A Cost-Effective and Fault Tolerant T-Type Modular Multilevel DC–DC Converter

The rising penetration of renewable energy sources promotes the development of the high-voltage direct current (HVDC) systems for large-scale power integration and transmission. To meet the future demands of meshed HVDC grids, high-voltage high-power dc-dc converters are required to serve as essential interfaces to bridge the HVDC links with different voltage levels. This paper proposes a T-type modular multilevel converter (T-MMDC) composed of two energy buffering arms to transfer partial power and an active filtering arm for removing bulky passive filters. By utilizing the coordination of arms, the proposed T-MMDC not only enables flexible power regulation and bidirectional fault ride-through, but also has the advantages of cost-efficiency, small footprint, and high efficiency. The topology configuration, quantitative characterization of operating principle, analytical parameter design, and fault ride-through control scheme are presented sequentially, providing a straightforward and detailed guideline for engineers. Full-scale simulations from a 320kV@0.5GW case and down-scale experiments from a 750V@5kW prototype confirm the effectiveness of the proposed operating principle and fault ride-through capability of T-MMDC and its good potential for HVDC grids.