An approach for monitoring and updating the load margin of power systems in dynamic security assessment

摘要

The main contribution of this paper is to propose an approach for monitoring and updating the load margin of power systems related to Saddle-Node Bifurcations (related to voltage instabilities) and Hopf Bifurcations (related to small-signal instabilities) considering variations in load growth directions of power systems. First, a set of load margins related to the bifurcations are calculated using a direct method considering uncertainties in the power system operating conditions and load growth directions. Then, a PMU placement formulation is proposed to select the buses that provide useful information about these load margins. The proposed monitoring system evaluates if the currently considered load growth direction gives a compatible voltage profile when compared to the one actually measured by the PMUs. If the profile is incompatible with the predicted one, the load growth direction is updated based on an optimization model. The proposed approach was applied and evaluated in the reduced south-southeast Brazilian system. Case studies showed that daily load profile curves showed different directions of load growth that resulted in load margins associated with different bifurcations. These results highlight the importance of correctly identifying and constantly updating the load growth direction and the load margin of power systems.