Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1999-05-10
2001-09-04
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
Reexamination Certificate
active
06282884
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to turbine engines and more particularly, to controlling engine operation.
Known engine control units are configured to operate in multiple control modes for maintaining engine control under many different conditions. The control unit selects a mode of operation based on environmental and operating conditions, and the control unit supplies a fuel flow rate to an engine control processor. The engine control processor then utilizes the fuel flow rate supplied by the control unit to control engine operation.
Known control modes include, for example, a baseline mode, a combustor inlet pressure limiter mode, a fuel acceleration mode, and a fuel deceleration mode. The control unit output for each control mode is fuel flow. The baseline mode corresponds to normal operation of the aircraft engine. The combustor inlet pressure limiter mode is selected when combustor pressures approach maximum permissible limits. The fuel acceleration mode is selected during throttle burst transients to prevent compressor stall and turbine over-temperature. The fuel deceleration mode is selected during throttle chop transients to prevent combustor blowouts. Of course, many other modes are utilized to protect an engine from exceeding operability, mechanical integrity, and other limits, and to provide consistent engine responses.
For each control mode, and to ensure adequate engine control, many factors such as power level, rotor speeds, stall margins, temperatures, and demanded values of thrust are utilized in determining the control unit output. A typical control unit includes numerous single-input, single-output controllers, and each single-input. single-output controller is utilized to generate a value for one commanded actuator position. Specifically, each single-input single-output controller receives a single engine parameter as an input and outputs a value related to fuel flow rate.
The outputs from the controllers are selected based upon the current operation mode of the control unit. Particularly, the control unit output is generated by selecting the outputs from one of the controllers. For example, the controller outputs are selected when meeting a first set of conditions when the control unit is in the baseline mode, and the controller outputs are selected when meeting a second set of conditions when the control unit is in the fuel acceleration mode.
The known control unit described above utilizes simple controllers and selects from among controller outputs to generate the fuel flow rate. It would be desirable to modify the mode selector to improve engine performance. It also would be desirable to be able to set the appropriate control output when using several multivariable controllers.
BRIEF SUMMARY OF THE INVENTION
A control unit in accordance with an exemplary embodiment of the present invention includes multivariable model-based regulators and generates an output corresponding to actuator values rather than actuator rates. More particularly, and in the exemplary embodiment, the control unit supplies control values, i.e., actuator positions, for fuel flow (WF
36
), nozzle area (A
8
), and bypass area (A
16
) to an engine. The control unit includes regulators K
1
, K
2
, and K
3
for a baseline low-power mode, a baseline high-power mode, and an operability mode, respectively. The baseline mode corresponds to normal operation of the aircraft engine, and each sub-mode within the baseline mode coincides with a range of power levels. The operability mode corresponds to engine operation when engine fan stall margin approaches a specified level.
Respective gain schedulers are coupled to each regulator K
1
, K
2
, and K
3
, and each scheduler receives, as input, an operating point which corresponds to a power setting parameter and fan inlet conditions. Based on the operating point, each scheduler selects a set of gains to supply to its respective regulator K
1
, K
2
, and K
3
.
Regulators K
1
, K
2
, and K
3
are multiple input, multiple output type regulators, and each regulator K
1
, K
2
, and K
3
receives, as input, values for errors in thrust (E
fn
) and liner engine pressure ratio (E
lepr
). Additionally, regulator K
1
receives the error in engine pressure ratio (E
eprs
), regulator K
2
receives the error in engine temperature ratio (E
etr
), and regulator K
3
receives the error in fan stall margin (E
sm2
). Based on these inputs and the gains selected by the schedulers, each regulator K
1
, K
2
, and K
3
generates values for fuel flow (WF
36
), nozzle area (A
8
), and bypass area (A
16
).
The control unit further includes a mode selector which receives, as inputs, an engine control equivalent of throttle setting (PC), which varies from a value of 20 at ground idle to a value of 50 at military power, and stall margin (SMR), which is a ratio of stall margin (SM
2
) to a specified fan stall margin value (SM
2
DEM). The mode selector generates mode selection outputs A
1
, A
2
, and A
3
Outputs A
1
, A
2
, and A
3
are gains that have values in the interval [0,1], corresponding to the amount of contribution made by baseline low power regulator K
1
, baseline high power regulator K
2
, and operability regulator K
3
, respectively. The sum of outputs A
1
, A
2
, and A
3
is unity.
Specifically, outputs A
1
, A
2
, and A
3
are supplied to respective multiplication units which multiply the respective gains A
1
, A
2
, and A
3
by the respective regulator outputs. Outputs from the multiplication units are supplied to separate summation units which combine the respective gain-adjusted outputs for each parameter. That is, the gain-adjusted values for fuel flow (WF
36
) from each multiplier are added together at a first summation unit. Similarly, the gain-adjusted values for nozzle area (A
8
) are added together at a second summation unit, and the gain-adjusted values for bypass area (A
16
) are added together at a third summation unit. The summation unit outputs are supplied to the engine to control actuator positions.
In the exemplary embodiment, the mode selector transitions from the low power baseline mode to the high power baseline mode when the throttle setting (PC) is in the interval [37.5,42.5]. The selector transitions between the baseline mode and the stall margin mode as the stall margin limit is approached. The values for the respective gains output by the selector are determined in accordance with the following rules:
A
1
=(1.0−A
3
)max(0.0,min(1.0,(42.5−PC)0.2)),
A
2
=(1.0−A
3
)(
1.0−A
1
), and
A
3
=max (0.0,min(1.0,2.0(1.0−SMR))).
The mode selector utilizes fixed rules based on the engine parameters throttle setting (PC) and stall margin (SMR) to select a combination of individual modes for deriving values for fuel flow (WF
36
), nozzle area (A
8
), and bypass area (A
16
).
The above described control unit includes multivariable controllers rather than only single-input, single-output controllers. Such multivariable controllers enable robust control of the engine. In addition, the regulator outputs are actuator values rather than actuator rates, and model-computed parameters such as thrust (FN), engine temperature ratio (ETR), and stall margin (SM
2
) are used in addition to sensed parameters or simple ratios of sensed parameters. Also, a gradual transition between modes is possible by blending the outputs from each regulator. rather than selecting between controller outputs. Further, to function as the known control unit described above, one of gains A
1
, A
2
, and A
3
can be set to 1.0 at any given time with the other gains set at zero.
REFERENCES:
patent: 4258545 (1981-03-01), Slater
Paper entitled “Intelligent Mode Selection and Blending for Engine Control,” by M. Wiseman, G. Becus and S. Adibhatla, presented to the 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit Jul. 13-15, 1998, Cleveland, Ohio.
Adibhatla Sridhar
Becus Georges A.
Wiseman Matthew W.
General Electric Company
Herkamp Nathan D.
Hess Andrew C.
Rodriguez William H
Thorpe Timothy S.
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