Educating High School Students in Process Simulation and Control with a Simulink-Based Controller Design for Microbial Fuel Cells

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1 Educting High School Students in Process Siultion nd Control with Siulink-Bsed Controller Design for Microbil Fuel Cells Cleent Ekputr nd Zuyi (Jcky) Hung Gret Vlley High School/Villnov University Abstrct U.S. high school students re often wek in th nd science, thus it is iportnt to broden the prticiption of high school students in these fields before they strt to lose confidence nd interest in the. One wy to ttrct ore high school students in th nd science is through interesting reserch projects. This work presents n exple for educting high school students to design controller for lb-scle icrobil fuel cell (MFC) tht cn generte electricity fro the orgnic copounds in the wste wter. Upon the introduction of MFC, ODE odels, PID controllers nd MATLAB Siulink, the student, during prt-tie suer internship, successfully developed Siulink odel for MFC nd used it to evlute the perfornce of vrious PID controllers. The strtegies for teching high school students with odeling nd progring skills, long with the evlution of the teching effectiveness, re lso introduced in this work. Keywords Microbil fuel cells, Siulink, Process Siultion nd Control, PID controller. Introduction High school students fro the U.S. lg behind other high school students in STEM fields round the world. According to the Ntionl Mth nd Science Inititive, 56% of US high school grdutes in 2013 were not redy for college-level th, nd 64% were not redy for collegelevel science. In study by the Orgniztion for Econoic Co-opertion nd Developent (OECD), the U.S. is rnked 25 th in th perfornce nd 21 st in science perfornce copred to other countries, with Finlnd, South Kore, nd the Netherlnds in the top 3. A country once known for being t the vngurd of technology nd industry, such s during the World Wr II er or in the spce rce, is now being beten. The iplictions re treendous: wek eduction during the erly stges of developent will only led to weker professionl lbor force lter. In fct, study by the President s Council of Advisers on Science nd Technology sttes tht econoic forecsts point to need for producing, over the next decde, pproxitely 1 illion ore college grdutes in STEM fields thn expected under current ssuptions. If the USA is to rein t the forefront of innovtion, the qulity of eduction t the high school stge ust rise. Whether it is substndrd STEM teching force or generl disinterest in the STEM fields, it is uncler, but wy to ttrct ore students ttention to these topics is through erly reserch experience nd projects. Such experiences should boost the interest nd confidence of students in STEM relted res, nd encourge the to pursue higher eduction nd degrees in the, while giving the n introduction to such topics. The gol of this work is to deonstrte

2 tht eduction in engineering, such s process siultion nd control, t high-school level cn be effective in grnering interest nd knowledge, with project in which high school student ws educted to design controller for lb-scle icrobil fuel cell during the suer of High school students ust be interested in the odeling topics. Modeling techniques cn be pplied to such wide vriety of topics tht high school student is sure to find subject tht ttrcts their ttention. Microbil fuel cells (MFCs) re selected in this work, which generte electricity fro wstewter by ens of bcteril functions on the surfce of the node electrode, nd thus could potentilly resolve the issues of energy production nd wste tretent siultneously 1. Insted of introducing nuericl ethods to solve ODE, MATLAB Siulink ws selected s the pltfor for ODE siultion. While other softwre for theticl odeling often requires knowledge of progring lnguges, Siulink contins set of odules to represent different theticl opertions, such s ddition, subtrction, derivtives, nd integrls. Much like building with LEGO, the user connects the odules together in Siulink to crete systes tht visully represent the equtions. The friendly userinterfce nd intuitive pplictions of Siulink ke representing high-level theticl equtions doble nd even esy for high school students. After n interesting project nd userfriendly siultion pltfor were deterined, which ws essentil to retin high school students in the project, interctive teching strtegies were pplied to educte the students with the processes in the icrobil fuel cells, nd the relevnt concepts for ODE developent nd siultion, nd PID controller design. Since the rtionl design of PID controllers is bsed up systeic trining on Lplce trnsfor, the coonly used tuning ethods of PID controllers were not introduced in this project. Insted, the Siulink odel ws used s pltfor for the student to evlute the influence of the proportionl (P) nd integrl (I) coponents on the controller perfornce so tht the student cn obtin quick intuition nd understnding of PID control. In ddition, Siulink provides PID controller odule tht cn be esy to use by the student fter he understnds the physicl ening of ech coponent of the PID controller. After introductions to ordinry differentil equtions nd Siulink siultion, the high school student ws ble to develop the Siulink ODE odel for MFC contining five equtions nd 25 preters within one onth by working s prt-tie internship student nd eeting the instructor once week. The student then spent nother onth to integrte Siulink odel for the MFC with the built-in PID controller odule to evlute the perfornce of PID controllers with different vlues in the proportionl nd integrl coponents. The teching strtegies were lso evluted in this work. The student successfully creted Siulink siultion odule, nd the iproveent of the student s skills in Siulink-bsed process siultion nd control ws ssessed by poster syposiu for senior college students to present their suer reserch projects t Villnov University. Thus, we show n eduction project in which high school student lerned MATLAB Siulink, siulted n ODE odel of MFC, nd developed PID controllers for lb-scle MFC. It cn be concluded fro these ssessents tht these teching ethods effectively enhnce the student s skill nd interest in STEM topics. Bckground Mterils Microbil fuel cells

