Extended Operation of Brushless DC Motors Beyond 120° Under Torque Ripple Reduction Control

Abstract

Hall-sensor-based brushless dc (BLDC) motors are extensively utilized in many applications due to their simple manufacturing and straightforward control. The conventional commutation method uses the 120° commutation logic, which can be directly derived from the Hall signals. The advantage of this method is that it naturally approximates the maximum torque per Ampere (MTPA) operation, but the high torque ripple and low dc voltage utilization are undesirable features. Many algorithms have been proposed in the literature to minimize the torque ripple during the conduction and commutation intervals. This paper proposes a new torque control strategy that can continuously extend the operation from 120° to 180° and maintain the torque ripple reduction during both conduction and commutation intervals by dynamically adjusting the duty cycle based on the reference torque, the estimated torque, and the derivative of torque. The proposed method reduces the torque ripple during the commutation interval, even in high-speed operation, by increasing the conduction angle. The proposed method is analyzed under different speed and back EMF shapes, and its effectiveness is demonstrated experimentally on a typical industrial BLDC motor.