SiC Modular Multilevel Converters: Sub-Module Voltage Ripple Analysis and Efficiency Estimations

Two important technical challenges associated with the Modular Multilevel Converter (MMC) are the reduction of the voltage ripple of the Sub-Module (SM) capacitors and the reduction of the converter losses. This paper conducts a study focused on these two topics. Firstly, the effect of a circulating current with a predefined second harmonic on the SM voltage ripple is assessed. Secondly, an efficiency study for two different MMCs, one with silicon (Si) and the other with silicon carbide (SiC) devices is carried out. Results suggest that a SiC MMC converter with a circulating current including a second harmonic represent a good solution since it achieves a reduction of the SM capacitors together with a high efficiency operation.