Frequency control is one of the important control problems in interconnected power system design and operation, and is becoming more significant today due to the increasing size, changing structure, emerging renewable energy sources and new uncertainties, environmental constraints, and the complexity of power systems. The frequency in a power system is usually under control using well-known automatic generation control (AGC) loop. AGC markets require increased intelligence and flexibility to ensure that they capable to maintain generation-load balance, following serious disturbances. In a conventional power system, the majority of supply demand balancing is achieved by controlling the output of dispatch able generation resources to follow the changes in demand, and typically, a smaller portion of the generation capacity in a control area is capable of and is designated to provide frequency regulation service in order to deal with the more rapid and uncertain demand variations provide by renewable energy sources (RESs). Integration of RESs into power system grids have impacts on frequency control as well as other control issues. Increases in distributed generation, micro grids and active control of consumption open the way to new control strategies with a more control hierarchy/intelligence and decentralized property. The frequency control/AGC systems in a modern power system should handle complex multi-objective regulation optimization problems characterized by a high degree of diversification in policies, control strategies, and widely distribution in demand and supply sources; so it surely must be intelligent. The core of such intelligent system should be based on flexible intelligent algorithms, advanced information technology, and fast communication devices. The frequency control interacting with other ancillary services and energy markets should be also able to contribute to upcoming challenges of future power systems control and operation.
