CROSS-REFERENCE TO RELATED APPLICATIONS
The current application claims priority to U.S. Provisional Application, Ser. No.
611595,419, filed Feb. 6,2012, the entire disclosure of which is incorporated herein by
reference. The current application is related to U.S. Non-Provisional Application Methods
and Apparatuses for Non-Model Based Control for Counter-Rotating Open-Rotor Gas
Turbine Engine which is being filed concurrent to this application on October 11, 2012 under
Attorney Docket No. 034569.021521.
BACKGROUND OF THE INVENTION
The current disclosure pertains to counter-rotating open-rotor (CROR) gas turbine
engines; and, more specifically, control system implementations for such CROR gas turbine
engines. For CROR control, the two counter-rotating rotors are functionally coupled to each
other, and their operation is further impacted by fuel flow. The current disclosure provides
control solutions addressing such problems and relationships.
BRIEF DESCRIPTION OF THE INVENTION
The current disclosure provides simple, robust and systematic solutions that
mathematically decouple the two counter rotating rotors of a CROR engine by model-based
dynamic inversion, which allows application of single-input-single-output (SISO) control
concepts. The current solutions allow fuel flow to be treated as a known disturbance and
rejected from the rotor speeds control. Furthermore, the current control solutions allow a
simple and well-coordinated speed phase synchronizing among the four rotors on a twoengine
vehicle.
According to the current disclosure, a counter-rotating open-rotor gas turbine engine
includes: a forward un-ducted rotor including a plurality of forward rotor blades and
including a forward rotor angle actuator for setting blade pitch angles of the plurality of
forward rotor blades; an aft un-ducted rotor including a plurality of aft rotor blades and
including an aft rotor angle actuator for setting blade pitch angles of the plurality of aft rotor
blades; a gas turbine engine driving forward and aft un-ducted rotors and including a fuel
actuator for setting the fuel flow to the gas turbine engine; and an open rotor control system
including, a forward rotor blade pitch angle command (BetaF) electrically connected to the
forward rotor angle actuator, an aft rotor blade pitch angle command (BetaA) electrically
connected to the aft rotor angle actuator, a fuel flow command (Wf) electrically connected to
the fuel actuator, a forward rotor speed feedback signal (Nf), an aft rotor speed feedback
signal (Na), and an engine pressure ratio signal (EPR). The open rotor control system may
incorporate a control algorithm that includes: a 2x2 multi-input-multi-output (MIMO) control
solution for the forward rotor blade pitch angle command (BetaF), the aft rotor blade pitch
angle command (BetaA), the forward rotor speed feedback signal (Nf) and the aft rotor speed
feedback signal (Na); and a single-input-single-output (SISO) control solution for the fuel
flow command (Wf) and the engine pressure measurement feedback signal. More
specifically, the open rotor control system may include a control option that considers fuel
flow impact on rotor speeds but does not consider rotor blade pitch angles impact on gas
generator engine pressure ratio. Additionally, the gas generator fuel flow command (Wf)
impact on rotor speeds Nf and Na may be treated as known disturbance input in the 2x2
MIMO control. In a more detailed embodiment, the control algorithm may further include a
disturbance rejection path to account for disturbance effect of fuel flow on forward and aft
rotor speeds. Alternatively or in addition, the 2x2 MIMO control solution may utilize a
dynamic inversion approach.
Also according to the current disclosure, a counter-rotating open-rotor gas turbine
engine includes: a forward un-ducted rotor including a plurality of forward rotor blades and
including a forward rotor angle actuator for setting blade pitch angles of the plurality of
forward rotor blades; an aft un-ducted rotor including a plurality of aft rotor blades and
including an aft rotor angle actuator for setting blade pitch angles of the plurality of aft rotor
blades; a gas turbine engine driving forward and aft un-ducted rotors and including a fuel
actuator for setting the fuel flow to the gas turbine engine; and an open rotor control system
including, a forward rotor blade pitch angle command (BetaF) electrically connected to the
forward rotor angle actuator, an aft rotor blade pitch angle command (BetaA) electrically
connected to the aft rotor angle actuator, a fuel flow command (Wf) electrically connected to
the fuel actuator, a forward rotor speed feedback signal (Nf), an aft rotor speed feedback
signal (Na), and an engine core speed feedback signal or engine pressure ratio signal (EPR).
