An Improved Position Observer for Sensorless FOC Algorithm

Position observer is the key to estimate the rotor speed and position in sensorless field oriented control (FOC) algorithm. In order to drive the motor stably and improve the accuracy of rotor speed and rotor position, a tracking observer with high frequency pulse injection (HFP) is used at zero low speed, and a sliding mode observer (SMO) is used at medium high speed. In order to achieve stable switching between zero low speed and medium high speed, a dynamic switching of position observer based on actual speed is proposed. Since the traditional synovial observer uses the sign function as the switching function, which causes the discontinuity of the switching surface and chattering, therefore, this paper proposes an extended back electromotive force (EBEMF) estimation method based on sigmoid function. In order to avoid the influence of high frequency chattering on rotor position estimation, phase locked loop is used to estimate rotor position.