Abstract：In order to alleviate the chattering problem in conventional sliding mode observer (SMO), this paper proposes a soft switching(SS) SMO for sensorless control of permanent magnet synchronous motor(PMSM), in which the traditional switching function is replaced with a boundary-layer-flexible sinusoidal saturation function. Equivalent convergence interval is defined so as to obtain velocities of convergence of different saturation functions, based on which the equivalent convergence time of the sinusoidal saturation function is deduced from sliding mode state between the boundary layers, and compared with existing elementary, terminal sliding-mode and hyperbolic tangent saturation functions. Adaptive law of switching gain is regulated with the rotor speed to expend the functional range of SMO. Phase locked loop method is adopted to extract the rotor speed and position for compensating the phase lag resulted from filter. The effects of saturation function types, switching gain, equivalent convergence coefficient and boundary layer thickness on estimation accuracy and convergence time are analyzed according to simulation results. Experimental results show the SS-SMO is effective for speed and rotor position extraction and confirm its ability of chattering elimination.
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2015, Vol. 30 
