Recently

with power systems operating in increasingly complicated environment and influenced by wide area phenomena

a strategy based on the existing coordinated control between multiple control areas has aroused considerable interest in achieving reserve sharing and helping ensure higher level of control areas cooperation. The concept and driving force of coordinated control and a scheme for coordinated control technologies applied in different countries are discussed. Then

the state of the art of coordinated control technology is analyzed in two aspects of system frequency control and tie-line power control. Based on a review of various methods

problems and further research areas are pointed out.