A position sensorless control strategy for BLDCM based on an improved sliding mode observer

In order to achieve position sensorless control of brushless DC motors (BLDCM), this paper proposed an improved line back electromotive force (back-EMF) sliding mode observer (SMO). To reduce chattering of the system, a smooth hyperbolic tangent function was employed in the observer. In this way, not only the low-pass filter and phase compensation module were eliminated, but also smooth line back-EMF signals were obtained, thus the phase lag of the estimated line back-EMF was avoided. Besides, the estimated line back-EMF signals corresponded to three virtual Hall signals, and six discrete commutation signals were obtained directly. The simulation and experimental results show that the proposed method can accurately estimate the line back EMF of brushless DC motors, the position sensorless control of the brushless DC motor can be realized. © 2015 Chin. Soc. for Elec. Eng.