Patent ID: 8713946

Claim:
A method for controlling an operating point of a gas turbine that includes a compressor, a combustor and at least a turbine, the method comprising: determining an exhaust pressure drop at an exhaust of the turbine; measuring a compressor pressure discharge at the compressor; determining a turbine pressure ratio based on the exhaust pressure drop and the compressor pressure discharge; calculating an exhaust temperature reference curve of the turbine as a function of the turbine pressure ratio; determining whether both conditions (1) and (2) are true, wherein condition (1) is IGV min +ΔIGV 1 ≦IGV set point ≦IGV max +ΔIGV 2 , and condition (2) is ttx≧ttxh+Δttx 3 , with IGV set point being a target angle of inlet guide vanes (IGV) to be provided at an inlet of the compressor, IGV min is a minimum value for the IGV, IGV max is a maximum value for the IGV, ΔIGV 1 is a first predetermined positive IGV angle increase for lean-lean to premixed transfer, ΔIGV 2 is a second predetermined negative IGV angle increase for lean-lean to premixed transfer, ttx is a current exhaust temperature, ttxh is the exhaust temperature reference curve, and Δttx 3 is a predetermined negative temperature characterizing an exhaust temperature dead band for lean-lean to premixed transfer; and changing, if both conditions (1) and (2) are true, a split fuel quantity from a first value to a second value or otherwise maintaining the first value, the first value characterizing a lean-lean steady state mode and the second value characterizing a premixed secondary mode of a premixed mode, wherein the premixed mode is defined as providing fuel to primary burners and to a second burner of the combustor and igniting the provided fuel in a secondary region of the combustor while primary regions are free of flames, the primary regions being adjacent to the secondary region, the lean-lean mode is defined as providing fuel to both the primary burners and the secondary burner and igniting the provided fuel both in the primary regions and the secondary region, and the split fuel quantity describes in percentages a first amount of the total fuel that is received by the primary burners and a second amount of the total fuel that is received by the secondary burner.