Note: Descriptions are shown in the official language in which they were submitted.
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FUEL CONTROL METHOD AND APPARATUS
FOR COMBINED PLANT
This is a divisional of Application Serial
No. 2,435,891 filed July 23, 2003.
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a fuel control method and
apparatus for a combined plant, and a program for allowing a computer
to execute the fuel control method for tne combined plant. More
particularly, the present invention relates to a fuel control method for a
combined plant that is not affected by the engagement or
disengagement of a clutch, a control apparatus for use therein, and a
program for allowing a computer to execute the fuel control method for
the combined plant.
2) Description of the Related Art
A single-shaft combined plant is constructed by connecting a
gas turbine, a power generator, and a steam turbine via a single shaft.
In recent years, a single-shaft combined plant in which a clutch is
disposed in a shaft between the power generator and the steam turbine
has come on the market of the single-shaft combined plants. Such a
single-shaft combined plant with a clutch is featured in that two rotors
can be connected to or disconnected from each other via the clutch,
and the gas turbine and the steam turLine can be started or stopped
independently.
In such a single-shaft combineci plant with a clutch, the clutch is
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disengaged until steam generated from an exhaust gas boiler that
utilizes exhaust gas supplied from the gas turbine can be charged into
the steam turbine, and, only the gas turbine and the power generator
are first started in use. Then, once the steam turbine reaches a
predetermined revolution number, the clutch is engaged. To the
contrary, when the combined plant is stopped, the steam to be supplied
to the steam turbine is first decreased, the clutch is disengaged, and
thereafter, a fuel control valve is throttled, thereby stopping the gas
turbine.
Fig. 8 is a diagram showing the configuration of a control system
for the single-shaft combined plant with the clutch. First, the case
such that a control system called a load limiting control system is
adopted is explained. A gas turbine 81 and a steam turbine 82 are
uni-axially connected to each other via a power generator 83 and a
clutch 84. An output of the gas turbine 81 is controlled based on a
control output 88 obtained by adding a value of a PID controller 87 to a
difference E between a target load set value 85 from a host computer
and an actual load 86.
The control output 88 is converted into a lift of a fuel control
valve 89, and thereby a fuel flow rate is adjusted. Finally, the output of
the gas turbine is controlled. The target load set value 85 from the
host computer is appropriately reviewed according to the situation of
power consumption. At this time, if the target load set value 85 is
rapidly changed, the temperature around a burner and a blade of the
gas turbine is changed, and as a result, the gas turbine is broken. In
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view of this, a change rate limiter 90 for suppressing a change rate is
inserted immediately after the operation of the target load set value 85.
Fig. 9 is a diagram showing the configuration of another control
system for the single-shaft combined plant with the clutch. This
system is called a governor control system. In the case of output
control of a gas turbine 91 in this system, a difference between a target
load set value 92 from a host computer and an actual load 93 is first
taken, and then, a revolution number command (SPSET) is produced
accordingly, to be stored in a memo!-y M. The output is controlled
based on a control output 95 obtained by adding a gain K to a
difference between the revolution number command value and an
actual revolution number 94 of the gas turbine 91. Incidentally, a
change rate limiter 96 is disposed immediately after the operation of the
target load set value, which is the same as that of the load limiting
control system.
When the single-shaft combined plant with the clutch such
controlled as described above is adopted, torque required for the start
is decreased since only the gas turbine and the power generator are
first started in the state in which the clutch is disengaged.
Consequently, it is possible to dispense with a starting device or reduce
a capacity of the device. Furthermore, while only the gas turbine and
the power generator are started, the steam turbine can be rotated at a
low speed so as to ignore a windage loss. During this period of time,
no cooling steam is needed. Consequently, it is possible to dispense
with an auxiliary boiler or reduce a capacity of the boiler.
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However, in the single-shaft combined plant with the clutch,
there arise problems described below when the clutch is engaged and
disengaged.
Since the torque of the stearri turbine is applied to the power
generator at a dash when the clutch is engaged, an output (i.e., an
actual load) from the power generator is rapidly increased at a dash
(the clutch cannot be engaged unless the torque of the steam turbine is
applied at a dash). At this time, although the target load is constant in
the combined plant control system, the actual load is rapidly increased,
so that the fuel control valve is throttled at a dash. Such a fuel control
abruptly changes the combustion state of the gas turbine, thereby
leading to a danger of damage on a burner or a misfire.
