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Conventional modular multilevel converters (MMCs) are promising converters for high-voltage high-power applications. Unlike DC-AC conversion, DC-DC conversion of MMCs suffers from unbalanced capacitor voltages due to the energy drift problem. In this study, a new modular DC-DC converter is proposed, which consists of front-end half-bridge MMC with half-bridge submodules followed by full-bridge MMC with full-bridge submodules. The proposed modular multilevel DC-DC converter can be used effectively for connecting two different DC voltage levels in high-/medium-voltage DC grids. The proposed architecture provides successful DC-DC conversion with balanced capacitor voltages throughout the arm interchange concept. It also provides a high conversion ratio, bidirectional power flow, low losses, low current stresses, reduced number of submodules, and DC fault blocking capability. Detailed illustration, operational concept, and design of the proposed architecture with the arm interchange concept are presented. Simulation results for a high-voltage high-power DC-DC converter with the suggested approach are presented to demonstrate the system performance during different normal as well as abnormal operating conditions. Finally, a scaled-down prototype has been implemented for validation. The extracted simulation and experimental results elucidate the presented claims. [ABSTRACT FROM AUTHOR]