Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GAS TURBINE PLANT AND
METHOD OF CONTROLLING GAS TURBINE PLANT
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a gas turbine plant used in a power
generation
plant and to a method of controlling such a gas turbine plant.
Description of the Related Art
Fig. 9 shows the general structure of a conventional single-shaft combined
plant
(i.e., gas turbine plant}.
In the shown single-shaft combined plant, reference numeral 101 indicates a
compressor for absorbing and compressing the air, reference numeral 102
indicates a
combustor to which combustion oil and combustion air (which has been
compressed in
the compressor 1 O1 ) are supplied, reference numeral ~ 03 indicates a gas
turbine which
rotates when receiving a combustion gas generated by the combustor 102,
reference
numeral 104 indicates a steam turbine coupled with the gas turbine 103, and
reference
numeral 105 indicates a generator.
The above gas turbine 103, compressor 101, steam turbine 104, and generator
105 are coupled with each other via a coupling shaft 106.
The drive source for the steam turbine 104 is an exhaust heat recovery boiler
108. . The exhaust heat recovery boiler 108 generates steam by using heat
collected
from the high-temperature exhaust gas output from the gas turbine 103, and
introduces
the generated steam into the steam turbine 104. Reference numeral 107
indicates a
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condenser into which exhaust steam from the steam turbine 104 is introduced.
The
condenser I07 condenses the introduced steam and returns condensate (i.e.,
condensed
water) to the exhaust heat recovery bailer 108.
Reference numeral 109 indicates a fuel valve for controlling the amount of
fuel
S supplied to the combustor 102. This fuel valve 109 is controlled by a
controller 110.
The combustor 102 has a stnzcture shown in Fig. 10. In Fig. 10, reference
numeral I 12 indicates a main combustor, and reference numeral I 13 indicates
a tail pipe
of the main combustor. Fuel is supplied to the main combustor 112 via the fuel
valve
109, and air 114 is also supplied to the main combustor I I2 Pram the
eornpressor 10I,
thereby combusting the fuel.
Reference numeral 11 S indicates a bypass valve which is controlled by the
controller 110. Depending on the degree of opening of the bypass valve I I S,
the
distribution of air from the compressor 101, that is, the ratio of air
supplied to the main
combustor 112 to air supplied to the tail pipe I 13, is determined.
1 S In the combined plant explained above, when the frequency of the electric
power system is changed due to a load change, the frequency must be stabilized
by
controlling the generated power. The above controller I 10 controls the fuel
valve 109
so as to recover a suitable frequency, thereby controlling the output of the
gas turbine
103.
A concrete example of such a control will be explained below.
In Fig. 11, reference symbol Sl indicates a governor CSO (control signal
output) signal output by the controller 1 I O to the fuel valve I 09 so as to
control the
output of the gas turbine 103.
As shown by reference symbol "a", in the normal state, the controller 1 I 0
2S suitably varies the governor CSO signal SI (corresponding to the output
ofthe gas
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3
turbine 103) so as to fix the frequency.
When the amount of load suddenly decreases, the relevant revolution speed
suddenly increases, and thus the frequency also increases. In this case, as
shown by
reference symbol b1, the controller 110 decreases the level of the governor
CSO signal
S 1 so as to avoid a sudden increase of the revolution speed.
On the other hand, when the amount of load suddenly increases, the relevant
revolution speed suddenly decreases, and thus the frequency also decreases. In
this
case, as shown by reference symbol c1, the controller 110 increases the level
of the
governor CSO signal SI so as to avoid a sudden decrease of the revolution
speed.
However, if the governor CSO signal S I is suddenly increased, the temperature
of the gas turbine 103 suddenly increases. It is not preferable because the
gas turbine
103 should have a stress. Therefore, the controller I 10 calculates, in
advance, a
load-limiting CSO signal S2 shown by reference symbol S2. In the normal state,
the
load-limiting CSO signal S2 has a level higher than that of the governor CSO
signal Sl
I 5 by a predetermined tracking width TW. When the governor CSO signal S 1
suddenly
increases or decreases, the load-limiting CSO signal S2 is increased or
decreased by a
specif c rate. The controller 110 uses the load-limiting CSO signal S2 as an
upper-limit
value of the governor CSO signal S1.
