Research On Optimum Design Methodology Of High-Frequency Magnetic Components

Playing important roles in switch-mode power supplies,e.g.,galvanic isolation,voltage transformation and energy buffer,magnetic components,i.e.,transformers and inductors,are the key components influencing the efficiency,volume and power density of the converters.With the application of wide-band-gap devices,such as Ga N HEMTs and Si C MOSFETs,the switching frequency of the converters are increased,which makes the impact of the design accuracy of magnetic components on the performance of converters more remarkable.Reported optimum design methodologies of high-frequency magnetic components are only applicable in particular cases and lack of generality due to the employment of complicated winding loss models.Moreover,with the neglect of the discreteness of design variables,the influence of eddy current loss and other factors,the calculation conditions are ideal,which makes the optimization results deviated from the optimum point.To address these issues,a winding loss modeling method with effective ac resistance factors is employed.The discreteness of design variables,e.g.,core size variables and number of turns,is considered.The local optimum design methods for conductor sizes,windings,air gaps,and cores are proposed respectively.The optimization objectives are the size and loss of magnetic components.A compositive optimum design methodology is finally given.Compared with reported design methodologies,the proposed methodology is more general and accurate.The main work and novelties of the thesis are summarized in the following:1)A state-of-art review of the design methods of high-frequency magnetic components are presented with the investigation of the design difficulties.It is clarified that because the constraints in the design process are ideal,the discreteness of design variables are ignored and so on,reported design methods have the possibilities to be improved in the generality and accuracy.2)An optimum conductor size design method for high-frequency magnetic components is proposed.The method takes into account the constraints on winding areas and conductor sizes.Reported design methods are usually aimed at a single winding.With the neglect of the constraints on winding areas and conductor sizes,the optimum objective is hard to be attained when the reported methods are applied.On the other hand,in the methods directly aimed at multi-winding magnetic components,the objective is the minimum dc resistance loss.However,a large amount of winding loss comes from the eddy current loss.When the objective is only the dc resistance loss without the eddy current loss,the resulted actual winding loss would be deviated from the optimum one.To address these issues,a winding loss modeling method considering eddy current effects with effective ac resistance factors is employed.The inequality constraints on winding areas and conductor sizes are introduced.Then,the optimum design methods of conductor sizes are proposed,which lowers the winding loss.3)An optimum winding and air gap design method for high-frequency magnetic components is proposed.The method considers the discreteness of design variables,e.g.,core size variables and number of turns,and does not take the maximum allowable temperature rise as a specification.In reported optimum design methods of high frequency magnetic components,the maximum allowable temperature rise and optimum ratio of winding loss to core loss are employed in the whole design process,which ignores the discreteness of design variables.In addition,the optimization of the ratio of winding loss to core loss does not take the eddy current loss into account.These factors make the design point deviated from the optimum point.To address these issues,the ratio of winding loss to core loss is optimized with eddy current loss considered,according to which,an optimum winding and air gap design method is proposed.The method does not need the maximum allowable temperature rise,and conducts designs according to the discreteness of design variables,which achieves lower power loss and temperature rise.4)Aimed at the selection of sizes of non-powered and powdered cores,calculation methods for optimum area products are proposed respectively.Reported calculation methods are inaccurate because of the neglect of eddy current effects,or only applicable for two winding cases and lose generality due to the employment of a complicated winding loss model when the eddy current effects are considered.In addition,the reported methods do not take into account the coupling between permeability and loss characteristics in powdered cores,which makes the methods need several iteration times.To address these issues,area product calculation methods are proposed for the nonpowdered and powdered cores respectively.In the method for non-powdered cores,a concept of effective ac resistance factors is introduced which increases the accuracy and ensures the generality.In the method for powdered cores,the optimization process is employed for each permeability,which decreases the iteration times.The curves of design variables vs.the power of magnetic components are investigated,according to which,the empirical values used for calculations of area products in conventional methods are explained.In addition,the performance factor for the selection of core materials is investigated,and the relationship between the performance factor and the transferred power is derived,according to which,the reason why the performance factor can be used for core material selection is given.The optimum design method of high-frequency magnetic components is verified by simulation and experimental results,confirming the effectiveness of the proposed methods.Additionally,appendixes are presented for the review and comparison of thermal models of magnetic components,core loss models and winding loss models,which are essential in the optimum design of high-frequency magnetic components.