Research On Bidirectional Full-bridge Four Element Resonant Converter

Bidirectional DC/DC converter is widely employed in new energy generation,uninterruptible power supply systems and electric vehicles because of the advantages of high power density,simple control and flexibility.There are many topologies and control methods of bidirectional DC / DC converters,each of which has its own advantages and disadvantages.Among them,bidirectional LLC resonant converters have features of high efficiency,soft switching and dual energy flow.Thus,it is widely used nowadays.However,there is a problem that the normalized voltage gain of LLC resonant converter is no more than one and it can not boost during reverse mode.In this dissertation,a new bidirectional full-bridge four element resonant converter is proposed.An auxiliary capacitor is added to T-4 LLC resonant converter.The reverse characteristic of T-4 LLC resonant converter is improved by using the characteristics of LCC resonant converter.It can realize the voltage up and down during forward and reverse mode.In this dissertation,the new resonant converter is taken as the research object.The operation principle of the proposed resonant converter is analyzed in detail.The fundamental equivalent method is used to research the proposed new resonant topology.The forward and reverse voltage gain formula and characteristic curves are obtained.The influence of different variables on the voltage gain is analyzed,then the voltage gain characteristics of the forward and reverse operation are obtained.It is proved theoretically that the proposed resonant converter can realize boost and buck operational function during forward and reverse directions.A wide range of voltage characteristic is obtained.The working characteristics of the proposed resonant converter under different frequencies are analyzed in detail,and the influence of different frequencies on the soft switching characteristics is analyzed.The soft switching characteristics of the proposed resonant converter are proved theoretically.According to the voltage gain characteristic curve,the parameters of the proposed resonant converter are designed.The timefrequency analysis of the proposed system is completed based on the extended description function method.The small signal model of the proposed resonant converter is established.Single zero and single pole compensation network and Pulse Frequency Modulation(PFM)control strategy are used to complete the closed-loop design.The simulation of the proposed resonant converter is conducted on the basis of theoretical analysis.The simulation results show that the normalized voltage gain of the proposed resonant converter can be greater than one during forward and reverse directions.Boost and buck operational function is realized.Then an experimental prototype is built for the experiment.The results show that the proposed resonant converter can achieve soft switching and has wide voltage range,which verifies the feasibility of the proposed resonant converter.