Influence of Submodule Capacitance on MMC Performance and Its Optimum Sizing

Modular Multilevel Converter (MMC) has gained popularity in the last decade since it is a transformer-less multilevel converter topology most commonly used in medium and high voltage power conversion applications. There are several component values as well as control parameters which contribute to the operation of MMC. However, the submodule capacitor which is used for energy storage during AC/DC or DC /AC power conversion is one of the most important components in MMC that has a very big impact on the system performance and contributes to large share of the total weight and volume. Under dimensioning the submodule capacitance causes a high capacitor voltage ripple and deteriorate the system performance and on the other hand over dimensioning the submodule capacitance results in higher system cost and system oversize. It is therefore of great importance to dimension the capacitor optimally.