Influence of PWM Schemes and Commutation Methods for DC and Brushless Motors and Drives

Currently, many different types of dedicated PWM motor control IC’s are available in the market to control DC and brushless DC motors. Unfortunately, switching schemes of these IC’s are either fixed or limited in flexibility, resulting in higher noise and poor efficiency in many cases. In this article, more than 5 different switching schemes are presented and relative advantages and drawbacks of each mode are compared. It was found that selection of the switching scheme affects performance characteristics such as current ripples in DC link, line current harmonics, and losses in the motors and drives. Based on the motor parameters and application requirements, selection of optimal switching scheme and PWM frequency can improve operating efficiency and motor/drive sizing. In addition, a simple DSP-based programmable brushless motor controller design capable to select any one of the above 5 switching schemes or Hall sensor-based sinusoidal scheme is demonstrated.