Maximum Efficiency Point Tracking Technique for LLC-Based PEV Chargers Through Variable DC Link Control

In this paper, a variable dc link technique is proposed to track the maximum efficiency point of the LLC converter for plug-in electric vehicle battery-charging applications over a wide battery state-of-charge (SOC) range. With the proposed variable dc link control approach, the dc link voltage follows the battery pack voltage. The operating point of the LLC converter is always constrained to the proximity of the primary resonant frequency so that the circulating current in the magnetizing inductor and the turning-off currents of MOSFETs are minimized. In comparison with conventional approaches, the proposed variable dc link voltage methodology demonstrates efficiency improvement across the wide SOC range. Efficiency improvements of 2.1% at the heaviest load condition and 9.1% at the lightest load condition are demonstrated.