Opportunities to support the restoration of electrical grids with little numbers of large power plants through converter‐connected generation and storages

Abstract

The nuclear phase‐out in Germany and the decarbonization of the energy supply are accompanied by a profound upheaval of the generation fleet. The decommissioning of large power plants and their replacement by decentralized, renewable generation plants (DG) as well as storage facilities leads to a shift in generation output from power plants connected to the transmission grid to a large number of renewable and decentralized plants connected to the distribution grids. This significantly impacts the approach to restore the interconnected system after a large‐scale blackout. In order to be able to plan and instruct the dispatch of generating power from the network operator's control centres when restoring the grid after a large‐scale blackout, two aggregation and forecasting methods differentiated by voltage level are presented. For larger farms connected to the high‐voltage grid, a structure‐based node approach is chosen; for the multitude of small and microunits connected to the medium‐ and low‐voltage grids, an area‐based approach is used. These methods do provide the network operator with active power/frequency management in the medium and long‐term range. The provision of fast frequency response (FFR) by inverter‐coupled units or storage systems stabilizes the frequency in the short‐term range. In this way, the frequency nadir following a load connection can be mitigated during network restoration, which accelerates the process. This is particularly relevant against the background of the nuclear and coal phase‐out, as it can compensate for the reduction in inertia and controllable feed‐in power caused by power plant shutdowns. In a case study, it is shown that in a grid island typical for the early phase of network restoration, the inertia of a 500 MW coal‐fired power plant can almost be replaced by a battery storage system of 50 MW which provides FFR.

Cold Load Pickup Model Adequacy for Power System Restoration Studies

“…• To provide parameter fits of CLPU models for additional disturbance events beyond those 10 published in [8], now totalling 31 events; • To provide parameter fits based on actual measurements of a real load composition to the delayed exponential decay model of CLPU according to [13], where it was analytically derived for space heating only; • To determine the degree to which the load profile, caused by CLPU, can be adequately represented using simplified models and to quantify the impact of these simplifications on simulation results with respect to frequency nadir and active power sharing in the use case demonstrated in [12] with a grid structure similar to [14,15].…”

Areal power plant: aggregation system to control a multitude of distributed generators during power system restoration - demonstration results

“…In the extreme rare event of a supraregional blackout, the network has to be restored from the scratch. The electricity market is then suspended, and the personnel in the grid operator control centres obtain time limited extra authority to allocate the power plants according to technical possibilities and necessities [1], [2], [3], [4]. First, black-start capable power plants energise predefined island grids.…”