Research On Sensorless Control Strategy For Permanent Magnet Synchronous Motor Based On Sliding Mode Observer

To achieve accurate rotor position and speed signal is quite crucial for the implementation of the closed-loop control of permanent magnet synchronous motor.The traditional mechanical sensor would increase the system cost and impose restrictions on the operating environment.Therefore,sensorless control technology with high reliability and simple implementation displays a broad application prospect.Sliding-mode observer shows strong robustness since it is insensitive to external disturbances and changes of internal parameters.Moreover,it can meet the requirements of the speed regulating system of permanent magnet synchronous motor which sets high demands on the frequent changes of parameters and dynamic performance.Aiming at the problems of sliding-mode observer method,like the high-frequency buffeting and inaccurate estimation of rotor position,improvements are made in this paper,realizing the speed-regulating control of permanent magnet synchronous motor when it is lack of position sensors.Firstly,a EEMF-based(Extended electromotive force)sliding-mode observer mathematical model is established.To solve the severe buffeting of traditional methods and phase lag,continuous function is adopted to replace the control function in the algorithm,and the low pass filter is improved to be back EMF observer with an adaptive organization.Moreover,the traditional sliding-mode observer method is improved by combining the phase-locked loop system.As a result,the buffering problem of the improved sliding-mode observer is reduced,the phase lag is improved,and the estimation accuracy of rotor position is increased.The robustness of observer is verified through theoretical derivation and simulated analysis.Based on the 5.5kW power level vector control system of permanent magnet synchronous motor(PMSM),the influence of the instantaneous rotor error on the vector control system is studied.The relationship between the amplitude of the error angle and the amplitude of the electromagnetic torque ripple is analyzed by taking the rotor error angle as a special case.In order to keep the control performance of the system under different operating conditions,the influence of the rotor angle error on the electromagnetic torque of iq is considered.Based on the theory of automatic control,the precision of the rotor position estimation is obtained.Finally,sensorless control experiment for the permanent magnet synchronous motor based on the sliding-mode observer is carried out on the experiment platform of the Myway system.Firstly,constant-speed no-load and varying-speed no-load observation experiments are carried out on the platform.Secondly,the robustness of sliding-mode observer is verified.To prove that the rotor position estimation accuracy of improved sliding-mode observer is better than the traditional methods,contrast experiment is conducted.Finally,with the estimated rotor position and rotational speed as the feedback,sensorless closed-loop control is implemented.According to the result,the sensorless control strategy of permanent magnet synchronous motor based on the sliding-mode observer proposed in this paper receives good dynamic performance and strong robustness,and can even implement the accurate observation of rotor position and rotational speed.