Modular Multilevel Converters for Power Transmission Systems
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Abstract
In this research, novel Modular Multilevel Converters (MMCs) intended for various type of power transmission systems are studied. Currently, the MMC, which is built based upon stack of identical half- or full-bridge submodules (SMs), is the dominant Voltage Source Converter (VSC) topology for power transmission systems, because of its salient features including (i) scalability/modularity to meet any voltage/power level requirements, (ii) excellent harmonic performance, (iii) very high efficiency, and (iv) redundancy in the converter configuration. The application of power converters could be extended to novel transmission schemes that might be under research, such as High-frequency Half-Wavelength (HFHW) Transmission Line. Therefore, introducing suitable power converter topologies not only improves the developed technologies, but also facilitates the implementations of novel related ideas. This research introduces three topologies of MMCs optimized for various type of power transmission systems. The first two topologies are intended for AC/AC applications such as HFHW system and the third converter is proposed for HVDC systems. Compared to conventional MMC, the proposed converters have fewer power switches with a major portion of them operating in soft-switching mode. Beside the theoretical studies, the viability of the proposed topologies, as well as the effectiveness of the control strategy are confirmed by both simulation and experimental results. Furthermore, the economical aspect of HFHW power system is discussed and it is shown that this system can benefit from employing the proposed AC/AC converters.