Patent Application
20080041063
In the exemplary embodiment, gas turbine engine 14 is controlled by control system 10 through a gas turbine and fuel control subsystem 22. Other equipment such as steam turbine 16, a heat recovery steam generator 24, and balance of plant equipment 26 are controlled by control system 10 through respective control subsystems in power generation plant 12. The respective subsystems are adapted to communicate with sensors and control members (not shown) that are coupled to the equipment and provide signals that are a function of the operating parameters of the equipment. The subsystems for each unit communicate with each other and with a plant control system 28 through a unit data bus 30 which may be a single, double redundant or triple redundant bus system. Plant control system 28 communicates with an engineering workstation 32, at least one operator workstation 34 and other display and human machine interfaces 36, such as printers and a data historian that receives and stores data transmitted to it from respective subsystems coupled through unit data bus 30.
The subsystems include for example, a generator excitation and protection subsystem 38, a static starter subsystem 40, a steam turbine and bypass control subsystem 42, heat recovery steam generator (HRSG) and steam cycle mechanical auxiliaries subsystem 44, and a unit auxiliary control subsystem 46.
Fuel supply pressure sensor 108 generates a signal P1 that is a function of the fuel supply pressure upstream from pressure control valve 106 and intervalve pressure sensor 110 generates an intervalve pressure signal P2 that is a function of the fuel control pressure downstream from pressure control valve 106. A position of pressure control valve 106 is controlled by an actuator 112 coupled to pressure control valve 106. Actuator 112 is controlled from an output y of a gas turbine engine fuel control subsystem 114.
Gas turbine engine fuel control subsystem 114 includes a component model 116 that is adapted to represent the response of the fuel supply components including the valves, piping, and sensors to process parameters affecting control system 10 and an integral plus state feedback module 117. An inner loop of integral plus state feedback module 117 is a feedback parameter 118. Fuel supply pressure signal P1 provides feedforward for fuel control subsystem 114. Intervalve pressure signal P2 is the controlled parameter of fuel control subsystem 114. Intervalve pressure signal P2 and a pressure setpoint signal from control system 10 are summed to generate an error signal 120, which is fed into an integrator 122 and a gain 124 is applied. The integrated error signal 126 and the state feedback signal 128 are combined at a summer 130. The resultant signal is transmitted to component model 116 for further processing. Uncertainties in the parameters used to describe the fuel supply components in component model 116 or disturbances acting on the fuel supply components may cause steady-state control errors. To reject such effects the state-feedback configuration is used in the inner loop of fuel control subsystem 114.
In operation, a demand for fuel may change slowly as gas turbine engines being supplied the fuel increase mechanical output to supply increasing electrical load from, for example, an electrical power grid. Additionally, the demand for fuel may change rapidly, such as a step rise due to a rapid rise in electrical demand. Pressure sensors 108 and 110 sense the pressure change in their respective lines due to the increased fuel demand. P1 provides a pressure feedforward signal to component model 116 and intervalve pressure signal P2 is summed with the intervalve pressure setpoint received from control system 10. Error signal 120 is integrated and a predetermined gain applied. The resultant integrated signal is summed with a gain adjusted state-feedback signal from component model 116. Component model then applies the model parameters and pressure feedforward signal P1 to the processed error signal to generate a control output y that is transmitted to actuator 112 to modulate pressure control valve 106 to adjust the intervalve fuel pressure back to the setpoint value. Using an integral plus state feedback control circuit in gas turbine engine fuel control subsystem 114 provides an improved dynamic response over known fuel control systems. The improved dynamic response includes a smaller rise time in response to a step change in the controlled parameter and improved tracking action for higher frequency command reference signals.
Although described with respect to a gas fuel supply system, embodiments of the present invention are not intended to be so limited. Accordingly, fuel supply systems controlling other forms of fuel are also able to be used in other embodiments of the present invention. Moreover, references to a fuel control valve also include other fuel flow and pressure modulating devices such as dampers, conveyors, and variable speed fans and blowers.
A technical effect of the present invention is to facilitate reducing the effect of gas fuel system supply pressure variations on regulated gas intervalve pressure.
The above-described gas turbine engine fuel supply control sub-system is cost-effective and highly reliable. The subsystem permits an improved dynamic response for the fuel supply pressure control valve such that fuel supply pressure changes due to fuel demand changes are mitigated in a relatively shorter period of time. Accordingly, the gas turbine engine fuel supply control sub-system facilitates the operation of the gas turbine engine in a cost-effective and reliable manner.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
