Hybrid Control and Optimal Parameters Design for Wide Input Range Series Half-Bridge Three-Level <i>LLC</i> Resonant Converter in AUV Power Supply System

Power supply system significantly impact the endurance capabilities and operational reliability of unmanned underwater vehicles (UUVs). Due to the battery-based power supply architecture of UUV systems, input voltage fluctuations are inherent to the system, making conventional variable frequency modulation (VFM) ineffective in maintaining optimal efficiency across the full operating range. To address this issue, a VFM plus phase shift modulation (PSM) hybrid control strategy based on simplified state-plane analysis is proposed in this article. This approach facilitates smooth transitions between VFM and PSM while maintaining robust dynamic response. Furthermore, an optimal parameter design method for implementing the hybrid control strategy has been developed, and a voltage balancing method to resolve the inherent input capacitor voltage imbalance in series half bridge three level (SHBTL) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters has been introduced. The efficacy of the proposed methods is validated through experimental testing on a 3 kW prototype. Experimental results demonstrate superior performance in terms of efficiency, dynamic response, and voltage balancing across the entire operational range.