Probabilistic Assessment on Area-Level Frequency Nadir/Vertex for Operational Planning

Local heterogeneity of the frequency response of modern grids becomes more severe than ever before due to 1) weaker grid connection strength brought by the favorable grid interconnection, and 2) more uncertainties and less system inertia brought by the increasing renewable integration. This dominant characteristic is difficult to be accurately characterized and evaluated by the classic aggregated system frequency response (SFR) model. Therefore, this paper proposes a framework for assessing the risk of area-level frequency nadir/vertex (FN/FV) for operational planning in a practical and effective manner. Firstly, a multi-point sensitivity (MPS) is proposed based on the classical SFR model to evaluate the system FN/FV, where the impact of different Renewable Energy Sources (RESs) on system FN/FV are considered. The method can be extended for regional frequency evaluation, but the influence of generator frequency oscillation cannot be effectively considered, which might impact assessment accuracy. To address this issue, a multi-interval sensitivity (MIS) method is further proposed to calculate the probabilistic distribution of the area-level FN/FV. The probabilistic results are evaluated by the FN/FV RAM, i.e., Risk Assessment Matrix, to provide a two-dimensional analysis for system operational planners. The accuracy and efficiency of the proposed MPS and MIS methods are critically validated via scenario-based simulation (SBS) in a modified IEEE 16-machine 68-bus benchmark system.