Method of and device for controlling fuel for gas turbine

1. A gas turbine fuel control method of controlling a lift amount of a pressure control valve provided at a piping in which fuel for a gas turbine flows, by feeding back an actually obtained differential pressure across a flow rate control valve also provided at the piping to the pressure control valve and making the differential pressure follow a desired target value of the differential pressure, the gas turbine fuel control method comprising:

expressing a conductance of the pressure control valve using

a pressure used to supply fuel gas that is detected upstream of the pressure control valve at the piping,

a pressure in a combustor casing of the gas turbine,

an output of a generator connected to the gas turbine, and

a controlled output for the flow rate control valve that is calculated based on a difference between an output target value of the generator and an actual output of the generator;

obtaining an additional lift amount of the pressure control valve from a relationship between the conductance of the pressure control valve and lift; and

adding the additional lift amount to the lift amount.

2. A gas turbine fuel control method of controlling a lift amount of a pressure control valve provided at a piping in which fuel for a gas turbine flows, by feeding back an actually obtained differential pressure across a flow rate control valve also provided at the piping to the pressure control valve and making the differential pressure follow a desired target value of the differential pressure, the gas turbine fuel control method comprising:

obtaining a mass flow rate of inflow fuel to the gas turbine that is derived from a relationship with an output of a generator connected to the gas turbine;

obtaining density of the fuel by multiplying a pressure for fuel gas supply detected upstream of the pressure control valve by a proportional constant for a relationship between the pressure of the fuel gas supply and the density of the fuel;

obtaining the differential pressure across the flow rate control valve by multiplying a square of the mass flow rate by the density of the fuel to obtain a product, and dividing the product by a square of a conductance of the flow rate control valve which is obtained from a controlled output for the flow rate control valve using a function between the controlled output for the flow rate control valve and the conductance of the flow rate control valve, the controlled output being calculated based on a difference between an output target value of the generator and an actual output of the generator;

obtaining a conductance of the pressure control valve by dividing a product between the mass flow rate and a square root of the fuel density, by a square root of a differential pressure across the pressure control valve, the square root of the differential pressure being expressed by subtracting a pressure in a combustor casing of the gas turbine from the pressure for the fuel gas supply to obtain a pressure and further subtracting the differential pressure from the obtained pressure;

determining an additional lift amount of the pressure control valve using a function between the conductance of the pressure control valve and lift; and

adding the additional lift amount to the lift amount.

3. The gas turbine fuel control method according to claim 2 , wherein the mass flow rate of inflow fuel to the gas turbine is expressed by a first-order progress function of an output of the generator connected to the gas turbine, and the conductance of the flow rate control valve is expressed by a first-order lag function of the controlled output for the flow rate control valve.