Therefore, when the governor CSO signal SI suddenly decreases, the level of
the load-limiting CSO signal S2 is never less than the level of the governor
CS0 signal
S 1 (refer to reference symbol b 1'); however, when the governor CSO signal S
1 suddenly
increases, the level of the load-limiting CSO signal S2 may be higher than the
level of
the governor CSO signal Sl (refer to reference symbol c1'). Therefore, the
governor
CSO signal SI is limited so as not to increase with a rate higher than the
above-explained specific rate (refer to reference symbol dl).
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i
4
If the Load suddenly increases immediately after a sudden decrease of the
load,
then the governor CSO signal S1 is controlled in a manner such that the signal
suddenly
decreases. and then suddenly increases (see Fig. 12).
That is, when the load suddenly decreases, as shown by reference symbol b2,
the governor CSO signal S 1 decreases without limitation, and the load-
limiting CSO
signal S2 decreases by a specific rate (see reference symbol b2').
After that, when the load suddenly increases, the governor CSO signal Sl
suddenly increases (see reference symbol c2). In this case, the load-limiting
CSO
signal S2 continuously decreases until the load-Limiting CSO signal S2 obtains
a level
1 Q 5% higher than that of the governor CSO signal S I (see reference symbol
b2'). The
load-limiting CSO signal S2 then enters an increase phase, where the increase
is
performed at a specif c rate because of a sudden increase of the governor CSO
signal S 1
(see reference symbol c2'). Accordingly, the governor CSO signal S I is
limited so as
not to increase with a rate higher than the specific rate (see reference
symbol d2), that is,
the load-limiting CSO signal S2 functions as an upper-limit level of the
governor CSO
signal S I .
In the above operation as shown in Fig. 12, in a time period t2 (i.e., before
the
increase of the governor CSO signal S1 is limited), fuel is also suddenly
increased so
that the gas turbine I 03 has a stress.
In addition, the combustor 102 operates according to the variation of the
governor CSO signal 51; as follows: when the load suddenly decreases, the
controller
110 limits the amount of fuel supplied to the main combustor 1 I2 by suitably
closing the
fuel valve 109, thereby suppressing the increase of the relevant revolution
speed. 1n
this process, the controller 110 opens the bypass valve 1 I S so as to
maintain a suitable
fuel-air ratio, so that the amount of air supplied from the bypass valve 1 I S
to the tail
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f
0
pipe I 13 of the combustor increases. Accordingly, the amount of air supplied
to the
main combustor I I 2 is decreased, and the suitable fuel-air ratio is
maintained.
However, in the conventional combined plant, the opening/closing speed of the
bypass valve I 15 is fixed. Therefore, the operation of opening the bypass
valve I I 5
cannot follow the sudden closing of the fuel valve 109, so that an excessive
amount of
air is introduced into the main combustor 1 I2, and this situation causes
unstable
combustion or the like.
SUMMARY OF THE INVENTION
In consideration of the above circumstances, an objective of the present
invention is to provide a gas turbine plant and a method of controlling a gas
turbine plant,
for limiting a sudden increase of the load of the gas turbine, that is, a
sudden increase of
the amount of fuel; and suppressing a stress imposed on the gas turbine.
Another
objective of the present invention is to provide a gas turbine plant and a
method of
controlling a gas turbine plant, for maintaining a suitable fuel-air ratio.
