An Optimized Power Allocation Control Strategy for Efficiency Improvement of Hybrid DC--DC Converters

DC transformers (DCTs) are crucial for electrical isolation and voltage conversion in DC distribution grids. With the integration of distributed generation sources, conventional DCT topologies need to incorporate numerous active devices and auxiliary circuits to achieve bidirectional power transmission, resulting in high hardware costs and poor reliability. Therefore, in the scenarios of bidirectional asymmetric power flow (BAPF), the hybrid DC-DC converter that combines low-cost, high-capacity diode bridges with actively controlled small-capacity active bridges are receiving attention due to reducing the prominent cost and reliability issues. Regarding to the hybrid topology, this paper further establishes a unified power loss model by integrating switching characteristics under extended-phase-shift (EPS) modulation, together with consideration of feasible operating region. On this basis, a power allocation control strategy is proposed through optimization of phase-shift anglesD1andD2to minimize power losses. The theoretical analysis shows efficiency improvements of 0.31%–1.05% in different operating modes, while experimental results on a prototype demonstrate efficiency improvements of 2.39%–7.65%. These results validate the proposed unified power loss model and loss-oriented power allocation strategy for hybrid DCTs under BAPF within the scope of the theoretical analysis and prototype experiments.