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 multicarrier 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 MC-PWM 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.