Comparative Analysis of Several Designs of Modular Multilevel Converters with Interleaved Half-Bridge Submodules

Abstract: The Modular Multilevel Converter (MMC) is one of the most commonly used active converters in the high-/medium-voltage sector due to its many advantages such as high scalability, high efficiency, modularity and low harmonic contents. However, in low-voltage and high-current applications, classical MMC designs are not very economical. Recently there has been interest in a new design of modular multilevel converter with interleaved submodules (ISM-MMC) capable of using lower cost, lower current switches. The aim of this study is to compare several different design configurations for a given ISM-MMC topology including classical MMC and to give the best design approach taking into account the efficiency and energy density of the system. The power loss of ISM-MMC influence the final efficiency. The loss studied in this thesis mainly consists of conduction losses and switching losses in the semiconductor devices and inductor losses. An analytical calculation method is summarized and validated by the simulation result. The simulation result is carried out in PLECS model with different system components. Power density is determined by the output power and the converter dimension. The volume of semiconductor devices and passive components determine the general dimension of the converter. This thesis discusses the selection of semiconductor devices, inductor and capacitor in the system, with semiconductor devices constraining interleaved leg current and submodule voltage, inductor constraining output current ripple and capacitor constraining capacitor voltage fluctuation. After the specific components are designed, their dimensions are evaluated, and thus the power density of different configurations can be compared.