The open rotor control system may include a multiple-input-multiple output (MIMO) control
algorithm including a dynamics inversion approach for at least the forward rotor blade pitch
angle command (BetaF), the aft rotor blade pitch angle command (BetaA), the forward rotor
speed feedback signal (Nf) and the aft rotor speed feedback signal (Na). More specifically,
the open rotor control system may include a multiple-input-multiple output (MIMO) control
algorithm including a dynamics inversion approach for at least the forward rotor blade pitch
angle command (BetaF), the aft rotor blade pitch angle command (BetaA), the fuel flow
command (Wf), the forward rotor speed feedback signal (Nf), the aft rotor speed feedback
signal (Na) and the gas generator core speed feedback signal (N2). More specifically, the
open rotor control system may include a 3x3 multiple-input-multiple output (MIMO) control
algorithm including a dynamics inversion approach for at least the forward rotor blade pitch
angle command (BetaF), the aft rotor blade pitch angle command (BetaA), the fuel flow
command (Wf), the forward rotor speed feedback signal (NO, the aft rotor speed feedback
signal (Na) and the gas generator core speed feedback signal (N2).
Also, according to the current disclosure, with such counter-rotating open-rotor gas
the open rotor control system may further include a speed phase synchronizing control
architecture positioned between forward and aft rotor and/or between two engines. In certain
embodiments, the speed phase synchronizing control may include a single-input-singleoutput
(SISO) control solution. In certain embodiments the speed phase synchronizing
control includes a speed phase synchronization controller that provides a correction input
signal to a rotor speed regulator.
Also, according to the current disclosure, a counter-rotating open-rotor gas turbine
engine includes: a forward un-ducted rotor including a plurality of forward rotor blades and
including a forward rotor angle actuator for setting blade pitch angles of the plurality of
forward rotor blades; an aft un-ducted rotor including a plurality of aft rotor blades and
including an aft rotor angle actuator for setting blade pitch angles of the plurality of aft rotor
blades; a gas turbine engine driving forward and aft un-ducted rotors and including a fuel
actuator for setting the fuel flow to the gas turbine engine; and an open rotor control system
including, a forward rotpr blade pitch angle command (BetaF) electrically connected to the
forward rotor angle actuator, an aft rotor blade pitch angle command (BetaA) electrically
connected to the aft rotor angle actuator, a fuel flow command (Wf) electrically connected to
the fuel actuator, a forward rotor speed feedback signal (Nf), an aft rotor speed feedback
signal (Na), and an engine core speed signal N2; where the open rotor control system has a
control algorithm that may include a 3x3 multi-input-multi-output (MIMO) control solution
for the forward rotor blade pitch angle command (BetaF), the aft rotor blade pitch angle
command (BetaA), the fuel flow command (Wf), the forward rotor speed feedback signal
(Nf), the aft rotor speed feedback signal (Na) and the engine core speed feedback signal (N2).
Also the current disclosure is directed to any of the control systems described herein
andlor any of the methods described herein. For example, the current disclosure provides a
method for controlling a counter-rotating open-rotor gas turbine engine that includes, (a) a
forward un-ducted rotor including a plurality of fonvard rotor blades and including a forward
rotor angle actuator for setting blade pitch angles of the plurality of forward rotor blades, (b)
an aft un-ducted rotor including a plurality of aft rotor blades and including an aft rotor angle
actuator for setting blade pitch angles of the plurality of aft rotor blades, and (c) a gas turbine
engine driving the forward and aft un-ducted rotors and including a fuel actuator for setting
fuel flow to the gas turbine engine, where the method may include steps of (not necessarily
performed in any specific order): (1) generating forward and aft control signals respectively
for the forward rotor angle actuator and the aft rotor angle actuator; (2) generating a fuel flow
command for the fuel actuator; (3) receiving forward and aft rotor feedback signals; and (4)
receiving at least one of an engine pressure feedback signal and an engine core speed
feedback signal; where the steps of (I) generating the forward and aft control signals and (2)
generating the fuel flow signal utilize a control algorithm that may include, a multi-inputmulti-
output (MIMO) control solution for the forward and aft control signals and the forward
and aft rotor feedback signals, and a single-input-single-output (SISO) control solution for
the fuel flow command and the at least one of the engine pressure feedback signal and the
engine core speed feedback signal. In a more detailed embodiment, the control algorithm
may consider fuel flow impact on rotor speeds but does not consider rotor blade pitch angles
on gas generator engine pressure ratio. Alternatively, or in addition, the fuel flow command
impact on forward and aft rotor feedback signals may be treated as a known disturbance to
the MIMO control solution. Alternatively, or in addition, the MIMO control solution utilizes
a dynamic inversion control approach.
