Research On Sensorless Control Strategy For PMSM Based On Treble Sliding Mode Structure

In contrast with the traditional asynchronous motor,permanent magnet synchronous motor(PMSM)which doesn’t need complex excitation device is excited by permanent magnet and is easy to be maintained and repaired.The structure of PMSM is simpler and its volume is smaller than the traditional asynchronous motor.PMSM can be applied to a variety of complex environments with high power factor and efficiency.Therefore,PMSM has been widely applied in many industrial fields,such as aviation,electrical appliances,servo drive,transportation and so on.In order to deal with the various problems resulting from some uncertain factors such as load disturbance,sliding mode chattering,poor observation accuracy of sliding mode observer and so on for the traditional PMSM sliding mode control system,this thesis takes PMSM vector control system as the research object and conducts some studies on speed loop sliding mode controller using novel reaching law,improved extended state observer and two-stage filtering sliding mode observer.Firstly,the decoupling mathematical model of PMSM is established.By intensive analysis,the reason why inherent sliding mode chattering exists in exponential reaching law is pointed out.Then,a novel reaching law based on hyperbolic sine function and exponential reaching law is proposed and an integral sliding mode controller using the proposed reaching law is designed in the speed loop of PMSM vector control system.The controller designed can improve the chattering problem in sliding mode control,and also can effectively improve the response speed and performance of system.Secondly,to improve the anti-disturbance performance of the system effectively,the sliding mode control law is added to the traditional extended state observer,an improved extended state observer is devised to calculate the disturbance torque in the system,and the estimated value is fed back to speed loop as input signal.To ensure that the rotor speed and position can be estimated accurately,a two-stage filtering sliding mode observer is designed.In the proposed observer,the sigmoid function is used to smooth the estimated signal,a low pass filter based on variable cut-off frequency is used to ensure the adaptive filtering ability of the sliding mode observer when PMSM starts and a modified back-EMFs observer is used for secondary filtering to ensure the observation accuracy of extended back-EMFs.Then,the rotor speed and position are extracted and compensated by arctangent function reasonably.Finally,according to the control method proposed in this thesis,the simulation models including speed loop integral sliding mode controller based on novel reaching law,improved extended state observer and two-stage filtering sliding mode observer are built in Matlab/Simulink enviromnet,and then the overall model of the sensorless control system of PMSM based on the three sliding mode structure is completed.The simulation results show that PMSM can quickly reach the given speed when starting,and the control system has good control effect and excellent response when the load torque is disturbed.