Calculation Of Transformer Iron Loss Based On Dynamic JA Hysteresis Model Under DC Bias

Power transformers facing great challenges to work at direct current(DC)bias conditions with the application of high voltage direct current(HVDC)transmission system and the rapid development of Urban Rail Transit.With the DC penetrating into the windings,the transformer is tending towards half-cycle saturation,distorting the magnetization waveform which leads to the increase of vibration,core loss and subsequent overheating.In DC bias conditions,many factors such as flux distribution,excitation current characteristics,core loss and loss distribution under DC bias should be considered to analysis the problem of DC bias.These factorss are closely related to the characteristics of the core material,therefore,the simulation of the magnetic characteristics of the core material is the basis for solving the problem of DC bias.Based on this,the main points of this thesis are:(1)This thesis proposes a new method to simulation of the magnetic characteristics of the core material and calculate the core loss and its distribution by the FEM incorporated with the J-A dynamic hysteresis model,which integrates the hysteresis,eddy current,and excess losses.(2)To eliminate the error caused by inaccurate parameter determination,the dynamic J-A model parameters are fitted to the measured data by a hybrid optimization algorithm which based on PSO and genetic algorithm.(3)The relationship between the model parameters and the peak flux densitits is determined by the curve fitting method(4)The proposed J-A dynamic model was experimentally verified by comparing the major and minor loops and core losses of different types of materials at different flux densities.The comparison showed that the J-A dynamic hysteresis model can provide accurate results with error less than 5%,which is sufficiently accurate to simulate the magnetic properties and calculate the core losses.(5)To consider the influence of core losses on circuit,a dynamic circuit model is proposed.Both hysteresis and circuit model are used calculate the core losses of laminated core model.Based on the field-circuit coupled method,an experimental verification was given by comparing total core losses and dynamic hysteresis loops at normal and DC bias condition.the comparison shows that the J-A dynamic model is able to reflect the magnetization process occurring in laminations accurately,and the calculated and measured core losses are very close.It has been demonstrated that proposed the proposed methods of this thesis is sufficiently accurate for numerical simulation under various excitations.And the theoretical results which obtained by proposed method can provide references for the optimal design and performance evaluation of electrical equipment.