Unlike other supplies, electricity generally cannot be stored for later use; it must be used as it is generated. Therefore, generation must be dispatched instantaneously to respond to real-time changes in demand for electricity. To support this issue and to balance the generation and load, a secure and online control system known as automatic generation control (AGC) is needed. The AGC is required for simultaneous minimization of system frequency deviation and tie-line power changes to match the total generation and load demand, which is required for successful operation of interconnected power systems. The AGC system is responsible for frequency control and power interchange, as well as economic dispatch. The AGC 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 AGC systems of tomorrow 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. Therefore, they require increased intelligence and flexibility to ensure that they capable to maintain generation-load balance, following serious disturbances. The core of such robust and intelligent system should be based on flexible algorithms, advanced information technology, and fast electronic communication devices. The AGC interacting with other ancillary services and energy markets will be able to contribute to upcoming challenges of future power systems control and operation. The present section summarizes the fundamentals of AGC system and main relevant concepts, which are extensively given in Refs. 1 and 2.Moreover, here, some updates as well as new issues are addressed.