Therefore, the present invention provides a gas turbine plant comprising:
a gas turbine;
a combustor for supplying a combustion gas to the gas turbine;
a fuel valve for controlling an amount of fuel supplied to the combustor, and
a controller for controlling the fuel valve, including:
a governor control signal calculating section for calculating a governor
control signal for controlling the degree of opening of the fuel valve, based
on a
revolution speed of the gas turbine;
a load-limiting control signal calculating section for calculating a
load-limiting control signal for following the governor control signal,
wherein when the
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governor control signal decreases, the load-limiting control signal is larger
than the
governor control signal by a predetermined value, while when the governor
control
signal increases, the increase rate of the load-limiting control signal has a
predetermined
upper limit; and
a limiting section, into which the governor control signal and the
load-limiting control signal are input, for limiting the upper value of the
governor
control signal by using the load-limiting control signal as an upper limit of
said upper
value, thereby controlling the fuel valve.
In this gas turbine plant, when the level of the governor control signal
(corresponding to the governor CSO signal in the embodiment explained below)
decreases (even when the signal suddenly decreases), the load-limiting control
signal
(corresponding to the load-limiting CSO signal in the embodiment explained
below)
follows the governor CSO signal. When the governor control signal suddenly
increases,
the load-limiting CSO signal increases at an increase rate having the
predetermined
upper limit, so that the level of the governor control signal may be larger
than that of the
load-limiting control signal. Therefore, the limiting section limits the
governor control
signal by using the load-limiting control signal as the upper limit, thereby
avoiding a
sudden increase of the output of the gas turbine. As the load-limiting control
signal
follows the governor control signal during a sudden decrease of the governor
control
signal, the limitation of the increase rate of the governor control signal
becomes quickly
effective even when the output of the gas turbine suddenly increases
immediately after a
sudden decrease of the gas turbine output. This is a distinctive feature in
comparison
with the conventional example shown by Fig. 12.
The present invention also provides a method of controlling a gas turbine
plant
comprising a gas turbine, a combustor for supplying a combustion gas to the
gas turbine,
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and a fuel valve for controlling an amount of fuel supplied to the combustor,
the method
comprising the steps of-.
calculating-a governor control signal for controlling the degree of opening of
the fuel valve, based on a revolution speed of the gas turbine;
calculating a load-limiting control signal for following the governor control
signal, wherein when the governor control signal decreases, the load-limiting
control
signal is larger than the governor control signal by a predetermined value,
while when
the governor control signal increases, the increase rate of the load-limiting
control signal
has a predetermined upper limit; and
controlling the fuel valve based on a control signal for limiting the upper
value
of the governor control signal by using the Load-limiting control signal as an
upper limit
of said upper value.
Also according to this method, the governor control signal is limited by using
the Load-limiting control signal as the upper limit arid the limited signal is
output to the
fuel valve, thereby avoiding a sudden increase of the output of the gas
turbine. In
addition, when the level of the governor control signal suddenly decreases,
the
load-limiting control signal follows it, so that also in this method, the
limitation of the
increase rate of the governor control signal becomes quickly effective even
when the
output of the gas turbine suddenly increases immediately after a sudden
decrease of the
gas turbine output.
The present invention also provides a gas turbine plant comprising:
a gas tuxbine;
a combustor to which fuel and air are supplied, including:
a main combustor into which the supplied fuel and air are introduced;
a tail pipe, to which a combustion gas is introduced from the main
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combustor, for introducing the combustion gas to the gas turbine; and
a bypass valve for introducing a portion of the air supplied to the main
combustor into the tail pipe;
a fuel valve for controlling an amount of the fuel supplied to the combustor;
a bypass valve controller for controlling the bypass valve at an
opening/closing
speed according to a variation of the output of the gas turbine; and
a fuel valve controller for controlling the fuel valve.
According to this gas turbine plant, even whem the variation of the output of
the
gas turbine is large, the opening/closing operation of the bypass valve can be
quickly
performed according to the sudden opening/closing operation of the fuel valve.
In this gas turbine plant, a single controller may function as both the bypass
valve controller and the fuel valve controller.
