Paralleling of LLC resonant converters using frequency controlled current balancing

Abstract

Paralleling of two LLC resonant converters leads to a significant reduction of current stress in the output filter capacitor, provided that the driving signals of both converters are of equal frequency and with constant phase shift of 90deg. However, non influenceable tolerances of the circuit elements, especially those of the resonant tank circuit, cause unbalanced power distribution between the paralleled converters, resulting in suboptimal circuit design. Frequency controlled current balancing is proposed as remedy in this paper, and prototype measurements are presented to demonstrate the functional capability.