Comparison of Total Harmonic Distortion and Common Mode Voltage in Cascaded H-bridge Multilevel Inverter with Switching Angles Derived Using Non-iterative Calculation Techniques

Abstract

Compared to 3-phase 2-level PWM inverter, multilevel inverter (MLI) offers several advantages, such as higher efficiency, lower voltage stress on power switches, reduced output voltage total harmonic distortion (THD), lower CMV, and less electromagnetic interference. Switching angles applied to MLI must be computed carefully to produce an output voltage with lower THD. In this paper, four non-iterative switching-angle calculation techniques, denoted as SMA, SMB, SMC and SMD, are investigated. A PSIM simulation model was developed to evaluate the THD and CMV of the output voltage of 3-phase cascaded H-bridge multilevel inverter (CHBMLI) controlled using switching angles derived from the four calculation techniques. The phase and line-to-line voltage THDs, as well as the fundamental and root-mean-square CMV for 3- to 11-level CHBMLI are compared. SMC shows the lowest phase voltage THD and CMV, whilst SMD shows the lowest line-to-line voltage THD. However, the CMV resulted from the SMD techniques, especially for higher number of voltage levels, is higher than those resulted from other techniques.