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 HVDC transmission and static VAr compensation using metallized poly-propylene film (MPPF) capacitors. The dominant ageing mechan-isms of the MPPF capacitors are reviewed to define their operational limits. A straight-forward 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