Adaptive state estimation algorithm for sensorless vector control of permanent magnet synchronous motors at medium and high speeds under parametric uncertainty

An adaptive estimation algorithm is proposed to improve the accuracy of rotor speed and position determination for a permanent magnet synchronous motor (PMSM) in a sensorless control system, without requiring prior knowledge of the exact motor parameters. The method is developed to eliminate the shortcomings of conventional sliding mode observers, which are unable to accurately estimate the rotor speed and position under uncertainty of the PMSM parameters due to the indirect estimation of these variables through the observed back EMF. For this purpose, a novel sliding-mode adaptive observer with a smooth switching function is designed to estimate the back-EMF in α–β coordinates. The use of a smooth switching function suppresses the chattering phenomenon (high-frequency oscillations), inherent in sliding modes, thereby improving the quality of the estimated back-EMF signals. Simultaneously, an adaptive parameter tuning law is implemented using a parameter projection operator for quantities such as stator resistance and inductance. This adaptive law ensures the boundedness of all observer signals and the convergence of parameter estimates to a neighborhood of their true values. An adaptive algorithm is also applied to smooth and improve the form of these raw back-EMF estimates. The processed back-EMF signal is fed into a normalized phase-locked loop (PLL) subsystem for precise rotor speed and position estimation without requiring prior knowledge of the flux linkage. The stability and convergence of the proposed observer are rigorously proven using the Lyapunov function method. Comparative simulation results demonstrate that the proposed observer significantly outperforms conventional (non-adaptive) sliding-mode observers, providing stable and accurate state estimation in medium and high-speed ranges, even under substantial motor parameter uncertainty.

Authors: Duy Khanh Nguyen, V. V. Putov, V. N. Sheludko

Direction: Electrical Engineering

Keywords: permanent magnet synchronous motors, sensorless vector control, adaptive sliding mode observer, smooth switching function, parameter projection operator, adaptive back-EMF observer, normalized phase-locked loop, Lyapunov function method, simulation

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