Variable structure sliding mode based unknown input observer for speed identification of brushless DC motors

A variable structure sliding mode unknown input observer (VSSM-UIO) is investigated to estimate the speed of permanent magnet brushless DC motor (BLDC) in this paper, which features in very good robustness to the parameters uncertainty and disturbance. Using the phase voltage mathematical model of BLDC, the observer is deduced by supposing back-EMF as an input disturbance, which has a good performance of speed and rotor position identification. By means of the designed Lyapunov function, the observer is proved to be stable in the infinite time and robust, even if the load torque disturbance, the parameter uncertainties exist. Simulation results show the validity of the proposed strategy.