Capacitor Selection for Modular Multilevel Converter

Submodule (SM) capacitor is a key component in a modular multilevel converter (MMC), the selection of which must consider the component's specifications and the requirements of the targeted converter application. This paper focuses on the capacitor selection for MMCs in applications including high-voltage direct current (HVDC) transmission and static VAr compensation using metalized polypropylene film (MPPF) capacitors. The dominant ageing mechanisms of the MPPF capacitors are reviewed to define their operational limits. A straightforward computational procedure and a set of curves are presented to assist the capacitor selection, taking into account criteria in the aspects of maximum capacitor voltage, capacitor voltage ripple, SM voltage capability, and capacitor ripple current stress. Simulation shows the validity of the method and demonstrates its use in design examples.