الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Medium- and high-voltage DC networks offer an appealing opportunity for the integration of renewable energy sources. Therefore, the role of DC-DC converters is pivotal in facilitating this integration. The Modular Multilevel Converter has recently emerged as a promising candidate for DC-AC and DC-DC conversion in high-voltage, high-power applications due to its distinctive features. However, a significant drawback of conventional MMCs in DC-DC conversion is arm energy drift, leading to submodule voltage imbalance. Various techniques have been explored in the literature to address the energy drift issue in the DC-DC conversion process.In this thesis, two topologies of bidirectional modular multilevel DC-DC converters are proposed: the DC-DC modular multilevel converter with simultaneous arm energy equalization and the second DC-DC modular multilevel converter with sequential arm energy equalization, which offers DC fault-blocking capability for HVDC systems. These proposed converters incorporate a parallel-connection strategy between upper-arm capacitors and lower arm capacitors during the equalization process, enabling energy transfer between upper and lower arms and mitigating the energy drift problem. The thesis provides a comprehensive overview of the operational principles, mathematical analysis, design, and efficiency evaluations of the converters. Simulation and experimental results illustrate the bidirectional power flow capability and promising performance of the proposed converters under normal operating conditions with balanced arm energy. Furthermore, a comparative analysis between the proposed converters and other existing topologies demonstrates their advantages over existing topologies. The first proposed converter boasts a lower count of IGBTs and eliminates the need for isolating transformers when compared to the energy equalization module approach. Additionally, unlike other alternatives, the second proposed converter incorporates a DC fault-blocking capability