3 MFCs re bio-electrocheicl systes tht drive currents through bcteri nd their nturl processes. As shown by Fig. 1, MFCs hve lyer of biofil coprised of nodophilic bcteri on the surfce of the node electrode. These bcteri convert the substrte, in this cse cette, nd wter into crbon dioxide, electrons, nd protons in the node coprtent. The produced protons diffuse through the ction exchnge ebrne into the cthode coprtent. The oxidized for of the intrcellulr editor protein M ox, such s cytochroe proteins 2, ccepts the electron nd crries it in the reduced for M red, which releses the electron on the surfce of the node electrode nd returns bck to its oxidized for. Through externl electricl circuit, the electrons ove to the cthode electrode on which the oxygen cts s the electron cceptor nd rects with the protons into the wter. In ddition to the nodophilic bcteri, ethnogenic bcteri y consue cette nd produce ethne nd crbon dioxide. The MFC configurtion shown in Fig.1 is presented by Pinto et l., Although other MFC configurtions exist, the bio-electrocheicl principle reins the se. Anode Coprtent Cthode Coprtent H + +e - +O 2 H 2O Figure 1. Schetic digr of bio-cheicl processes in icrobil fuel cell. This figure is dpted fro Pinto et l., Chiefly, MFCs re source of renewble energy, s the nodophilic bcteri cn produce electricity fro orgnic copounds in the wstewter. In prticulr, the nodophilic bcteri used to drive the rection grow by nturl processes, nd s long s they hve the necessry nourishent, they continue to crete electricity. Secondly, MFCs cn ssist wstewter tretent. In the wstewter tretent process, ertion, which is the puping of ir into wste to fuel the degrdtion of orgnic tter by bcteri, coprises between 45% nd 75% of the plnt energy costs. Additionlly, sludge tretent ccounts for bout 20% of tretent plnt costs 4. Microbil fuel cells cn reove the orgnic copounds fro wstewter nd use the cette found in sludge s the substrte in the rection. MFCs thus benefit the wstewter tretent by eliinting the energy costs of ertion entirely nd with soe electricity left over, nd t the se tie cutting sludge tretent costs significntly. The ODE MFC odel The ODE MFC odel presented by Pinto et l., ws used in this work to quntify the tie profiles of substrte concentrtion (i.e., S given by Eqution (1)), icrobil popultions (i.e., x for the nodophilic bcteri given by Eqution (2) nd x for the ethnogenic bcteri given by

