Short-Circuit Current Control Strategy for Full-bridge LLC Converter

The short circuit problem is a difficult issue in LLC converter. This paper derives the state-plane trajectory of the full-bridge LLC converter based on state-plane analysis and the characteristics of the trajectory performance are provided under short circuit mode. Two types of control scheme for power switches, respectively based on phase-shift frequency-boost and frequency-drop method, are deduced for full-bridge LLC converter under short circuit mode. By designing the trajectory of the state variables, two schemes would achieve controllable short current output while maintain the advantage of ZVS. Comparing with traditional solution with increasing switching frequency only, the concept presented in this paper would bring better short current limitation performance. The simulation and experiment results show agreement with theoretical analysis.