To the contrary to the phenornenon, the torque of the steam
turbine is eliminated at a dash when the clutch is disengaged, although
it is necessary to disengage the clutch while the combined plant is
stopped, and therefore, the output (i.e., the actual load) from the power
generator rapidly drops in an instant at a dash. In other words, the
clutch is successfully disengaged orily when the valve is closed in such
a manner that the torque of the steam turbine is reduced at a dash. At
this time, since the target load is coistant and the actual load rapidly
drops, the fuel control valve is released at a dash. Such fuel control
may also cause a damage given to the burner.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a fuel control method
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and apparatus in a combined plant tiat are not affected by the
engagement or disengagement of a clutch, and a program for allowing a
computer to execute the fuel control method for a combined plant.
The fuel control method, according to one aspect of this
invention, of controlling an increase or decrease of the fuel for the
combined plant according to a difference between a target load set
value input from a host computer and a value obtained by feeding back
an actual load is applied in a combined plant that includes a gas turbine
and a steam turbine connected to each other via a clutch. The fuel
control method comprises steps of detecting an engagement period or a
disengagement period of the clutch to output a period detected signal
when either of the periods is detected, and switching the target load set
value to the actual load during a fixed period before and after the
engagement of the clutch and a fixed period before and after the
disengagement of the clutch upon receipt of the detected signal as a
trigger.
According to this invention, the engagement period of the clutch
not only signifies the physical engagement time of the clutch but also
includes a time immediately before the physical engagement time of the
clutch at which the clutch is about to be engaged. Likewise, the
disengagement period of the clutch includes a time immediately before
the physical disengagement time of the clutch. The detection unit that
detects the engagement period and the disengagement period of the
clutch may be a position sensor additionally attached to the clutch or a
sensor in synchronism with an electromagnetic clutch.
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The fuel control method, according to another aspect of this
invention, of controlling an increase Dr decrease of the fuel for the
combined plant according to a difference between a target load set
value input from a host computer and a value obtained by feeding back
an actual load is applied in a combined plant that includes a gas turbine
and a steam turbine connected to each other via a clutch. The fuel
control method comprises steps of detecting an engagement period or a
disengagement period of the clutch to output a period detected signal
when either of the periods is detected, and substituting a predetermined
constant value for the difference stored on a memory during a-fixed
period before and after the engagement of the clutch and a fixed period
before and after the disengagement of the clutch upon receipt of the
detected signal as a trigger.
The fuel control method, according to still another aspect of this
invention, is applied in a combined plant that includes a gas turbine and
a steam turbine connected to each other via a clutch. The method
includes producing a revolution number command of the gas turbine
according to a first difference between a target load set value input from
a host computer and a value obtained by feeding back an actual load,
and controlling an increase or decrease of the fuel for the combined
plant according to a second difference obtained by comparing an actual
revolution number of the gas turbine with the revolution number
command. The fuel control method comprises steps of detecting an
engagement period or a disengagenient period of the clutch to output a
period detected signal when either of the periods is detected, and
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substituting a predetermined constarit value for the revolution number
command stored on a memory during a fixed period before and after the
engagement of the clutch and a fixed period before and after the
disengagement of the clutch upon receipt of the detected signal as a
trigger.
The program according to still another aspect of this invention
allows a computer to execute any of the fuel control methods.
The fuel control apparatus according to still another aspect of
this invention is applied in a combined plant that includes a gas turbine
and a steam turbine connected to each other via a clutch. The fuel
control apparatus controls an increase or decrease of the fuel for the
combined plant according to a difference between a target load set
value input from a host computer and a value obtained by feeding back
an actual load. The fuel control apoaratus comprises an input unit that
receives input about a target load sE~t value output from a host
computer and an actual load, and a trigger unit that detects an
engagement period and a disengagement period of the clutch to output
a period detected signal when eithef of the periods is detected. The
apparatus also comprises a calculation unit that, when receiving the
detected signal, switches the target load set value to the actual load for
a fixed perio.d from the receipt of thE, detected signal or substitutes a
predetermined constant value for the difference stored on a memory,
and determines a control output for a fuel control valve by multiplying
the difference being the constant value by a gain, and an output unit
that outputs the control output to the fuel control valve.
