A Soft Start-up Strategy of LLC Resonant Converter Based on Event Trigger Control

Soft start-up is necessary for LLC converter to avoid high inrush current. In this paper, an event trigger control (ETC) method for the start-up process is proposed. It firstly establishes the piecewise state space model, which can reveal the relationship between resonant capacitor voltage and resonant current during start-up. And then an event-trigger function is established to control the switching state according to the model. Experimental results verify that the proposed method can successfully limit the peak current to be the pre-setting current during the start-up process and that the build-up time of output voltage can be reduced. The biggest advantage of the ETC method is smoothly transition between the start-up and steady state.