Abstract
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.
Highlights
T HE integration of various renewable energy sources (RES) reduces the synchronous system inertia and brings more active power uncertainties into the modern power system [1], [2]
VALIDATION OF multi-interval sensitivity (MIS), multipoint sensitivity (MPS), AND system frequency response (SFR)-BASED METHODS FOR SYSTEM frequency nadir (FN)/frequency vertex (FV) After obtaining the required sensitivities, the probabilistic distributions of system FN/FV assessed by the SBS, the proposed MIS and MPS, and the traditional SFR method are presented in Fig. 6, and the assessment result and related absolute errors compared with SBS are in Table 7 and 8 separately
VALIDATION OF MIS AND MPS-BASED METHODS FOR AREA-LEVEL FN/FV The probabilistic distributions of individual area-level FN/FV evaluated by the MIS and MPS methods are presented in Table 10-11 separately, and the related absolute errors compared with the SBS-based results are given in Table 12 and 13
Summary
T HE integration of various renewable energy sources (RES) reduces the synchronous system inertia and brings more active power uncertainties into the modern power system [1], [2]. The MIS based on MPS is proposed to quantify the impact of frequency/power oscillation on area-level FN/FV evaluation by using different sets of sensitivities w.r.t different combinations of the RES outputs. Method 1 can achieve fast assessment on system FN/FV using a single sensitivity derived from the SFR model but fails to quantify the impact of RES locations and excitation system To address this issue and improve the accuracy of estimated FN/FV, Method 2 is proposed, where the traditionally single sensitivity is replaced by the M sensitivities, defined as a set of sensitivity (M is the number of RESs). In each cycle/interval, one set of data are collected via historical information or simulation results, which contain the stochastic outputs of M RES and the corresponding FN/FV, and the MPS of the concerned FN/FV is computed according to (14). Compared with traditional Monte Carlo simulations, the proposed methods can achieve satisfactory accuracy as well as efficiency
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