Research On Sensorless Control Technology Of Synchronous Motor Based On I-F Startup

Precise position information of rotor is a real necessity in high performance control of permanent magnet synchronous motor(PMSM).Due to strict limitations of the mechanical sensor,sensorless control has gradually become the research hotspot.A large impulse current usually appears under the traditional motor starting mode,causing a great impact on the motor itself and the power supply.Current-frequency(I-F)control based on limited current can avoid this problem,but tends to have some drawbacks such as low efficiency and losing synchronism easily.Therefore,this thesis deeply studies the sensorless control technology of the motor under I-F startup,and tries to realize the sensorless stable operation of the motor within the full speed range under current limiting startup.The reason why open-loop I-F scheme is prone to lose synchronism is that the stable range of torque angle is small and cannot be observed,which leads PMSM into the unstable region easily when the load condition changes.So the high-frequency injection method is applied to observe the position at zero-low speed range.Aiming at the phase deviation problem existing in the traditional high-frequency injection method,the filter is improved and the phase-locked loop is added to eliminate the error.In order to simplify the control structure of the combination of I-F and the high frequency injection method,the position estimation structure in the high frequency injection method is removed,and the current amplitude and current angular velocity are compensated directly by using the signal containing the rotor position information to keep the motor always in the stable region at zero-low speed range.Owing to the advantage of strong robustness and little dependence on motor parameters,the sliding mode observer method is chosen in the case of medium and high speed.In order to solve the chattering problem in the sliding mode observer method,the symbol function is replaced by the saturation function,and the back electromotive force with feedback gain is introduced to improve the accuracy of rotor position acquisition.In view of the characteristics of the overlap of the two observation axis in the compound control strategy,the hysteresis control switching mode is adopted to achieve a smoother and faster switching.Based on the compound control strategy proposed in this thesis,a simulation model was built on Matlab/Simulink to verify the effectiveness and superiority of the control strategy.The control effect at low speed was tested on the experimental platform.The simulation and experimental results show that the torque angle can be controlled to 90° at low speed to achieve high efficiency control.The simulation results at medium and high speed show that the rotor position is accurately obtained and the static and dynamic performance is good.The switching process is smooth and the fluctuation is small.