4 Eqution (3)), the oxidized editor frction per nodophilic bcteri (i.e., M ox given by Eqution (4)), nd the current (i.e., I MFC given by Eqution (5)). ds dt dx dt dx dt q x q x D( S 0 S) (1) x K, x Dx (2) d d x K, x Dx (3) dm I 1 dt I MFC ox MFC Yq (4) F Vx R Eocv R Ext Int M M where q nd q re the substrte consuption rtes by nodophilic nd ethnogenic bcteri, respectively; D is the dilution rte; S 0 is the influent substrte concentrtion; µ nd µ re the growth rtes of the bcteri; K d, nd K d, re the decy rtes of the bcteri; Y is the editor yield; γ is the editor olr ss; is the nuber of electrons trnsferred per ol of editor; F is Frdy s constnt; V is the volue of the nodic coprtent; E OCV is the open circuit voltge; R Ext nd R Int re the externl nd internl resistnces, respectively; M red is the reduced editor frction per nodophilic bcteri; nd ε is constnt. There re 25 preters in this ODE odel. Due to the spce liittion, the vlues of these preters long with the equtions to quntify q, q, µ, nd µ re not shown here. The MATLAB progr for the ODE odel will be provided upon the request by interested reders. PID controller PID controllers re coonly used in cheicl plnts. PID controllers cn be generlly represented by Eqution (6) 5 : red red t de( t) u( t) K pe( t) Ki e( ) d K (6) d 0 dt where u(t) is the controller output; e is the error vlue representing the difference between the esured output nd the set point vlue of the output; K p is the proportionl gin tht deterines the controller response to the present error; K i is the integrl gin tht deterines the controller response to the ccuultion of historicl error; nd K d is the derivtive gin tht deterines the controller response to future error. K p, K i, nd K d re tuning preters for PID controllers. The PID control syste is bsed on negtive feedbck loop, which iniizes the esured output with its set point vlue. Good PID controllers cn intin the syste perfornce regrdless of disturbnces fro the surrounding environent. In this work, the current output fro MFCs is selected s the syste output, while the inlet substrte flow-rte is the syste input tht cn be nipulted overtie to intin the current to the desired vlue. The control syste ipleented in this work is shown in Fig. 2. Generlly, the chnge of inlet cette flow- (5)

5 rte leds to the chnge of the popultion of nodophilic bcteri on the node electrode, which in turn results chnge in the electron production. The error vlue is processed by the PID controller, which contins set of vlues to deterine how uch to shift the vlve, which controls the substrte flow-rte. The PID keeps chnging the substrte flow-rte until the esured current is equl to the set point vlue. Figure 2. Representtion of control syste bsed on feedbck loop PID controller design theory is topic typiclly introduced only to junior or senior college students, deling with Lplce trnsfor nd other theticl knowledge not expected of high school students. In this work, we only del with the bsic knowledge of PID controller design, nd use the built-in Siulink PID controller odule to study the ipct of the P, I, nd D coponents on the controller perfornce. We i to tech the concept of control systes nd the negtive feedbck loop nd provide pltfor for the high school student to lern the ore intricte echnics of controller design. Results Developent of the Siulink MFC odel The MFC odel consists of Equtions (1)-(5) tht represent the vrious popultions (substrte, nodophilic icroorgniss, ethnogenic orgniss, editor) nd the current (I MFC ) of the fuel cell. Much like LEGO, the vrious preters were connected to crete the equtions, which were siulted to deterine the current bsed on the substrte flow rte (Fig. 3). The siultion results fro the Siulink odel were the se to the results produced fro script-bsed odel tht ws built by the instructor in the cond line. Copred to the script-bsed odel, which is coplicted due to the highly coupled rections nd the lrge ount of odel preters, the Siulink pltfor llows MATLAB lyn to siulte ODE odels. The Siulink odel ws further vlidted by king sure the results were logicl: for instnce, if the popultion of nodophilic icroorgniss ws incresed, then the current should increse becuse of the higher nuber of bcteri. Before designing the PID controller, the stedy stte current vlue versus the substrte flow-rte ws plotted to deterine the xiu current vlue tht cn be obtined fro the MFC syste (Fig. 4). If the substrte flow is too sll, the nodophilic bcteri do not hve enough nutrients for bcteri to survive nd produce the electron flow. However, if the substrte flow ws too lrge, the icroorgniss could not digest ll the substrte nd thus could not further iprove the electron production rte. In ddition, soe nodophilic icroorgniss would be pushed out of the fuel cell, which in turn reduced the current production. As shown by Fig. 4, the xiu stedy stte current tht could be produced by the studied MFC ws 11.4 A, which occurred t substrte flow rte of 1 L/in. Fro this vlue, n obtinble objective of stedy stte less thn 11.4 A could be used s stndrd to study the perfornce of vrious PID controllers.

