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DC­DC converters with a high voltage and a high power rating are identified as a key element and enabling technology for these future grids. Thus, the vision of the future electrical grid seems to point towards a new paradigm: a meshed grid that combines the existing AC system with a multi­terminal DC transmission grid. Finally, the simulation and experimental results are verified to evaluate the effectiveness of the proposed DC-DC MMC.ĭue to the renewable energy generation expansion experimented over the last decades and to the constant increase of energy demand, it appears that the current electrical grid will not be sufficient to answer correctly the future needs and requirements. Through theoretical analysis and a control strategy, the proposed DC-DC MMC has been analyzed comprehensively. The middle cells of the proposed DC-DC MMC are supplied with the function of the active filter, which enables the DC-DC MMC system to escape the bulky LC components. On the other hand, through appropriate control of the middle cells, compensated components can be developed to eliminate the undesirable voltages on the output DC side. On the one hand, the alternative currents, used for balancing the SM capacitor voltages, are arranged for flowing only within the phase legs of the proposed DC-DC MMC without disturbing the input current. It is intended to achieve DC voltage conversion without adopting bulky passive LC filters. For interconnecting different DC voltages in medium-voltage applications, this paper presents a non-isolated DC-DC MMC equipped with the proposed middle cells. However, this solution is based on the cost of adopting the bulky LC filter components. Typically, the alternative voltages and currents should be injected to achieve SM capacitor voltage balance in the DC-DC MMC.

This is mainly caused by no balanced alternative powers being used for balancing SM capacitor voltages, which can be absorbed from the input or output DC sides of the converter. Unlike the modular multilevel converter (MMC) topology operated under the rectifier or inverter modes, control of the balanced state for the submodule (SM) capacitor voltage has emerged as the key issue for DC-DC MMCs.