A Sensitivity-based Approach to Adaptive Under-Frequency Load Shedding

This paper proposes a Lagrange multipliers-based adaptive under-frequency load shedding (UFLS) method for frequency control in power systems. UFLS is one of key factors for frequency stability especially in stressed power grids with high penetration of renewable energy generation and deregulated electricity market. Conventional UFLS methods usually shed fixed amount of predetermined loads at predetermined locations which can lead to over or under load curtailment. This paper presents an adaptive method, based on Lagrange multipliers of power balance constraints, to determine not only the amount of the load-step to be shed but also the best locations for load shedding. This method applies a two-stage strategy for load-shedding. In the first stage, the deficit/disturbance power is computed based on the initial rate of change of frequency. In the second stage, the optimization analysis is performed so as to calculate Lagrange multipliers, which are used in the determination of the location and the amount of load-step to be shed. The proposed method is implemented on several test systems including the reduced 9-bus 3-machine Western Electricity Coordinating Council (WECC) system and the New England 39-bus 10-machine system. The results show that the proposed UFLS approach can effectively bring the system back to normal state after contingencies.