Backward Step-Up Control for Bidirectional LLC Resonant Converter Based on Dual Phase Shifting

The LLC resonant converter is known for its simple structure and excellent soft-switching characteristics. However, it faces challenges in achieving a normalized voltage gain higher than one in the backward operation. To address this drawback, a control strategy for enhancing voltage regulation is suggested This strategy involves phase shifting the inverter switch to the diagonal position and introducing a phase shift between the inverter and rectifier switches. By implementing these phase shifts, the resonant circuit stores a large amount of energy, which is then transmitted to the load, enabling the realization of the control strategy while maintaining soft switching characteristics for both switches. This paper thoroughly analyzes the working principle of the bidirectional LLC resonant converter and presents the backward step-up control strategy. Simulation results demonstrate that this control strategy not only achieves a significantly higher normalized voltage gain in reverse operation, but also ensures simultaneous soft switching of the inverter and rectifier switches, leading to improved efficiency. To validate the proposed method, a prototype is constructed and tested.