Also in this gas turbine plant, preferably, the bypass valve controller
includes:
a bypass valve opening-degree calculating section for calculating a set value
of
the degree of opening of the bypass valve corresponding to the output of the
gas turbine;
an opening/closing speed calculating section for calculating a width of the
variation of the output of the gas turbine, and calculating an openinglclosing
speed of the
bypass valve based on the calculated width of the variation; and
a first change rate limiter for controlling the bypass valve by using the
openinglclosing speed calculated by the opening/closing speed calculating
section as a
change rate of the set value of the degree. of opening of the bypass valve
calculated by
the bypass valve opening-degree calculating section.
In this structure, the bypass valve opening-degree calculating section
calculates
a suitable degree of opening of the bypass valve according to the output of
the gas
turbine. The opening/closing speed calculating section provides the
openinglclosing
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speed of the bypass valve, which is used when the degree of opening of the
bypass valve
is changed from the current degree to one indicated by the relevant set value.
The
larger the width of the variation of the output of the gas turbine, the higher
the calculated
opening/closing speed becomes. The first change rate limiter outputs a signal
for
controlling the bypass valve based on the obtained opening/closing speed.
Also preferably, the opening/closing speed calculating section includes:
a second change rate limner, into which the output of the gas turbine is
input,
for convening an increaseldecrease change rate of the output of the gas
turbine into a
predetermined change rate, and outputting a reference output having the
predetermined
change rate;
a subtracter, into which the output of the gas turbine and the reference
output
are input, for calculating a difference between the output of the gas turbine
and the
reference output; and
a change rate calculator far calculating the opening/closing speed of the
bypass
1 S valve according to the calculated difference.
In this structure, when the output ofthe gas turbine greatly decreases, the
second change rate limiter outputs a signal Which decreases with a
predetermined change
rate (refer to Figs. 7A and 7B in the embodiment explained below). The
subtracter
calculates a difference between the output from the second change rate limiter
and the
output of the gas turbine (refer to Fig. '7C in the embodiment explained
below). The
larger this difference, the higher the opening/closing speed of the bypass
valve
(calculated by the change rate calculator) becomes.
The present invention also provides a method of controlling a gas turbine
plant
which comprises:
a gas turbine;
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a combustor to which fuel and air are supplied, including:
a main combustor into which the supplied fuel and air are introduced;
a tail pipe, to which a combustion gas is introduced from the main
combustor, for introducing the combustion gas to the gas turbine; and
5 a bypass valve for introducing a portion of the air supplied to the m ain
combustor into the tail pipe; and
a fuel valve for controlling an amount of the fuel supplied to the combustor,
and
wherein the method comprises the step of controlling the bypass valve at an
opening/closing speed according to a variation of the output of the gas
turbine.
10 Accordingly, even when the variation of the output of the gas turbine is
Large,
the openinglclosing operation of the bypass valve can be quickly performed
according to
the sudden opening/closing operation of the fuel valve.
In this method, the step of controlling the bypass valve may include:
calculating a width of the variation of the output of the gas turbine;
calculating an opening/elosing speed of the bypass valve based on the
calculated width of the variation; and
controlling the opening/closing operation of the bypass valve by using the
calculated opening/closing speed.
When the degree of opening of the bypass valve is changed from the current
value to a set value, the opening/closing speed of the bypass valve is
necessary.
According to this method, the larger the width of the variation of the output
of the gas
turbine, the higher the calculated opening/closing speed becomes.
In this method, the step of controlling the bypass valve rnay include:
converting an increase/decrease change rate of the output of the gas turbine
into
a predetermined change rate;
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determining a reference output having the predetermined change rate;
calculating a difference between the output of the gas turbine and the
reference
output; and
determining the calculated difference as the width of the variation of the
output
S of the gas turbine.
Also in this case, even when the output of the gas turbine greatly decreases,
a
reference output having the predetermined change rate is determined in advance
(refer to
Figs. 7A and 7B in the embodiment explained below), and a difference between
the
reference output and the output of the gas turbine (corresponding to the
difference
between Figs. 7A and 7B) is calculated. The larger this difference, the higher
the
opening/closing speed of the bypass valve becomes.
