A new phase-delay-free method to detect back EMF zero-crossing points for sensorless control of spindle motors

This paper introduces a new rotor position detecting method for the sensorless control of spindle motors in hard disk drives. The method applies a digital filtering procedure to identify the true and false zero-crossing points of phase back electromotive forces, the latter of which are caused by the terminal voltage spikes due to phase commutations. The proposed method is phase-delay free and independent of motor parameters. It is especially suitable for high-speed sensorless brushless dc motors. We used the method to drive many kinds of spindle motors for different hard disk drives. The experimental results confirmed the effectiveness of the proposed method in a wide speed range.