Total Harmonic Distortion Reduction of Brushless DC Motor using SVPWM Commutation Topology

This article demonstrates the reduction of harmonic distortion using field oriented commutation (FOC) technique in sensorless BLDC motor. The conventional sensorless drive techniques in brushless DC (BLDC) motor involve a six MOSFET based six-step inverter that is fed with Pulse Width Modulated (PWM) commutation signals. The aforesaid method uses trapezoidal back EMF for the detection of rotor position. The trapezoidal or six step commutation method is the simplest scheme available for both speed control and drives in sensorless Brushless DC motor, however such technique fails to perform at lower rotational speeds (rpm) and exhibits high torque ripples. To reduce the torque ripples as well as harmonic distortion in conventional BLDC drives, this work presents Space Vector Pulse Width Modulation (SVPWM) technique. This SVPWM based commutation topology changes the switching time in the said six-step inverter by altering the duty cycle of the gate pulse signals in accordance with the average variation of reference voltage vector. Due to this commutation methodology, the output torque ripple of BLDC is smoothening significantly. The design and dynamic performance of the developed SVPWM drive are evaluated in MATLAB/SIMULINK based platform. The performance analysis is estimated in terms of rise time and total harmonic distortion (THD) at low as well as high rpm and finally the rise time of rotor speed is compared with that of trapezoidal based commutation technique (both sensored and sensorless) at different speed which shows satisfactory results over a wide range of speed.