Sensorless control of permanent magnet spindle motors used in hard disk drives

Spindle motors and their control are a very important part of hard disk drives (HDDs). As HDDs tend to be high spin-speed and small form factor, the sensorless control of spindle motors is facing new challenges. This paper explores a new rotor position detecting method for the sensorless PWM control of brushless DC (BLDC) motors, which was originally developed to filter the noises caused by phase commutations. Collaborating with the special PWM chopping sequence of switching devices of the inverter, the proposed method employs the digital filtering procedure to detect the true zero-crossing points of phase back EMFs in PWM BLDC mode as rotor position signals. This paper focuses on how to filter out the noises around the back EMF zero crossing caused by PWM chopping. Also the trends and potential developments of the spindle motor sensorless control are discussed at the end of this paper.