Magnetic-Coupling Current-Balancing Cells Based Input-Parallel Output-Parallel LLC Resonant Converter Modules for High-Frequency Isolation of DC Distribution Systems

The input-parallel output-parallel (IPOP) dc-dc converters are suitable for low-voltage and high-current applications, especially using high-frequency isolation instead of traditional line-frequency transformer for ac-dc converters in dc distribution. Compared to the existing closed-loop control for IPOP dc-dc converters, the magnetic-coupling current-balancing (MC-CB) cells based IPOP LLC resonant converter modules are proposed in this paper, which can realize the IPOP system work under open-loop operating condition naturally. The LLC modules can be used as a high-frequency isolation dc transformer operating under the quasi-resonant mode, which can achieve zero-voltage switching (ZVS) for inverter side and zero-current switching (ZCS) for rectifier side ensuring high power density and high efficiency. The proposed MC-CB cells for IPOP LLC resonant converter modules can adaptively ensure both the input-current sharing (ICS) and the output-current sharing (OCS) among constituent modules to make the IPOP system operate stably. Additionally, the steady-state and dynamic-state current-sharing performance of MC-CB cells for the IPOP converter system are analyzed based on a magnetic model. In the end, a hardware prototype has been designed and tested. The experimental results have verified the validity and performance of the proposed MC-CB cells for the IPOP LLC resonant converter modules.