In an alternate detailed embodiment, the method may include providing a speed phase
synchronizing control architecture between (a) the forward and aft rotor feedback signals and
(b) input signals to the gas turbine engine. In addition, the speed synchronizing control may
include a single-input-single output (SISO) control solution. Alternatively, or in addition, the
speed phase synchronizing control may include a speed phase synchronizing controller that
provides a correction input signal to a rotor speed regulator.
Another exemplary method provided by the current disclosure is a method for
controlling a counter-rotating open-rotor gas turbine engine that includes, (a) a forward unducted
rotor including a plurality of forward rotor blades and including a forward rotor angle
actuator for setting blade pitch angles of the plurality of forward rotor blades, (b) an aft unducted
rotor including a plurality of aft rotor blades and including an aft rotor angle actuator
for setting blade pitch angles of the plurality of aft rotor blades, and (c) a gas turbine engine
driving the forward and aft un-ducted rotors and including a fuel actuator for setting fuel flow
to the gas turbine engine; where the method may include steps of (not necessarily performed
in any specific order): (1) generating forward and aft control signals respectively for the
forward rotor angle actuator and the aft rotor angle actuator; (2) generating a he1 flow
command for the fuel actuator; (3) receiving forward and aft rotor feedback signals; and (4)
receiving at least one of an engine pressure feedback signal and an engine core speed
feedback signal; where the steps of (1) generating the forward and aft control signals and (2)
generating the fuel flow signal may utilize a control algorithm that includes a multi-inputmulti-
output (MIMO) control solution including a dynamic inversion approach for the
forward and aft control signals, the fuel flow command, the forward and aft rotor feedback
signals and the least one of an engine pressure feedback signal and an engine core speed
feedback signal. In a more detailed embodiment the MIMO control solution may be a 3x3
MIMO control solution.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic block diagram representation of a basic control system
architecture for counter-rotating open-rotor (CROR) gas turbine engine;
Fig. 2 is another schematic block diagram representation of a basic control system
architecture for counter-rotating open-rotor (CROR) gas turbine engine;
Fig. 3 is a matrix representation of controlled plant input and output mapping for the
CROR of Figs. 1 and 2;
Fig. 4 is a block diagram representation of an exemplary control architecture
according to the current disclosure;
Fig. 5 is a block diagram representation of the exemplary control architecture of Fig.
4, including phase synchronization;
Fig. 6 is a block diagram representation of the exemplary control architecture of Figs.
4 and 5 as applied to two engines;
Fig. 7 is another matrix representation of controlled plant input and output mapping
for the CROR of Figs. 1 and 2; and
Fig. 8 is a block diagram representation of another exemplary control architecture
according to the current disclosure.
DETAILED DESCRIPTION
The current disclosure provides simple, robust and systematic solutions that
mathematically decouple the two counter rotating rotors of a CROR engine by model-based
dynamic inversion, which allows application of single-input-single-output (SISO) control
concepts. The current solutions allow fuel flow to be treated as a known disturbance and
rejected from the rotor speeds control. Furthermore, the current control solutions allow a
simple and well-coordinated speed phase synchronizing among the four rotors on a twoengine
vehicle.
The basic control system architecture for CROR is presented in Figs. 1 and 2. As
shown in Figs. 1 and 2, an example CROR gas turbine engine 10 includes a differential
gearbox 17 mechanically coupled between a forward un-ducted rotor 15 and an aft un-ducted
rotor 13, so that the rotor speeds of the respective forward and aft un-ducted rotors 15, 13 are
coupled for a given input torque. The example CROR gas turbine engine includes a fuel
actuator 16 for setting the fuel flow to the engine and gear box 17. The example CROR gas
turbine engine 10 includes (on a very basic level) three inputs: BetaF and BetaA, which are
the forward and aft rotor actuator pitch angle input signals, respectively provided by the
forward and aft blade pitch angle actuators 14 and 12; and Wf, which is the fuel flow input
signal provided by the fuel flow actuator 16. Outputs (again, on a very basic level) from the
CROR gas turbine engine 10 include Pa and Pf, which are aft and forward power signal
outputs, Na and Nf, which are the aft and forward rotor speed signal outputs, and P46, which
is a pressure signal output (an indication of core engine power). The control system includes
an open rotor control section 18 and a gas path control section 20. Inputs to the open rotor
control section 18 may include, for example, rotor speed Na and Nf, rotor speed phase Pa
and Pf feedback signals from the engine 10; and inputs to the gas path control section 20
may include, for example, P46 feedback signal from the engine 10 and an FMV position
signal from the fuel actuator 16.
