Method of air-flow measurement and active operating limit line management for compressor surge avoidance

A method of controlling a gas turbine to optimize performance thereof, comprising:

• providing a control system including a controller coupled to a plurality of turbine actuator systems, said actuator systems being coupled to a gas turbine that includes an inlet plenum, inlet guide vanes (IGV), a compressor, a combustor, and a combustion turbine, so as to control the operation of the gas turbine in response to respective actuator system control signals generated by the controller, said control system further comprising an operator interface;
• the controller comprising a processor for generating said respective actuator system control signals in correspondence with input from said operator interface and a plurality of turbine operating condition signals, said control system being programmed to define a pressure ratio Operating Limit Line that provides a surge margin from a surge line defined by pressure ratios associated with physical limits to compressor operation for the gas turbine;
• sensing a fluid pressure Ps at a first sensing location;
• sensing a fluid pressure Pt at a second sensing location;
• sensing a fluid temperature Tt at said second sensing location;
• and
• determining an inlet air-flow rate Wp based on detected values of pressures Ps, Pt, and temperature Tt, and as a function of IGV angle, pressure ratio, and speed;
• comparing said determined air-flow rate to a stored air-flow rate;
• and
• when said determined air-flow rate is less than said stored air-flow rate, determining a surge line degradation from pressure ratio loss (ΔXs) and corrected flow loss (ΔWs) using the following equations:
• ΔWs=K1ΔWo
• ΔXs=K2ΔWo
• where:
• the values of K1 and K2 vary as a function of corrected speed (%Nc);
• and
• ΔWo is the difference between the determined air-flow rate and the stored air-flow rate, thereby to determine a deteriorated surge line;
• and
• using a predetermined target margin to the degraded surge line to determine and establish an adjusted Operating Limit Line.