I. Introduction
Traditionally, power system stability is ensured by synchronous machines connected to the grid. They are automatically reacted with its their stored kinetic energy to a sudden power imbalance, such as additional severe load or a loss of generation unit. However, the power systems are forced to change from conventional generation to renewable energy sources (RESs) because of the main reasons as fossil fuels and climate changes [1], [2]. The load-frequency control structure, even though there are some special regulations according to the countries, basically defined by ENTSO-E is shaped by different processes and periods at specific time ranges. Ancillary services of frequency regulation; are frequency containment reserve (FCR), frequency restoration reserve (FRR), replacement Reserve (RR), ensuring to adjust the generation/load unbalance, and restore nominal grid frequency [3]–[5].
Load-frequency control process[5]