电力系统低频减载的单调控制特性

新能源占比的不断提高使得频率稳定问题日渐突出，因此迫切需要研究系统的频率稳定量化评估分析方法，也需对频率安全控制的最后一道防线低频减载进行更深入的分析。将单调控制系统理论运用到低频减载分析过程中，根据单调控制系统的输入-输出判定条件，推导单机和多机系统低频减载时频率分别需要满足的保序特性量化关系。此外，分析时采用全状态模型，在保证电网规律性和解析性的同时获得更高的可扩展性，综合频率与功角、电压以及相关参数间的耦合关系。并结合灵敏度分析了电网内部变量之间的相关关系，以指导电网故障时的参数设置。最后，分析目前光伏参与调频的3种常见情况，分别说明单调控制理论的适用性，并通过算例进行验证。

Monotonic control characteristics of under-frequency load shedding in power system

The continuous increase in the proportion of new energy sources has made the problem of frequency stability increasingly prominent. Therefore, it is urgent to study on a quantitative evaluation and analysis method of system frequency stability, and it is also necessary to have a deep analysis on under-frequency load shedding, that is the last line of defense for frequency safety control. The monotonic control system theory is applied to the under-frequency load shedding analysis process. According to the input-output judgment conditions of the monotonic control system, the order-preserving quantification relationship which the frequency needs to satisfy is deduced in the single-machine and multi-machine systems respectively during the under-frequency load shedding. In addition, the full-state model is used in the analysis to obtain higher scalability while ensuring the regularity and analyticity of the power system, and to synthesize the coupling relationship between frequency and power angle, voltage and related parameters. Combined with the sensitivity analysis, the correlation between the internal variations of the power system is analyzed, which is helpful to guide the parameter setting when the power system is faulty. Finally, the three common situations in which photovoltaics participate in frequency regulation are analyzed, the applicability of the monotonic control theory is respectively illustrated and it is also verified by examples.