Backflow Power Optimization for LLC Resonant Converter with Phase Volume Analysis Method

LLC converters are extensively employed in the industry. However, when LLC converter is controlled by frequency conversion, there exists a phase difference between the current and voltage, resulting in backflow power within the converter. The presence and increase of backflow power contribute to higher through-state losses and reduced efficiency of the converter. The existing literature often improves the backflow power by optimizing resonant parameters, which cannot be applied to already operational converters. To enhance the efficiency of the LLC converter, this paper proposes a method for optimizing the backflow power of a full bridge LLC converter. By establishing a unified power phase quantity model, the phase angle between the current and voltage is controlled using the phase quantity analysis method. This ensures that the input-side voltage transitions from the original two-level positive and negative states to three-level positive-negative-zero state. Consequently, the current zero crossing point aligns with the voltage zero level, facilitating a reduction in backflow power, alleviating current stress, and enhancing the converter's efficiency. Finally, simulation results based on Simulink validate the accuracy of the theoretical analysis and demonstrate the feasibility of the proposed strategy.