Extreme start-up response of LLC converters using average geometric control

Resonant power converters have become ubiquitous to efficiently process electrical energy, however, their complicated structure challenges linear controllers in anticipating their large signal performance. Since small-signal modeling techniques do not provide sufficient information regarding the large signal behavior of power converters, nonlinear geometric controllers can be employed to tackle the poor large signal dynamic response. In this paper, a nonlinear controller called the average geometric controller is introduced for the LLC converter with the ability of providing an extreme start-up dynamic response and eliminate overshoot. A novel average large signal model is developed and serves as the foundations to develop the average geometric controller for LLC converters. The average large signal model significantly simplifies the large-signal behavior analysis and results in obtaining the average circular trajectories of the LLC converter. In order to validate the theoretical analysis, experimental and simulation results of a 500W prototype LLC converter employing the average geometric controller are presented. The experimental results show a significant increase in start-up performance while the overshoot is eliminated.