Systematic Review of the Design Process for LLC Resonant Converters: Modelling, Voltage Gain Range, and Efficiency Optimization

ABSTRACT The proliferation of power conversion requirements in renewable energy systems and rail transit systems demands LLC resonant converters with enhanced voltage adaptability and efficiency. This review systematically studies three elements in the design progress for LLC resonant converters: (1) modelling methodologies; (2) extended voltage gain range solutions; and (3) efficiency optimization strategies. Existing modelling approaches, including time‐domain analysis (TDA), fundamental harmonic approximation (FHA), and hybrid analytical methods, are systematically compared, revealing inherent limitations in predicting parasitic parameter effects and mode transition boundaries under high voltage operation. For voltage gain extension, methods are categorized into topology modifications (e.g., dual bridge architectures, resonant tank morphing) and control‐based solutions (e.g., hybrid frequency‐pulse width modulation), with detailed analyses of their impacts on component stress and dynamic stability. Efficiency optimization is analysed through three key approaches: light‐load efficiency improvement, resonant frequency tracking techniques for loss minimization, and synchronous rectification implementations. By comparing the key parameters with the multi‐objective optimization framework, the application boundaries of the existing design methods are summarized, and the current challenges and future development directions in this field are discussed.