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This paper proposes a sensorless speed control strategy for a permanent-magnet synchronous motor (PMSM) based on a new sliding-mode observer (SMO), which substitutes a sigmoid function for the signum function with a variable boundary layer. In order to apply a sensorless PMSM control which is robust against parameter fluctuations and disturbances, a high-speed SMO is proposed, which estimates the rotor position and the angular velocity from the back EMF. In the conventional SMO, a low-pass filter and an additional position compensation of the rotor are used to reduce the chattering problem that is commonly found in the SMO using the signum function. In order to overcome the time delay caused by the low-pass filter, in this research, a sigmoid function is used for the switching function instead of the signum function. Also, the variation in the stator resistance is estimated to improve the steady-state performance of the SMO. The stability of the proposed SMO was verified using the Lyapunov second method to determine the observer gain. The validity of the proposed high-speed PMSM sensorless velocity control has been demonstrated with simulations and real experiments.
Date of Publication: Sept. 2011