基于多物理场分析的双轴励磁汽轮发电机运行能力基础研究

When an ordinary turbine generator in a power system shuts down as the occurrence of faults, dual-excited turbine generators may continue working. Their maximal power angles can be as high as 180 degree. Dual-excited turbine generators may even run asynchronously with alternatively positive and negative excitation. Dual-excited turbine generators are helpful to enhance security of the electric power system, especially suited to supply power reliably for crucial region. Domestic research mainly focus on the excitation control strategies, while foreign literatures place emphasis on general theory and product presentation and avoid key technologies. This project will study the major factors influencing dual-excited turbine generator operation capacity and the basic approach enhancing the capacity to withstand the fault. We combine the time-stepping finite element analysis and multiple physical field analysis to study the relation between dual-excited turbine generator operation capacity and structural parameter, the parameter identification of dual-excited turbine generator through time-stepping finite element analysis, the transient velocity field of the cooling flow, transient temperature field analysis, and the test of the model generator. Meanwhile, we will make a explore in nonlinear model parameter identification methods and the key technology involve the structure optimization of dual-excited turbine generator, and provide theoretical foundation and technical support for the design of high-power dual-excited turbine generator and the operation of unidirectional dual-excitation and alternatively positive and negative dual-excitation.

电力系统发生严重故障导致普通发电机停机后，双轴励磁汽轮发电机(简称双励机)仍可继续运行，双轴单向励磁的功角可达180 ，双轴正负交替励磁则可异步运行；可见，双励机对提高电力系统安全运行水平，对保障要害区域的可靠供电具有重大意义。国内以往主要研究励磁控制策略，国外文献侧重介绍一般理论及产品性能，而回避关键的设计技术。本项目针对大功率双励机研制的需要，以300MW普通汽轮发电机为实例，改变为双励机结构，研究其本体部分的特殊结构（励磁绕组、转子阻尼、冷却系统等）与其在系统故障条件下运行能力之间的关系。将多因素非线性建模研究与多物理场耦合分析结合，通过时步有限元动态分析、暂态速度场、温度场分析并结合模型机实验进行研究；还将探索基于有限元计算结果的模型简化及参数辨识。为大功率双励机的研制及双轴单向励磁和双轴正负交替励磁的后续研究提供理论依据及技术基础。

本项目主要围绕大功率双轴励磁汽轮发电机（双励机）结构特点及运行能力展开研究。提出了两种大功率双励机转子结构方案，针对不同转子绕组结构提出了相应的励磁控制方式，揭示了不同励磁方式下磁动势之间的关系；建立了用于分析大功率双励机稳态特性、运行能力及发热冷却问题的多物理场数学模型，通过计算对双励机转子绕组结构及参数进行了优化，获得了既能提高基波磁密又能减小谐波磁密的双励机转子绕组的结构；提出了在保持励磁磁动势不变的情况下，将双励机静态稳定极限增加到360°的励磁控制策略，对比分析了单轴励磁、双轴励磁对双励机暂态稳定性的影响，揭示了双励机暂态稳定性随q轴励磁投入时间、励磁大小的变化规律。计算了双励机不同励磁方式下同步电抗的差异，揭示了双轴励磁时，分别选取合成励磁磁动势位置及转子d绕组轴线作为直轴时，同步电抗随运行工况的变化规律。研制了对于大功率双励机具有高保真度的多功能模型机及相关实验研究平台，既能反映各种非线性因素又能实现转子阻尼导条拆卸及温度测试；研制了双励机的自动励磁控制装置，通过协调控制两套励磁绕组中的电流大小实现对双励机有功、无功的独立控制，从而提高了双励机的稳定运行能力。