Patent ID: 7608938

Claim:
A method of operating a combined-cycle power system coupled to an electric power grid, the combined-cycle system including at least one electric power generator, a steam turbine coupled to the at least one electric power generator, a combustion turbine coupled to the at least one electric power generator, and a steam source having a thermal energy reservoir, the thermal energy reservoir being in flow communication with the steam turbine via at least one control valve, said method comprising: operating the steam turbine at a first electric power output, operating the combustion turbine at a first electric power output, and operating the steam source at a first thermal energy level, the steam turbine having at least one control valve in a first position, the combustion turbine having at least one air inlet guide vane in a first position, the steam turbine and the combustion turbine being synchronized to an operating frequency of the grid, so that the steam turbine, the combustion turbine, and the grid are operating at a frequency substantially similar to a standardized grid frequency value; and upon sensing a grid frequency deviation away from the standardized grid frequency value, then: determining a current thermal energy capacity of the thermal energy reservoir; determining a rate of frequency recovery available using the current thermal energy capacity of the thermal energy reservoir and a predetermined rate of change of the at least one steam turbine control valve; if the determined rate of frequency recovery available is greater than the grid frequency deviation and a predetermined recovery period then, moving the at least one steam turbine control valve to a second position thereby inducing a thermal energy transfer between the thermal energy reservoir and the steam turbine, moving the thermal energy reservoir energy level to a second energy level, thereby facilitating a predetermined rate of a grid frequency recovery for a predetermined period of time, the predetermined rate of frequency recovery being substantially uniform; and if the determined rate of frequency recovery available is less than the grid frequency deviation and a predetermined recovery period then, substantially simultaneously moving the at least one combustion turbine air inlet guide vane to a second position and the at least one steam turbine control valve to a second position thereby changing a power level output of the combustion turbine, inducing a thermal energy transfer between the thermal energy reservoir and the steam turbine, moving the thermal energy reservoir energy level to the second energy level, and changing the power output level of the combustion turbine, thereby facilitating a predetermined rate of a grid frequency recovery for a predetermined period of time, the predetermined rate of frequency recovery being substantially uniform.