Sensorless Control of a High-Speed BLDC Motor Using Commutation Timer

This paper presents an improved sensorless control of a high-speed BLDC (Brushless Direct Current) motor for a cordless vacuum cleaner. In conventional sensorless control, the error increases proportionally with speed due to the short conduction period and increased fundamental current frequency. Moreover, the varying conduction period generates additional torque and speed ripples. In this paper, a continuous rotor position sensing method utilizing alpha beta voltage derived from detected pole voltage is proposed. The commutation position is determined based on the position duration between the estimated rotor position and the next commutation point. An additional timer is used to determine the commutation point independently based on the position error for accurate commutation. The control for speed, current, and rotor position estimation is synchronized to the PWM switching period and implemented periodically. The proposed method ensures balanced conduction periods at any speed range and adopts H-PWM and L-PWM method to minimize current ripple caused by PWM switching. The effectiveness of the proposed high-speed sensorless control scheme is verified through experiments using a cordless vacuum cleaner BLDC motor operating at 40,000 to 100,000 r/min.