Research Of A Wide Input Dual-bridge Llc Resonant Converter

Many applications require the power conversion circuits to operate under the condition of wide input voltage range, which puts forward higher requirement on the power converters that can cope with a wide input voltage range while maintaining high efficiency. However, the conventional half-bridge(HB) or full-bridge(FB) LLC converter is not suitable for wide input voltage applications.This paper proposes a novel fixed-frequency dual-bridge(DB) LLC resonant converter for wide input applications. The topology can be seen as a combination of the HB LLC circuit and the FB LLC circuit. The voltage of the resonant tank can be changed by controlling the percentage of operating time of the FB and HB during a switching circle, and then the output voltage can be regulated. The fixed-frequency pulse width modulation(PWM) control is employed and a range of twice the minimum input voltage can be covered. And the switching frequency equals to the resonant frequency, which facilitates the design of magnetic elements. Unlike the LLC resonant converters which are controlled by traditional pulse frequency modulation(PFM), the voltage gain range is independent of the quality factor. Moreover, the magnetizing inductor has little influence on the voltage gain, which means that the parameter design process can be simplified, and the magnetizing inductor can be designed as large as possible to reduce the conduction loss. Over the full load range, zero voltage switching(ZVS) and zero current switching(ZCS) can be achieved for primary switches and secondary rectifier diodes, respectively, which significantly decreases the switching loss and the reverse recovery loss.The topology of the DB LLC resonant converter and modulation strategy are first presented. The operating process and phase plane analysis are also disscused. Then, the voltage gain is calculated and the gain characteristics of the converter are analysized. By comparing the gain characteristics, the advantages of the DB LLC converter are shown. After that, hybrid modulation strategies to further broaden the input voltage range are proposed and the corresponding modulation strategies are introduced. Detailed analysis on the ZVS and resonant parameters are given as well. And combined with the above analysis, the design of resonant parameters is presented. Finally, all theoretical analysis and characteristics are verified by experiment on a 120V-240 V input 24V/20 A output converter prototype. Based on the prototype, the experiment result about using PFM+PWM modulation strategy to further broaden the input voltage range is also presented.