MC-SPWM and MC-THIPWM Methods for Symmetric and Asymmetric Design of CHB-MLI: A Study

Abstract

: Cascaded H-bridge multilevel inverters (CHB-MLI) are employed in a variety of medium/high power applications. These inverters are known to inject unwanted harmonics into the grid, which negatively affects the grid and connected loads. CHB-MLI topology can reduce many of these harmonics by producing multiple output voltage levels and improves the fundamental component using a suitable modulation technique. However, the CHB-MLI topology configuration requires multiple isolated input sources which must be balanced either with the modulation technique or with an additional method. This paper analyzes multi-carrier pulse width modulation (MC-PWM) techniques for CHB-MLIs. In this study, two basic configurations of CHB-MLI symmetrical and asymmetrical are reviewed, followed by their mathematical analysis. Also, this paper analyses multi-carrier based sinusoidal pulse width modulation (MC-SPWM) and multi-carrier based third-harmonic injected pulse width modulation (MC-THIPWM) techniques with phase-shifted (PS) and level-shifted (LS) carrier arrangements for the CHB-MLI. Moreover, a simulation study has been conducted using MATLAB Simulink to analyze the performance of MC-PWM techniques for the symmetrical and asymmetrical type CHB-MLIs. The 7-level and 9-level CHB-MLIs were evaluated for the stated MCPWM techniques in terms of harmonics and fundamental components. In addition, discharging current of all input sources was checked to verify the ability of all MC-PWM techniques to balance all input sources.