Design and analysis of an UFLS scheme for low-inertia based power grid

A Significant change to power systems’ dynamic behavior, especially frequency responses, following a contingency event is a major concern due to the high penetrations of low/inertia-less renewable energy sources. Power system inertia can be getting weaker with the integrations of renewable energy into the grid. As a result, sometimes the under frequency load shedding (UFLS) schemes fail to protect the frequency decline below the threshold limits with conventional settings. This paper addresses this problem and analyse the impacts of penetration of renewable energies into the power systems. Furthermore, a modified load-shedding method is proposed by considering the rate of change of frequency (ROCOF) and the total system’s damping factor. Then a comparison study between proposed method and other methods (conventional and MILP) is presented. A 13-bus real power system is considered as test bus and several case studies are conducted using the Python based PSS/E simulation software platform. From the simulation results it is found that, the proposed load shedding method successfully restricts the frequency decline within a safe limits and thereby, avoids the possibility of major blackouts.