Small-Signal Modeling and Control of a Boost Integrated LLC Resonant Converter

The boost integrated LLC (BI-LLC) resonant converter has less switches and higher conversion efficiency compared with the traditional two-stage cascade converter. By employing fixed-frequency pulse width modulation (PWM) to control output voltage, the gain range and optimal operation area can be easily regulated. However, small-signal modeling of this topology is rarely discussed, and the design of control system is not specific. In this paper, the small-signal model of BI-LLC resonant converter is derived using both state space averaging (SSA) method and extended describing function (EDF) method. According to the obtained small-signal model, a feasible PI controller is designed and applied. Finally, the accuracy of the small-signal model and the performance of the controller is verified by simulation.