As explained above, according to the present invention, the upper value of the
governor control signal is limited by the load-limiting control signal,
thereby preventing
a sudden increase of the temperature of the gas turbine. In addition, the
limitation of
I S the governor control signal by using the load-limiting control signal
becomes quickly
effective, thereby reducing the stress imposed on the governor control signal,
in
comparison with the conventional gas turbine plant.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. I is a block diagram showing the structure of a controller provided in
the
gas turbine plant as an embodiment according to the present invention.
Fig. 2 is a block diagram showing the structure of an upper-limit value
calculating section in the load-limiting CSO signal calculating section in the
controller.
Fig. 3 is a block diagram showing the structure of a load-limiting CSO signal
2S computing circuit in the load-limiting CSO signal calculating section in
the controller.
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Fig. 4 is a graph showing a relationship between the governor CSO signal and
the load-limiting CSO signal.
Fig. S is a graph showing a relationship hetween the governor CSO signal and
the load-limiting CSO signal when the load suddenly increases immediately
after a
S sudden decrease thereof.
Fig. 6 is a block diagram showing the structure of a bypass valve control
circuit
provided in the controller.
Figs. 7A to 7E are graphs showing a variation of the relevant signals from the
input of a gas-turbine output to the output of a bypass valve control command
in the
I O bypass valve control circuit.
Fig. 8 is a graph showing a relationship between an amount of difference
relating to the output of the gas turbine and a rate of change of the bypass
valve stored in
the bypass valve control circuit.
Fig. 9 is a diagram showing the general structure of a conventional gas
turbine
I S plant.
Fig. I O is a diagram showing the general structure of a combustor used in the
conventional gas turbine plant.
Fig. 1 I is a graph showing a relationship between the governor CSO signal and
the load-limiting CSO signal in the conventional gas turbine plant.
20 Fig. l2 is a graph showing a relationship between the governor CSO signal
and
the load-limiting CSO signal when the load suddenly increases immediately
after a
sudden decrease thereof in the conventional gas turbine plant.
Fig. 13 is a diagram showing the general structure of a gas turbine plant as
an
embodiment of the present invention.
2S Fig. I4 is a diagram showing the general structure of a combustor used in
the
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gas turbine plant of the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments according to the present invention will be explained
S in detail with reference to the drawings.
Fig. 13 is a diagram showing the general structure of a single-shaft combined
plant (i.e., gas turbine plant) as an embodiment of the present invention.
In: the shown single-shaft combined plant, reference numeral 1 indicates a
compressor for absorbing and compressing the air, reference numeral 2
indicates a
combustor to which combustion oil and combustion air (which has been
compressed in
the compressor I ) are supplied, reference numeral 3 indicates a gas turbine
which rotates
when receiving the combustion gas generated by the combustor 2, reference
numeral 4
indicates a steam turbine coupled with the gas turbine 3, and reference
numeral 5
indicates a generator.
The above gas turbine 3, compressor 1, steam turbine 4, and generator 5 are
coupled with each other via a coupling shaft 6.
The drive source for the steam turbine 4 is an exhaust heat recovery boiler 8.
The exhaust heat recovery boiler 8 generates steam by using heat collected
from the
high-temperature exhaust gas output from the gas turbine 3, and introduces the
generated
steam into the steam turbine 4. Reference numeral 7 indicates a condenser into
which
exhaust steam from the steam turbine 4 is introduced. The condenser 7
condenses the
introduced steam and returns condensate (i.e., condensed water) to the exhaust
heat
recovery boiler 8.
Reference numeral 9 indicates a fuel valve for controlling the amount of fuel
supplied to the combustor 2. This fuel valve 9 is controlled by a controller i
Q.
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The cornbustor 2 has a structure shown in Fig. 14. In Fig. 14, reference
numeral 12 indicates a main combustor, and reference numeral I3 indicates a
tail pipe of
the main combustor. Fuel is supplied to the main combustor 12 via the fuel
valve 9,
and air I4 is also supplied to the main combustor 12 from the compressor l,
thereby
combusting the fuel.
