Due to the advantages of low cost and high-reliability, the bidirectional asymmetric power flow (BAPF) DC/DC converters are regarded as the competitive DC/DC candidate for power electronics transformers (PETs) in low-penetration renewable energy systems. For this converter, this paper researches the active operation mode and analyzes the circulating current caused by the parallel connection of two full bridges on the low-voltage (LV) side. Based on that, the circulating current suppression method based on extended-phase-shift (EPS) modulation is proposed in the BAFP converters. The simulation results clearly verify the correctness of theoretical analysis and the effectiveness of the proposed method.

As the core equipment for interconnection and energy transmission of DC power systems with different voltage levels, the improvement of DC transformers' performances has an extremely important impact on the development and application of DC power system. Given the asymmetric characteristics of DCTs' power flow in low-penetration renewable energy networks, a hybrid isolated DC-DC converter with bidirectional asymmetric power flow is proposed. The proposed converter topology can not only satisfy the power flow requirements, but also reduce the number of active power semiconductor devices, decrease the system cost and improve the converter capability. For the proposed converter, the power transfer modes are studied, the operating principles of the converter in different modes are analyzed. Finally, the feasibility of the proposed topology and the correctness of the theoretical analysis are verified by simulation results.

In low-penetration-renewable-energy DC distribution networks, the bidirectional power flows in power electronic transformers are asymmetric. Based on the above power transmission characteristics of power electronic transformers, this article proposes an isolated DC/DC converter topology. The proposed topology not only meets with the power transmission requirements, but also reduces the active device quota and system cost, increases the number of power paths and improves the power density. The operating principles, soft switching characteristics, return power characteristics and device stress of the proposed converter topology are analyzed in detail. The feasibility of the proposed topology is verified by simulation results.

In distribution networks integrated distributed generation, the forward and reverse power of power electronic transformers may be unequal. For this regard, this paper proposes a bidirectional asymmetric-power-flow isolated DC/DC (BAI-DC/DC) converter topology, which not only meets the requirements of bidirectional asymmetric power transmission, but also reduces the active device rating and increases the number of power paths, which can decrease system cost and improve system reliability. Simulation and preliminary experimental results verify the feasibility of the proposed topology.