基于交交变频器的风电接入系统对电网稳态及动态特性影响

Fractional frequency transmission system(FFTS) is to use lower frequency , e.g. 50/3 Hz, to improve the utilization of wind power and reduce the disturbances generated by wind power randomness. The key equipment of FFTS is cycloconverter. Its impact on grid stability and fault identification is an urgent problem to study. The first task of this research is to establish cycloconverter 's mathematical model for simulation study and quasi-steady-state model for power system computation, which based on cycloconverter's topological structure, control strategy and operating characteristics. In order to ensure the models' accuracy, the verification, which based on cycloconverter's physical model, would be done. On the basis of the practical models, the rest of the work would firstly study the harmonics and reactive power variation, during the changing of system frequency. Then, the failure mode of cycloconverter and mechanism of fault transfer would be analyzed. Lastly, the characteristics of steady and dynamic state response of large-scale power system, which contains FFTS, would be deeply studied. The results of the research will provide decision basis for the design of filter and reactive power compensation device in FFTS. In addition, it provides the design index for relay protection in FFTS.In the long run, the research can further improve the basic theory of FFTS.

分频风电系统利用交交变频器将风机发出的低频电能并入工频电网，为提高风电利用效率、减小风电随机性对电网的扰动提供了新的解决途径。交交变频器作为其关键设备引入输电系统，对电网稳态控制策略及故障模式的影响是迫切需要解决的问题。本课题将基于交交变频器拓扑结构、控制策略及自身的运行特点建立适用于仿真研究的变频器数字模型及适用于电力系统计算的准稳态模型，并利用物理模型验证两模型的准确性，以使分频风电系统的仿真分析更符合实际运行工况。在此基础上，首先对该系统变频运行时谐波、无功变化规律进行研究；然后，分析交交变频器故障模式、系统故障的传递机理；最后，对含有分频输电的大型电力系统稳态、动态性能等方面进行深入的研究。项目的研究成果，将为分频风电系统的滤波器、无功补偿装置的设计提供决策依据；同时为现有继电保护对分频风电系统的适应性提供评估手段，进一步完善分频输风电系统的基本理论。

分频风电系统利用交交变频器将风机发出的低频电能并入工频电网，为提高风电利用效率、减小风电随机性对电网的扰动提供了新的解决途径。交交变频器作为其关键设备引入输电系统，对电网稳态控制策略及故障模式的影响是迫切需要解决的问题。本文首先建立了交交变频器数字仿真模型及用于系统分析和计算的准稳态模型，并通过算例和动模实验验证了模型的准确性和有效性。在此基础上，对交交变频器两种典型故障情况下的故障特征及其对系统故障的传递机理进行理论分析，为分频风电系统的保护配置和整定提供了依据。然后研究了谐波、功率因数随变频器工作状态变化的规律。最后，对含分频输电的大型电力系统稳态及动态特性进行了深入研究，提出了分频/工频混联系统的潮流算法，仿真与潮流计算两种方法所得的结果误差少于3%，交交变频器的模型与统一迭代法满足工业计算的精度，其准确性满足要求；对分频风电系统的暂态稳定性分析结果表明，当工频系统发生故障时，含分频风电的电力系统中各发电机与纯工频系统中发电机的振荡在幅值和阻尼上均未有明显的区别。这说明，与传统的风电并网方式相比，分频风电系统的引入不会使得原有系统的暂态稳定性能恶化。项目的研究成果，将为分频风电系统的滤波器、无功补偿装置的设计提供决策依据；同时为现有继电保护对分频风电系统的适应性提供评估手段，进一步完善分频输风电系统的基本理论。