Influence of placement of small space vectors on the performance of PWM techniques for three level inverters

The performance of three level inverters depends on the PWM technique. The three level space vector PWM (SVPWM) has improved performance in terms of the THD and the D.C. bus mid point voltage balance compared to three level sine triangle PWM (SPWM). The objective of this paper is to study the importance of the space vectors, the influence of their placement in the switching sequence on the performance of the PWM techniques and address the basic issue of why the SVPWM has superior performance over SPWM technique. Such a basic understanding will help in designing optimal PWM with desired performance. The study has shown that the superior performance of SVPWM is because of the placement of the small space vectors as the beginning and ending vectors in each sequence, with equal dwell times. The simulation results are presented to validate the theoretical observations. The SVPWM is implemented on a general purpose DSP based digital controller and applied to constant v/f drive.