HARMONIC PERFORMANCE COMPARISON OF MMC AND CHB MULTILEVEL CONVERTERS FOR HVDC SYSTEMS UNDER PSPWM CONTROL
Keywords:
HVDC systems, Modular Multilevel Converter (MMC), Cascaded H-Bridge (CHB), multilevel converters, harmonic analysis, Total Harmonic Distortion (THD), Phase-Shifted Pulse Width Modulation (PSPWM), MATLAB/Simulink, Fast Fourier Transform (FFT), Power Quality (PQ).Abstract
High-voltage direct current (HVDC) transmission systems have become a key technology for efficient long-distance power transfer and integration of renewable energy resources. The performance of such systems is significantly influenced by the harmonic behavior of power electronic converters. This paper presents a comparative harmonic performance analysis of two widely used multilevel converter topologies, namely the Modular Multilevel Converter (MMC) and the Cascaded H-Bridge (CHB) converter, under Phase-Shifted Pulse Width Modulation (PSPWM) control.
Detailed simulation models of both converters are developed in MATLAB/Simulink using identical operating conditions and a 13-level configuration to ensure a fair comparison. The harmonic performance is evaluated using Fast Fourier Transform (FFT) analysis of the output voltage waveforms.
The results demonstrate that both converters are capable of generating high-quality multilevel output voltages; however, the MMC exhibits superior harmonic performance. The total harmonic distortion (THD) is reduced from 5.52% in the CHB converter to 3.38% in the MMC, corresponding to an improvement of approximately 38.7% under identical operating conditions.
The improved performance of the MMC is attributed to its modular structure, distributed energy storage, and enhanced voltage synthesis capability. The findings of this study provide a clear benchmark for selecting appropriate multilevel converter topologies for HVDC applications under PSPWM control, where stringent harmonic performance and high power quality are critical requirements
