Sensorless control of high-power interior permanentmagnet synchronous motor drives at very low speed

A novel sensorless control scheme is proposed for an interior permanent-magnet synchronous motor drives at very low speed based on sliding-mode observer (SMO) in this study, which substitutes a sigmoid function for the sign or saturation function with a variable boundary layer, overcomes the time delay caused by the low-pass filter and the chattering problem used in the conventional SMO. In this study, an adaptive SMO is employed to estimate the rotor speed and extended electromotive force, a three-phase soft phase-locked loop technology is used to estimate rotor position because of its strong robustness since under voltage phase unbalance or polluted and variable-frequency environment. The global asymptotic stability of the proposed adaptive SMO is verified using Lyapunov stability analysis with considering motor parameter variations. Experimental results are presented to verify the principles and to demonstrate the effectiveness of the proposed method at very low speed from 2 to 17 r/min.