Analysis of dynamic behavior of modular multilevel converters: Modeling and control

In recent years, Modular Multilevel Converters (MMCs) have received an increasing attention, because they are seen as a viable solution for high power applications. An MMC is characterized by a modular arm structure, composed of a cascade connection of a large number of simple dc/dc cells with floating capacitors. These cells can be easily assembled into a converter for high- or medium-voltage power conversion systems. The aim of this paper is the comparison of two control schemes for MMC. The analysis is focused on a single leg of the converter. The converter model is expressed as a system of differential equations that can be used to analyze both the steady state and the dynamic behavior of the MMC. The control of the converter requires balancing the arm voltages and controlling the leg total energy in order to achieve a stable behavior in all practical operating conditions. The effectiveness of the proposed control schemes is confirmed by numerical simulations