A Bidirectional Fixed‐Frequency Resonant Converter Using on Bridge‐Leg Voltage Control

ABSTRACT This paper proposes a bidirectional resonant converter with fixed‐frequency LLC operation, in which the bridge‐leg voltage is actively regulated to interface a DC bus and an energy storage system. The converter integrates a bidirectional buck/boost stage in series with one bridge arm of a bidirectional LLC resonant converter. By controlling the bridge‐leg voltage via the buck/boost stage, the system enables output‐voltage regulation while maintaining constant‐frequency LLC operation. The buck/boost stage operates in a variable‐frequency overcritical conduction mode (OCRM), which ensures zero‐voltage switching (ZVS) and reduces circulating current–related losses, thereby improving overall efficiency. A 500‐W experimental prototype with a 40‐ to 60‐V low‐voltage side and a 400‐V high‐voltage side was built to validate the concept. The converter achieves a peak efficiency of 96.8 in forward operation and 97 in reverse operation.