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The fuel control apparatus according to still another aspect of
this invention is applied in a combined plant that includes a gas turbine
and a steam turbine connected to each other via a clutch. The
apparatus produces a revolution number command of the gas turbine
according to a first difference between a target load set value input from
a host computer and a value obtained by feeding back an actual load,
and controls an increase or decrease of the fuel for the combined plant
according to a second difference obtained by comparing an actual
revolution number of the gas turbine with the revolution number
command. The fuel control apparatus comprises an input unit that
receives input about a target load set value from a host computer, an
actual load, and an actual revolution number of the gas turbine, and a
trigger unit that detects an engagement period and a disengagement
period of the clutch to output a period cetected signal. The apparatus
also comprises a calculation unit that, when receiving the detected
signal, substitutes a predetermined corstant value for the revolution
number command stored on a memory for a fixed periocl from the
receipt of the detected signal, and detErmines a control output for a fuel
control valve by niultiplying the revolution number cornmand being the
constant value by a gain, and an output unit that outputs the cont.rol
output to the fuel control valve.
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According to still anothEr aspect of the
invention, there is provided a fuel control method for a
combined plant that includes a gas turbine and a steam
turbine connected to each other via a clutch, of controlling
an increase or decrease of the fuel for the combined plant
according to a difference between a target load set value
input from a host computer and a value obtained by feeding
back an actual load, the fuel control method comprising
steps of: detecting an engagement period or a disengagement
period of the clutch to output a period detected signal when
either of the periods is detected; and substituting a
predetermined constant value for tr.e difference stored on a
memory during a fixed period before and after the engagement
of the clutch and a fixed period before and after the
disengagement of the clutch upon receipt of the detected
signal as a trigger.
These and other objects, features and advantages
of the present invention are specifically set forth in or
will become apparent from the following detailed
descriptions of the invention when read in conjunction with
the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing a fuel control method for a
combined plant according to a first embodiment of this invention,
Fig. 2A and Fig. 2B are explcnatory diagrams showing a control
apparatus, in which Fig. 2A is a functional block diagram and Fig. 2B is
a hardware configuration,
Fig. 3 is a flowchart showing the flow of the control method for
the first embodiment,
Fig. 4 is a block diagram shovving an example of elements
required for detecting a clutch engacement or disengagement period,
Fig. 5 is a block diagram showing a fuel control method for a
combined plant according to a secord embodiment of this invention,
Fig. 6 is a flowchart showing the flow of the control method
according to the second embodiment,
Fig. 7 is a graph showing a change in actual load in the
combined plant,
Fig. 8 is a block diagram showing the configuration of a control
system for a conventional combined plant with a clutch, and
Fig. 9 is a diagram showing the configuration of another control
system for the conventional combined plant with the clutch.
DETAILED DESCRIPTIONS
Embodiments of the present invention are explained in detail
below with reference to the accompanying drawings. It is noted that
the present invention is not limited to the embodiments. Furthermore,
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constituent elements in the embodinients include replaceable elements
or elements easily handled by one skilled in the art, or substantially the
same elements.
A first embodiment of this invention will be explained below.
Fig. 1 is a block diagram showing a fuel control method for a combined
plant according to the first embodiment. In a combined plant 1, a gas
turbine 2 and a steam turbine 3 are connected to each other via a
clutch 4. Here, an example of a sirigle-shaft combined plant in which a
power generator 5 is disposed between the gas turbine 2 and the steam
turbine 3 to be connected to one another via a single shaft, is
explained.
Fuel in the combined plant 1 is fed to the gas turbine 2 via a fuel
control valve 6 to rotate the turbine and then is exhausted. The
exhausted gas generates pressurized steam in an exhaust gas boiler
(not shown). The pressurized stearn is fed to the steam turbine via a
steam regulating valve 7 to rotate the turbine. In this manner, the
power generator 5 constitutes a part. of power generating equipment,
and generates electric power by rotation of both the rotary machines,
that is, the gas turbine 2 and the steam turbine 3.
