Device loading and efficiency of Modular Multilevel Converter under various Modulation strategies

Modular Multilevel Converter (MMC) has been becoming a very important solution for high power and medium power applications, where the efficiency and reliability performance are crucial design considerations. In this paper, three widely used modulation methods for MMC, Phase Shift PWM (PSPWM), Phase Disposition PWM (PDPWM) and Nearest Level Modulation (NLM), are comprehensively investigated to uncover the desired solution for high transmission efficiency and system reliability. An important part of this paper is also devoted to reveal the impact of modulation schemes on the loading stress of the power devices in terms of power loss and thermal profiles, which are critical issues in terms of efficiency and reliability of the MMC. Special attention is given to the performance comparison of MMC under various modulation indexes as well as different switching frequencies when applying those modulations.