U.S. patent application number 09/972672 was filed with the patent office on 2002-09-19 for system and method for modular control of a multi-fuel low emissions turbogenerator.
This patent application is currently assigned to Capstone Turbine Corporation. Invention is credited to Dickey, James Brian, Edelman, Ed, Gilbreth, Mark G., Pont, Guillermo, Willis, Jeffrey W..
Application Number | 20020129609 09/972672 |
Document ID | / |
Family ID | 23802220 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020129609 |
Kind Code |
A1 |
Pont, Guillermo ; et
al. |
September 19, 2002 |
SYSTEM AND METHOD FOR MODULAR CONTROL OF A MULTI-FUEL LOW EMISSIONS
TURBOGENERATOR
Abstract
A system and method for modular control of a multi-fuel
turbogenerator include separate controllers for controlling fuel
supplied to the combustor and power output from the generator. The
power controller generates a fuel command based on the required
turbine exhaust temperature, where the fuel command is independent
of the particular fuel being used. Fuels may include natural gas,
diesel, propane, waste gas, or gasoline, for example. The power
controller communicates the fuel command and the airflow or
calculated air/fuel ratio to the fuel controller which selects an
appropriate mode of operation for the injectors. Injector operating
modes include one or more pilot modes where fuel is not mixed with
air prior to combustion, and one or more premix modes where fuel is
highly mixed with air prior to combustion. The fuel controller
implements closed-loop feedback control of a fuel metering device
and controls the fuel injectors in the appropriate operating mode
based on the fuel command, the energy content of the fuel being
used, and the air/fuel ratio.
Inventors: |
Pont, Guillermo; (Los
Angeles, CA) ; Dickey, James Brian; (Agoura Hills,
CA) ; Edelman, Ed; (Agoura Hills, CA) ;
Gilbreth, Mark G.; (Woodland Hills, CA) ; Willis,
Jeffrey W.; (Lexington, KY) |
Correspondence
Address: |
Rachele Wittwer
IRELL & MANELLA LLP
Suite 900
1800 Avenue of the Stars
Los Angeles
CA
90067
US
|
Assignee: |
Capstone Turbine
Corporation
|
Family ID: |
23802220 |
Appl. No.: |
09/972672 |
Filed: |
October 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09972672 |
Oct 5, 2001 |
|
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|
09453825 |
Dec 1, 1999 |
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6405522 |
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Current U.S.
Class: |
60/776 ;
60/39.281 |
Current CPC
Class: |
F02C 9/28 20130101 |
Class at
Publication: |
60/776 ;
60/39.281 |
International
Class: |
F02C 009/26 |
Claims
What is claimed is:
1. A method for controlling a turbogenerator, comprising: in a
first controller, determining an air/fuel ratio based on an air
flow and fuel flow; communicating the air/fuel ratio to a second
controller; and in the second controller, selecting a fuel injector
mode of operation based upon the air/fuel ratio to maintain flame
stability.
2. The method of claim 1 wherein determining an air/fuel ratio
includes determining current air flow of the turbogenerator in the
first controller.
3. The method of claim 2 wherein determining current air flow
comprises determining current air flow based on ambient air
temperature, ambient air pressure, and turbine speed.
4. The method of claim 3 wherein determining current air flow
comprises referencing a lookup table based on the ambient air
temperature, the ambient air pressure, and the turbine speed.
5. The method of claim 2 wherein determining current air flow
comprises measuring actual air flow through the turbogenerator.
6. The method of claim 1 wherein determining fuel flow comprises
determining fuel demand to maintain a desired turbine exhaust
temperature.
7. The method of claim 1 wherein determining fuel flow comprises
determining a minimum fuel demand based on a computed air flow, a
maximum air/fuel ratio to sustain combustion, and energy content of
a particular fuel being used.
8. The method of claim 7 wherein the maximum air/fuel ratio and the
energy content of the particular fuel being used are communicated
from the second controller to the first controller.
9. The method of claim 1 wherein determining fuel flow comprises
estimating fuel flow into the turbogenerator.
10. The method of claim 1 wherein determining fuel flow comprises
measuring fuel flow into the turbogenerator.
11. The method of claim 1 wherein determining fuel flow comprises
determining fuel temperature and fuel pressure across a
proportioning valve.
12. The method of claim 1 wherein determining fuel flow comprises
measuring fuel flow into the turbogenerator using a fuel flow
meter.
13. The method of claim 1 wherein determining an air/fuel ratio
comprises calculating the air/fuel ratio based on a fuel command
from the first controller.
14. The method of claim 1 wherein determining an air/fuel ratio
comprises calculating the air/fuel ratio in the first controller
using a measured fuel flow into the turbogenerator as determined by
the second controller.
15. The method of claim 1 wherein determining an air/fuel ratio
comprises calculating the air/fuel ratio using a fuel command in
the second controller.
16. The method of claim 1 further comprising: selecting an
operating mode for at least one injector of the turbogenerator
based at least in part on the determined air/fuel ratio, wherein
the step of controlling the fuel supplied to the turbogenerator
includes controlling fuel supplied to the injector based on the
injector operating mode.
17. The method of claim 16 wherein selecting an operating mode
comprises selecting a pilot mode or a premix mode.
18. The method of claim 1 further comprising: selecting an
operating mode for a plurality of injectors of the turbogenerator
based at least in part on the determined air/fuel ratio, wherein
operating modes include premix and pilot modes.
19. The method of claim 18 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting the premix mode and the step of controlling the
fuel supplied to the turbogenerator includes energizing at least
one of the premix injectors.
20. The method of claim 18 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting the premix mode and the step of controlling the
fuel supplied to the turbogenerator includes energizing any
combination of the premix injectors.
21. The method of claim 18 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting a premix mode and the step of controlling the
fuel supplied to the turbogenerator includes sequentially
energizing any combination of the premix injectors.
22. The method of claim 21 wherein sequentially energizing any
combination of the premix injectors comprises sequentially
energizing the premix injectors to promote swirl within a
combustor.
23. The method of claim 18 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode and the step of controlling the
fuel supplied to the turbogenerator includes energizing at least
one of the pilot injectors.
24. The method of claim 18 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode and the step of controlling the
fuel supplied to the turbogenerator includes energizing any
combination of the pilot injectors.
25. The method of claim 18 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode and the step of controlling the
fuel supplied to the turbogenerator includes sequentially
energizing any combination of the pilot injectors.
26. The method of claim 25 wherein sequentially energizing any
combination of the pilot injectors comprises sequentially
energizing the pilot injectors to promote swirl within a
combustor.
27. The method of claim 18 wherein selecting an operating mode
comprises selecting a pilot mode and wherein the step of
controlling the fuel supplied to the turbogenerator includes
energizing all of the injectors.
28. The method of claim 1 further comprising: transitioning between
selected operating modes based on a change in air/fuel ratio of the
turbogenerator; and energizing an ignitor of the turbogenerator
while transitioning.
29. The method of claim 1 further comprising: transitioning between
operating modes based on a change in determined air/fuel ratio of
the turbogenerator; and increasing the quantity of fuel supplied to
injectors of the turbogenerator while transitioning to improve
combustion stability.
30. The method of claim 29 wherein increasing the quantity of fuel
while transitioning comprises modifying a desired operating
temperature of the turbogenerator.
31. The method of claim 30 wherein modifying a desired operating
temperature comprises raising desired turbine exhaust temperature
while transitioning between operating modes.
32. The method of claim 29 wherein transitioning between operating
modes includes transitioning between a premix mode in which fuel is
well mixed with air prior to delivery into a combustor of the
turbogenerator and at least one pilot mode in which fuel is not
substantially mixed with air prior to delivery into a
combustor.
33. The method of claim 32 wherein the pilot mode comprises a
plurality of pilot modes each corresponding to operation of a
varying number of injectors.
