Aggregate equivalent models of flexible distribution systems for transmission-level studies

Increased penetration of variable resources in the power grid have resulted in variable power flow patterns, volatility in system stress and higher reserve capacity requirements. New approaches are emerging for dealing with these problems. Specifically, flexible assets, such as storage, Thermostatically Controlled Loads, smart appliances, flexible load and other flexible customer resources are expected to provide practical solutions for mitigating the variability. In this paper, a state-transition model of aggregate flexibility of a distribution feeder with responsive loads and flexible generation is derived. The method is general enough to handle any feeder with flexible resources. It yields a concise and tractable “aggregate virtual plant” model of feeder flexibility. Results using simulation data verify the model´s predictive capabilities and its applicability to the transmission level multi-period dispatch problem.