a normalized control system for a turbojet engine

RAFAEL Ltd. A NORMALIZED CONTROL SYSTEM for a TURBOJET ENGINE 1

A NORMALIZED CONTROL

SYSTEM FOR A TURBOJET

ENGINE

Ori Yekutiel, Yinon AmirRAFAEL Ltd- P.O.B 2250 (39)

Haifa 31021, Israel

6th Symposium on Jet Engines and Gas TurbinesNovember 2006


APPROACH:

–Normalization of fuel flow and RPM

correction for altitude, mach, DISA, and

linearization

–Normalize Measurements

–Design single controller (for all flight

conditions)

– "de-normalize” output (normalized fuel

flow) and apply to engine


FEATURES:

Engine normalization

simplifies control system design for all control design approaches

Only a simple PI example

included in presentation


A PREVIOUS CONTROLLER(1/5)

GAIN SCHEDULING (Mach,Altitude,

RPM)

Requires Tables – extensive testing

for modeling and verification

Limited use of knowledge of the

physical engine behavior



COMMAND

LIMITER

RPM comACCELERATION

LIMITER

CONTROLLER

( P I )

LIMITER

ELECTRONIC

INTERFACE

UNIT

AMPLIFIER

&

PUMPENGINE

RPM XDUCER

P2, T2, T5

XDUCERS

CUTOFF

MIN/MAX RPM BW, ACCEL

error

Wf com

[Volt]

RPM,...

satlo, sathi

RPM

Wf com

[g/s]

RPM

T5

+

-

PUMP RPM

XDUCER

Mach, Altitude

Other Telemetry Data

(Temperatures, Pressures, ...)



PI RPM2Wfcom Wfcom2RPM

ENGINE

DYNAMICS

(GAIN=1)

RPM

Measurement

RPMcom

RPMmeas

CTRLLR ENGINE

LIMIT



RPMcom

RPMmeas

LIMIT

s eng1 +

1

s

KI1 + 1 OL

KI

eng

1


THE NORMALIZED CONTROLLER

T0 = 288.15

TISA = T0 - 0.0065 * Alt

Tamb = TISA + DISA

Beta = 1+ ( Mach ^ 2 ) / 5

Ttot = Tamb * Beta

Delta = ( ( TISA / T0 )^5.256 ) * Beta^3.5

= Ptot/P0

Theta = Ttot / T0

RPM* = RPM / Sqrt ( Theta )

Wf* = Wf / ( Delta * Sqrt ( Theta ) )


THE CONCEPT:

RPM * RPM

RPMcom * e Wf ' Wf * Wf

Wf ' (RPM *)

Engine with normalized controller

Tau

ENGINEC TJ

C TJ

Wf MachCorrection

inverseC TJ

Dynamics

RPMNormalization

Wf-TagLIMITER

C TJRPM MachCorrection

C TJC TJ Wfde-normalization

RPM MachCorrection

C TJ

RPMNormalization

RPMcom *LIMITER

PI

6 M, H, DISA

5 M, H, DISA 4M

3M 2M, H, DISA

1RPMcom

red: physical normalization (valid for all engines);cyan: Engine-dependent blocks (note: only 2 different

types) yell: PI parameters, per individual controller requirement

(BW, Disturbance Rejection, …).


FEATURES (1/2):

Gain is practically constant and unity

over RPM, altitude, mach and DISA

A single gain P and Fuel Flow limits

can be designed.

Other Controller designs (not PI) also

simplified (no, or less, envelope

dependence)


FEATURES (2/2):

Integral Gain I is dependent on engine dynamics.

A mach-Altitude-RPM table may be used (as in

the Present Solution)

Alternately a model of Corrected Tau can be

explored.

– Otto, E.W. and Taylor, B.L, "Dynamics of a Turbojet Engine Considered

as a Quasi-Static System," NACA TR 1011, 1951.


FUEL LIMITER:

OBJECTIVES:

Avoid surge, stall, over-temperature,

blowout

DESIGN:

In normalized controller !!

IMPLEMENTATION (PI case):

Include anti-windup


SIMULATION RESULTS (1/2):

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

80

100

RP

M [

%]

RPM C.L. Step response: Full envelope

RPM COM

RPM-Meas

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

50100

No

rm W

f [%

]

Sat-High

Sat-Low

Wf-Tag

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-100

0100

Normalized timeNo

rm.

en

ve

lop

e

Mach [%]

Alt [%]

DeltaISA: -100 -> 100 [%]

0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.7472

99

RP

M [

%]

RPM C.L. Step response: Full envelope

RPM COM

RPM-Meas

0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74

55.5106.

No

rm W

f [%

]

Sat-High

Sat-Low

Wf-Tag

0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74-100

0

100

Normalized timeNo

rm.

en

ve

lop

e

Mach [%]

Alt [%]

DeltaISA: -100 -> 100 [%]


SIMULATION RESULTS (2/2):

20 30 40 50 60 70 80 90 10030

40

50

60

70

80

90

100

Corrected Air Mass Flow [%]

Pre

ss

ure

Rati

o:

P0

3/P

02

[%

]

COMPRESSOR MAP.M=0 [%] ; H=0[%]; DISA=0[K];

Corrected RPM [%]

38 47

55

64

73

82

91

100

Surge Line

Steady-State Line

SM = 5% Line

response

0 0.2 0.4 0.6 0.8 140

60

80

100

RP

M [

%]

RPM C.L. Step response: M=0 [%] ; H=0[%]; DISA=0[K];

RPM COM

RPM-Meas

0 0.2 0.4 0.6 0.8 10

0.5

1

No

rm W

f [%

]

Normalized time

Sat-High

Sat-Low

Wf-Tag

(Increased gain !!)


BENEFITS of the APPROACH:

good physical basis for design

simple controller - single design

simple limiter - single design

easier testability - fewer envelope points

simpler transportability of the controller to

other engines


THANK YOU

a normalized control system for a turbojet engine

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