Performance comparison of Two PWM techniques applied to BLDC motor control

Abstract

The BLDC motor is a highly efficient, low weight and maintenance free motor. A BLDC motor is controlled through a PWM drive where the average voltage applied across the motor winding is altered to vary the speed. In this paper, two PWM techniques are compared for their performance as BLDC motor drives. In both the PWM techniques, pulses are removed during the non-flat portion of the trapezoidal back emf. However, in one of the techniques (technique 1), complementary pulses are given to the upper and lower switches of a phase having flat back emf region. In the second technique (technique 2), the pulses are given to either the upper or the lower switch depending upon whether the EMF is positive or negative. Using the two techniques, the BLDC motor's performance is evaluated in terms of the torque ripple, current ripple, speed response, efficiency etc. Technique 2 shows superior performance. The torque ripple, dc current ripple and losses are less for this PWM technique. The BLDC motor drive with closed loop speed control utilizing both the PWM techniques is simulated in the MATALB/Simulink. Preliminary hardware results are also included.