6 The odule for the substrte concentrtion The odule for the nodophilic popultion The odule for the ethnogenic popultion The PID controller The odule for the editor concentrtion The function for current Figure 3. The Siulink odel developed for the MFC Figure 4. The current I MFC versus vrious vlues of F substrte predicted by the Siulink MFC odel

7 Evlution of the perfornce of PID controllers The Siulink odel llowed the high school student to try different cobintions of K p nd K i. In this work, we only nlyzed the effect of the proportionl nd integrl gins on the controller perfornce, s PI controllers re the ost coonly used controllers. We studied the controller perfornce first for the set-point chnge nd then for the lod chnge. To deterine the effectiveness of the controller, the tie profiles of current production for PID controllers with different K p nd K i vlues were plotted together in the se figure for direct coprison. In the set-point chnge, the output current ws iproved fro 1.5 to 9 A. Vrious vlues were ssigned to only one of the two preters (i.e., K p nd K i ) while the other preter ws kept constnt. The current profiles for the MFC regulted by PID controllers with vrious K p were shown in Fig. 5A, while the corresponding profiles for different K i vlues were plotted in Fig. 5B. According to Fig. 5A, PID controller with lrger K p vlue cn ccelerte the chnge of current initilly but rech the new stedy stte vlue ore slowly. No overshoot ws observed here s the tie constnt for this MFC is lrge due to the slow growth of nodophilic bcteri. Without K i ter, the P controller could not copletely eliinte the residul error (results not shown). According to Fig. 5B, controller with lrger K i (e.g., K i = 10) could ccelerte process towrds the set-point vlue, while controller with sller K i (e.g., K i = 2) responded uch ore slowly. Therefore, high K i vlue is necessry to eliinte the stedy-stte offset produced by controller with only K p ter. (A) (B) Figure 5. Effect of preters K p nd K i on controlling the current dynics: (A) K p ws chnged with K i = 5; (B) K i ws chnged with K p = 10 In the lod chnge, pulse disturbnce ws introduced to the MFC syste by incresing or decresing of the inlet substrte concentrtion by 5% during Dy 91. The pulse disturbnce only lsted for one dy. For ech disturbnce stiultion, ultiple K p vlues (Fig. 6) nd K i vlues (Fig. 7) were tested using the se pproch s the one for the set point chnge. As shown by Fig. 6, higher K p vlue hd sller overshoot/undershoot during the disturbnce. As shown in Fig 5A, higher K p resulted in longer tie for the syste to rech the new stedy stte. This y explin the sller overshoot/undershoot for higher K p vlue. This indictes tht PID controller of the best perfornce for the set-point chnge y not be of the best perfornce

8 for the lod chnge control (i.e., disturbnce rejection). It is nontrivil to deterine the K p vlue for the PID controllers designed for both the set-point nd lod chnges. On the other hnd, Fig.7 showed tht higher K i vlue ws ble to iniize the ipct fro the disturbnce. Cobining Fig 5B nd Fig. 7, we conclude tht higher K i vlue y be better option for both the setpoint nd lod chnges. (A) (B) Figure 6. Effect of K p vlues on the response speed to disturbnce stiultion in which the substrte concentrtion ws incresed (A) nd decresed (B) by 5% during Dy 91. K i ws equl to 5. (A) (B) Figure 7. Effect of K i vlues on the response speed to disturbnce stiultion in which the substrte concentrtion ws incresed (A) nd decresed (B) by 5% during Dy 91. K p ws equl to 10. Teching strtegies Teching strtegies for educting high school students with Siulink-bsed odeling skills

