A 3,6 kW Single-Stage LLC Converter Operating in Half-Bridge, Full-Bridge and Phase-Shift Mode for Automotive Onboard DC-DC Conversion

Automotive DC-DC converters linking the traction battery to the auxiliary battery are characterized by the wide input and output voltage ranges resulting from the varying state-of-charge of the traction and auxiliary battery. The wide voltage transfer ratio needs to be covered for the entire load range conventionally requiring two-stage converter architectures. Considering a less complex single-stage solution potentially enabling cost and weight advantages, traditional LLC converters are unsuitable topologies since it results in a too wide operating frequency range. Most alternative topology candidates show comparable difficulties. To overcome this issue, the gain range of the LLC with full-bridge inverter can be extended by operation in half-bridge mode for low voltage transfer ratios. Phase-shift operation is utilized for intermediate gains and low loads. This paper describes a detailed design methodology for the resonant tank. The experimental results with a peak efficiency of 96.5 % and a power density of 2.1 kW/l prove the proposed concept.