A centralized automatic generation control for island systems dominated by inverter-based resources

The on-going decarbonization of electrical systems sets storage and renewable resources in a dominant role for the provision of regulation services. Even in the absence of synchronous generation, the operation of power converters in a so-called droop-based grid-forming mode creates the need for secondary frequency regulation. Established centralized secondary control schemes focus on the interplay between storage and conventional units, with the coordination between storage and renewables receiving less attention. In this work a central automatic generation control scheme is introduced for non-interconnected systems operating solely on renewables and batteries, prioritizing the provision of upward reserves by renewables, when faced with curtailments. When the state of charge of a battery system approaches its limits, its power reserves are smoothly reallocated to other battery facilities. In case of an emergency state, any output power limitations imposed on renewables to maximize the utilization of the hosting capacity of the network, are temporarily alleviated for the minimum time necessary to avoid load shedding. Time-domain simulation results from an island grid supplied by 100% inverter-based resources demonstrate the effectiveness of the proposed method in managing major contingencies.