High-efficiency And High-power Density For Building DC Microgrid Dc/DC Converter Research

The LLC resonant circuit topology is extensively used in the research of high-efficiency and high-power density DC/DC converters because of the characteristics of soft-switching operation in the full load range.In the field of community-level building DC microgrid,it is important to examine the high-efficiency and high-power density DC/DC converters on the user-side for the high requirements of power quality and power supply reliability.Based on the LLC circuit topology,the design method and optimization strategy of a novel integrated magnetic for high-efficiency and high-power density DC converter are proposed.The key issues of structural integration,inductor controllability principle and losses of the novel integrated magnetic are analyzed;A system-level optimization strategy for DC/DC converters is proposed.The premise and process of coupling the numerical model of the circuit and the finite element model of the novel integrated magnetic are described.Afterwards,the optimization results of the overall converter are presented.This study adopts the design method of matrix transformer with four 2:1:1 transformer sets to improve the efficiency of the converter.The main work of this dissertation is shown as follows:First,we analyze the conditions of soft-switching operation in the full load range of LLC.The operation of the LLC circuit topology at a switching frequency slightly below the resonant frequency operating condition is described.The design requirements of the converter for this topic are 400V input,48V output,and 3k W.For the requirements of high-efficiency and high-power density DC converter on magnetic components,this study adopts the design method of matrix transformer with four 2:1:1 transformer sets to improve the efficiency of the converter.In this paper,a new magnetic integration component design method and optimization strategy for high-efficiency and high-power density DC/DC converters are proposed based on the LLC circuit topology.Key issues such as structural integration of the new magnetic integration component,controllable inductance principle,and losses are analyzed.On this basis,a system-level optimization strategy for DC/DC converters is proposed,and the coupling premise and process of the circuit numerical model and the finite element model of the new magnetic integration component are elaborated,and the overall optimization results of the converter are presented.The resonant inductor and matrix transformer are proposed as the novel integrated magnetic design method.The inductor controllability principle is analyzed through the magnetic circuit model.The core loss problem of the novel integrated magnetic design method is derived for its influencing factors.The optimization strategy of minimizing the core loss of the novel integrated magnetic instantly when the inductor flux component is equal to that of the transformer flux component is proposed.By adjusting the inductor and transformer core cross section S_L,S_T and air gap l _L,l _T to achieve B_L=B_T.To address the optimization difficulties caused by multi-parameter variables,S_L,S_T,l _L,and l _T are expressed in terms of transformer core radius Core＿r and core length Core＿a.The number of finite element scan parameters is reduced.To address the problem that single module optimization is not effective for the overall optimization of the converter,a system-level optimization strategy for DC/DC converter is proposed.The converter circuit model is coupled into the novel integrated magnetic finite model.The loss results of the converter are obtained through finite element calculations.The optimization of the converter is completed by selecting the design parameters with the lowest losses that match the design in the loss results.This method further improves the efficiency and power density of the converter.Finally,the novel integrated magnet LLC resonant converter prototype with 400V input,48V output and 3k W is built based on the novel integrated magnetic.The measured leakage inductance of the novel integrated magnetic is 2.68%compared to the design value.The error of the measured value of excitation inductance compared to the design value is 3.21%.The errors are within 5%.The inductor core loss and transformer core loss of the novel integrated magnetic are equal and consistent with the theory.The power density of the novel integrated magnet LLC resonant converter is 5.36W/cm~3,and the full load efficiency reaches 98.17%.Achieving soft-switching operation over a wide load range and stable 48VDC output.The validity and correctness of the novel integrated magnet LLC resonant converter design has been verified.The setup meets the design specifications for high-efficiency and high-power density DC/DC converters.