This paper presents the operation, analysis, design, simulation, and experimental results for a proposed Dual-Transformer DC-DC Resonant Converter (DTRC). A three-arm bridge is employed on the input side and an H-type bridge is employed on the output side of the DTRC, and the two bridges are connected with two high-frequency (HF) transformers. By optimizing the ratio k of the two HF transformers, the proposed DTRC has a lower boundary power for losing zero-voltage switching (ZVS). That means the DTRC has a wider ZVS operation range and lower switching loss when compared with a traditional soft-switching pulse width modulation (PWM) resonant converter. The operation principle, power transfer, ZVS characteristics, and design procedures are analyzed in detail. Both simulation and experimental results prove the feasibility and superiority of the proposed Dual-Transformer DC-DC Resonant Converter.

To overcome the weakness of the narrow conversion gain of dual bridge resonant converter, a half-dual bridge resonant converter (H-DBRC) with voltage match modulation (VMM) is proposed and implemented for wide voltage range applications. The H-DBRC, including a full bridge on the primary side and a half bridge on the secondary side, is adopted to realize the bidirectional power flow and wide voltage operation. Owing to the synergy between the H-DBRC structure and VMM strategy, the converter can operate in full-bridge state and half-bridge state with maximized ZVS (zero-voltage switching) operation and minimized circulating current. The steady-state analysis is performed and the solutions for both forward and backward modes could be obtained uniformly by using the fundamental harmonics approximation approach. The soft-switching characteristics, implementation process and design example are analyzed in detail. Finally, to confirm the theoretical analysis and feasibility, both simulation and experimental verifications are demonstrated in this paper. Since the converter consistently achieves voltage-matching operation, the optimal ZVS range can be obtained when the voltage gain M is between 0.5 to 1. Moreover, the economic cost and control complexity are greatly reduced because only six switches are required in the converter.

In this paper, an isolated bidirectional three-level neutral-point-clamped dual-bridge series resonant converter (3L-NPC-DBSRC) is proposed for the wide-voltage range dc-dc applications in energy storage systems, which consists of a neutral-point-clamped (NPC) three-level bridge on the primary side, a LC-type series-resonant tank, and a full bridge on the secondary side. The proposed 3L-NPC-DBSRC is able to realize increased voltage gain and reduced harmonic components in the primary-side high-frequency-link voltages and currents. By using fundamental harmonic analysis (FHA), the steady-state operation principles of 3L-NPC-DBSRC are thoroughly analyzed in both forward and backward power-flow directions. Furthermore, a control algorithm based on globally optimal condition (GOC) is proposed for achieving zero-voltage switching (ZVS) in all switches and minimum root-mean-square (RMS) ac-link current, thus simultaneously reducing the switching and conduction power losses, and eventually resulting in high overall efficiency. Finally, to verify the effectiveness of the proposed 3L-NPC-DBSRC and its control method, both simulations and experiments are carried out on a designed example.

The DC-DC converter is a crucial component of an electric vehicle (EV) charger, and its performance is essential for the charging speed and driving range of EVs. Despite recent advancements in converter topology and modulation techniques, enhancing both switching and conduction losses in dual active bridge (DAB) converters continues to be challenging. This paper introduces a novel dual unbalanced modulation (DUM) for EV chargers. The DUM strategy, when combined with a CLCLC-type immittance resonant DAB (IRDAB) converter, can simultaneously reduce the switching and conduction losses. When the rated output power exceeds 25%, the DUM strategy operates in full-bridge mode, achieving zero-voltage switching (ZVS) operation of all switches, minimizing backflow power on both sides, and maintaining near-minimum root mean square (RMS) currents. For output power rated below 25%, the DUM strategy shifts to half-bridge mode. This mode slightly increases the RMS currents, yet it still ensures ZVS operation of all switches and minimum backflow power on both sides. Theoretical analysis and experimental results demonstrate that, when compared to conventional modulation strategies, DUM strategy maintains the highest efficiency across the entire load range.