Dual Interleaved 3.6 kW LLC Converter Operating in Half-Bridge, Full-Bridge and Phase-Shift Mode as a Single-Stage Architecture of an Automotive On-Board DC-DC Converter

Abstract

On-board DC-DC converters are required to operate over a wide input and output voltage range depending on the state-of-charge of the input and output battery. Conventionally, the power transfer between these batteries is enabled by a two-stage converter concept where a galvanically-coupled DC-DC converter regulates the input voltage of the second-stage galvanically-isolated DC-DC converter. This paper presents a single-stage interleaved 3.6 kW LLC converter for this purpose. While LLC converters are usually not suitable for such a wide voltage range, this LLC converter is operated in full-bridge mode for large gains and in half-bridge mode for low gains. For intermediate gains and loads, the LLC makes use of phase-shift mode. To operate the interleaved LLCs at an equal switching frequency enabling output current ripple cancellation, again phase-shift mode is utilized to balance the output currents during full-bridge mode while asymmetrical duty-cycle mode is proposed for current balancing during half-bridge mode. This paper analyzes the converter design for these modes of operation. A 3.6 kW-prototype employing Si-superjunction MOSFETs achieves a power density of 2.1 kW/1. The maximum efficiency reaches 96.5 % while for most operating points it is kept well above 90 %.