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This paper proposes a medium-/high-voltage high-power hybrid modular dc–dc converter to interconnect two different dc-voltage levels in medium-/high-voltage dc grids. The converter consists of half-bridge submodules (SMs) rated at a moderate voltage level, i.e., series connection of semiconductor devices is avoided while connecting two high dc-voltage levels. The proposed architecture provides self-balancing operation, i.e., unlike conventional modular converters, no need for capacitor voltage measurement, which enhances the system reliability and simplicity. Sequential charging/discharging of SMs capacitors is adopted in the proposed approach to ensure a self-balanced operation. The proposed architecture can provide a high conversion ratio as well as power transfer in both directions, i.e., bidirectional dc–dc converter. Detailed illustration of the proposed approach operational concept, design, and overall control system is presented. Simulation and experimental results are presented to show the viability of the proposed configuration and validate the claims. [ABSTRACT FROM AUTHOR]

Renewable energy sources, such as offshore wind farms, require high voltage gains in order to interface with power transmission networks. These conversions are normally made using bulky, complex, and costly transformers and high-voltage ac–dc converters with unnecessary bidirectional power flow capability. Multiple modules of single-switch single-inductor dc–dc converters can reach high gains without transformers in these applications due to low semiconductor conduction loss in high-power devices. This paper describes a new approach for high-gain high-voltage dc–dc converters using multiple modules of single-switch single-inductor transformerless converters. Results for low-voltage experimental prototypes show gains of up to 29 p.u. and demonstrate the potential of the approach as high-gain dc–dc converters for offshore wind farms. This paper then demonstrates the viability of multiple-module converters compared to a conventional high-voltage dc converter and a theoretical full-bridge converter due to fewer devices and valves, comparable isolation levels, and ease of interleaving for increased reliability. [ABSTRACT FROM AUTHOR]