Adaptive Under-Frequency Load-Shedding Considering Load Dynamics and Post Corrective Actions to Prevent Voltage Instability

The conventional under frequency load shedding (UFLS) strategies disconnect the preset amount of the load from the power grid in specific steps. These approaches ignore the daily load variations and the total outage costs, leading to a non-optimal solution. This paper proposes an adaptive UFLS scheme that considers the daily profiles of the different load types to minimize the total outage cost. To obtain the exact amount of the load to be shed, the dynamic performance of the load clusters is modeled. Furthermore, a series of post load-shedding corrective actions (PLSA) are implemented after the UFLS to satisfy the voltage constraints, using the installed reactive power control apparatus and static VAR compensators (SVCs). Two static (frequency-domain) and transient (time-domain) indexes are defined to evaluate the feasibility of possible UFLS/PLSA scenarios. The promising solutions are ranked and the most favorable ones are embedded in a number of look-up tables. The proposed UFLS/PLSA approach is applied to the main grid as well as the potential islands. The performance of the proposed adaptive UFLS/PLSA approach is tested on the IEEE 39-bus system via numerous scenarios, and the results show feasibility, fast and optimal performance of the proposed method.