An improved microcontroller-based sensorless brushless DC (BLDC) motor drive for automotive applications

The direct back EMF detection method previously described in a sensorless BLDC motor drive system [5] synchronously samples the motor back EMF during the PWM off time without the need to sense or re-construct the motor neutral. Since this direct back EMF sensing scheme requires a minimum PWM off time to sample the back EMF signal, the duty cycle is limited to something less than 100%. In the paper, an improved direct back EMF detection scheme which samples the motor back EMF synchronously during either the PWM on time or the PWM off time is proposed to overcome the problem. In this paper, some techniques for automotive applications, such as motor rotation detection, and current sensing are proposed as well. Experimental results are presented.