34. The method of claim 1 further comprising transitioning between
a first premix operating mode and a second premix operating mode
based on a change in determined air/fuel ratio of the
turbogenerator.
35. The method of claim 34 wherein transitioning between first and
second premix operating modes includes transitioning from operation
of a first premix injector to an additional plurality of premix
injectors.
36. The method of claim 35 wherein the plurality of premix
injectors comprises three premix injectors.
37. The method of claim 1 further comprising transitioning between
a first pilot operating mode and a second pilot operating mode
based on a change in determined air/fuel ratio of the
turbogenerator.
38. The method of claim 37 wherein transitioning between first and
second pilot operating modes includes transitioning from operation
of a first pilot injector to an additional plurality of pilot
injectors.
39. The method of claim 38 wherein the plurality of pilot injectors
comprises three pilot injectors.
40. The method of claim 1 further comprising transitioning between
a first pilot operating mode and a first premix operating mode
based on a change in determined air/fuel ratio of the
turbogenerator.
41. The method of claim 37 wherein transitioning between the first
and second pilot modes comprises energizing injectors in a sequence
which generates a desired swirl within a combustor of the
turbogenerator.
42. The method of claim 1 wherein communicating the desired
air/fuel ratio comprises communicating the desired air/fuel ratio
via external communications.
43. The method of claim 1 further comprising: transitioning between
operating modes based on a change in determined air/fuel ratio of
the turbogenerator; communicating a transitioning signal to the
first controller; and increasing target turbine exhaust temperature
to improve combustion stability during transitioning.
44. The method of claim 1 further comprising: transitioning between
operating modes based on a change in determined air/fuel ratio of
the turbogenerator; communicating a transitioning signal from the
second controller to the first controller; and energizing an
ignitor while transitioning.
45. A method for controlling a turbogenerator, comprising: in a
first controller, determining a desired fuel command in units
independent of a specific fuel based on a turbogenerator operating
parameter; communicating the desired fuel command to a second
controller; in the second controller, converting the independent
fuel command to a fuel command specific to the fuel currently
utilized in the turbogenerator; and controlling the delivery of
fuel to the turbogenerator, including communicating fuel command
limits from the second controller back to the first controller.
46. The method of claim 45 wherein the turbogenerator operating
parameter is turbine exhaust temperature.
47. The method of claim 46 wherein communicating the desired fuel
command comprises communicating the desired fuel command from the
first controller to the second controller via an external
communications bus.
48. The method of claim 46 further comprising: converting the
desired fuel command in the second controller to a fuel quantity
based on energy content of the fuel being combusted.
49. The method of claim 45 wherein the desired fuel command is in
units of energy per unit time.
50. The method of claim 45 further comprising: determining a fuel
command upper limit in the second controller based on a maximum
amount of fuel which can be delivered to the turbogenerator and
energy content of the fuel.
51. The method of claim 45 further comprising: determining a fuel
command lower limit in the second controller based on a maximum
air/fuel ratio for combustion and current airflow through the
turbogenerator.
52. The method of claim 51 wherein the fuel command lower limit is
determined by dividing the maximum air/fuel ratio by the current
airflow and inverting the result.
53. The method of claim 45 wherein the desired fuel command is
determined to maintain a substantially constant turbine exhaust
temperature.
54. The method of claim 53 wherein determining the desired fuel
command comprises: measuring turbine exhaust temperature; comparing
turbine exhaust temperature to a desired turbine exhaust
temperature to generate an error signal; and determining the
desired fuel command based on the error signal.
55. The method of claim 45 wherein controlling the delivery of fuel
comprises controlling a fuel metering device.
56. The method of claim 55 wherein controlling the fuel metering
device comprises: determining a desired fuel flow command based on
the desired fuel command and energy content of the fuel;
determining actual fuel flow; comparing measured fuel flow to the
desired fuel flow command to generate an error signal; and
controlling the fuel metering device to reduce the error
signal.
57. The method of claim 56 wherein determining actual fuel flow
includes estimating actual fuel flow.
58. The method of claim 56 wherein determining actual fuel flow
includes measuring actual fuel flow using a flow meter.
59. The method of claim 56 wherein determining actual fuel flow
includes calculating actual fuel flow based on fuel temperature and
pressure across a proportioning valve.
60. A method for controlling a turbogenerator, comprising: in a
first controller, determining current airflow of the turbogenerator
and a desired energy flow; communicating the desired energy flow
and the current air flow to a second controller; and in the second
controller, calculating an air/fuel ratio and selecting a fuel
injector mode of operation based upon the air/fuel ratio to
maintain flame stability.
61. The method of claim 60 wherein the desired energy flow is
determined in units independent of the particular fuel being
combusted.
62. The method of claim 60 wherein determining actual fuel flow
includes calculating actual fuel flow based on fuel temperature and
pressure across a proportioning valve.
63. The method of claim 60 wherein selecting a fuel injector mode
comprises selecting a pilot mode or a premix mode.
64. The method of claim 60 wherein selecting a fuel injector mode
comprises selecting one of a plurality of pilot modes.
65. The method of claim 64 wherein each of the plurality of pilot
modes corresponds to activation of a varying number of pilot
injectors.
66. The method of claim 64 wherein the plurality of pilot modes
includes a first pilot mode which activates one pilot injector and
a second pilot mode which activates at least one additional pilot
injector.
67. The method of claim 66 wherein the second pilot mode activates
all of the pilot injectors.
68. The method of claim 60 wherein selecting a fuel injector mode
comprises transitioning from a pilot mode to a premix mode.
69. The method of claim 60 further comprising energizing an ignitor
to improve combustion stability during transitioning.
70. The method of claim 60 wherein selecting a fuel injector mode
includes sequentially transitioning from a first pilot mode to a
second pilot mode and then to a first premix mode.
71. The method of claim 70 wherein the first pilot mode supplies
fuel to one pilot injector, the second pilot mode supplies fuel to
two additional pilot injectors, and the first premix mode supplies
fuel to three premix injectors.
72. The method of claim 71 wherein transitioning from the first
pilot mode to the second pilot mode comprises energization of a
second pilot injector adjacent the first pilot injector followed by
energization of a third pilot injector adjacent the second pilot
injector to facilitate ignition of fuel from the second and third
pilot injectors by the first and second pilot injectors,
respectively.
73. The method of claim 70 wherein transitioning from the second
pilot mode to the first premix mode comprises energizing a
plurality of premix injectors followed by sequentially
de-energizing the pilot injectors.
74. The method of claim 70 wherein transitioning from the second
pilot mode to the first premix mode comprises de-energizing a first
pilot injector, energizing a plurality of premix injectors, and
then sequentially de-energizing any remaining pilot injectors.
75. The method of claim 70 wherein transitioning from the second
pilot mode to the first premix mode comprises sequentially
de-energizing first and second pilot injectors, energizing a
plurality of premix injectors, and then sequentially de-energizing
any remaining pilot injectors.
76. The method of claim 60 wherein selecting a fuel injector mode
includes transitioning from a premix mode to a pilot mode.
77. The method of claim 76 wherein the pilot mode comprises a
plurality of pilot modes, the method further comprising
transitioning from a first pilot mode to a second pilot mode.
78. The method of claim 60 wherein selecting a fuel injector mode
includes transitioning from a premix mode with a plurality of
premix injectors energized to a pilot mode with at least one pilot
injector energized.
79. The method of claim 78 wherein the premix injectors and the
pilot injectors are the same injectors operated in a premix mode
and pilot mode, respectively.
80. The method of claim 78 wherein the plurality of premix
injectors includes three premix injectors and the at least one
pilot injector includes three pilot injectors.
81. The method of claim 80 wherein transitioning from a premix mode
to a pilot mode comprises energizing at least one pilot injector
prior to de-energizing the premix injectors.
