Transmission system operators target to maximize renewable power injection into the grids while preserving power lines' safety. Recently, decentralised approaches are developed using Power Transmission Distribution Factors (PTDFs), and consider model-based control strategies for local sub-transmission area. However, the computation of the models is complex due to the time-varying nature of the parameters. In order to answer these shortcomings, the present paper proposes a realtime parameter estimation using past observations of the power flow on a finite time window. Simulations results validate the proposed approach.