A New Starting Method of BLDC Motors Without Position Sensor

This paper presents a novel method to detect the rotor position of the brushless dc (BLDC) motor of a hard disk drive (HDD) at a standstill and a startup method to accelerate the rotor up to a certain speed where the conventional position sensorless control methods based on the back electromotive force could work reasonably. The proposed initial rotor-position-estimation method is suitable to avoid the temporary reverse rotation or the starting failure of the HDD. The principle of the estimation is based on the variation of the current response caused by the magnetic saturation of the stator core of the BLDC motor when the current flows along the magnetic axis. This method can be implemented using only one current sensor at the dc link of the inverter, which is a prerequisite for the HDD drive. It does not depend on the model of the motor, and it is robust to motor parameter variations. Using the proposed method, it is demonstrated experimentally that a stable start-up can be achieved even with a severe mechanical disturbance