实际工况下基于微磁结构磁化机理的电工钢片综合磁特性定量模拟研究

With the rapid increasing request on design and running of high efficiency electrical power plant and a large number of nonlinear loads connected to the grid, the iron core in the power transformer more often works at the non-standard magnetization conditions such as high frequency, highly distorted magnetic flux, dc biased field, and so on, which may increase the loss and even damage the cores. The traditional models of magnetic property fitted from a great number of experimental data are lack of deep study on the magnetization mechanism of micromagnetic structure; as a result, they have limited modeling accuracy for magnetic property under the real operating conditions. The variation of magnetic domain structure under different magnetization patterns determines the multiple magnetic properties of ferromagnetic material, such as magnetic hysteresis property, loss property and magnetostrictive property. In this research, a multi-function measurement system combining the magnetic domain viewing and magnetic property measurement under non-standard magnetization conditions was developed. The physical theory of magnetic domain wall movements under non-standard magnetizations in electrical steel sheets was deeply investigated, which established a research bridge of magnetic property over mesoscopic and macroscopic models. Based on micromagnetic theory, the two-scale loss model, dynamic vector hysteresis model and magnetostrictive essential model were proposed to model multiple magnetic properties quantitatively and improve the reliability of models. A strongly coupled three dimensional finite element computation method that addressed hysteresis and eddy current effect simultaneously in laminated cores was presented, and its effectiveness was verified with an experimental test. This research will be helpful to the development of electrical equipment manufacturing industry in China.

随着高效发电厂设计和运行需求的不断增加，以及大量非线性负荷接入电网，电力变压器铁心更加频繁地工作在高频、高畸变磁通、直流偏磁等非标准磁化条件下，引起损耗的增加，甚至导致变压器铁心的损坏。现有磁特性模型通常基于大量实验数据的拟合，缺少对微磁结构磁化机理的深入研究，导致对实际工况下磁特性模拟的精度有限。不同磁化方式下磁畴结构变化直接决定了磁性材料的综合磁特性（磁滞特性、损耗特性、磁致伸缩特性）。本项目研制非标准磁化下磁畴观测与磁特性测量相结合的多功能测量系统，深入探究电工钢片在非标准磁化下畴壁运动的物理机理，搭建介观尺度到宏观尺度磁特性研究的桥梁。基于微磁学理论，提出非标准磁化下损耗计算两尺度模型、动态矢量磁滞模型及磁致伸缩本质模型，定量模拟材料磁特性，提高模型的可靠性。提出直接耦合叠片铁心磁滞与涡流效应的三维涡流场有限元计算方法，制作实验模型验证理论方法的有效性，促进我国电工装备制造业发展。

电力变压器铁心频繁地工作在高频、高畸变磁通、直流偏磁等非标准磁化条件下，引起损耗增加，甚至导致铁心损坏。因此，深入开展电工钢片在不同磁化方式下磁滞、损耗及磁致伸缩等综合磁特性的研究工作具有重要意义。本项目改进实验室现有测试系统搭建了单片电工钢片磁畴动态磁化过程观测系统、单片电工钢片非标准磁化下磁滞及磁致伸缩特性测量系统。基于磁光克尔效应，改进磁体双向励磁方式实现了不同牌号10余种电工钢片磁畴动态演变过程的观察和定性分析，探明单片电工钢片磁畴磁化机理，测量并分析了磁通密度峰值、磁化方向、偏磁磁场大小、磁化轨迹对电工钢片磁滞及磁致伸缩性能的影响。在此基础上，从微磁学磁化理论角度，引入磁滞能量密度函数表述磁化历史对当前磁化状态的影响，提出磁畴能量最小化模型表征磁滞各向异性；引入磁畴磁矩旋转特性到J-A磁滞模型中，提出了三项式矢量逆J-A磁滞模型，有效地表征了旋转磁化下电工钢片的矢量磁滞特性。提出了考虑谐波权重及损耗各向异性特征的非线性交变谐波损耗计算模型和考虑旋转磁化轨迹的变系数正交分解椭圆形旋转损耗模型，并应用到电机铁心损耗计算中，利用搭建的电机铁心局部损耗测量系统，测量并验证了计算模型的可靠性。提出了描述磁致伸缩主应变与磁通密度矢量关系的动态矢量模型，将磁致伸缩主应变沿水平和垂直两个方向的分量表达为三项之和，并将该模型应用于电机铁心局部形变的有限元计算，验证了模型的有效性。提出一种反向传播神经网络BPNN模型，用于模拟直流偏磁下的磁致伸缩曲线，并针对传统梯度下降算法训练网络具有收敛速度过慢的问题，采用LM算法替代GD算法来训练网络，与测量数据的对比有效地验证了算法的计算精度和效率。项目研究成果为计算电磁学中电工材料电磁特性精细模拟提供了大量的特性数据和有效的模拟方法，为变压器等电工装备电磁性能的准确预估奠定了基础。