The clutch 4 is disengaged when the combined plant 1 is started,
and is engaged when the revolution number of the steam turbine 3
becomes equal to that of the gas tur'bine 2. In contrast, the steam
regulating valve 7 is throttled during the stoppage of the combined plant
1 to reduce the revolution number of the steam turbine 3 at a dash, and
thereby the clutch 4 is disengaged. Incidentally, the types of clutch 4
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include a friction clutch, an interlock clutch, and the like, and among
these clutches, the interlock clutch 4 such as a helical spline is
preferable from the viewpoint of the magnitude of transmission power or
reliability.
A control system comprises a subtractor 10, a PID controller 11,
and a clutch engagement or disengagement period detection unit 13.
The subtractor 10 performs subtraction between a target load set value
8 output from a host computer and a value 9 obtained by feeding back
an actual load (hereinafter referred to as an actual load). A difference
between the two values is determined to be then calculated by the PID
controller 11 disposed downstream of the subtractor 10, and thus, a
control output 12 is obtained. The control output 12 is converted into a
lift of the fuel control valve 6 based on a function thereafter (or
calculation, not shown), so that the fuel is controlled to be increased or
decreased. Incidentally, it is general that a change rate limiter 16 is
provided upstream of the subtractor 10, for suppressing an abrupt
change in target load set value 8.
Immediately after the start of the combined plant 1 or during a
rated operation, the clutch 4 is in a completely disengaged or engaged
state, and thus, the fuel is controlleci by the control method. In the
meantime, when the clutch 4 is engaged and disengaged, the target
load set value 8 is switched to the actual load 9 in response to a signal
from the clutch engagement or disengagement period detection unit 13
as a trigger. That is to say, the signal from the target load set value 8
in Fig. 1 is switched to a signal 14 from the actual load 9.
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The clutch engagement or disengagement period detection unit
13 for the clutch 4 may be any unit such as a position sensor
additionally attached to the clutch 4 or a sensor in synchronism with an
electromagnetic clutch. When the clutch 4 is engaged or disengaged
depending on the revolution number or rotational speed of the steam
turbine 3, for example, when a difference in speed between the gas
turbine and the steam turbine becomes smaller than a predetermined
value, this period is detected as the engagement period. When the
steam regulating valve is throttled in a stop mode, this period is
detected as the disengagement period. In these cases, the detection
unit 13 may be a unit such as an encoder, a pulse generator, a
tacho-generator, a resolver, or a solenoid valve.
Although the change rate limiter 16 is provided downstream of a
switching selector 15 in Fig. 1 and these two constituent elements 15
and 16 are disposed independently from each other in order to explain
the concept, the constituent elemew's 15 and 16 may be realized by
single equipment or software. In tris case, it is preferable that the
function of the change rate limiter 1(3 should be turned off at the same
time when the target load set value 8 is switched to the actual load 9.
In this manner, when the target load set value 8 output from the
host computer is switched to the actual load 9, the difference in the
subtractor 10 becomes zero. In other words, a sudden change in load
generated at the time of the engagement or disengagement of the
clutch can never influence on the control system downstream of the
subtractor 10. Consequently, the fuel control valve 6 is not suddenly
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opened or throttled, unlike in the prior art, thereby preventing any
damage on a burner of the gas turbine 2.
Fig. 2A and Fig. 2B are block diagrams showing a control
apparatus that performs the control method, in which Fig. 2A is a
functional block diagram and Fig. 2B is a block diagram showing a
hardware configuration. As shown n Fig. 2A, a control apparatus 20
comprises an input section 21, a trigger section 22, a calculation
section 23, and an output section 24. For the purpose of maintenance
or monitoring, a user interface unit such as a monitor (not shown) may
be provided in addition to the constituent elements.
The target load set value 8 and the actual load 9 are input into
the input section 21. Furthermore, a trigger signal from the clutch
engagement or disengagement period detection unit 13 is input into the
trigger section 22. The calculation section 23 is adapted to perform
the calculation in the change rate limiter 16, the subtractor 10, the PID
controller 11, or the like based on the values input into the input section
21.
When the trigger section 22 detects the clutch engagement or
disengagement period (i.e., the trigcer signal), the calculation section
23 performs the switching. The ou_put section 24 outputs the control
output 12 led out by the calculation section 23 as an electric signal.
