A Partial-Power Regulated Hybrid Modular DC-DC Converter to Interconnect MVDC and LVDC Grids

High-power modular dc-dc converters are key enabling components for interconnection of MVDC and LVDC grids, for which both the efficiency and controllability are of great importance. Although the state-of-the-art modular dual-active bridge (DAB) dc-dc converter presents a high controllability with the soft-switching turn-on operation, the peak efficiency is ultimately limited by turn-off losses of semiconductor devices. On the other hand, unregulated series resonant converters (SRCs) operating under the resonant condition can realize a very high efficiency, but presents no controllability of the dc voltage. This paper presents a novel modular dc-dc converter topology with the input-series-output-parallel (ISOP) configuration, which combines SRCs as the majority modules for the bulky power transfer and only a small number of DAB converter modules for the dc-voltage control. Benefiting from the hybrid circuit topology, the proposed converter can achieve a higher efficiency than the modular DAB converter with a reduced complexity in the communication and control, while maintaining the controllability of the dc voltage. The operation principle of this topology and optimization procedure of key design parameters are presented. Finally, the performance of the proposed hybrid modular dc-dc converter is verified by both simulative studies and experiments of a laboratory converter prototype.