Reference numeral I S indicates a bypass valve which is controlled by the
controller 10. Depending on the degree of opening of the bypass valve 15, the
distribution of air from the compressor I, that is, the ratio of air supplied
to the main
combustor 12 to air supplied to the tail pipe 13, is determined.
In the combined plant having the structure explained above, when the frequency
of the electric power system is changed due to a load change, the frequency
must be
stabilized by controlling the generated power. The above controller I O
controls the fuel
valve 9 so as to recover a suitable frequency, thereby controlling the output
of the gas
turbine 3.
1 S A concrete example of such a control will be explained below. Fig. I shows
a
block diagram of the structure of the controller 10.
The controller 10 comprises a governor CSO signal calculating section 20
(corresponding to the governor signal calculating section of the present
invention), a
load-limiting CSO signal calculating section 21 (corresponding to the load-
limiting
signal calculating section of the present invention), and a lower value
selecting circuit 22
(corresponding to the limiting section of the present invention).
The revolution speed of the gas turbine 3 is input into the governor CSO
signal
calculating section 20, and the governor CSO signal calculating section 20
calculates the
amount of load of the gas turbine 3 based on the received revolution speed,
and
calculates (the value of) the governor CSO signal SI for controlling the
degree of
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IS
opening of the fuel valve 9 based on the calculated amount of load.
The load-limiting CSO signal calculating section 21 calculates (the value of)
the load-limiting CSO signal S2 for satisfying the conditions that (i) when
the governor
CSO signal Sl decreases, the load-limiting CSO signal S2 follows the governor
CSO
signal S 1 in a manner such that the level of the load-limiting CSO signal S2
is higher
than the governor CSO signal Sl by a predetermined tracking width, and (ii)
when the
governor CSO signal S I increases, the load-limiting CSO signal S2 follows the
governor
CSO signal S 1 with an increase rate having a predetermined limit.
The lower value selecting circuit 22 limits the upper level of the governor
CSO
signal SI by using the load-limiting CSO signal S2.
Figs. 2 and 3 show the detailed structure ofthe Load-limiting CSO signal
calculating section 21. The load-limiting CSO signal calculating section 21
comprises
a calculator 21 a for calculating a predetermined tracking width with respect
to the
governor CSO signal S 1, an adder 21 b for adding the tracking width to the
governor
CSO signal S1, and an increase-rate calculator 21c for calculating a specific
increase rate
based on the governor CSO signal SI. The load-limiting CSO signal calculating
section 21 also comprises a change rate limiter 21 d into which the outputs
from the
adder 21 b and the increase-rate calculator 21 c are input. In the change rate
limiter 2I d,
for a given input value x output from the adder 21 b (into the change rate
limner 21 d), the
increase rate of the input value x is limited by the value output from the
increase-rate
calculator 2I c, while the decrease rate is not limited. The increase or
decrease rate is
then output from the change rate limiter 21 d, and the output is input into a
PI controller
in Fig. 3 (explained below) as an upper-limit value S2' with respect to the PT
controller
for computing the load-limiting CSO signal (called "LRCSO signal",
hereinbelow).
Fig. 3 shows the structure of a load-limiting CSO (LDCSO) signal computing
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circuit 200 included in the load-limiting CSO signal calculating section 21.
In this
circuit 240, reference numeral 22a indicates a subtracter for calculating a
difference
between a load-limiting set value (i.e:, current load-limiting value) and the
generator
output, and reference numeral 22b indicates a PI controller into which the
difference
calculated by the subtracter 22a is input. In addition, in the present
embodiment, the
upper value output from the PI controller 22b is limited by an LRCSO signal
S2'.
In Fig. 4, reference symbol Sl indicates a governor CSO signal, and reference
symbol TW shows the tracking width. The governor CSO signal SI is output by
the
controller 10 to the fuel valve 9, so as to control the output of the gas
turbine 3.
In the normal state, as shown by reference symbol "a", the controller 10
suitably
varies the governor CSO signal S I (i:e., the output of the gas turbine 3) so
as to fix the
frequency of the electric system.
