Adaptive Main-Module-Based Partial Power Processing for Wide-Range Operation of Current-Source Driven Modular MVDC

Constant current (CC) is widely employed in submarine observatory systems to transmit power over several thousand kilometers to the seabed, due to its robustness against cable impedance and short-circuit faults. Given the low current required to minimize transmission losses, a current-source-driven modular medium-voltage DC/DC converter (MVDC) is necessary to convert CC to constant voltage (CV) for powering the observatory equipment. However, this conversion faces challenges related to achieving a high voltage transfer ratio while maintaining efficiency over a wide load range. In this paper, an adaptive main-module-based partial power processing (PPP) approach is presented for the current-source driven modular MVDC. Unlike traditional strategies, where each module has the same droop characteristics, leading to a narrow voltage gain range and low efficiency under light load conditions, the proposed method features voltage-current droop curves that are different for each module and can be continuously arranged. The main module can be adaptive set to operate or bypass depending on the load condition, enabling a wide voltage gain range from 0 to the rated value, while maintaining high efficiency under light load conditions. Moreover, all modules can function flexibly, either as compensation or as main units, ensuring high redundancy. Finally, a CC-to-CV prototype consisting of four modules with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{1}~A$</tex-math></inline-formula> input current, 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{1.5}~kV$</tex-math></inline-formula> input voltage and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{375}~V/1.5~kW$</tex-math></inline-formula> output, is built to validate the proposed approach.