Soft Computing Applications on SR-30 Turbojet Engine

10.07.2015 Views
AIAA 2004-6444II. SR-30 TURBOJET ENGINE AND FACILITYTurbine Technologies’ SR-30 Turbojet EngineThe SR-30 engine is a turbojet engine with asingle-stage radial-flow compressor with a maximumpressure ratio of, PR=3.4, a single-stage axial-flowturbine, and a reverse-flow annular combustionchamber and it operates obeying the Braytonthermodynamic cycle in the same fashion as largeturbojet engines (Figure 1). The engine, as produced byTurbine Technologies, includes five pressuretransducers, five thermocouples, a load-cell for thrustmeasurements, a custom motor winding for reading theengine RPM, and a fuel-flow-rate measurement systemto monitor/measure the operating parameters of theengine. The engine generates . 20 lbs of thrust at 90,000RPM while ingesting m = 1.1 lb/sec of air. The enginehas a length of 10.75 in., and the exit exhaust diameterof D exit =2.25 inches. Further details can be found in thepaper by Watanabe et. al [1].the A/D board using cables. While one of these units(NI-SC-2345) houses the thermocouple input modules(NI-SCC-TC02), the millivolt range input modules (NI-SCC-AI06), a connector block for digital outputsignals, and the analog output modules, the other unit(NI-CA-1000) houses a connector block (NI-CB-68LPR) to connect other analog inputs. Each inputmodule includes self-contained signal-conditioningunits such as low pass filters and instrumentationamplifiers.While the thermocouple input modules are used toread the temperatures, the millivolt input range modulesare used to read the load-cell output voltage and one ofthe pressure signals. Digital I/O lines are used togenerate TTL signals to turn on and off the relays.Relays (BASCO Company, ELK 924) are used toreplace manual switches, which are used to start and tostop the ignition, the fuel flow and to turn on and offthe valve for high-pressure air.Fuel Flow Valve ControllerThe control output signal for the Single-inputsingle-output(SISO) system under study is the signal tocontrol the fuel-flow rate. The fuel-flow rate in theengine is adjusted by controlling valve opening toobtain a desired thrust value. The operation of thecontrol-valve is automated with the use of aCompumotor-ES22BS stepper motor. The ES22BSstepper motor is mounted on a simple stand to hold themotor steadily. The stepper motor has a maximumtorque of 9.4 lb-in, a maximum resolution of 128,000Step/rev with the use of the GT-L5 drive, and the shaftinertia is 1.1 oz-in 2 .Figure 1 SR-30 Turbojet EngineThe engine system is equipped with a dataacquisition board, addition of connection panels for thesensors, a stepper motor as fuel-flow rate valvepositioner, and several relays to control severalswitches for engine operation.Data Acquisition SystemThe current system at the University of Alabamaincludes a National Instruments NI PCI-6031E A/Dboard, which has a 16-bit resolution, 100 kSamples/secsampling rate, 64 analog input, 2 analog output, and 8digital I/O ports. Signal connections to the A/D boardare made using two enclosures, which are attached to2American Institute of Aeronautics and AstronauticsIII. PID CONTROLLER DESIGN USING THEFREQUENCY-RESPONSE METHODA PID type classical controller was designed andimplemented using the frequency-response method toidentify and learn the engine characteristics duringclosed-loop operations. This section outlines the stepby-stepdesign of the PID controller and the results ofits implementation.A series of data sets for the frequency-responsedesign was obtained using a LabVEW program. Thechosen input and output for the plant, the SR-30turbojet engine, are the fuel flow valve position indegrees and the thrust force in pounds, respectively. Togive the sinusoidal input excitation, the valve positionwas excited in a sine-wave manner with 5 degrees of amean position, corresponding to a steady-state thrustvalue of about 5.3 pounds, and 4 degrees of peak-to-

AIAA 2004-6444peak amplitude. Different frequencies of the excitationwere attempted to cover a frequency range of interest.In order to construct a pair of Bode Plots for thefrequency-response design method, gains and phasesneed to be calculated in the region of frequencies.However, raw measurements of signals fromtransducers usually contain noise. The load-cell systemof the SR-30 engine is not an exception and the thrustoutput signal contains such noise. Therefore, the thrustoutput signal was conditioned using the “filtfilt”command of MATLAB is used to condition the thrustoutput signals. After the signal conditioning, the peaksof the thrust output were found by seeking sign changesof signal derivatives. A Gain at each frequency wascalculated finding an average of the peak-to-peakvalues. An example of the raw measurement and thefiltered signals of the thrust output with the input signalfrequency of 6.0 rad/sec are shown in Figure 2.Thrust Output [lbs]0.30.20.10.00 1 2 3 4 5-0.1-0.2-0.3Time [sec]Figure 2 Raw and Filtered ThrustIII-A. PLANT IDENTIFICATIONfilteredThe frequency region of our interest ranges from0.1 rad/sec to 11.0 rad/sec. The data obtained from thesine-wave data collection is plotted on the pair of BodeDashed/SL App.Solid/ModelStar/F-R DataFigures 3a & 3b Open-Loop Bode PlotsrawDashed/Model without DelaySolid/Model with DelayStar/F-R Data-180plots in Figures 3a and 3b. The plant is modeled withMATLAB. Assuming a second order system, cornerfrequencies of 0.5 and 9.0 rad/sec were identified. Theassumed open-loop transfer function of the plant is:4.5P =(1)() s( s + 0.5)( s + 9.0)Although, the first-estimated model, the red solidline, matches in a satisfactory manner in the magnitudeBode plot, there is an obvious discrepancy between thefirst-estimated model (black-dashed) and the frequencyresponsedata in the phase Bode plot. Therefore, thepresence of a time-delay in the model was suspected.After several attempts of time-delay modeling, adding0.2 seconds of time-delay model with the MATLAB“pade” command to the plant (red-solid) showed aconsistent matching with the frequency-response data.The estimated model with the time delay is plotted inthe Bode plots with dashed-blue lines. The assumedopen-loop transfer function of the plant with the timedelayis:P() s4.5−0.2s= e (2)( s + 0.5)( s + 9.0)The assumed open-loop transfer function of theplant with the 4 th order “pade” approximation timedelay is:( )( )( )( )( )( )224.5 s −57.9s+ 914 s − 42.1s+ 1149P()s =22s + 0.5 s + 9.0 s + 57.9s+ 914 s + 42.1s+ 1149….(3)III-B. PID CONTROLLER DESIGN AND TESTProportional-Integral-Derivative (PID) controlapproach was chosen for the engine control since it isone of the popular closed-loop control approaches thatcan be applied to a wide range of engineering problems.One customary representation of such controller can beexpressed as:⎛ 1()⎟ ⎞G⎜cs = Kp1 + + Tds (4)⎝ Tis ⎠After attempting several combinations of numbersfor the PID gains using MATLAB SISO tool program,a combination of K p = 3.68, T i = 2.16 sec, and T d =0.061 sec was found to be a reasonable controller forthe application.3American Institute of Aeronautics and Astronautics

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fuzzy

valve

thrust

logic

controller

input

output

simulation

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algorithm

computing

applications

turbojet

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