Control device, gas turbine, control method, and program

1. A control device comprising:

a fuel flow rate command calculation unit configured to select and execute:

normal control including calculating a fuel flow rate command value through feedback control based on a deviation between a target output and an actual output of a gas turbine and

load decreasing control including creating a fuel reduction plan for reducing the fuel flow rate command value at a predetermined first rate to reduce the actual output of the gas turbine to a predetermined target output during a predetermined first time without performing feedback control, and calculating the fuel flow rate command value in accordance with the fuel reduction plan, wherein the predetermined first time is set to be longer than a time of two seconds below which a possibility of an occurrence of a surge in a compressor of the gas turbine increases and shorter than a time of five seconds above which a possibility of an occurrence of an instrument burnout in a combustor of the gas turbine increases from a time that load decreasing control is selected;

an air suction flow rate control unit configured to create an air suction flow rate reduction plan for reducing a flow rate of air flowing into the compressor of the gas turbine to a predetermined target flow rate at a predetermined second rate such that a fuel-air ratio settles within a predetermined range, in parallel with the load decreasing control executed by the fuel flow rate command calculation unit, and

wherein the control device is configured to, within the predetermined first time, perform control of the flow rate of air to the predetermined target flow rate in accordance with the air suction flow rate reduction plan and perform control of a flow rate of fuel of the gas turbine to the fuel flow rate command value in accordance with the fuel reduction plan without performing feedback control.

2. The control device according to claim 1 , wherein when the load decreasing control is selected, the fuel flow rate command calculation unit changes the predetermined first rate, in accordance with an atmospheric air temperature.

3. The control device according to claim 1 , wherein when the load decreasing control is selected, a difference between the predetermined first time and a predetermined second time taken until the flow rate of air flowing into the compressor is reduced to the predetermined target flow rate is equal to or smaller than a predetermined value.

4. The control device according to claim 3 , wherein the predetermined second time is within a range of two seconds to five seconds.

5. The control device according to claim 1 , wherein when the load decreasing control is selected, the predetermined first rate is such that the actual output of the gas turbine is reduced at a rate higher than 100% per minute.

6. The control device according to claim 1 , wherein when the load decreasing control is selected, the predetermined first rate is such that the actual output of the gas turbine is reduced at a rate within a range of 800% per minute to 2,000% per minute.

7. The control device according to claim 1 ,

wherein when the load decreasing control is selected, the predetermined target output of the gas turbine is within a range of 30% to 40% of a rated output of the gas turbine.

8. The control device according to claim 1 further comprising:

an abnormality detection unit configured to detect an occurrence of an abnormal combustion, wherein the abnormality detection unit determines that the abnormal combustion has occurred when a temperature of the gas turbine fluctuates to an extent of a predetermined value or higher per unit time; and

a fuel distribution control unit configured to execute stop control of stopping fuel supply from a first nozzle, of a plurality of nozzles provided in the combustor, provided on a side furthest upstream at a timing when the fuel flow rate command value reaches a value corresponding to the predetermined target output when the occurrence of the abnormal combustion in the combustor during the load decreasing control is detected by the abnormality detection unit, and to execute distribution switch control of switching a fuel supply distribution ratio between the remaining nozzles excluding the first nozzle to a distribution ratio after the stop control.

9. The control device according to claim 8 , wherein the fuel distribution control unit performs correction of compensating for a fuel supply amount which has dropped temporarily due to stop of fuel supply from the first nozzle regarding the fuel supply distribution ratio for the nozzles, of the remaining nozzles excluding the first nozzle, for forming a premixed flame for retaining a premixed combustion flame formed by the combustor.

10. The control device according to claim 8 , further comprising:

a second fuel distribution control unit configured to perform correction of a fuel distribution ratio for a second nozzle of the plurality of nozzles provided in the combustor to avoid a relationship between a combustion load command value corresponding to a load at one time during the load decreasing control and the fuel distribution ratio for the second nozzle at the one time becoming a relationship having a high likelihood of occurrence of combustion vibration regarding the fuel distribution ratio for the second nozzle related to combustion vibration.

11. A gas turbine comprising:

the control device according to claim 1 ;

the compressor;

the combustor; and

a turbine.

12. A control method comprising:

selecting and executing normal control of calculating a fuel flow rate command value through feedback control based on a deviation between a target output and an actual output of a gas turbine;

selecting and executing load decreasing control of creating a fuel reduction plan for reducing the fuel flow rate command value at a predetermined first rate to reduce the actual output of the gas turbine to a predetermined target output during a predetermined first time without performing feedback control, and calculating the fuel flow rate command value in accordance with the fuel reduction plan, wherein the predetermined first time is set to be longer than a time of two seconds below which a possibility of an occurrence of a surge in a compressor of the gas turbine increases and shorter than a time of five seconds above which a possibility of an occurrence of an instrument burnout in a combustor of the gas turbine increases from a time that load decreasing control is selected;

creating an air suction flow rate reduction plan for reducing a flow rate of air flowing into the compressor of the gas turbine to a predetermined target flow rate at a predetermined second rate such that a fuel-air ratio settles within a predetermined range, in parallel with execution of the load decreasing control; and

performing, within the predetermined first time, control of the flow rate of air to the predetermined target flow rate in accordance with the air suction flow rate reduction plan and control of a flow rate of fuel of the gas turbine to the fuel flow rate command value in accordance with the fuel reduction plan without performing feedback control.

13. A non-transitory computer-readable storage medium storing a program, wherein when executed by a computer the program causes the computer to perform operations including:

selecting and executing normal control of calculating a fuel flow rate command value through feedback control based on a deviation between a target output and an actual output of a gas turbine;

selecting and executing load decreasing control of creating a fuel reduction plan for reducing the fuel flow rate command value at a predetermined first rate to reduce the actual output of the gas turbine to a predetermined target output during a predetermined first time without performing feedback control, and calculating the fuel flow rate command value in accordance with the fuel reduction plan, wherein the predetermined first time is set to be longer than a time of two seconds below which a possibility of an occurrence of a surge in a compressor of the gas turbine increases and shorter than a time of five seconds above which a possibility of an occurrence of an instrument burnout in a combustor of the gas turbine increases from a time that load decreasing control is selected;

creating an air suction flow rate reduction plan for reducing a flow rate of air flowing into the compressor of the gas turbine to a predetermined target flow rate at a predetermined second rate such that a fuel-air ratio settles within a predetermined range, in parallel with execution of the load decreasing control; and

performing, within the predetermined first time, control of the flow rate of air to the predetermined target flow rate in accordance with the air suction flow rate reduction plan and control of a flow rate of fuel of the gas turbine to the fuel flow rate command value in accordance with the fuel reduction plan without performing feedback control.