For CROR control, the two counter-rotating rotors are hnctionally coupled to each
other, and their operation is further impacted by fuel flow. For example, the controlled plant
input and output mapping for the CROR can be represented in general as shown in Fig. 2
matrix, where Nf and Na are the forward and aft rotor speed signals outputs, BetaF and
BetaA are the forward and aft rotor actuator pitch angle actuator input signals, Wf is the fuel
flow actuator signal, and EPR is an engine pressure ratio signal.
Previous approaches to solve this problem have ignored the interactions between the
forward and aft rotor speed signals, Nf and Na, and have attempted to utilize single-inputsingle-
output control to attempt to maintain each rotor speed tracking their own reference.
However, as shown in the controlled plant matrix of Fig. 2, the interactions between the six
signals will impact the rotors' constant speed holding control and the rotors' speed phase
synchronizing significantly, because this coupling always exists.
First Exemvlarv Control Solution
Refemng again to Fig. 2, where Nf and Na are the forward and aft rotor speed signals
outputs, BetaF and BetaA are the forward and aft rotor actuator pitch angle actuator input
signals, Wf is the fuel flow actuator signal, and EPR is an engine pressure ratio signal; if the
gas generator fuel flow command Wf impact on rotor speeds Nf and Na are treated as known
disturbance, such that the control algorithm may include a disturbance rejection path to
account for disturbance effect of fuel flow on forward and aft rotor speeds, a 2x2 multi-inputmulti-
output (MIMO) control solution may be developed for the forward and aft rotor speed
signals outputs (Nf and Na) and the forward and aft rotor actuator pitch angle actuator input
signals(BetaF and BetaA).
Choose the states, control inputs, outputs and disturbance for open rotor control
below:
Assume the original open rotor controlled plant is:
r) At sample k , the system states x, , the inputs u,-, , and the disturbances d, are known.
Thus, the deviation variables are expressed about this current operating condition, i.e. x, ,
Uk-, 9 d,, Y; =h(x,,u,-,,d,).
Define the deviation variables from these conditions,
0 The local linearized model of the system in terms of deviation variables may be
derived
Approximate Fk 2, = xk - xk-, , and it is treated as a known initial condition for x- ~a+t sa~mp le k, or, autonomous response of the system states over one control sample ffroere
from any control action update, i.e. ii, = 0.
The state space perturbation model for open rotor control is:
Where ?(k) = 0, d"(k) = 0, and y(k) = 0 by definition.
Approximations:
Since Gas Path is decoupled from the open rotor inputs, Wf - EPR loop can be
treated as a SISO plant and non-mode$based SISO control can be used for Wf - EPR loop,
e.g., PID control. As a SISO plant, it can be model based SISO control or traditional Gainscheduling
SISO control. It is also within the scope of the current disclosure that Wf - EPR
loop can be incorporated into the above state space model, but it may not be necessary for a
well known SISO plant to do so.
Let EPR,, = EPRref - EPR . From a typical PID implementation,
1
Wf = ( K , + Kds+ K, -)EPR,
S
0
Use Tustin transformation, i.e.
Then the discrete-time transfer function is:
And the discrete-time state space model for PID controller is obtained via
Observability Canonical Realization as:
For open rotor controlled plant model, assume N, and N, both have relative degree
1, respectively, which is reasonable because actuator command to torque is algebraic
relationship, and torque to rotor speed is 1" order dynamics, then,
Let ji(k+j?=y,(k+j)-yi(k), j=O,1
* The desired output tracking response is:
( f i (k + 1) - yui (k + 1)) + k,,o ( j , (k) - Fi(k)) = 0
Properly choose ki,o, i = 1,2 such that the following polynomial
p+ ki,o = 0
has its eigenvalue within the unit circle, then the output tracking is asymptotically stable.
