Wide Voltage Gain Control For Three-level LLC Resonant Converter

DC-DC converter is an important factor affecting the efficiency and volume of the whole renewable energy system.So it needs to meet the requirements of isolation,wide gain range,high frequency and high efficiency.To solve these problems,a three-level wide range LLC topology is proposed,and a corresponding wide range control strategy is proposed for the topology.The converter has the advantages of simple parameter design,wide gain range and whole load range soft switch at constant frequency.Firstly,this paper mainly introduces the circuit structure and working modes of the topology and verified the proposed structure by Matlab/Simulink.On this basis,the asynchronous working mode with high loss in dual-channel working path is excluded,which lays a foundation for the design of the control strategy.Then,based on the fundamental harmonic analysis model,the gain expression of the converter is deduced,and the gain curve of each working path is plotted.By establishing the control strategy of the corresponding three-level wide range LLC converter,the smooth gain transition between each working path of the converter is realized.Secondly,the resonant current RMS formula of the three-level wide range LLC converter is derived,and the key parameters of the circuit are determined according to the soft switching conditions of the converter.Based on these parameters,the devices used in the converter are selected and designed.Finally,a three-level wide range LLC converter prototype is designed with Ga NFET.The parameter of protype has power of 200 W,input voltage of 200 V and output voltage range of 6-20 V.The correctness of the proposed converter and control strategy is further verified by the validation of the three working paths and control strategy.The efficiency of the prototype is compared with that of the traditional LLC converter,and the results show the proposed converter maintains relatively consistent efficiency in a wide working range.