A novel nonsingular fast terminal sliding mode observer combining I-F method for wide-speed sensorless control of PMSM drives

Based on the consideration of optimizing speed piecewise and transitioning smoothly, a hybrid position sensorless control strategy integrating with a novel nonsingular fast terminal sliding mode observer (NFTSMO) and the current-frequency (I-F) control method for surface-mounted permanent magnet synchronous motor (PMSM) is proposed in this paper. In zero-low speed regions, the I-F control method is employed for starting steadily and possessing the ability of anti-interference. In middle-high speed regions, an improved sliding mode observer (SMO) based on a novel nonsingular fast terminal sliding surface is designed for the closed-loop sensorless operation. Making use of the novel sliding surface, not only the estimated errors of rotor position caused by the conventional sliding surface can be eliminated effectively with a faster rate of convergence to improve the stability of system, but also the chattering of the estimated back EMF can be restrained by the sigmoid function. Meanwhile, the phase-locked loop is utilized to lessen the burden of calculation and phase delay. Furthermore, a transition function is designed so as to fulfill the smooth transition between two different control ideologies. The effectiveness of the proposed hybrid sensorless control strategy for both dynamic and steady state operations during wide-speed region is verified by simulation and experimental analyses.