State-space modeling of modular multilevel converters including line frequency transformer

This paper presents a detailed state-space modeling of a Modular Multilevel Converter (MMC) in combination with line frequency transformer (LFT). The classical MMC topology is compared with the recently proposed Open-End Winding MMC (OEWMMC) topology, which integrates the LFT in the converter arm. The line frequency transformer parameters are added in the model, some of which are often neglected in the available literature. Both models are verified and compared by means of numerical simulations in open-loop. Despite integration attractiveness offered by the OEWMMC topology, there are also some inherent drawbacks affecting the overall system sizing that are discussed in the paper.