Sensorless Control Of PMSM With Improved Sliding Mode Observer

With the application of Permanent Magnet Synchronous Motor(PMSM)is more widespread in many industrial and scientific fields,the high-performance PMSM control strategy has become a research hotspot for domestic and foreign scholars.To solve the problems of low precision,high loss and large volume caused by sensors in PMSM control system,sensorless control technology has become an important part of PMSM control strategy.Frstly,research status of PMSM sensorless control at home and abroad are introduced,as well as the open loop control strategy,which is applicable to the operation of motor at zero and low speed.The traditional sensorless control algorithm’s advantages and disadvantages are described in detail.Then,in this paper,the Sliding Mode Observer(SMO)control algorithm and Intensity Frequency Ratio(I/F)open loop control algorithm are selected to control PMSM.In addition,PMSM’s physical model and mathematical model are introduced.The principles of vector control based on rotor field orientation and Space Vector Pulse Width Modulation(SVPWM)are expounded.Secondly,the basic principles of the two control algorithms used in this paper are introduced,and the switching process is analyzed.The sliding mode observer control and the cause of its inherent chattering are studied.Based on this,the traditional sliding mode observer is improved.A sign function is used as the switching function of traditional sliding mode observer’s approach law,and chattering is obvious.In this paper,an improved saturation function is introduced to replace sign function,which adds the power function of boundary layer thickness on the basis of the elementary saturation function.Thus,an improved exponential approach law can be obtained to effectively suppress the chattering problem of sliding mode observer.Besides,the switch gain of traditional sliding mode reaching law is constant,which can’t adapt to the needs of different working speed at the same time,when speed changes,the chattering phenomenon will intensify.Aiming at this problem,in this paper,the switch gain is improved to be a variable proportional to the given speed,thus further improves the reaching law and effectively improves the chattering exacerbation when speed switches.In addition,a tracking Differentiator(TD)is introduced to filter the given speed signal,in order to solve the problem that speed estimation error increases and dynamic response becomes worse,which due to the sudden change of the given speed.The proposed PMSM sensorless control system based on the improved sliding mode observer is theoretically analyzed.Compared with the control system based on traditional sliding mode observer,it can effectively reduce the chattering problem,and control system’s dynamic performance and robustness are significantly improved.Finally,through simulation analysis,the feasibility and effectiveness of the proposed PMSM sensorless control system based on improved sliding-mode observer are verified.Compared with the control system based on traditional sliding mode observer,the control system’s estimation accuracy is improved by about 8.3 times at high speed and 11.6 times at low speed.The experimental platform of motor was built,and the good control performance of PMSM vector control was verified.