82. The method of claim 80 wherein transitioning from a premix mode
to a pilot mode comprises energizing a first pilot injector,
de-energizing all premix injectors, then sequentially energizing
any remaining pilot injectors.
83. The method of claim 80 wherein transitioning from a premix mode
to a pilot mode comprises energizing a plurality of pilot injectors
prior to de-energizing any premix injectors.
84. The method of claim 80 wherein transitioning from a premix mode
to a pilot mode comprises energizing all pilot injectors prior to
de-energizing any premix injectors.
85. The method of claim 60 wherein selecting a fuel injector mode
includes transitioning from a first fuel injector mode to a second
fuel injector mode based on a first value of an operating parameter
of the turbogenerator and transitioning from the second fuel
injector mode to the first fuel injector mode based on a second
value of the operating parameter.
86. The method of claim 85 wherein the operating parameter is the
air/fuel ratio.
87. The method of claim 60 wherein selecting a fuel injector mode
includes transitioning from a first pilot mode to a second pilot
mode based on a first value for the air/fuel ratio and
transitioning from the second pilot mode to the first pilot mode
based on a second value for the air/fuel ratio.
88. The method of claim 60 wherein selecting a fuel injector mode
includes transitioning from a pilot mode to a premix mode based on
a first value of the air/fuel ratio and transitioning from the
premix mode to the pilot mode based on a second value of the
air/fuel ratio.
89. A system for controlling a turbogenerator, the system
comprising: a first controller for determining an air/fuel ratio
based on an air flow and fuel demand; a communications bus; a
second controller in communication with the first controller via
the communications bus, the second controller selecting a fuel
injector mode of operation based upon the air/fuel ratio to
maintain low emissions combustion and flame stability.
90. The system of claim 89 wherein the first controller determines
current air flow of the turbogenerator to determine the air/fuel
ratio.
91. The system of claim 89 wherein the first controller determines
current air flow based on ambient air temperature, ambient air
pressure, and turbine speed.
92. The system of claim 89 wherein the second controller determines
the fuel demand and communicates the fuel demand to the first
controller via the communications bus.
93. The system of claim 89 wherein the second controller determines
the fuel demand based on a maximum air/fuel ratio to sustain
combustion and energy content of the fuel being used.
94. The system of claim 93 wherein the second controller
communicates the maximum air/fuel ratio and the energy content of
the fuel being used to the first controller.
95. The system of claim 89 wherein the communications bus is an
external communications bus.
96. The system of claim 89 wherein the second controller estimates
fuel flow into the turbogenerator.
97. The system of claim 89 further comprising: a fuel metering
device controlled by the second controller for controlling quantity
of fuel delivered to at least one injector.
98. The system of claim 97 wherein the fuel metering device
comprises a proportioning valve.
99. The system of claim 97 further comprising: an upstream pressure
sensor for sensing pressure of the fuel between a fuel source and
the fuel metering device; and a downstream pressure sensor for
sensing pressure of the fuel between the fuel metering device and
the injector.
100. The system of claim 97 wherein the fuel metering device
comprises a fuel flow meter.
101. The system of claim 89 further comprising a plurality of
injectors each being operable in a pilot mode and a premix mode,
the injectors being controlled by the second controller.
102. The system of claim 89 wherein the second controller selects
an operating mode for at least one injector based at least in part
on the determined air/fuel ratio and controls fuel supplied to the
injector based on the injector operating mode.
103. A method for controlling a turbogenerator, comprising:
determining an air/fuel ratio based on power output of the
turbogenerator; and selecting an operating mode for at least one
fuel injector based upon the air/fuel ratio to maintain flame
stability.
104. The method of claim 103 further comprising determining power
output of the turbogenerator based on measured power.
105. The method of claim 103 further comprising determining power
output of the turbogenerator based on at least measured
voltage.
106. The method of claim 103 further comprising determining power
output of the turbogenerator based on at least measured
current.
107. The method of claim 103 further comprising determining the
air/fuel ratio by referencing a look-up table based on the
turbogenerator output power.
108. The method of claim 103 further comprising determining a fuel
flow based on the air/fuel ratio.
109. The method of claim 108 wherein determining a fuel flow
comprises determining fuel demand to maintain a desired turbine
exhaust temperature.
110. The method of claim 108 wherein determining fuel flow
comprises determining a minimum fuel demand based on a computed air
flow, a maximum air/fuel ratio to sustain combustion, and energy
content of a particular fuel being used.
111. The method of claim 110 wherein the maximum air/fuel ratio and
the energy content of the particular fuel being used are
communicated from a second controller to a first controller, the
first controller determining the air/fuel ratio based on the power
output of the turbogenerator.
112. The method of claim 108 wherein determining fuel flow
comprises estimating fuel flow into the turbogenerator.
113. The method of claim 108 wherein determining fuel flow
comprises measuring fuel flow into the turbogenerator.
114. The method of claim 108 wherein determining fuel flow
comprises determining fuel temperature and fuel pressure across a
proportioning valve.
115. The method of claim 108 wherein determining fuel flow
comprises measuring fuel flow into the turbogenerator using a fuel
flow meter.
116. The method of claim 108 wherein determining fuel flow
comprises determining current airflow through the
turbogenerator.
117. The method of claim 103 further comprising: selecting an
operating mode for at least one injector of the turbogenerator
based at least in part on the determined air/fuel ratio; and
controlling fuel supplied to the injector based on the injector
operating mode.
118. The method of claim 117 wherein selecting an operating mode
comprises selecting an operating mode based on the air/fuel
ratio.
119. The method of claim 117 wherein selecting a operating mode
comprises selecting an operating mode based on the output power of
the turbogenerator.
120. The method of claim 117 wherein selecting an operating mode
comprises selecting a pilot mode or a premix mode.
121. The method of claim 103 further comprising: selecting an
operating mode for a plurality of injectors of the turbogenerator
based at least in part on the determined air/fuel ratio, wherein
operating modes include premix and pilot modes.
122. The method of claim 121 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting the premix mode, the method further comprising
controlling fuel supplied to the turbogenerator by energizing at
least one of the premix injectors.
123. The method of claim 121 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting the premix mode, the method further comprising
controlling fuel supplied to the turbogenerator by energizing any
combination of the premix injectors.
124. The method of claim 121 wherein the plurality of injectors
includes premix injectors and wherein selecting an operating mode
comprises selecting a premix mode, the method further comprising
controlling fuel supplied to the turbogenerator by sequentially
energizing any combination of the premix injectors.
125. The method of claim 124 wherein sequentially energizing any
combination of the premix injectors comprises sequentially
energizing the premix injectors to promote swirl within a
combustor.
126. The method of claim 121 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode, the method further comprising
controlling fuel supplied to the turbogenerator by energizing at
least one of the pilot injectors.
127. The method of claim 121 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode, the method further comprising
controlling fuel supplied to the turbogenerator by energizing any
combination of the pilot injectors.
128. The method of claim 121 wherein the plurality of injectors
includes pilot injectors and wherein selecting an operating mode
comprises selecting a pilot mode, the method further comprising
controlling fuel supplied to the turbogenerator by sequentially
energizing any combination of the pilot injectors.
129. The method of claim 128 wherein sequentially energizing any
combination of the pilot injectors comprises sequentially
energizing the pilot injectors to promote swirl within a
combustor.
130. The method of claim 121 wherein selecting an operating mode
comprises selecting a pilot mode, the method further comprising
controlling the fuel supplied to the turbogenerator by energizing
all of the injectors.
131. The method of claim 103 further comprising: transitioning
between injector operating modes based on a change in the
determined air/fuel ratio of the turbogenerator; and energizing an
ignitor of the turbogenerator while transitioning.
132. The method of claim 103 further comprising: transitioning
between injector operating modes based on a change in output power
of the turbogenerator.