When the amount of load suddenly decreases, the relevant revolution speed
suddenly increases, and thus the frequency also increases. In this case, as
shown by
I 5 reference symbol b3, the governor CSO signal calculating section 20
decreases the Level
of the governor CSO signal S1 so as to stabilize the frequency of the electric
system.
On the other hand, when the amount of load suddenly increases, the relevant
revolution speed suddenly decreases, and thus the frequency also decreases. In
this
case, as shown by a reference symbol c3, the governor CSO signal calculating
section 20
increases the level of the governor CSO signal S I so as to stabilize the
frequency of the
electric system.
However, if the governor CSO signal S 1 is suddenly increased, the temperature
of the gas turbine 3 suddenly increases. It is not preferable because the gas
turbine 3
should have a stress. Therefore, the load-limiting CSO signal calculating
section 21 of
the controller 10 successively calculates a load-limiting CSO signal S2. In
the normal
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state or when the governor CSO signal SI suddenly decreases, the load-limiting
CSO
signal S2 has a level obtained by adding the predetermined tracking width TW
to the
governor CSO signal SI, that is, the level ofthe load-limiting CSO signal S2
is higher
than that of the governor CSO signal SI by the tracking width TW. When the
governor
CSO signal SI suddenly increases, the load-limiting CSO signal S2 is increased
by a
specific rate calculated by the increase-rate calculator 21c. The lower value
selecting
circuit 22 of the controller I O limits the upper value of the governor CSO
signal S 1 by
using the load-limiting CSO signal S2 as the limit value for the upper value
of signal Sl .
Therefore, when the governor CSO signal SI suddenly decreases, the level of
the load-limiting CSO signal S2 follows the governor CSO signal Sl and thus
decreases
as shown by reference symbol b3', and when the governor CSO signal Sl suddenly
increases, the relationship between the'levels of the load-limiting CSO signal
S2 and the
governor CSO signal S I (i.e., which is larger) is reversed when a
predetermined time has
elapsed after the start of the sudden increase (refer to c3'). Therefore, the
governor
I 5 CSO signal Sl is limited by the lower value selecting circuit 22, so that
the load-limiting
CSO signal S2 whose increase rate does not excess a specific rate is selected
and output
to the fuel valve 9.
Fig. 5 shows variations of the signals when the load suddenly increases
immediately after the load suddenly decreases. During the sudden decrease, the
governor CSO signal Sl decreases without limitation, as shown by reference
symbol b4,
and the load-limiting CSO signal S2 decreases while following the governor CSO
signal
S 1, as shown by reference symbol b4'.
In the sudden increase of the load immediately after the above sudden
decrease,
the governor CSO signal SI also suddenly increases (see reference symbol c4),
and the
Load-limiting CSO signal S2 increases at a specific rate (see reference symbol
c4'). As
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explained above, the lower value selecting circuit 22 limits the increase of
the governor
CSO signal SI by using the load-limiting CSO signal SZ as the upper-limit
value.
Therefore, when a predetermined time has elapsed after the start of the sudden
increase,
the load-limiting CSO signal S2 by which the increase of the governor CSO
signal S 1 is
S limited is selected and output to the fuel valve 9.
As explained above, when the governor CSO signal S l is in the normal state
(that is, does not suddenly change) or suddenly decreases, the load-limiting
CSO signal
S2 always has a value (or a level) higher than that of the governor CSO signal
S 1 by a
predetermined tracking width: When the governor CSO signal SI suddenly
increases,
I 0 the load-limiting CSO signal SZ is increased at a specific rate. The
controller 10 limits
the upper value of the governor CSO signal S 1 by using the load-limiting CSO
signal S2,
thereby preventing a sudden increase of the temperature of the gas turbine 3.
