Research On Wide Voltage Gain Range Multi-element Resonant Converters

Wide voltage gain range DC/DC converters have been widely applied in many power systems, such as renewable power systems, battery chargers for electrical vehicles and power supplies for servers. Compared with conventional wide gain range converters, multi-element resonant converters, simply embedding a notch filter in the conventional LLC resonant tank, have the merits including simple topology and easy implemention.In this paper, firstly, the LCLCL converter, embedding the notch filter at primary side, is researched. The working principles and gain characteristics based on FHA analysis are analyzed in detail. Theoretical analysis show that the LCLCL converter can not only achieve wide gain range, but also can take advantage of third harmonics for power delivery and provide inherent current protection as well. To achieve high efficiency, the influences of the resonant tank parameters on the converter are analyzed and then the optimized design goal is determined. Based on the analysis, an optimized design method is proposed. Following the approach, a 3.3kW prototype is fabricated and tested in the lab and the experimental results have demonstrated the correctness of the theoretical analysis and parameters design.In order to be applied in applications with low-input and high-output voltages, the LLC-LC converter is proposed by embedding the notch filter at secondary side. Compared with LCLCL converter, the LLC-LC converter can provide higher voltage gain at resonant frequency and reduce RMS current as well as conduction losses associated with the notch filter. The working principles and gain characteristics are analyzed in detail and the similarities and differences of the two converters are discussed. Also, the key parameters design considerations are given. To verify the analysis, two 400 W prototypes based on the LLC-LC converter and LCLCL converter, respectively, are built and tested. The measured efficiencies numbers show that the LLC-LC converter is more suitable in voltage step-up applications.