133. The method of claim 103 further comprising: transitioning
between operating modes based on a change in determined air/fuel
ratio of the turbogenerator; and increasing a quantity of fuel
supplied to injectors of the turbogenerator while transitioning to
improve combustion stability.
134. The method of claim 133 wherein increasing the quantity of
fuel while transitioning comprises modifying a desired operating
temperature of the turbogenerator.
135. The method of claim 134 wherein modifying a desired operating
temperature comprises raising desired turbine exhaust temperature
while transitioning between operating modes.
136. The method of claim 133 wherein transitioning between
operating modes includes transitioning between a premix mode in
which fuel is well mixed with air prior to delivery into a
combustor of the turbogenerator and at least one pilot mode in
which fuel is not substantially mixed with air prior to delivery
into a combustor.
137. The method of claim 132 wherein the pilot mode comprises a
plurality of pilot modes each corresponding to operation of a
varying number of injectors.
138. The method of claim 103 further comprising transitioning
between a first premix operating mode and a second premix operating
mode based on a change in determined air/fuel ratio of the
turbogenerator.
139. The method of claim 138 wherein transitioning between first
and second premix operating modes includes transitioning from
operation of a first premix injector to an additional plurality of
premix injectors.
140. The method of claim 139 wherein the plurality of premix
injectors comprises three premix injectors.
141. The method of claim 103 further comprising transitioning
between a first pilot operating mode and a second pilot operating
mode based on a change in determined air/fuel ratio of the
turbogenerator.
142. The method of claim 141 wherein transitioning between first
and second pilot operating modes includes transitioning from
operation of a first pilot injector to an additional plurality of
pilot injectors.
143. The method of claim 142 wherein the plurality of pilot
injectors comprises three pilot injectors.
144. The method of claim 103 further comprising transitioning
between a first pilot operating mode and a first premix operating
mode based on a change in determined air/fuel ratio of the
turbogenerator.
145. The method of claim 141 wherein transitioning between the
first and second pilot modes comprises energizing injectors in a
sequence which generates a desired swirl within a combustor of the
turbogenerator.
146. The method of claim 103 further comprising: transitioning
between operating modes based on a change in determined air/fuel
ratio of the turbogenerator; and increasing target turbine exhaust
temperature to improve combustion stability during
transitioning.
147. The method of claim 103 further comprising: transitioning
between operating modes based on a change in determined air/fuel
ratio of the turbogenerator; and energizing an ignitor while
transitioning.
148. A method for controlling a turbogenerator, the method
comprising: determining an air/fuel ratio for operation of the
turbogenerator based on at least one operating parameter of the
turbogenerator and physical characteristics of a fuel selected from
a plurality of fuels which may be combusted within the
turbogenerator; and selecting an operating mode for at least one
fuel injector of the turbogenerator based at least in part on the
air/fuel ratio.
149. The method of claim 148 wherein determining an air/fuel ratio
comprises determining an air/fuel ratio based on power output of
the turbogenerator.
150. The method of claim 148 wherein determining an air/fuel ratio
comprises calculating at least one fuel index based on the physical
characteristics of the selected fuel.
151. The method of claim 148 further comprising: determining an
amount of fuel required to obtain the determined air/fuel ratio
based on the selected operating mode; and controlling a fuel
metering device to deliver the required fuel to the
turbogenerator.
152. The method of claim 151 wherein controlling a fuel metering
device comprises controlling a fuel metering device based on the
physical characteristics of the selected fuel.
153. The method of claim 152 wherein the fuel metering device is a
proportioning valve.
Description
TECHNICAL FIELD
[0001] The present invention relates to a system and method for
controlling a multi-fuel turbogenerator using a modular control
architecture for power and fuel control.
BACKGROUND ART
[0002] Turbogenerators typically include a permanent magnet
generator coupled to a turbine to convert heat energy produced by
combustion of a fuel into electrical energy for distribution to a
load, such as a utility grid. A compressor, driven by the turbine,
provides compressed air which is heated by the exhaust gases of the
combustion process in a recuperator (heat exchanger) prior to being
combined with the fuel in the combustor.
[0003] Low emission combustion systems have been developed which
introduce excess air into the combustor to lower the combustion
temperature and reduce production of nitrogen oxides. The
introduction of excess air increases the air/fuel ratios (AFR) to
values which approach the weak extinction limit of the fuel. When
operating in this low-emissions mode, the fuel is well mixed with
the air prior to ignition to produce a homogenous mixture to
sustain lean-burning combustion which has a lower peak temperature
than stoichiometric combustion. Operation of the turbogenerator in
this premixed mode is designed for high generator electrical loads
which have associated higher turbine and compressor speeds.
Transitions between a premixed operating mode and diffusion modes
which service lower loads with higher AFRs must be carefully
controlled to provide sustained stable combustion and avoid flame
outs. The transition between operating modes is highly dependent
upon the particular fuel which is being utilized. Various fuels may
include natural gas, diesel, propane, waste gas, and gasoline, for
example, which have very different combustion characteristics.
DISCLOSURE OF INVENTION
[0004] The present invention provides a modular control
architecture to facilitate control of a low emissions
turbogenerator so it may be utilized with a variety of different
fuels. While control of the system is preferably separated into
physically different electronics components and associated hardware
which define a power control subsystem and a fuel control
subsystem, alternative embodiments employ a modular control
architecture within a single controller. For the discrete
controller embodiments, the discrete controllers of the power and
fuel subsystems communicate via an external intra-controller bus.
In both the discrete controller and integrated controller
embodiments, the power controller determines an appropriate fuel
command to maintain a predetermined turbine exhaust temperature
that is based on the current engine speed. The fuel controller
selects an appropriate operating mode for one or more injectors
based on the AFR. Operating modes include a low-emissions premix
mode where fuel is highly mixed with air prior to delivery into the
primary combustion zone and a pilot or diffusion mode where fuel is
directly delivered via a pilot tube to the primary combustion zone
without substantial mixing. The fuel controller determines and
controls the quantity of fuel provided to the selected injector(s)
based on the fuel command communicated by the power controller and
the characteristics of the particular fuel being used, such as
energy content. Because the fuel command generated by the power
controller is in units independent of the particular fuel being
utilized, the power control subsystem may be utilized with various
fuel subsystems corresponding to a variety of liquid and/or gaseous
fuels. The fuel control subsystem controls a fuel metering device
based on energy content of the particular fuel being utilized such
that the same fuel metering hardware may be used with a variety of
fuels having different energy content.
[0005] A fuel controller according to the present invention
controls the operating mode (premix or pilot) and the number of
injectors operating in pilot or premix mode based on the fuel
command and required air/fuel ratio. The required air/fuel ratio
may be determined directly based on the required air and fuel
determinations, or indirectly based required power. Transitions
between operating modes include corresponding hysteresis bands to
eliminate oscillation between adjacent modes. The combustor ignitor
can be energized during transitions to improve combustion
stability. In one embodiment, an increased quantity of fuel is
provided to one or more injectors during transitions between
operating modes by temporarily increasing the target turbine
exhaust temperature which provides additional combustion stability.
Preferably, the fuel subsystem includes three injectors and six
operating modes including three pilot or diffusion modes and three
premix modes. The pilot modes utilize a single injector for low
electrical loads and all three injectors for moderate electrical
loads. When operating in the pilot modes, fuel is delivered through
a pilot tube of the injectors to the combustion zone. A premix mode
is selected to service high electrical loads and includes operating
all three injectors such that the fuel mixes with air within the
injector prior to delivery to the combustion zone within the
combustor.
[0006] A modular fuel control subsystem according to the present
invention includes an electronic fuel controller, a fuel
metering/controlling device such as a proportioning valve or pump,
and associated temperature and pressure sensors. In addition, the
fuel subsystem may include appropriate switching valves, fuel
injectors, fuel manifold, and corresponding fuel lines, all of
which may be selected depending upon the particular fuel being
utilized.
