In order to provide principles and basis for design of coordinated control system(CCS)for gassteam combined cycle units

the characteristics of control strategy of an actual gas-steam combined cycle unit was analyzed.The results show that

the fast response to unit load demand should be executed by gas turbine

and the steam turbine load only follows the variation of exhaust gas parameters of the gas turbine.After the coordinated control system was put into service

the gas turbine load controller

to which the coordinated control loop provides load set point

still needs to be placed in control loop of the gas turbine side.The main steam pressure is regulated by both the steam turbine governing valve and the bypass system which should be always put into automatic operation.Correction of power and fuel quantity of primary frequency regulation can be realized independently by the gas turbine load control loop.To meet the stress margin requirements of heat recovery boilers and steam turbines

the CCS should regulate the set point of exhaust gas temperature of the gas turbine.The inlet guide vane(IGV)regulation ought to have precedence over fuel regulation in controlling the exhaust gas temperature of the gas turbine.