Furthermore,
Yi (k + 1) = f i (k + 1) + ki,,ji (k)
e For open rotor speed references are constant in general, therefore,
Compare the above desired output response with ~,,,=+ E,i Ek+ CiFk+ D,;, ,
Where K, is diagonal, K, = E-' , K, = E-' K, , j(k) = y, (k) - y(k),
F, = x(k) - x(k - I), &k) = Wf (k) - Wf (k - 1).
The decoupled control architecture 30 with disturbance rejection for holding constant
speed is presented in Fig. 4.
As shown in Fig. 4, the controlled plant perturbation model 30 is described by A, B ,
C , B, , D,, with control input vector Beta actuator (BetaF and BetaA) increment ilk , output
vector rotor speed (Nf and Na) perturbation yk, and disturbance fuel flow (Wf) perturbation
2, , which are defined in [0025]-[0030]. The controlled plant input ii, and the output 7, are
coupled. The decoupled control introduces K, , K, , K, , where K, decouples and cancels
the original dynamics by increment state feedback F, , KO decouples and cancels the
original disturbance by increment disturbance 2, , K, decouples the coupled input ik and
output yk and reshapes the desired controlled plant with new control input VK and output yk
in SISO relationship. The output tracking control introduces K, to close the rotor speeds
(Nf and Na) to their command references (NfR and NaR) such that the closed-loop SISO .
control based on the decoupled controlled plant (the input VK and output y,+)a chieves the
desired control performance: Nf tracks NfR, and Na tracks NaR. The decoupling control law
is < = K,, ;k+ K,F, + KO&, the increment actuator control input ii, needs to be integrated to
generate the actuator control input u, , i.e., BetaF, and BeatA, , which are applied to Beta
Actuators, respectively.
/ Since y, and y, are decoupled, that is, v, (k) = E-'(1,1)K, ( l , l ) j l (k) = K,,j, (k)
affects y, only, and v,(k) = E-' ( 2 , 2 ) ~(2, ,2)j,( k)= K,,j, (k) affects y, only. Therefore,
the speed phase synchronizing between y, and y, can be treated as an inner loop correction
of any of the two decoupled SISO control loops.
The phase feedback is defined as the average value in a certain time period (e.g., 6
samples):
1
avePh = - (ph,, - ph,, ) = Ph, - Ph,,
6 i-1
errPh = PhDmd - avePh = 0 - avePh = Ph,, - Ph ,
Then speed phase sync between the two rotors - R2R Sync control can be done by locally
adjusting v, to keep y, phase synchronizing with y, .
The R2R Sync control structure is presented in Fig. 5. The Phase Sync Regulator 40
determines the sign of dv, based on the following rules:
If 0' < errPh 5 180' or - 360' < errPh 5 -180°, Na is leading Nf,
Na needs to be slowed down, i.e., dv, < o ;
elseif 180' < errPh < 360' or - 180" < errPh < o', Na is behind Nf,
Na needs to be speeded up, i.e., dv, > o ;
For engine to engine (E2E) speed phase sync, since Nf and Na are decoupled for each
engine, the Nfs from two engines need to be synchronized. Assume that Engine1 is specified
as Master, Engine2 needs to be synchronized to Enginel. Define
The E2E Sync control structure is presented in Fig. 6, where a second engine control
architecture 30' and corresponding Phase Sync Regulator 40' are provided. The E2E Phase
Sync Regulator 50 determines the sign of dv, based on the following rules:
If 0' < errPhEng 5 180' or - 360' < errPhEng 5 -180°, E2 is leading El,
E2 needs to be slowed down, i.e., dv, < O;
elseif 180' < errPhEng < 360' or - 180' < errPhEng < 0' , E2 is behind El,
E2 needs to be speeded up, i.e., dv, > 0;
With the decoupled speed control, the rotor to rotor speed phase sync and engine to engine
speed phase sync become classical SISO control design in the very simple system structure.
Second Exemularv Control Solution
For open rotor control, when the two counter-rotating rotors are mechanically coupled
by a differential gearbox, the core speed N2 and the open rotor speeds are highly coupled.
The controlled plant input and output mapping can be represented in general as in Fig. 7,
where BetaF and BetaA are forward rotor and aft rotor actuator inputs, respectively, Wf is
fuel flow actuator. Nf and Na are BetaF forward rotor and aft rotor speeds, N2 is engine core
speed.