[0007] The present invention provides a number of advantages
relative to prior art strategies. For example, the present
invention allows individual fuel systems to be changed to a new
fuel without a corresponding change to the engine or engine
controller. The modular control strategy and architecture
facilitates independent development and testing of the power
controller and fuel controller. Precise monitoring of AFR assures
that the minimum fuel is correctly controlled to provide combustion
stability and accurate switching between different modes of
injector operation. This provides high efficiency low emissions
operation for a variety of fuels.
[0008] The above advantages and other advantages, objects, and
features of the present invention, will be readily apparent from
the following detailed description of the best mode for carrying
out the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a block diagram illustrating one embodiment for a
modular multi-fuel turbogenerator control according to the present
invention;
[0010] FIG. 2 is a partial cut-away view of a low emissions
turbogenerator for use with a modular control system or method
according to the present invention;
[0011] FIG. 3 is a cross-sectional view of a gaseous fuel injector
capable of operation in a pilot mode or premix mode for use with a
modular turbogenerator control according to the present
invention;
[0012] FIG. 4 is a block diagram illustrating operation of one
embodiment of a power controller for a modular turbogenerator
control according to the present invention;
[0013] FIG. 5 is a block diagram illustrating operation of one
embodiment of a fuel control system for a modular turbogenerator
control according to the present invention;
[0014] FIG. 6 is a diagram illustrating transitions between
injector control modes including hysteresis bands for a modular
turbogenerator control according to the present invention;
[0015] FIGS. 7-10 are timing or sequencing diagrams illustrating
injector control for transitions between a premix mode and pilot
modes within a fuel system controller of a modular turbogenerator
control according to the present invention;
[0016] FIG. 11 is a graph illustrating operating mode transitions
based on generator output power as a function of normalized ambient
temperature in a system using a modular turbogenerator control
according to the present invention;
[0017] FIG. 12 is a graph illustrating air/fuel ratio (AFR) at full
power as a function of ambient temperature for two turbine exhaust
temperatures in a modular turbogenerator control according to the
present invention;
[0018] FIG. 13 is a graph illustrating variation of AFR over a
range of generator output power for two turbine exhaust
temperatures in addition to selection of operating modes for a
modular turbogenerator control according to the present invention;
and
[0019] FIG. 14 is a flow chart illustrating operation of a system
or method for modular control of a turbogenerator according to the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] Referring now to FIG. 1, a block diagram illustrating one
embodiment for a modular multi-fuel turbogenerator control system
according to the present invention is shown. System 20 preferably
includes a modular fuel control subsystem 22, a modular power
control subsystem 24, and a turbogenerator 26. Power control
subsystem 24 includes a first controller 28 which performs a
variety of functions related to generation and distribution of
electrical power produced by electrical generator 30 which is
provided to a load, indicated generally by reference numeral 32.
Load 32 may be an isolated load or a utility power grid, for
example.
[0021] Power controller 28 provides a distributed generation power
networking system with bi-directional power converters connected
via a common DC bus for permitting compatibility between various
energy components. Power controller 28 controls the power
converters which operate as bi-directional switching converters to
provide an interface for a specific energy component to the DC bus.
Power controller 28 regulates the DC bus voltage, turbine exhaust
temperature (TET), inverter power flow, and power flow of generator
30. A more detailed description of a power controller which may be
used to perform the functions of power controller 28 in a modular
control according to the present invention may be found in U.S.
patent application Ser. No. 09/207,817 filed Dec. 8, 1998 commonly
owned by the assignee of the present invention entitled "POWER
CONTROLLER," the disclosure of which is hereby incorporated by
reference in its entirety.
[0022] Controller 28 communicates with a second controller 34 of
fuel control subsystem 22 via a communications bus, indicated
generally by reference numeral 36. Preferably, communications bus
36 is an external intra-controller communications bus which
conforms to a standard bus architecture, such as the RS-485
architecture. Communications bus 36 is used to exchange various
information between controller 28 and controller 34 as explained in
greater detail with reference to FIGS. 4-5.
[0023] Fuel controller 34 receives a fuel command in units
independent of the particular fuel being utilized from power
controller 28, and controls a fuel delivery subsystem 38 to provide
an appropriate quantity of fuel from a source 40 to at least one
injector 42. Depending upon the particular application, fuel
control subsystem 22 may control delivery of a single fuel, or
multiple fuels which are used based on availability. The modular
fuel control system of the present invention facilitates use with a
variety of fuels including high pressure natural gas, low pressure
natural gas, diesel, propane, waste gas, and gasoline, for example.
Depending upon the particular fuel being utilized, fuel delivery
subsystem 38 may include various types of fuel metering/controlling
devices. In one embodiment, fuel delivery subsystem 38 includes a
shut-off valve 44 positioned upstream relative to a first pressure
transducer 46 (upstream pressure sensor), proportioning valve 48,
and a second pressure transducer 50 (downstream pressure sensor).
Alternative fuel delivery subsystems may be utilized in place of
fuel delivery subsystem 38. For example, for liquid fuels, a
pressurization and control system which utilizes helical flow pumps
such as described in U.S. Pat. No. 5,752,380 may be used. For
gaseous fuels, one or more helical flow compressors (also referred
to as vortex compressors or radial flow compressors) may be used as
described in U.S. Pat. No. 5,819,524.
[0024] Fuel controller 34 controls the quantity and/or pressure of
fuel delivered to injector solenoid/manifold block 52. Likewise,
fuel controller 34 controls the solenoids of injector block 52 to
control delivery of the fuel to one or more injectors 42. In one
preferred embodiment, three injectors are used, only two of which
are specifically illustrated in FIG. 1. Each injector includes two
fuel delivery lines 54 which are independently controllable via
injector solenoid block 52 to provide a pilot mode and premix mode
of operation. In the pilot mode, fuel is delivered through a
corresponding pilot line 56 to a pilot tube of injectors 42 such
that the fuel is delivered to the combustion zone of the combustor
without being mixed with air. In a premix mode of operation, fuel
is delivered via a corresponding premix fuel line 58 to a mixing
chamber within injectors 42 where it is mixed with air prior to
delivery to the primary combustion zone. Injector operation is
explained in greater detail with reference to FIG. 3 and in U.S.
Pat. No. 5,850,732, which is hereby incorporated by reference.
[0025] A partial cut-away view of a low emissions turbogenerator
for use with a modular control system or method according to the
present invention is shown in FIG. 2. Turbogenerator 26 includes a
permanent magnet generator 70 driven by a power head 72. Fuel
delivered by injectors 42 is burned in combustor 74 with the
exhaust gasses driving turbine wheel 76 of turbine 78 which is
connected to compressor 80 by bearing rotor (shaft) 82. Compressor
80 is in turn connected to permanent magnet rotor or sleeve 84 via
a tie rod 86.
[0026] In operation, ambient air is inducted between outer sleeve
88 and permanent magnet generator stator 90 as indicated generally
by arrow 92. The inducted air passes through stator cooling fins 94
before reaching impeller 96 of compressor 80. Rotation of impeller
96 produces compressed air which then passes through heat transfer
section 98 of recuperator 100 where it is heated by exhausting
exhaust gasses. A portion of the air then travels toward injectors
42 where it may be combined with the fuel within a mixing chamber
of injectors 42 prior to entering combustion zone 102 when
operating in a premix mode. Alternatively, fuel may be delivered
directly to combustion zone 102 via a pilot tube (best illustrated
in FIG. 3) such that it is not substantially mixed with air prior
to combustion. Hot exhaust gasses are expanded by turbine wheel 78
and flow between combustor dome 104 and exhaust gas dome 106 prior
to passing through heat transfer section 98 and being exhausted
through exhaust 108.
