A Fixed-Step Under Frequency Load Shedding Scheme Based on Load Criticality

Under frequency load shedding (UFLS) schemes are the last resort protection mechanism in order to avoid the collapse of a power system upon a sudden large loss of generation. These schemes disconnect load if the frequency decline exceeds a pre-established threshold. Although existing multi-stage UFLS schemes are not considered an optimal solution, they are widely deployed in practice for their simplicity and reliability. Typically, UFLS operators exclude critical facilities from shedding, while the remaining load is divided among the UFLS stages in an arbitrary way. This current approach does not take into account load sensitivity to outages. In this paper, the concept of a multistage criticality-informed UFLS scheme is introduced to demonstrate the benefits of including high-granularity criticality data in the load assignment process. Employed criticality functions can potentially include social, economic, and demographic data, which are more detailed than the blunt aggregation of loads based on types. In addition, the developed methodology supports time-dependent criticality functions, which are taken into account in the load assignment process. This approach is valid for existing traditional power systems structures, without the need for additional resources. The proposed concept is verified with the Quebec 29-bus system in a MATLAB/Simulink testbed. The results show that the proposed approach effectively constrains the criticality of loads shed across the system.