Abstract: Due to the wide switching frequency range and low overall efficiency, traditional LLC resonant converters are not suitable for wide voltage gain applications such as photovoltaic energy storage system, this paper proposes a three-channel three-level wide voltage range LLC resonant converter. The proposed converter operates in dual-channel or three-channel modes, achieving a wide voltage range by combining the gains in different modes. It enables soft switching over the full voltage range, operates at a constant switching frequency, and offers advantages such as simple parameter and magnetic component design. The article details the working principles, gain characteristics, and the conditions for achieving zero voltage switching（ZVS）. Finally, A GaN-based 200 W prototype with 200 V input and 5-20 V output is designed and built to verify the feasibility of the proposed converter and the correctness of the theoretical analysis.