Research On Harmonic Loss Of Iron Core Under High Frequency Based On The Statistical Theory Of Loss

With the rapid development of new power system structures such as the energy internet and new energy power systems,the application of power electronic transformers is becoming more and more widespread.As the core component of power electronic transformers,the input signal of high frequency transformers is often various harmonic signals,and the traditional loss calculation model under sinusoidal excitation conditions cannot adapt to the new operating conditions,and the calculation accuracy of core losses cannot meet the requirements.Therefore,based on the Bertotti loss separation theory,this paper investigates the magnetic properties of grain-oriented silicon steel sheets and the loss characteristics under harmonic excitation,and proposes an improved loss separation calculation method to extend the loss prediction range to a larger frequency range as well as a higher flux density range,the specific work of the paper is as follows:In order to consider the effect of harmonic excitation and to improve the traditional Bertotti loss separation model,this paper proposes a loss prediction model under high frequency harmonic excitation.The fixed-point technique is introduced for operating conditions at higher frequencies and higher flux densities.Instead of approximating the magnetic intrinsic relationship of the material as linear,a non-linear magnetic intrinsic relationship including a fixed-point reluctance is introduced for finite element calculations,which takes into account the effect of the skin effect of the silicon steel sheet and allows for more accurate prediction of eddy current losses in the core at high frequencies and high magnetic densities.In order to apply the above improved loss prediction model to the core of a high frequency transformer and to investigate the effect of harmonics on the magnetic loss model,the magnetic properties and loss data of the core model at different harmonic orders,contents and phases at 1 k Hz frequency and at different frequencies under harmonics were first measured by means of the Epstein square circle experimental method,and based on the magnetic properties measurement results,the effect of different harmonic characteristic quantities on the the effects of different harmonic characteristics on the losses are qualitatively analysed and the losses under the corresponding excitation are predicted using the above model.The accuracy of the improved model is verified by comparing the experimental measurements under harmonic excitation,the COMSOL simulation results and the prediction results of the improved model in this paper,based on the verification of the accuracy of the COMSOL simulation model.The accuracy of the improved model is also verified by comparing the conventional loss separation model,the loss model with linear permeability,with the improved model and the experimental measurements.