A New Approach on Development of Power System Operational Flexibility Index by Combination Generation Unit Flexibility Indices

Power system flexibility is the ability of power system to cope with the uncertainty and variability both in generation and load sides. This ability should be quantified and measured by a suitable index to show the level of system flexibility in different situations. Flexibility area index, proposed by the authors is a suitable metric for power system flexibility evaluation especially in the presence of renewable sources as large scale wind and solar farms. Similar other system flexibility indices, this index is defined at first for one generation unit and then extended to the power system by combination the unit indices. In this way an accurate and meaningful combination routine should be established to reflect the effect of each unit flexibility index in the combined system flexibility index correctly.This paper proposes a suitable and justified method to combine the unit flexibility indices achieving the system flexibility index. The performance of the proposed index is verified by the wind/load curtailment in economic load dispatch incorporated wind power. Achieving this purpose, the mentioned index is decomposed into two components, one for ramp up and maximum generation system capabilities (upper component) and another for ramp down and minimum generation system capabilities (lower component) each of them related to the load or wind curtailment respectively which is another contribution of this paper. Finally by establishment a correlation between upper/lower component and load/wind curtailment, a suitable validity evaluation for the proposed system flexibility index is done which is another contribution of this paper.