A Partial-Power-Processed CLLC-DAB DC/DC Transformer with Voltage Self-Balancing Capability for Bipolar LVDC Distribution Systems

The bipolar low-voltage DC (LVDC) distribution system is an excellent approach to facilitate the flexibility and reliability of DC microgrids. This paper proposes a DC-DC transformer with bipolar multi-voltage output and self-balancing property. First, this configuration combines the efficient CLLC with the flexible DAB, in which the main power transferring via the CLLC and the DAB carrying partial power. Moreover, to achieve self-balancing, a pair of resonant LC branches are implemented on the secondary side of the CLLC and DAB converters, forming a new series resonant dual-active-half-bridge (SR-DHB) converter that enables partial self-balancing. Additionally, following the principle of volt-second balancing, inductors and capacitors can be added to the first/second arm of secondary side, completing the self-balancing property. Furthermore, precise regulation of output voltage can be achieved by merely adjusting the phase shift angle of the DAB. To improve the system’s dynamic response, a model-based voltage control method is proposed. Lastly, simulations reveal outputs of ± 750 V and ± 375 V, and experiments are conducted to prove the proposed scheme.