Incidentally, the calculation section 23 includes a storage section
therein, and thus, carries out the calculation by reading or writing data
from or in the storage section.
As shown in Fig. 2B, the hardware configuration of the control
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apparatus 20 includes a processor 25 such as a CPU that is a complex
instruction set computer (CISC) or a reduced instruction set computer
(RISC) or a digital signal processor ~DSP), a ROM 26, a RAM 27, an
input-output interface (I/O) 28, and a user interface 29, each of which is
connected to one another via a bus 30.
An execution program of the processor 25 is previously stored in
the ROM 26. Furthermore, a comrriunication program used to
communicate with the input-output interface 28 and a program used to
input or output data in or from the user interface 29 are also stored in
the ROM 26. Although not shown i i the figure, an A/D converter or a
D/A converter is disposed in the inpiat-output interface 28 according to a
device to be connected thereto. TI-e explanation is given based on the
assumption that digital processing is performed by the software, but
analog processing may be performed by hardware.
Fig. 3 is a flowchart showing the flow of the control method in
the first embodiment. First, a target load set value and an actual load
are input into the control apparatus (steps S101 and S201). Then, it is
detected whether a trigger signal indicating the engagement or
disengagement period of the clutch is input (step S103). If the trigger
signal is input, a timer switches the target load set value to the actual
load for a fixed period of time (i.e., a time until the engagement or
disengagement state of the clutch is stabilized) (step S104). When the
trigger signal is not input, the target load set value and the actual load
are handled as respective values a:i they are.
A difference is obtained by subtracting the actual load from the
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target load set value (step S105). The PID controller calculates the
obtained difference, thereby introducing it out as a control output (step
S106). Thereafter, 'the control apparatus outputs the control output as
an electric signal (step S107). The control apparatus repeats the
routine of processing (step S108).
Fig. 4 is a block diagram showing an example of elements
required for detecting the clutch engagement or disengagement period.
First, an example of detection of the clutch engagement period is
explained. There is a particular period such that the clutch
engagement or disengagement period detection unit 13 receives a gas
turbine revolution number 32 and a steam turbine revolution number 33,
and that a difference between these revolution numbers becomes a
fixed small value or less. The detection unit 13 judges this period as a
period when the clutch is just about to be engaged, namely, judges that
the clutch enters the engagement period, and outputs a trigger signal
34. The trigger signal 34 is designed to be output for a fixed period of
time that has been previously set by a timer or the like. In this manner,
the target load set value is switched to the actual load until a
stabilization period such that the fluctuation in load after the clutch
engagement is stabilized.
An example of detection of the clutch disengagement period is
explained below. There is a particular period such that the clutch
engagement or disengagement period detection unit 13 receives a
signal 35 indicating a stop mode and a signal 36 from the steam
regulating valve in the steam turbine, the clutch is in the stop mode,
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and that the steam regulating valve :36 is throttled. The detection unit
13 judges this period as a period when the clutch is just about to be
disengaged, namely, judges that the clutch enters the disengagement
period, and outputs the trigger signal 34. In this case, also, the trigger
signal 34 is designed to be output for a fixed period of time that is
previously set by the timer or the like. In this manner, the target load
set value is switched to the actual load until a stabilization period when
the fluctuation in load after the clutcn disengagement is stabilized.
The flow is embodied in a computer program to be executed on
a computer. In this way, it is possible to construct the control
apparatus that performs the combined plant control method in which the
target load set value is or is not switched to the actual load in response
to the trigger signal.
A modification of the first embodiment will be explained below.
The same effect as that in the first embodiment can be produced
also when the difference obtained ir the subtractor 10 is set to a
constant value in response to the trigger signal from the clutch
engagement or disengagement period detection unit 13 shown in Fig. 1.
In other words, the subtractor 10 can be constructed by the hardware or
software, and in any case, there is provided the processing of
temporarily storing the difference or7 the memory. When the clutch 4
enters the engagement period or the disengagement period, the
difference is substituted by the precetermined constant value in
response to the trigger signal from the clutch engagement or
disengagement period detection un t 13.