Choose the states, control inputs, controlled outputs for open rotor control shown in
Fig. 7.
The rotor speed dynamics, the engine core speed dynamics, the coupling between the
two rotors, and the coupling between the gas generator and the rotors are all characterized in
the following perturbation model:
Where E(k) = 0, and y(k) = 0 by definition.
For open rotor controlled plant model, assume Nf , N, and N, all have relative
degree 1, respectively, which is reasonable because actuator command to torque is algebraic
relationship, and torque to rotor or turbine speed is 1" order dynamics, then,
Let ji(k+ j)= y,(k+ j)-yi(k), j=0,1
The desired output tracking response is:
Properly choose k,,,, i = 1,2,3 such that the following polynomial
has its eigenvalue within the unit circle, then the output tracking is asymptotically stable.
Furthermore,
For rotor speed references are constant in general, therefore,
Compare the above desired output response with Fish+=, EiZk+ CiFk
K,j, (k) = EiZk + C, Fk
Where K, is diagonal, j(k) = yr (k) - y(k), F, = x(k) - x(k - 1)
The decoupled control 60 for holding constant speed is presented in Fig. 8. This
solution is essentially a 3x3 multi-input-multi-output variant of the embodiments of Figs. 4-6
when both rotor-rotor coupling and rotor-core coupling relationships are substantial. Fig. 8
provides a system level diagram of the 3x3 MIMO control for Open Rotor Engine Control.
Dynamic inversion provides mathematical decoupling of control inputs (BetaF, BetaA, Wf)
and outputs (Nf, Na, N2) relationships.
As shown in Fig. 8, the controlled plant perturbation model 60 is described by A, B ,
C, with control input vector Beta actuator (BetaF and BetaA) and fuel actuator (Wf)
increment ik, o utput vector rotor speed (Nf and Na) and core speed (N2) perturbation yk,
which are defined in [0049]-[005 11. The controlled plant input ik and the output yk are
coupled. The decoupled control introduces K, , K, , where K, decouples and cancels the
original dynamics by increment state feedback FK, K, decouples the coupled input ik and
the output yk and reshapes the desired controlled plant with new control input VK and output
yk in SISO relationship. The output tracking control introduces K, to close the rotor speeds
(Nf and Na) to their command references (NfR and NaR) and core speed (N2) to its
command reference (N2R) such that the closed-loop SISO control based on the decoupled
controlled plant (the input VK and output yk) achieves the desired control performance: Nf
tracks NfR, Na tracks NaR, and N2 tracks N2R. The decoupling control law is
Zk = K, vk+ K , 4 , the increment actuator control input Ek needs to be integrated to generate
the actuator control input u, , i.e., BetaF, and BeatA,, and Wf, which are applied to Beta
Actuators and fuel actuator, respectively.
With the current embodiment, when the rotor blade pitch angles BetaF and BetaA
impact on gas generator output(s) can be neglected, then the corresponding elements in the
3x3 decoupling matrix transfer function can be simply zeroed out. The resulting control can
be functionally equivalent to the control of Fig. 4, except that the controlled output for gas
generator is core speed N2 rather than engine pressure ratio EPR.
Since y, and y, are decoupled from each other, and both they are decoupled from y , ,
that is, v, affects y, only, and v, affects y, only. Therefore, the speed phase synchronizing
between y, and y, , or between y, of engine 1 and y, of engine 2 can be substantially the
same as shown in the embodiment of Figs 4 and 5.
It is to be understood the control system architectures disclosed herein may be
provided in any manner known to those of ordinary skill, including software solutions,
hardware or firmware solutions, and combinations of such. Such solutions would incorporate
the use of appropriate processors, memory (and software embodying any algorithms
described herein may be resident in any type of non-transitory memory), circuitry and other
components as is known to those of ordinary skill.
Having disclosed the inventions described herein by reference to exemplary
embodiments, it will be apparent to those of ordinary skill that alternative arrangements and
embodiments may be implemented without departing from the scope of the inventions as
disclosed herein. Further, it will be understood that it is not necessary to meet any of the
objects or advantages of the invention(s) stated herein to fall within the scope of such
inventions, because undisclosed or unforeseen advantages may exist.

