Fixed-Frequency-Based Continuous Topology-Morphing Control for CLLLC Resonant Converters

With the rapid development of electric vehicles and renewable energy technologies, research on wide voltage gain techniques for bidirectional converters has attracted significant attention. This paper addresses the technical bottleneck of limited voltage gain adjustment range in bidirectional CLLLC resonant converters, particularly the flat gain characteristics in the aboveresonance operating region, by proposing a resonant converter control strategy based on hybrid bridge-arm structure. The inverter-side switching network can operate in three configurations: half-bridge structure, full-bridge structure, and full-halfbridge structure. Through effective coordination of these three configurations, the step-down capability of the resonant converter can be significantly enhanced while maintaining fixed switching frequency. The proposed strategy requires no additional components and effectively avoids the issue of wide-range sudden changes in switching frequency during full-bridge/half-bridge transitions encountered in conventional solutions. Furthermore, multiple parameters are introduced to derive the voltage gain and loss distribution of the proposed control method, with analysis conducted on its extensibility to other bridge-arm configurations. Finally, the feasibility of the proposed control method is experimentally verified using a 10kW prototype