Aiming at the torque ripple problem of brushless DC motor（ BLDCM）

an improved double closed-loop speed controller based on equivalent input disturbance method is designed

which can effectively suppress the slope ripple caused by the back electromotive force（ EMF） in the start-up phase of the traditional double closedloop speed control system and achieve high-precision control. Speed loop adopts integral separation proportionalintegral-differential（ PID） controller to meet the needs of low-speed and high-precision applications. Twelve sectors are divided to eliminate the torque estimation error caused by misjudgment of flux linkage angle. Equivalent input interference estimator is designed to compensate the system error caused by neglection and simplification in engineering design of double closed-loop speed control system

and to suppress the oblique wave pulse caused by back EMF in start-up stage. The simulation results verify the method can suppress the oblique wave ripple pulse

and the torque Baud rate can be reduced to 4 % when the system is running stably

and the requirement of highprecision control is achieved.