Research On Core Loss Performance Of High Frequency Transformer Under PWM Excitation

With the continuous development of power electronics technology,it has become more and more common to achieve high power conversion at high frequency.As a key component of power electronic transformer,the size and performance of high-frequency transformer depend on the operating frequency of the core and the magnetic properties of the material.Increasing the operating frequency may reduce the weight and size of the transformer,but it may make losses,especially core losses,increase and restrict the efficiency of the high-frequency transformer.The core loss of high-frequency transformer is closely related to the core material and excitation form used.As a core material commonly used in high-frequency transformer,soft magnetic ferrite or nanocrystalline,its magnetic properties and loss characteristics and the accurate calculation of core loss under non-sinusoidal excitation have yet to be further solved.This paper focuses on the magnetic properties of soft magnetic ferrite or nanocrystalline ring samples and the core loss model excited by square wave and PWM wave.Based on the measurement of the magnetic properties and loss characteristics of the core material excited by square wave and PWM wave,an improved form of loss separation model under non-sinusoidal excitation is proposed and applied to the simulation calculation of high-frequency transformer core performance.The further optimization design of the core structure of the frequency hightransformer provides a powerful reference basis.The main research contents are as follows:Firstly,based on the existing measurement system in the laboratory,the non-sinusoidal magnetic characteristic measurement system of the ring core is built up,and the ring sample of the soft magnetic ferrite and nanocrystalline materials was experimentally measured.In order to more accurately know magnetic characteristics of the core under different excitation patterns,the sinusoidal wave,square wave and PWM wave excitation are used to measure,and the magnetization curve,loss curve and hysteresis loop are drawn,which lays a foundation for the establishment of the core loss model and also provides reference data for the design and fabrication of the high frequency transformer.Then,sevral loss models which are often applied by domestic and foreign scholars are introduced and analyzed.Based on the core loss measurement data,the Barbisio algorithm based on the iron loss separation model is improved,and the excess loss coefficient is expressed as a function of frequency and flux density.At the same time,the eddy current path for a soft magnetic ferrite with rectangular cross section is analyzed and the eddy current loss calculation formula is derived.Finally,the above loss model parameters are fitted according to the experimental data,the database of excess loss parameters is established,and the effectiveness of the model under square wave and PWM wave excitation is verified.The magnetic field simulation of a highfrequency transformer is performed by using MagNet commercial finite element calculation software,and the magnetic field information in the core at the peak current is collected and the data are output.The loss data of each acquisition node of the core are calculated by the proposed loss model,and the loss distribution of the core of the high-frequency transformer is finally obtained.