[0027] The low-emissions combustion system is designed to produce
low emissions when operating at or near full power. This is
accomplished using the premix mode of operation which provides very
lean combustion and reduced flame temperatures. When operating in
the premix mode, the system operates near its flammability or
extinction limit for the particular fuel being utilized. One or
more pilot modes are provided to increase the overall operating
range of the system. However, transitions between the premix and
pilot modes must be carefully controlled to sustain combustion. The
system is designed with a large primary zone volume which provides
longer residence times to achieve more complete combustion of CO
(carbon monoxide) and THC's (total hydrocarbons). The lower flame
temperatures produced in the lean-burn premix mode reduce
production of oxides of nitrogen.
[0028] In a preferred embodiment, the combustion system is operated
in three different operating modes depending on the current
operating conditions. The operating modes include at least one
pilot mode and at least one premix mode. Mode selection is
primarily based on the desired air/fuel ratio (AFR) as explained in
greater detail below. Preferably, multiple pilot modes are
provided. The first pilot mode may include operation of only one of
injectors 42. A second pilot mode would include operation of two
injectors 42 while the third pilot mode would include operation of
all three injectors 42. The mode of operation is controlled by four
solenoid valves as illustrated and described with reference to FIG.
1.
[0029] During off loading and low to medium power operation, the
AFR normally results in operation of the combustion system in the
third pilot mode which utilizes all three injectors 42 operating in
the pilot mode. During idle, start-up, or severe off loading, the
AFR normally results in operation in the first pilot mode using
only a single injector 42. When appropriate for the AFR, all three
injectors 42 can be operated in a three premix mode where the fuel
and air are highly mixed within a mixing chamber of each injector
42 prior to discharge into the combustion chamber as illustrated
and described in greater detail with reference to FIG. 3.
Alternatively, a single premix or dual premix mode can be selected
in one injector or two injectors, respectively, to provide the
appropriate AFR.
[0030] A cross-sectional view of a gaseous fuel injector capable of
operation in a pilot mode or premix mode for use with a modular
turbogenerator control according to the present invention is
illustrated in FIG. 3. Injector 42 is mounted to the outer wall of
the recuperator using flange 120. A coupler 122 is used to couple
premix fuel inlet tube 124 to outer tube 126 of injector 42. Fuel
passes through a fuel distribution centering ring 130 into
premixing chamber 132 where it is combined with air passing through
various apertures 134 prior to being discharged from injector 42
into the primary combustion zone. When operating in the pilot mode,
fuel is delivered via pilot fuel inlet 136 through pilot tube 128
to pilot flame holder 138 where it is discharged from injector 42
into the primary combustion zone of the combustor. As such, when
operating in the pilot mode, fuel is not substantially mixed with
air prior to delivery to the combustion zone.
[0031] FIG. 3 provides only one example of an injector which may be
used to provide pilot mode and premix mode operation. The injector
illustrated in FIG. 3 is preferably used for a gaseous fuel.
Various other injectors which may be used with gaseous or liquid
fuels are described in detail in U.S. Pat. No. 5,850,732. As will
be appreciated by one of ordinary skill in the art, the modular
control system of the present invention is independent of the
particular injector or combustion system, which may vary depending
upon the particular fuel or fuels being utilized.
[0032] FIG. 4 is a block diagram illustrating operation of one
embodiment of a power controller fuel control system for use in a
system or method according to the present invention. As will be
appreciated by one of ordinary skill in the art, power controller
24 preferably performs control functions in addition to those
illustrated which are not directly related to the modular control
system of the present invention and therefore not shown for clarity
and convenience. Power controller 24 is preferably a microprocessor
based controller with associated volatile and non-volatile memory,
conditioning circuitry, and the like. As one of ordinary skill in
the art will appreciate, the various functions performed by power
controller 24 as illustrated in FIG. 4, may be performed by
hardware, software, or a combination of hardware and software.
Control logic may be implemented in terms of instructions executed
by a microprocessor, or may be implemented in hardware via
application specific integrated circuits (ASICs). Similarly,
various functions may be completed simultaneously or in parallel
while other functions require appropriate sequencing to accomplish
the features, advantages, and goals of the present invention.
[0033] Power controller 24 determines the current airflow using
various sensors 150. In one preferred embodiment, an ambient
temperature sensor 152, an ambient pressure sensor 154, and a speed
sensor 156 are provided for use in determining the current airflow.
Speed sensor 156 may determine the rotational speed of a compressor
wheel or equivalently the turbine wheel. In one embodiment, signals
provided by sensors 150 are used to access a lookup table 158 to
determine the current airflow. Preferably, lookup table 158 is
stored in a computer-readable storage medium, i.e. a non-volatile
memory associated with, or accessible by power controller 24.
Depending upon the particular application, airflow may be
alternately obtained by an appropriate sensor rather than being
computed as illustrated in FIG. 4. For example, a venturi with
associated pressure sensors may be used to directly calculate
airflow.
[0034] The current airflow, either measured or calculated,
(W.sub.air) is used to determine limits for the fuel command as
represented by block 160, and to determine the calculated air/fuel
ratio (AFR) as represented by block 162. To establish limits for
the fuel command, values corresponding to the energy content of the
particular fuel being utilized, represented by reference numeral
163, and the maximum AFR to sustain combustion, represented by
reference numeral 164, are communicated by fuel controller 22 via
intra-controller communications bus 36 to power controller 24.
These values are used in block 160 to determine the lower limit of
the fuel command, preferably in terms of energy flow.
[0035] As also illustrated in FIG. 4, power controller 24
preferably communicates with a temperature sensor 168 which
monitors the turbine exhaust temperature (TET). A desired or target
TET is determined by power controller 24 depending upon the
particular operating conditions. When the system is started, the
target TET is ramped up from the light-off temperature to a final
temperature set point over a period of time to warm up the engine.
Once the final TET set point has been reached as determined by the
TET feedback signal monitored by temperature sensor 168, that
temperature is maintained substantially constant throughout the
electrical load cycle of the system for steady-state operation, or
maintained according to a predetermined value that is based on
speed. The feedback signal is compared to the TET target at block
170 to produce an error signal. A closed loop feedback controller
172 is used to generate a signal which reduces the error toward
zero. In one embodiment, closed-loop controller 172 is a
proportional-integral-differential (PID) controller. As described
in greater detail below, the target TET may be modified during
transitions between operating modes to improve combustion
stability. Operation of a turbogenerator to a turbine exit or
exhaust temperature (TET) is described in U.S. patent application
Ser. No. 09/080,892 filed May 18, 1998 commonly owned by the
assignee of the present invention entitled "Turbogenerator/Motor
Control System," the disclosure of which is hereby incorporated by
reference in its entirety.
[0036] Block 174 generates a fuel command in units independent of a
particular fuel being combusted in the turbogenerator based on a
required electrical load. In one embodiment, the fuel command
generated by block 174 is in terms of energy flow (BTU/sec). A
minimum energy flow value is provided by block 160 based on the
energy content and maximum AFR for the particular fuel being used
as indicated by fuel controller 22. The fuel command is also
limited to a maximum energy flow, represented by reference numeral
176 based on the maximum capacity of the fuel metering or delivery
device. The maximum capacity is also communicated by fuel
controller 22 over intra-controller communications bus 36. The fuel
command is used by block 162 to calculate the AFR. The fuel command
is also communicated from power controller 24 to fuel controller 22
via the intra-controller communications bus 36. Likewise, the
computed AFR is provided to fuel controller 22 via the
intra-controller communications bus 36. Preferably, the maximum AFR
value for each injector operating mode is empirically determined
for each fuel type.
