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Design of High-density Isolated Bi-directional Soft-switching Resonant DC-DC Converter with Partial Power Processing

Circuit Diagram
Fig.1. (a) Circuit Diagram
The demand for high-density, high-efficiency bi-directional battery chargers is driven by the fast development of an energy storage system in renewable energy system, micro-grid, and transportation electrification. An isolated dc-dc converter that interfaces a battery with a variable voltage range is one of the critical components. An input-parallel output-series (IPOS) partial power (PP) converter is considered a promising high-efficiency, high density solution because only a fraction of power is processed via multi-stage converters to regulate output voltage. However, due to the tight coupling between two dc transformers (DCXs), the design of the PP converter is complicated. To solve this issue, an overall design procedure for a bi-directional soft-switching resonant type PP converter is proposed. In the parameters design part, a decoupled design method is proposed to simplify the DCXs design. With this method, two DCXs can be designed separately and a typical optimization method can be easily applied. As for the hardware design part, to minimize the ac loop inductance and resistance, a 2-directions (2-D) flux cancellation method and an intra-leaving winding structure are proposed for circuit layout and HF transformer to obtain high operation efficiency and power density. Finally, the whole design procedure is verified by an 18 kW rated, 25 kW peak, prototype operating at 500 kHz. The realized PP converter features a peak efficiency of 98. 8% and a power density of 142 W/in3 as shown in Fig. 1.
Design Procedure
Fig.1. (b) Design Procedure
18 kW Prototype
Fig.1. (c) 18 kW Prototype
Total Efficiency.
Fig.1. (d) Total Efficiency.

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