太空生存太空生存太空生存 (40).pdf
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1、Acta Astronautica 63(2008) Hua,Hong Liub,Chenliang Yangb,Enzhu HuaaDepartment of Bioengineering,Beijing University of Aeronautics and Astronautics,Beijing 100083,ChinabDepartment of Environmental Engineering,Beijing University of Aeronautics and Astronautics,Beijing 100083,ChinaReceived 21 May 2007;
2、received in revised form 7 January 2008;accepted 20 February 2008Available online 7 April 2008AbstractAs a subsystem of the bioregenerative life support system(BLSS),light-algae bioreactor(LABR)has properties of highreaction rate,efficiently synthesizing microalgal biomass,absorbing CO2and releasing
3、 O2,so it is significant for BLSS toprovide food and maintain gas balance.In order to manipulate the LABR properly,it has been designed as a closed-loop controlsystem,and technology of Artificial Neural NetworkModel Predictive Control(ANN-MPC)is applied to design the controllerfor LABR in which gree
4、n microalgae,Spirulina platensis is cultivated continuously.The conclusion is drawn by computersimulation that ANN-MPC controller can intelligently learn the complicated dynamic performances of LABR,and automatically,robustly and self-adaptively regulate the light intensity illuminating on the LABR,
5、hence make the growth of microalgae inthe LABR be changed in line with the references,meanwhile provide appropriate damping to improve markedly the transientresponse performance of LABR.2008 Elsevier Ltd.All rights reserved.Keywords:BLSS;LABR;Control system;ANN-MPC1.IntroductionIn bioregenerative li
6、fe support system(BLSS),thecore issue is of food supply and gas balance.BLSS ismainly made of higher plants and animals.If the systemis under emergencies;however,with their own restric-tions on the rate of metabolism,it is very difficult forrelying on them to restore the system to stability andequil
7、ibrium 1,2.For example,with respect to gases(mainly refer to CO2and O2)balance in BLSS,be-causeoftheabovereasons,higherplantsoranimalscan-not instantaneously influence upon the concentrationsCorresponding author.Fax:+861082339837.E-mail address:(H.Liu).0094-5765/$-see front matter 2008 Elsevier Ltd.
8、All rights reserved.doi:10.1016/j.actaastro.2008.02.008of gases when some accidents happened to the system.As is well known,the system will undergo catastrophicdamage if the gases are in the state of imbalance fora long period.So it is necessary to choose the specieswhose reactions rate are faster a
9、nd easier to controlas controllable and renewable tools for BLSS,mi-croalgae are the most promising candidate species bycontrast with high plants and animals 14 becausethey have characteristics of high growth rate,rapidlydecomposing the waste,absorbing CO2,releasing O2and effectively regulating gas
10、composition.Here greenmicroalgae Spirulina platensis,has been selected to becultivated and used for BLSS,since besides precedingbenefits,S.platensis is a high nutrition food for crew,the protein,fat,carbohydrate and vitamin contents in1068D.Hu et al./Acta Astronautica 63(2008)10671075S.platensis are
11、 approximately 65%,4%,19%and6%,respectively,and can be digested and absorbedby humans more easily,furthermore its metabolism isextremely plastic and controllable 3,4,so finding amethodology for cultivating S.platensis will safeguardthe balance of material exchange as well as the equi-librium of the
12、system 15.In the following context,the word microalgae refers in particular to Spirulinaplatensis.LABR is a complex system,due to it having non-linear and time-varying characteristics,and there areusually no fixed operating points in real application,soit is very difficult to employ conventional met
13、hods toachieve effective control for such system.Technologyof artificial intelligenceArtificial Neural Network-Model Predictive Control(ANN-MPC)is applied here,and combined with mathematical model and com-puter simulation to realize potent and robust controlfor LABR,and the result proved that ideal
14、controllingeffect has been acquired.2.Materials and methods2.1.Light-algae bioreactorMicroalgae are photoautotrophs.Light undoubtedlyis the most important limiting factor for the photoau-totrophic growth of microalgae,and has a very great in-fluence upon its propagation,so light-algae bioreactor(LAB
15、R)has been designed as the form of microalgaecultured 5.LABR is a transparent device,in whichmicroalgae has been continuously cultivated by absorb-ing and decomposing various excretions or wastes,suchas urine and CO2in BLSS,and in the course of reac-tions microalgae will synthesize their own biomass
16、,andsimultaneously release O2.Because the full benefits of microalgae for BLSShave been realized,the technological process had torender microalgal cultivation sufficiently controllable,so it is necessary to design the configuration of LABRas a closed-loop control system.When in the presenceof intern
17、al or external disturbances,LABR can elimi-nate their influences imposed upon BLSS and keep gasbalance 6.The configuration of LABR is shown inFig.1.Suppose that initially the concentration of CO2isequilibrium at the required level in BLSS atmosphere,if some disturbances suddenly occur,the concentrat
18、ionsof CO2may deviate from its initial state,and simul-taneously LABR detects such change and executes toeliminate such deviation as following sequence.Firstly,the sensor1 measures the actual concentrationof CO2,the difference between current and desired con-centration of CO2can be considered a cert
19、ain functionof microalgal biomass which can be deemed as a refer-ence input for LABR,Secondly,the sensor2 measuresthe microalgal biomass in the bioreactor as a feedbacksignal and compares it with the reference,the ANN-MPC controller will use the difference between themto adjust the light intensity,t
20、hus stimulate or inhibit thegrowth of microalgae to speed up or slow down in thebioreactor to produce an ideal output in agreement withthe reference,and such procedure corresponds to indi-rectly influence on concentrations of CO2and O2asneeded,because these two gases are tightly correlatedwith assim
21、ilatory quotient of microalgae,hence makesthe gases in BLSS rebalance at required level.2.2.Development of mathematical model for LABRLife systems generally have highly nonlinear,time-varying specifications and lots of non-specific interac-tions in life systems cannot be ascertained now,hencethey ar
22、e essentially different from mechanical systems7,8.Herein kinetic equations just as Monod type orHenriMichaelisMenten type are utilized to describethe growth of microalgae.LABR was divided into threehierarchies,i.e.,gas phase,liquid phase and biologi-cal phase,the mathematical models for them have b
23、eendeveloped respectively,based on the theories of sys-tem dynamics,stoichiometry and experimental data aswell,and then multidimensionally coupled them intoa whole.In developing a reasonably simplified math-ematical model for LABR;however,some distributedparameters,nonlinearities and time-varying fa
24、ctors thatmaybepresentintheLABRhavebeenignoredbasedonapproximations and assumptions 9,10.Mathematicalmodel have been obtained in terms of first-order nonlin-ear ordinary differential equations to represent and de-pict the dynamics of the LABR 1116,the parametersin the mathematical model have been sp
25、ecified by ex-perimental data and quoting from the documents 11,and then the simulation model of LABR has been de-veloped by MatLab7.4/Simulink6.6 based on the math-ematical model to conduct the computer experiments.2.3.ANN-MPC for LABR as a closed-loop controlsystemThe dynamic features of biologica
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