[0037] Thus, power controller 24 will not generate a fuel command
that would cause the AFR to exceed the particular limits of the
fuel system that would cause the engine to flame out. This is
assured by calculating the airflow and dividing by the maximum AFR
value received from fuel controller 22. The result of this
calculation provides the minimum fuel flow which is then divided by
the energy content of the fuel to produce the minimum energy flow
required to sustain combustion. The minimum energy flow provides
the lower limit of the commanded fuel output to fuel controller 22.
Likewise, an upper limit is provided based on values indicated by
fuel controller 22 such that power controller 24 will not demand
more fuel than the particular fuel system can supply.
[0038] FIG. 5 is a block diagram illustrating operation of one
embodiment of a fuel control subsystem for a modular turbogenerator
controller according to the present invention. Similar to the power
controller 24, fuel controller 22 preferably includes a
microprocessor based controller which performs various functions
specific to the fuel control subsystem using appropriate hardware
and/or software. Fuel controller 22 receives a fuel command,
preferably in terms of energy flow, from power controller 24. The
fuel command is processed by fuel controller 22 as indicated by
block 180 to convert the fuel command to a quantity of fuel to be
delivered to at least one injector based on the energy content of
the fuel. Various fuel constants, such as the energy content of the
fuel, may be stored in a memory 182 associated with, or in
communication with fuel controller 22. Once the energy command has
been converted to a fuel command, fuel controller 22 controls fuel
delivery subsystem 38 to deliver the appropriate quantity of fuel
to one or more injectors. In one embodiment, a fuel command
(W.sub.f), fuel temperature, and fuel pressure across the
proportioning valve are used to determine an appropriate valve
position using a lookup table 186. These values are provided by
corresponding pressure sensors 188, 190, and a fuel ambient
temperature sensor 192.
[0039] The valve position or pump speed (depending on what metering
device is used) is controlled by a corresponding feedback
controller 194 which preferably implements a PID feedback control
using valve position feedback from an appropriate sensor 196. The
valve position or pump speed is controlled by controlling the
current supplied to the valve or pump, respectively, as indicated
by block 198 to reduce the error toward zero. To provide a flexible
control strategy which can be used with a variety of different
fuels, the present invention allows the user to enter various fuel
constants or fuel indices based on the physical fuel
characteristics associated with the particular fuel being utilized
as represented by block 182 of FIG. 5. In one preferred embodiment,
physical characteristics of a gaseous fuel are incorporated into
the control functions in the form of two indices as follows: 1 FUEL
11 = SG * ( 1327 HHV vol ) 2 and FUEL 12 = HHV vol 1668 * SG
[0040] where SG represents the specific gravity of the fuel with
respect to air and HHV.sub.vol represents the fuel gas higher
heating value in Btu/SCF. The FUEL.sub.I1 index is a parameter
related to the fuel density and energy content and is used in
controlling the fuel metering device to deliver an appropriate
quantity of fuel to provide the commanded energy flow. The
FUEL.sub.I2 index is a parameter proportional to the fuel gas
higher heating value on a mass basis and is used to modify the
operating mode transitions based on AFR as described in greater
detail below.
[0041] In one embodiment, the FUEL.sub.I1 index parameter is used
to modify the commanded position of the fuel proportioning valve so
that the same fuel metering hardware can be utilized with multiple
fuels. Preferably, empirical data relative to valve position and
fuel flow is stored in the form of a look-up table in a computer
readable storage media accessible by the fuel controller. The
empirical data may be stored in the form of sampled data with
intermediate points being interpolated. Alternatively, an equation
representing the proportioning valve response may be stored. The
equation may be analytically determined based on the construction
of the proportioning valve, or empirically determined using a curve
fitting routine based on collected data.
[0042] Fuel controller 22 also receives the AFR from power
controller 24 via the intra-controller communications bus 36. The
AFR is used to select or determine an appropriate operating mode
for one or more injectors as represented by block 200. In one
embodiment of the present invention, three different operating
modes are provided. Block 200 controls the selection of the
operating mode as seen in FIG. 6, in addition to the sequencing of
injectors during transitions between operating modes as illustrated
and described in greater detail with reference to FIGS. 7-10. In
this embodiment, the operating modes include a premix mode 202
which energizes all of the premix injectors in such a way as to
supply fuel to the premix chamber through the coupler, and a pilot
mode which is selected by controlling one or more injectors to
supply fuel to the pilot tubes of the injectors as indicated
generally by reference numeral 204.
[0043] A diagram illustrating transitions between control modes
based on AFR including hysteresis bands for a modular
turbogenerator control according to the present invention is
provided in FIG. 6. The diagram illustrates a first pilot mode
region 210, a first hysteresis band 212, a second pilot mode region
214, a second hysteresis band 216, and a premix mode region 218.
Hysteresis bands 212 and 216 are provided to eliminate oscillation
between adjacent operating modes when the operating region is near
a transition line. Hysteresis bands 212 and 216 may be empirically
determined (or theoretically calculated) based upon the particular
combustion system and fuel being utilized.
[0044] Operating mode transitions are indicated by transition lines
220, 222, 224, and 226. The actual values of AFR (whether
determined directly or indirectly based on generator output power)
which correspond to transition lines 220, 222, 224, and 226
preferably vary based on the particular fuel being utilized. In one
embodiment, a fuel index parameter, FUEL.sub.I2, is used to adjust
the transition values relative to a default or standard value as
described above. Transitions are completed over a predetermined
period of time as illustrated and described with reference to FIGS.
7-10. To determine the current operating mode within hysteresis
bands 212 and 216, it is necessary to determine the previous mode
and/or direction of transition as indicated generally by transition
diagram 228. Line 230 represents idle conditions while line 232
represents full power conditions. Beginning at idle, the system is
operating in the first pilot mode region 210 which preferably
energizes a single injector. As the electrical load increases, the
operating mode follows line 234, whereas a decrease in electrical
load follows line 236. For example, as the electrical load
increases and transition line 222 is crossed, the operating mode
changes from the first pilot mode (one pilot) to the second pilot
mode (three pilot). A subsequent reduction in the load would follow
line 236 such that the first pilot mode is not activated until
transition line 220 is crossed. The control operates in a similar
fashion with respect to hysteresis band 216.
[0045] In one preferred embodiment, operating mode transitions are
limited among a subset of available injector operating modes based
on the energy content of the fuel being utilized. As the energy of
the fuel decreases, so does flame stability. As such, users may
select a low BTU or medium BTU mode to improve flame stability at
the cost of increased emissions and/or lower efficiency. Low BTU
operation typically requires higher fuel gas supply pressures which
may be supplied by an external compressor, for example. In
addition, selection of a low BTU fuel operating mode to increase
flame stability preferably limits operation of the injectors to
premix mode only with all injectors energized. In addition,
light-off TET may be increased during transitions between open loop
light and closed loop acceleration to further improve stability
during lighting. Likewise, operation in a medium BTU fuel mode
preferably includes only a subset of the available injector
operating modes. For example, a medium BTU mode preferably prevents
switching to single injector operation under all operating modes,
operating in the multiple injector pilot and premix modes.
[0046] FIGS. 7-10 are timing or sequencing diagrams which
illustrate injector control during transitions between operating
modes within a fuel system controller of a modular turbogenerator
control according to the present invention. FIG. 7 illustrates
control of three injectors during a transition from a single pilot
mode to a three pilot mode. FIG. 8 illustrates a control sequence
for a transition in the opposite direction from three pilot mode to
single pilot mode. FIG. 9 illustrates alternative control
sequencing strategies for transitions between three pilot mode and
a premix mode. FIG. 10 illustrates alternative control sequencing
for transitions from premix mode to three pilot mode.
