Design and Implementation of an 18-kW 500-kHz 98.8% Efficiency High-Density Battery Charger With Partial Power Processing

The demand for high-density, high-efficiency bidirectional battery chargers is driven by the fast development of energy storage system in renewable energy system, microgrid, and transportation electrification. Isolated dc–dc converter that interfaces a battery with a variable voltage range is one of the critical components. 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 multistage converters to regulate the output voltage. However, due to the tight coupling between two dc transformers (DCXs), the design of PP converter is complicated. To solve this issue, an overall design procedure for a bidirectional 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 two-direction (2-D) flux cancellation method and an “intraleaving” winding structure are proposed for circuit layout and high-frequency (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. This article is accompanied by two videos demonstrating the dynamic voltage regulation test and the efficiency measurement.