What is claimed is:
WE CLAIM :
1. A counter-rotating open-rotor gas turbine engine comprising:
a forward un-ducted rotor including a plurality of forward rotor blades and including a
forward rotor angle actuator for setting blade pitch angles of the plurality of forward rotor
blades;
an aft un-ducted rotor including a plurality of aft rotor blades and including an aft
rotor angle actuator for setting blade pitch angles of the plurality of aft rotor blades;
a gas turbine engine driving forward and aft un-ducted rotors and including a fiiel
actuator for setting the fiiel flow to the gas turbine engine; and
^ P an open rotor control system including, a forward rotor blade pitch angle command
(BetaF) electrically connected to the forward rotor angle actuator, an aft rotor blade pitch
angle command (BetaA) electrically connected to the aft rotor angle actuator, a fuel flow
command (Wf) electrically cormected to the fiiel actuator, a forward rotor speed feedback
signal (Nf), an aft rotor speed feedback signal (Na), and at least two of the engine pressure
measurement feedback signals for calculating the engine pressure ratio (EPR) and an engine
core speed signal (N2);
the open rotor control system including a control algorithm including,
a 2x2 multi-input-multi-output (MIMO) control solution for the forward rotor
blade pitch angle command (BetaF), the aft rotor blade pitch angle command (BetaA), the
forward rotor speed feedback signal (Nf) and the aft rotor speed feedback signal (Na); and
1 ^ a single-input-single-output (SISO) control solution for the fuel flow
command (Wf) and the at least two of the engine pressure measurement feedback signals for
calculating the engine pressure ratio (EPR) and the engine core speed signal (N2).
2. The counter-rotating open-rotor gas turbine engine of claim 1, wherein the open rotor
control system includes a control option that considers fiiel flow impact on rotor speeds but
does not consider rotor blade pitch angles on gas generator engine pressure ratio.
19
3. The counter-rotating open-rotor gas turbine engine of claim 1, wherein the gas generator
fuel flow command (Wf) impact on rotor speed feedback signals (Nf and Na) is treated as a
known disturbance input to the 2x2 MIMO control solution.
4. The counter-rotating open-rotor gas turbine engine of claim 1, wherein the control
algorithm further includes a disturbance rejection path to account for disturbance effect of
fuel flow on forward and aft rotor speeds.
^ r 5. The counter-rotating open-rotor gas turbine engine of claim 1, wherein the 2x2 MIMO
control solution utilizes a dynamics inversion control approach.
6. The counter-rotating open-rotor gas turbine engine of claim 1, wherein the open rotor
control system further includes a speed phase synchronizing control architecture positioned
between (a) forward and aft rotor phase output feedback signals and (b) input signals to an
engine speed regulator.
7. The counter-rotating open-rotor gas turbine engine of claim 6, wherein the speed
synchronizing control includes a single-input-single-output (SISO) control solution.
8. The counter-rotating open-rotor gas turbine engine of claim 6, wherein the speed phase
synchronizing control includes a speed phase synchronizing controller that provides a
correction input signal to a rotor speed regulator.
9. A counter-rotating open-rotor gas turbine engine comprising:
20
a forward un-ducted rotor including a plurality of forward rotor blades and including a
forward rotor angle actuator for setting blade pitch angles of the plurality of forward rotor
blades;
an aft un-ducted rotor including a plurality of aft rotor blades and including an aft
rotor angle actuator for setting blade pitch angles of the plurality of aft rotor blades;
a gas turbine engine driving forward and aft un-ducted rotors and including a fiiel
actuator for setting the fiiel flow to the gas turbine engine; and
an open rotor control system including, a forward rotor blade pitch angle command
(BetaF) electrically coimected to the forward rotor angle actuator, an aft rotor blade pitch
angle command (BetaA) electrically connected to the aft rotor angle actuator, a fuel flow
^ F command (Wf) electrically coimected to the ftiel actuator, a forward rotor speed feedback
signal (Nf), an aft rotor speed feedback signal (Na), and at least one of an engine pressure
measurement feedback signal (EPR) and a gas generator core speed feedback signal (N2);
the open rotor control system including a multiple-input-multiple-output (MIMO)
control algorithm including a dynamic inversion matrix control solution for at least the
forward rotor blade pitch angle command (BetaF), the aft rotor blade pitch angle command
(BetaA), the forward rotor speed feedback signal (Nf) and the aft rotor speed feedback signal
(Na).