[0047] In FIGS. 7-10, the time axis is used to illustrate the
relative time sequence of activating or deactivating each injector
which is capable of operating in a pilot mode (PI) or in a premix
mode (PR). The sequencing of the injectors during a transition
between operating modes may depend upon the particular construction
of the combustion system. In a preferred embodiment, injectors are
positioned within the combustor to tangentially inject fuel into
the combustor. For this arrangement, it is desirable to follow the
swirl pattern created by the injectors when transitioning from
single pilot mode to three pilot mode. This allows the additional
injectors to be ignited by the flame produced by the single
injector active during the first pilot mode. Conversely, when
transitioning from a higher to a lower load, corresponding to a
transition from three pilot mode to single pilot mode, it is
desirable to sequence injector deactivation to oppose the swirl
pattern to improve combustion stability. A further improvement to
combustion stability may be provided by energizing the ignitor
during transitions. Alternatively, or in combination, additional
fuel may be provided during transitions to promote combustion
stability. Preferably, additional fuel is provided by increasing
the target or desired turbine exhaust temperature (TET).
[0048] In the single pilot mode, a single injector (PI.sub.1) is
active at time t.sub.0 as illustrated in FIG. 7. To transition to
the dual pilot mode, the second injector (PI.sub.2) is energized at
time t.sub.1 while the third injector (PI.sub.3) is energized or
activated at time t.sub.2. This sequencing pattern follows the
swirl or rotational pattern created by the tangential injection of
fuel within the combustor.
[0049] A transition from the dual pilot mode to the single pilot
mode having a sequence which opposes the swirl pattern is
illustrated in FIG. 8. In this transition, the first injector
(PI.sub.1) is deactivated at time t.sub.1 followed by the third
injector (PI.sub.3) at time t.sub.2 while the second injector
(PI.sub.2) remains on.
[0050] Alternative sequencing strategies are illustrated by dotted
lines to transition from a second pilot mode to the premix mode in
FIG. 9. For the premix mode, all of the premix injectors (PR.sub.1,
PR.sub.2, and PR.sub.3) may be activated at time t.sub.1, t.sub.3,
or alternatively t.sub.5 by supplying fuel to the coupler of the
injectors. As indicated in the diagram, each alternative includes
some overlap with operation of the injectors in the pilot modes.
For example, if the premix injectors are activated at time t.sub.1,
all three injectors have fuel supplied to both the premix port and
pilot port simultaneously for varying amounts of time. In this
scenario, the first pilot injector (PI.sub.1) is deactivated at
time t.sub.2 while the second and third pilot injectors (PI.sub.2
and PI.sub.3) are deactivated at time t.sub.4 and t.sub.6,
respectively. The second and third alternatives for transitioning
from the premix mode provide less overlap where fuel is supplied to
both the pilot and premix ports.
[0051] FIG. 10 illustrates alternative strategies for transitioning
from the premix mode to the three pilot mode. Each of these
strategies follows the swirl pattern created by the tangential
injection of fuel within the combustor. This facilitates ignition
of the pilot flames for the injectors. As illustrated, fuel
supplied to the premix ports may be shut off at time t.sub.2,
t.sub.4, or t.sub.6. Injectors 1, 2, and 3 are switched to pilot
mode at time t.sub.1, t.sub.3, and t.sub.5, respectively.
[0052] A graph illustrating operating mode transitions based on
generator output power as a function of normalized ambient
temperature is shown in FIG. 11. FIG. 11 illustrates lines of
constant AFR which may be used to control the operating mode of the
injectors. Line 250 represents the full rated power of the engine.
Line 252 corresponds to the AFR to transition from the premix mode
to the three pilot mode. Line 254 corresponds to the transition
line to transition from the three pilot mode to the single pilot
mode. When moving from lower to higher power, transition lines 256
and 258 are used to switch from the single pilot mode to the three
pilot mode, and from the three pilot mode to the premix mode,
respectively. As such, injector operating modes may be determined,
if desired, based on generator power output which is essentially an
indirect determination of AFR rather than operating based on a
direct determination as described above with reference to FIG.
6.
[0053] A graph illustrating air/fuel ratio at full power as a
function of ambient temperature for two turbine exhaust
temperatures is shown in FIG. 12. Line 270 represents AFR for a TET
of about 1050F. Line 272 corresponds to the AFR for a TET of about
1100F. Line 274 represents the transition line between the premix
mode corresponding to region 276 and the three pilot mode
corresponding to region 278. As this graph illustrates, the present
invention allows full power operation in the low-emissions premix
mode over the entire range of anticipated ambient temperatures.
[0054] FIG. 13 is a graph illustrating variation of AFR over a
range of generator output power for two turbine exhaust
temperatures. The graph also provides transition lines for a
selection of operating modes for a modular turbogenerator control
according to the present invention. The graph of FIG. 13
illustrates the variation of AFR for TET of about 1050F as
represented by line 288, and 1100F as represented by line 290. As
the system is operated near full rated power, it transitions into
premix mode region 292 from three pilot mode region 294 with an
appropriate hysteresis band as previously described. Likewise, as
the power level is decreased, the system transitions from the
premix mode to the second pilot mode when the AFR exceeds the
corresponding transition line 296.
[0055] A flowchart illustrating operation of a system or method for
modular control of a turbogenerator according to the present
invention is illustrated in FIG. 14. The current airflow is
determined as represented by block 302. This determination may be
made using a lookup table referenced by ambient air temperature,
air pressure, and turbine or compressor speed as indicated
generally by reference numeral 304. Alternatively, current airflow
may be determined directly by measuring the actual airflow through
the turbogenerator as represented by block 306.
[0056] The desired energy flow is determined as represented by
block 310. This desired energy flow is based on a turbogenerator
operating parameter such as turbine exhaust temperature and is
generated in units which are independent of the particular fuel
being used by the system. This provides the separation of control
functions to achieve modularity. Preferably, the fuel command is
limited by lower and upper limits based on a minimum energy flow to
sustain stable combustion, and a maximum energy flow based on the
maximum fuel flow and energy content of the fuel that the metering
device is capable of delivering as represented by block 312.
[0057] From the current airflow 302 and desired energy flow 310,
the AFR is calculated as represented by block 300. Both the AFR and
desired energy flow 310 are communicated from the power controller
or first controller to the fuel controller or second controller as
represented by block 316. Preferably, the fuel command is
communicated via an external communications bus. A quantity of fuel
to be supplied to the combustor is determined, as represented by
block 318, based on the fuel energy content 319 in the second
controller. Fuel supplied to the turbogenerator is then controlled
based on the determined quantity of fuel as represented by block
318 by the metering device block 320. In an alternative arrangement
the current airflow 302 and desired energy flow 310 are determined
in the power controller and communicated to the fuel controller
where the AFR is then calculated. In other words, block 300 drops
from the first controller to the second controller and block 316
communicates only energy flow and airflow to the second
controller.
[0058] In one preferred embodiment, an operating mode for at least
one injector of the turbogenerator is selected based at least in
part on the AFR as represented by block 322. The operating mode may
include a premix mode 326 and a pilot or diffusion mode as
represented by block 324. One or more injectors may be activated or
energized in either operating mode. Preferably, all injectors are
activated in the premix mode while varying numbers of injectors are
activated in a plurality of pilot modes.
[0059] Combustion stability may be improved by energizing the
ignitor of the turbogenerator during transitions 328 between
operating modes as represented by block 330. In addition, or
alternatively, combustion stability may be improved by increasing
the quantity of fuel supplied to the injectors during transitions
between control modes as represented by block 332. In one
embodiment, fuel is increased by modifying a desired operating
temperature, i.e. the turbine exhaust temperature, during a load
transition as represented by block 334.
[0060] Thus, the present invention provides a modular control for a
turbogenerator which has the capacity to run on a variety of
different fuels without significant system modification. Control is
separated into a power controller and a fuel controller with
communication provided through an intra-controller bus. This
approach allows the same turbogenerator to run on a variety of
available fuels with only a single fuel system change, thus making
it more versatile and cost effective than current systems.
[0061] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *