Enhancing Efficiency in Bidirectional CLLC Resonant Converters

The bidirectional CLLC resonant converter is a sophisticated power electronics system created to enable efficient energy transfer between two voltage sources and is commonly utilized in scenarios demanding bidirectional power flow, such as vehicle chargers. This paper presents a comprehensive examination of the bidirectional CLLC resonant converter, focusing on its setup, operational principles, and an innovative hybrid control technique that integrates frequency control and phase-shift approaches. The bidirectional CLLC resonant converter is designed with full-bridge configurations on both the primary and secondary sides, ensuring balance and enabling a smooth energy transfer in both directions. The key components of the system include the switching elements, body diodes, output capacitors, high-frequency transformers, resonant inductances, and capacitors. The ratio of turns in the transformer and excitation inductance is pivotal in determining the converter's performance. This study explores the operational principles of frequency control by employing an underlying examination to comprehend the operational properties of the converter. It discusses the influence of critical parameters, such as the inductance coefficient (k) and the quality factor (Q), on the voltage gain, providing an in-depth analysis of their impact under different conditions. A significant portion of this study is dedicated to an innovative hybrid control strategy that merges phase-shift control and frequency control methods. This strategy overcomes the limitations of using either control method independently by broadening the range of the voltage gain and developing the overall performance and stability of the converter. The hybrid control strategy, which comprises the steady current and voltage charging phases, is particularly advantageous during the vehicle charging process.