10. The counter-rotating open-rotor gas turbine engine of claim 9, wherein the open rotor
control system includes a 3x3 multiple-input-multiple-output (MIMO) control algorithm
^^ including a dynamics inversion approach for at least the forward rotor blade pitch angle
command (BetaF), the aft rotor blade pitch angle command (BetaA), the fuel flow command
(Wf), the forward rotor speed feedback signal (Nf), the aft rotor speed feedback signal (Na)
and the gas generator core speed feedback signal (N2).
11. The coimter-rotating open-rotor gas turbine engine of claim 9, wherein the open rotor
control system further includes a speed phase synchronizing control architecture positioned
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between (a) forward and aft rotor phase output feedback signals and (b) input signals to an
engine speed regulator.
12. The counter-rotating open-rotor gas turbine engine of claim 11, wherein the speed
synchronizing control includes a single-input-single-output (SISO) control solution.
13. The counter-rotating open-rotor gas turbine engine of claim 11, wherein the speed phase
synchronizing control includes a speed phase synchronizing controller that provides a
correction input signal to a rotor speed regulator.
14. A method for controlling a counter-rotating open-rotor gas turbine engine that includes,
(a) a forward un-ducted rotor including a plxirality of forward rotor blades and including a
forward rotor angle actuator for setting blade pitch angles of the plurality of forward rotor
blades, (b) an aft un-ducted rotor including a plurality of aft rotor blades and including an aft
rotor angle actuator for setting blade pitch angles of the plurality of aft rotor blades, and (c) a
gas turbine engine driving the forward and aft un-ducted rotors and including a fiiel actuator
for setting fuel flow to the gas turbine engine, the method comprising steps of:
generating forward and aft control signals respectively for the forward rotor angle
actuator and the aft rotor angle actuator;
generating a fuel flow command for the fuel actuator;
receiving forward and aft rotor feedback signals; and
receiving at least one of an engine pressure feedback signal and an engine core speed
feedback signal;
wherein the steps of generating the forward and aft control signals and generating the
ftiel flow signal utilize a control algorithm that includes,
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a multi-input-multi-output (MIMO) control solution for the forward and aft
control signals and the forward and aft rotor feedback signals, and
a single-input-single-output (SISO) control solution for the fuel flow
command and the at least one of the engine pressure feedback signal and the engine core
speed feedback signal.
15. The method of claim 14, wherein the control algorithm considers fiiel flow impact on
rotor speeds but does not consider rotor blade pitch angles on gas generator engine pressure
ratio.
•
16. The method of claim 14, wherein the fiiel flow command impact on forward and aft
rotor feedback signals is treated as a known disturbance to the MIMO control solution.
17. The method of claim 16, wherein the MIMO control solution utilizes a dynamic
inversion control approach.
18. The method of claim 14, fiuther comprising providing a speed phase synchronizing
control architecture between (a) the forward and aft rotor feedback signals and (b) input
signals to the gas turbine engine.
19. The method of claim 18, wherein the speed synchronizing control includes a singleinput-
single output (SISO) control solution.
20. The method of claim 18, wherein the speed phase synchronizing control includes a
speed phase synchronizing controller that provides a correction input signal to a rotor speed
regulator.
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21. A method for controlling a counter-rotating open-rotor gas turbine engine that includes,
(a) a forward un-ducted rotor including a plurality of forward rotor blades and including a
forward rotor angle actuator for setting blade pitch angles of the plurality of forward rotor
blades, (b) an aft un-ducted rotor including a plurality of aft rotor blades and including an aft
rotor angle actuator for setting blade pitch angles of the plurality of aft rotor blades, and (c) a
gas turbine engine driving the forward and aft un-ducted rotors and including a fiiel actuator
for setting ftiel flow to the gas turbine engine, the method comprising steps of:
generating forward and aft control signals respectively for the forward rotor angle
actuator and the aft rotor angle actuator;
^ F generating a fiiel flow command for the fuel actuator;
receiving forward and aft rotor feedback signals; and
receiving at least one of an engine pressure feedback signal and an engine core speed
feedback signal;
wherein the steps of generating the forward and aft control signals and generating the
ftiel flow signal utilize a control algorithm that includes a multi-input-multi-output (MIMO)
control solution including a dynamics inversion approach for the forward and aft control
signals, the fuel flow command, the forward and aft rotor feedback signals and the least one
of an engine pressure feedback signal and an engine core speed feedback signal.
W 22. The method of claim 21, wherein the MIMO control solution is a 3x3 MIMO control
solution.