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Specifically, when the subtra:;tor 10 is constructed by the
hardware, a signal that subtracts or is subtracted may be set to zero by
grounding, and in addition, may be set to a predetermined value by a
bias circuit or the like. In contrast, when the subtractor 10 is
constructed by the software, a value stored on the memory may be
continued to be substituted during a given period of time after the
output of the trigger signal from the clutch engagement or
disengagement period detection unit 13. Here, the reason for the
continuous substitute during the given period is that the actual load 9
from the power generator 5 or a connecting shaft 17 cannot be
stabilized for the given period after the physical engagement or
disengagement of the clutch. It is preferable to allow the given period
to be appropriate set by a timer in the hardware or software.
Even by adopting such a control method, a sudden change in
load occurring when the clutch is engaged or disengaged, can be
prevented from exerting any influence on the control system
downstream of the subtractor 10. Consequently, the fuel control valve
6 is prevented to be suddenly opened or throttled, unlike in the prior art,
and thus, the burner of the gas turb'ne 2 cannot be damaged.
A second embodiment of this invention will be explained below.
Fig. 5 is a block diagram showing a fuel control method for a
combined plant in a second embodiment of the present invention. Fig.
5 shows improvements made to the conventional governor mode. That
is to say, a subtractor 53 obtains a difference El 52 between a target
load set value 50 and an actual loa(1 51 from a host computer, thereby
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producing a revolution number comrriand (SPSET) 54 accordingly.
A memory 58 temporarily stores the value of the command
therein, and then, fuel control is performed based on a control output 57
obtained by giving a gain 56 to a difference E2 55 between a value
fetched from the memory 58 and an actual revolution number 62 of the
gas turbine. . Here, the present embodiment is the same as the first
embodiment in that a change rate limiter 59 is disposed downstream of
the target load set value.
In the second embodiment, a description will be mainly given of
a control method and a control apparatus in a configuration in which a
clutch engagement or disengagement period detection unit 60 and a
unit 61 that substitutes a value stored in the memory 58 with another
value are disposed in addition to the configuration. The clutch
engagement or disengagement period detection unit 60 may be a
position sensor additionally attached to a clutch 4, a sensor such as an
electromagnetic clutch, or a unit that receives a revolution number of a
gas turbine or a steam turbine, a stcp mode, or the switching state of a
steam regulating valve, like in the fir'st embodiment.
As described above, the SPSET 54 in the configuration is
produced according to the difference El 52. Consequently, when the
actual load 51 is suddenly changed according to the engagement or
disengagement of the clutch 4, the SPSET 54 is also suddenly changed.
Therefore, according to the present invention, the value of the SPSET
54 is substituted by a predetermined constant value on the memory 58
in accordance with the engagement or disengagement of the clutch 4.
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In this manner, no sudden change influences on a control
system downstream of the difference E2 55 between the revolution
number command 54 and the actual revolution number 62 of the gas
turbine. Incidentally, when the SPSET 54 is produced, a change rate
limiter may also be juxtaposed in order to suppress the sudden change.
In this case, the same effect as that described above can be obtained
even by substituting the change rate set by the change rate limiter with
zero according to the engagement or disengagement of the clutch 4.
The apparatus for using the control method has basically the
same configuration as that shown in Fig. 2A. Incidentally, the
apparatus is different from that shown in Fig. 2A in that the actual
revolution number 62 of the gas turbine is additionally input in the input
section 21 in Fig. 2A, and therefore, three signals in total are input.
The calculation to be performed by a calculation section 23 is also
varied depending upon the difference in configuration shown in each of
Figs. 2 and 5. Next, the flow of control including the difference is
specifically explained below.
Fig. 6 is a flowchart showing the flow of the control method in
the second embodiment. First, a target load set value R, an actual
load L, and an actual revolution number N of the gas turbine (steps
S301 to S303) are input into the control apparatus. Incidentally,
although the actual revolution number N of the gas turbine is input at
this point for the convenience in explanation, this number is not always
input at this point, and therefore, it is also allowed that the number is
input before the difference E2 as described later is obtained.
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The load L is subtracted frorn R, thereby obtaining the difference
El (step S304). The difference El is converted into the revolution
number command (SPSET) of the gas turbine in consideration of an
adjustment rate (step S305). Here, a change rate limiter may be
additionally disposed as a compensator in order to suppress an abrupt
change in the revolution number command. It is then confirmed that a
trigger signal is input (step S306).
