超低频振荡中的区间联络线功率振荡现象及机理

超低频振荡是指一次调频中阻尼不足引发的频率整体振荡,一般认为不存在相对振荡情况。然而,在实际区域互联电网的研究中发现,系统频率在超低频振荡的同时,区间交流联络线功率也存在同频振荡现象。文中以两区域互联系统为研究对象,首先,基于分区域等值的统一频率模型,仿真分析了超低频振荡中联络线功率振荡的现象和特征。然后,基于阻尼转矩理论定义了区域电网的综合频率调节效应系数,继而从线性系统稳态频率响应视角提出该现象的发生机理,并讨论了影响因素。研究表明,如果区域之间的综合频率调节效应系数存在差异,即使在超低频振荡达到稳态振荡后,也会导致区间联络线发生与超低频稳态振荡频率相同的功率振荡。最后,以实际电网算例进行了验证,并讨论了该现象可能存在的危害。

Phenomenon and Mechanism of Inter-area Tie-line Power Oscillation in Ultra-low Frequency Oscillation

Ultra-low frequency oscillation (ULFO) refers to overall frequency oscillation caused by insufficient damping during the primary frequency regulation process. In general, there is no relative oscillation. However, in the study of the actual regional interconnected power grid, it has been found that, as the system frequency oscillates with ultra-low frequency, the same-frequency oscillation phenomenon also exists in the AC tie-line between two interconnected areas. Taking a two-area interconnected system as the research object, this paper analyzes the phenomenon and characteristics of tie-line power oscillation in ULFO based on the unified frequency model established by equivalent areas. Then the comprehensive frequency regulation effect coefficient of power grid is defined based on the damping torque theory. The mechanism of this phenomenon is proposed from the perspective of steady-state frequency response of linear system, and the influencing factors are also discussed. The research shows that, if there are differences in the comprehensive frequency regulation effect coefficients between two areas, they will also cause the same-frequency power oscillation of the inter-area tie-line as the steady-state ULFO, even after the ULFO reaches a steady-state oscillation. Finally, an actual power grid case is given for verification, and the possible harm of this phenomenon is discussed.