In addition, as clearly understood by comparing the conventional example (see
Fig. i2) with the present embodiment (see Fig. S), when the governor CSO
signal Si
l S suddenly increases after a sudden decrease, the governor CSO signal S I
much more
quickly follows the load-limiting CSO signal S2 in the present invention, so
that the
increase of the governor CSO signal S I is quickly limited. Therefore, less
stress is
imposed on the gas turbine 3 in comparison with the conventional example.
Below, another embodiment of a circuit provided in the controller I0 will be
20 explained.
In this embodiment, the controller i0 comprises a bypass valve control circuit
30 as shown in Fig. 6. In the figure, reference numeral 31 indicates a bypass
valve
opening-degree calculating section into which an output value S4 from the gas
turbine 3
(called "GT output value", hereinbelow) is input. The bypass valve opening-
degree
2S calculating section 31 determines and outputs an opening-degree set value
SS which
CA 02442337 2003-10-02
19
indicates a suitable degree of opening of the bypass valve 15 corresponding to
the
received GT output value S4.
Reference numeral 32 indicates a change rate limiter (corresponding to the
second change rate Iimiter of the present invention) into which the GT output
value S4 is
input, where the GT output value S4 changes according to the amount of load.
The
change rate limiter 32 determines and outputs a signal (corresponding to the
GT output
value S4} having a predetermined (increase/decrease) change rate. For example,
as
shown in Fig. 7A, even when the GT output value S4 greatly decreases, the
change rate
limner 32 outputs a signal which decreases with a predetermined change rate
(see Fig.
7B}.
Reference numeral 33 indicates a subtracter for outputting a difference
obtained
by subtracting the output of the change rate limiter 32 from the GT output
value S4.
Fig. 7C shows the variation of the value output from the subtracter 33.
Reference numeral 35 indicates a change rate calculator into which the
difference (value} calculated by the subtracter 33 is input. The change rate
calculator
35 calculates and outputs a rate of change S6 of the bypass valve 15, suitable
for the
input value. Fig. 8 shows a relevant corresponding relationship. That is, when
the
difference is larger than a specific value, a rate of change al (%/min) is
output, while
when the difference is smaller than another specific value, a rate of change
a2 {%/min) is
output. If the difference varies as shown in Fig. 7C, the rate of change
varies as shown
in Fig. 7D.
The above change rate limiter 32, subtracter 33, and change rate calculator 35
constitute an opening/closing speed calculating section 36.
Reference numeral 37 indicates another change rate limiter (corresponding to
the first change rate limiter of the present invention} for controlling the
opening-degree
CA 02442337 2003-10-02
set value SS (output from the bypass valve opening-degree calculating section
31) based
on the rate of change S6, and outputting the controlled value as a bypass
valve
opening-degree command S7 to the bypass valve 1S. Accordingly, when the rate
of
change S6 varies as shown in Fig. 7D, the bypass valve opening-degree command
S7
S varies as shown by the solid line in Fig. 7E.
As explained above, according to the bypass valve control circuit 30 of the
present embodiment, when the load suddenly decreases and the fuel valve 9 is
suddenly
closed, the bypass valve control circuit 30 increases the rate of closing of
the bypass
valve 1 S. More specifically, when the GT output suddenly decreases as shown
in Fig.
10 7A, the value of the bypass valve opening-degree command S7 suddenly
increases as
shown by the solid line in Fig. 7E, thereby quickly controlling the degree of
opening of
the bypass valve 15.
Here, if it is assumed that the rate of change of the bypass valve 1 S be
fixed at
al as shown by the dotted line in Fig. 7E, the opening/closing timing of the
bypass valve
15 1 S should be late in comparison with the opening/closing timing of the
fuel valve 9.
However, in the present embodiment, the rate of change is increased to a2;
thus, the
operation of opening/closing the bypass valve 1 S is quickly performed,
thereby
stabilizing the fuel combustion in the main combustor 12.
In addition, in the above-explained embodiment, a single controller 10 is
20 provided for controlling the fuel valve 9 and the bypass valve 15. However,
separate
controllers for respectively controlling the fuel valve 9 and the bypass valve
1 S may be
provided.
