Online Demand Response of Voltage-Dependent Loads for Corrective Grid De-Congestion

During grid overload or upon occurrence of certain contingencies, a corrective action is required to eliminate congestion and reduce transmission line thermal limit violations. In this paper, we propose to use demand-responsive loads for such a purpose. Cost considerations include power retrieved from the slack reserves and the dis-utility of consumers for providing demand-response actions. Violations of voltage and generator reactive power limits are also accounted for. The idea is to topologically re-arrange the consumption of flexible loads to achieve grid de-congestion while maintaining the aggregate network power consumption constant to avoid interference with frequency control procedures. Our formulation is based on nonlinear power flows and easily allows the inclusion of voltage-dependent loads. An online gradient projection algorithm with closed-form updates is developed to solve the non-convex grid de-congestion problem. Approximate gradient calculations based on fast-decoupled load flow are further provided to simplify the algorithm and make it amenable to distributed implementation.