If the trigger signal is input, the value of the difference SPSET
stored in the memory is substituted with a given value "a", or the
change rate of the change rate limiter is set to zero (step S307). In
contrast, if the trigger signal is not input, the value SPSET is held as it
is. The SPSET is subtracted from the actual revolution number N of
the gas turbine, thereby obtaining tre difference E2 (step S308). The
difference E2 is multiplied by a gain K, thereby generating a control
output (step S309). Then, a final control output is output toward the
fuel control valve (step S310). The control apparatus repeats the
routine of processing (step S311).
The control prevents any change in the control output as long as
the revolution number (the system frequency) of the power generator is
not changed. When the load is stabilized with a brief lapse of time
after the engagement or disengagernent of the clutch, the SPSET is
varied at a preset change rate, so that fuel is controlled in such a
manner that the actual load follows the target load set value.
Fig. 7 is a graph showing a7-hange in actual load in the
combined plant when the present irvention is embodied. In the graph,
CA 02580664 2007-03-27
28964-96D
the ordinate represents a load while the abscissa represents a time. In
the graph, dotted lines indicate the load 71 of the gas turbine, long and
short dashed lines indicate the load 72 of the steam turbine, and solid
lines 73 indicate the sum of the two loads. As described above, only
the gas turbine is first started when the combined plant is started.
Therefore, the sum 73 in a time zone 74 is equal to the load of the gas
turbine, and its inclination depends upon the setting by the change rate
limiter.
At a time En when the revolution number of the steam turbine is
increased and the clutch is engaged, the sum 73 becomes equal to the
magnitude obtained by adding the Iclad 71 of the gas turbine to the load
72 of the steam turbine, and it is abruptly changed. According to the
present invention, since the differen--e takes a predetermined small
value even at the time of the abrupt change, the fuel is not reduced
excessively. Therefore, the fuel can be stably supplied without any
impulsive outburst of the load.
Since the difference in a control algorithm becomes constant
during the engagement period of the clutch, that is, during a zone 75 in
a brief period before the engagement time En, the load 71 of the gas
turbine is never changed, so that the sum 73 is moderately increased
by an increase in load of the steam turbine 72. After the zone 75, the
difference becomes equal to the difference between the target load set
value and the actual load, so that the load is increased at a rate set by
the change rate limiter.
In order to stop the combined plant, the stop mode is set (i.e., is
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28964-96D
selected by an operator), and then, _he steam regulating valve to the
steam turbine is throttled, whereby the load is abruptly decreased at the
time Re of the disengagement of the clutch. In this case, also, the
effect of the present invention can be exhibited, and thus, the fuel is
never supplied impulsively. In other words, the difference becomes
constant for a fixed period 76 from the disengagement time, and
therefore, the load of the gas turbine is not changed but is kept at a
constant value. The target load set value is decreased for a period 77
after the fixed period 76, so that the load is decreased at the rate set by
the change rate limiter, thereby stopping the gas turbine. Incidentally,
the same change in load can be obtained also by embodying the control
method in the first embodiment.
As described above, according to the fuel control method for the
combined plant as one aspect of the present invention, the sudden
change in load occurring when the clutch is engaged or disengaged
never influences on the control system disposed downstream thereof.
Consequently, it is prevented to suddenly open or throttle the fuel
control valve, unlike in the prior art, and thus, the burner of the gas
turbine is never damaged.
According to the program as another aspect of the present
invention, by executing the program on the computer, the fuel can be
stably controlled in the combined plant irrespective of the sudden
change in load at the time of the engagement or disengagement of the
clutch. Thus, it is possible to prevent any breakage of the burner of
the gas turbine.
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According to the fuel control apparatus in the combined plant as
still another aspect of the present invention, the fuel can be stably
controlled in the combined plant irrespective of the sudden change in
load at the time of the engagement or disengagement of the clutch.
Thus, it is possible to prevent any breakage of the burner of the gas
turbine.
Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the appended
claims are not to be thus limited but are to be construed as embodying
all modifications and alternative constructions that may occur to one
skilled in the art which fairly fall within the basic teaching herein set
forth.
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