Sensorless Speed Control for Brushless DC Motors System Using Sliding-Mode Controller and Observers

An improved sensorless operation scheme for the Brushless DC motors (BLDC) control system is proposed. A high-speed sliding-mode observer (SMO) for back electromotive force (back-EMF) estimation is employed to obtain the position and speed. A speed control algorithm for the BLDC control systems combining a sliding mode controller with disturbance observer (DOB) is developed to restrain the speed fluctuation caused by abrupt change of load torque. The DOB is used to estimate the load torque and generate a feed-back compensating signal for a controller. Detailed simulation results show that the proposed high-speed SMO could improve the estimation accuracy, and the designed compensating scheme could enhance the robustness against the abrupt load torque change effectively.