Restoring desired voltage security margin based on demand response using load-to-source impedance ratio index and PSO

Demand Response (DR) is an active role of end-users in responding to signals coming from the market or to emergency signals coming from system operators, asking for a load reduction to help facing criticalities and reduce blackout risks. Load reduction is one of the typical DR participation methods for large and small consumers which is generally considered as a final defence strategy against system instability when voltage collapse is anticipated and may potentially result in blackout. In this paper, an algorithm concerning load reduction based DR is proposed. Indeed, a two-state algorithm based on finding optimal load reduction pattern and estimating threshold voltage of initiating DR is presented to prevent power system from voltage collapse. In this regard, load-to-source impedance ratio (ZL/XTh) is adopted as an index for evaluating voltage security margin (VSM) and is utilized in an optimization algorithm aimed at obtaining minimum load to be cut down. The proposed approach has been implemented in IEEE 39-bus network demonstrating its effectiveness and applicability.