Multiscenario Underfrequency Load Shedding in a Microgrid Consisting of Intermittent Renewables

Underfrequency load shedding maintains the power system in a stable condition when a severe disturbance occurs. The underfrequency relay protects the power system against a blackout when the system frequency declines to predetermined settings. This paper determines the shed load at each stage for the underfrequency relay (81L) in a stand-alone microgrid considering multiple scenarios. In addition, the probabilities of all scenarios are defined based on historical meteorological data and the Markov two-state model. The shed load is minimized and the lowest swing frequency is maximized using the genetic algorithms. Due to many inequality constraints in the studied problem, an efficient tree-encoding chromosome and the penalty functions are presented as well. Moreover, applicability of the proposed method is demonstrated using a microgrid test bed with the gas-turbine, wind-turbine generator, and solar photovoltaic.