMSM control system is designed:the main control MCU and its peripheral circuits,the bridge inverter and the current sampling circuit.At the same time,the software system design of the researched control algorithm is carried out.Through the experimental platform built,it is proved that the fractional sliding mode can weaken the system chattering and improve the system control performance under the premise of ensuring robustness.