聚合物纳米复合介质中空间电荷输运的数值模拟及应用研究

In this project, numerical simulation of space charge behavior in polymer nanocomposite is study based on experiment research. The distribution of nano-filler in polymer and the interfaces between nano-filler and polymer matrix are investigated with microscopic analysis techniques, such as 3D X-ray microscope, transmission electron microscope (TEM). The relationship between space charge behavior and relaxation mechanism in nanocomposite are researched by simultaneous measurements of space charge and relaxation current. The thermally stimulated depolarization (TSDC) current and dynamic thermomechanic analysis (DMA) are also used to investigate the relaxation mechanism in nanocomposite. The variation of parameters, such as trap density, trap depth and apparent mobility, in nanocomposite with the introduction of nanosilica are evaluated by relevant theories based on experiment results. A new charge transport model is proposed, based on the experiment research of nanocomposite and traditional bipolar charge transport model. The numerical scheme of transport model is investigated and relevant numerical simulation software is designed for simultaneous simulation of space charge and relaxation current. Space charge behavior and relaxation current in nanocomposite are simulated based on the parameters evaluation by experiment results. The reliability of proposed transport model is assessed by the results comparison of simulation and experiment. The space charge distributions in ultra-thin/super thick specimens are simulated with the proposed transport model to understand charge transport in polymer. It could evaluate the feasibility of numerical simulation technology applying on research of space charge transport in polymer.

本项目以空间电荷数值模拟为主，实验研究为辅展开工作：采用X射线三维成像、电子透射电镜等微观分析技术，研究纳米颗粒在复合介质中的分散状态和界面结构；采用空间电荷与松弛电流联合测量技术，研究复合介质中空间电荷和松弛机理的相关性；通过热刺激退极化电流谱和动态机械谱对比分析，研究纳米颗粒填充对复合介质中各类松弛的影响；基于相关理论提取复合介质中陷阱能级、陷阱密度、视在迁移率等特性参数变化规律，为空间电荷数值仿真提供参数设置依据；基于复合介质实验研究得出的规律，在传统双极性载流子输运模型基础上构建新的电荷输运模型，并通过数值算法研究设计空间电荷数值模拟平台；以实验研究提取的特性参数为依据，通过空间电荷、松弛电流的同步模拟结果和实验结果比对分析，校验新输运模型的可靠性，并研究复合介质中的空间电荷输运；通过超薄/超厚介质中空间电荷的数值模拟研究，评估数值模拟技术在绝缘介质空间电荷输运研究中应用的可行性。

本项目以空间电荷数值模拟为主，实验研究为辅的方式开展了研究：以纯LDPE为基料，气相法生产的气相SiO2为纳米填料，制备了不同粒径和不同填充浓度的纳米复合介质平板试样；采用扫描电镜和透射电镜等微观成像技术定性分析了纳米粒径和填充浓度对复合介质内部颗粒分散性的影响，结果表明纳米复合材料中填充7nm气相SiO2的分散性较好，但填充浓度过高时纳米颗粒会发生团聚，团聚粒径可达数百纳米；采用空间电荷和松弛电流联合测量技术分析了空间电荷、载流子迁移率和介质内部陷阱能级分布之间的相关性，结果表明不同粒径对应的抑制空间电荷积累的最佳浓度各不相同，且相同纳米粒径下抑制空间电荷积累和抑制高场电导对应的最佳填充浓度亦各不相同，应用中需根据实际情况综合考虎复合材料的空间电荷和电导指标；通过对热刺激退极化电流的测量，获得到了纳米复合陷阱能态密度分布，并结合DMA实验结果甄别了与分子链相关的松弛，结果表明纳米复合介质相比纯LDPE内部存在更多能级的陷阱，且深陷阱的深度更深、密度更大；基于实验现象和数据分析，建立了新的载流子输运模型，设计了相应的数值算法，构建了一维平板试样结构的空间电荷数值模拟平台，并通过空间电荷和松弛电流联合数值模拟结果与实验波形的比对，验证了新输运模型的可行性。在此基础上进行了超薄/厚绝缘中空间电荷的数值模拟，将一维平板结构算法扩展到了二维同轴结构下，并研制了适测绝缘厚度在4.0mm-31.2mm范围的超高压直流电缆空间电荷检测仪，为后续超厚绝缘全尺寸电缆空间电荷数值模拟奠定了基础。此外，为验证纳米复合材料中空间电荷的瞬态变化，提出了适用于不同类型周期波电场下空间电荷检测的自动均分移相原理，为瞬态周期电场下空间电荷检测系统提供了理论指导。