Researches And Applications Of Magnetic Technology On High Power Density Power Converter

The power converters are rapidly developing toward the direction of high frequency,planarization and miniaturization,the researches and designs of high-power density of switching converter are absorbing more and more attention.During the design of high-power density,the magnetic components(such as filters,transformers and inductors)play an important role on the volume,weight,loss and thermal.To improve the switching frequency and take magnetic integration is a technical scheme with good chance.However,with the increase of switching frequency,the efficiency of switching power supply and the performance of EMI(Electromagnetic Interference)can be affected.Hence,the researches of magnetic components with high frequency are paid much attention,especially during the design of high-power density,an effective theory guidance can yield twice the results and half the efforts.Therefore,the researches of this paper foucs on the magnetic technology,and the key points are concerned about the computation of winding losses,the measurement of magnetic core loss and the analysis of EMI noise.Furhtermore,considering the flyback converter is of simple structure and is comprehensively used in small and medium sized power supply adapter,this paper also researches the magnetic integration of two indepedent flyback converter in order to reduce the volume of magnetic components and improve the power density.For the winding loss model,this paper puts forward that a circular conductor can be equivalent to a square conductor,and an improved eddy current loss model of circular conductor is proposed by comparing the eddy current distribution in these two kinds of conductors.Comparing to the Dowell model,the improved loss model can be more accurate when it turns to calculate the round conductor’s loss with strong proximity effect,which expands the frequency domain of winding loss computation.Furthermore,a current modified coefficient is put forward by analyzing the relationship between the computed current,which is evaluated by the magnetic field around the conductor,and the real current.Combining with the mirror image method and Biot-Savart law,the litz wire loss model is proposed,and its error can be controlled under 5% by comparing to the results of threedimensional finite element simulation,which solves the problem of loss calculation for litz wire windings which are widely used in high frequency conditions.Currently the magnetic core loss model is still mainly based on the fitting of measured data.For the problem of large capacity of excitation sources needed and big error happened on the high frequency magnetic components loss measurement,this paper designs a measurement device based on the DC law,which can test the magnetic components loss with the excitation of different kinds of PWM(Pulse Width Modulation)wave,and it has high accuracy,fast measurement and needs low excitation capacity.In order to ensure the measurement accuracy,each components loss of the inverter is detailed analyzed,and a high accuracy loss model of the device is proposed according to the analysis,combining the use of air inductor for the calibration,the accurate calibration deduction of inverter’s loss is realized.Furtherly,the error resources of the testing device and the effect of the rise and fall time of the PWM waveforms on the calibration accuracy are deeply analyzed.The distribution parameters of magntic components not only impact the EMI noise by itself high frequency impedance,but also by affecting the dynamic features of the circuit voltage and current waveforms.This paper analyses the formation mechanism of the distribution parameters of the flyback transformer and its influence on the waveforms,and theorectically construct the relatively accurate switching waveforms.Moreover,the impacts of distribution parameters on the differential and common noise are furtherly analyzed,which establishes a theorectical model for predicting the EMI noise of power supply.A magnetic integration of two indepedent flyback circuit with common magnetic circuit is designed,the whole volume of the magnetic components is reduced by integrate the two flyback transformers into one magnetic core.Considering the requirement of the design of magnetic integration,an improved magnetic core structure is proposed,which is helpful to the process control and realize the decoupling of magnetic circuits.