Capacitor volume evaluation based on ripple current in modular multilevel converter

Abstract

This paper discusses the overall volume evaluation of capacitors in Modular Multilevel Converter (MMC). First, a theoretical formula of the ripple voltage on each cell capacitor in the MMC is clarified. Second, a formula of the total electrostatic energy is clarified. As a result, it is difficult to evaluate the overall volume of the capacitors because the total electrostatic energy is constant even the number of cells changes. Against the problem, the overall volume of the capacitors is designed by using the database of commonly-marketed electrolytic capacitors which are generally implemented into many products. In conclusion, the parallel connection of the capacitor with the small ripple current is better than using one capacitor with the large ripple current in order to achieve the size reduction of capacitors. Finally, it is necessary to close the ratio of the charge voltage to the withstand voltage to 1.0 in order to achieve the volume minimization.