9 Selecting n interesting project is the first step to ttrct high school students in the eduction of process siultion nd control. MFC is selected in this work, becuse it cn generte electricity fro the orgnic copounds fro wste wter on the surfce of the node nd becuse it y resolve the chllenges to hndle energy crisis nd wste wter tretent t the se tie. A detiled introduction of MFC nd severl Youtube videos of MFC were given to the high school student in the first week of the project. The lrgest hurdle for educting high school students with odeling skills is tht they subconsciously resist the th nd they re not confident whether they re ble to hndle the th opertions. In this work, we used Siulink s the pltfor to ke process siultion nd control doble to high school students. Here is the strtegy for trining the student with Siulink. The student ws first tught the bsics of Siulink: how to crete siultion, how to ccess the odules, nd how to crete nd connect the odules. Siple exples for developing ODE odel in Siulink were given to build the student s confidence. An ssignent ws then given where the student hd to successfully reproduce digr representing single siple ODE nd run the progr. If the student s results tched with the ssignent, then the progr ws successful. The objective of this ssignent ws to tech the student how to ccess the odules nd connect the to crete digr. Next, the student hd to crete progr representing ODEs for the typicl enzytic rections (i.e., E + S < > ES > P). In this trining, no digr ws given. This ssignent not only entiled creting the digrs for the individul equtions, but lso connecting the equtions together. The gol of this ssignent ws for the student to lern how to recrete theticl functions without the ssistnce of digr, nd figure out how the equtions relte to ech other. This trining lsted for two weeks. The student ws confident with building ODE odels in Siulink fter this trining. The ODE odel given by Equtions (1) (5) ws introduced to the student with the detiled physicl ening for ech ter nd preter in the odel. This ws essentil for the success of the project, s the student ight be scred wy by the equtions. This took for one week. The student ws then sked to input one eqution into Siulink for one week. The instructor helped the student to check his Siulink odel nd offered dvice to further iprove his odel. After the student finished the first three equtions, he gined enough experience to finish Siulink odel one week erlier thn the schedule. Therefore, the developent of Siulink odel only took four weeks with the student working for only two dys per week. Finlly, the bsic skills of PID controller design were introduced to the student long with Siulink-bsed controller design odule, which llowed the student to evlute the ipct of the proportionl (P), integrl (I), nd derivtive (D) coponents on the controller perfornce. This trining lsted for one week. The student picked up the PID controller design skill fst nd ipleented it to the MFC syste within one week. Interctive trining nd effective lerning re essentil for educting high school students with coplicted skills in engineering such s process siultion nd control. The student ws required to redo ll the exples introduced in the trining, nd the instructor checked the student s progrs in detil nd offered tiely suggestions for the student to iprove his progrs. Hoework ssignents were designed to be siilr to the instruction exples but ore difficult (e.g., n ODE with lrge nuber of equtions). Beginning the trining with siple probles helped the student to build confidence. Breking coplicted odel/project

10 into sll steps which cn be finished by the student within one week lso helped the student to see the progress he de. Evlution of teching effectiveness The effectiveness of teching nd trining ws ssessed by the student s perfornce to independently develop Siulink siultion odule for MFC ODE odel tht consists of five ODE equtions nd 25 preters, nd controller design odule tht cn be used to evlute controller s perfornce. The Siulink odel developed by the student ws vlidted by coprison between it nd the script-bsed odel developed by the instructor. The siultion results for PID controllers offered the student quick intuition nd understnding of PID control. In ddition, the iproveent of the student s skills in Siulink-bsed process siultion nd control ws ssessed by poster tht ws presented in syposiu for senior college students to present their suer reserch projects t Villnov University. In the presenttion, the student showed his cler understnding of the key processes for MFC opertion nd the influence of proportionl nd integrl coponents on the PID perfornce. For exple, he knew tht the integrl coponent helps to eliinte the stedy-stte offset nd tht good vlue of K p for set-point chnge control y not be good for the disturbnce rejection. Since the high school student worked two dys per week nd et the instructor once week, his perfornce ws fr bove the expecttion of the instructor. It cn be concluded fro these ssessents tht the teching odules effectively enhnce the student s skill nd interest in process odeling nd control. While these results deonstrte tht it is possible for high school students to lern engineering concepts, with these ethods, it is unlikely tht ore thn few high school students will hve this chnce. Such trining requires n extreely sll student to techer rtio, s high school students need ore ttention thn college or grdute students to pply the concepts to this extent. The STEM preprtion of the student prticipting in the work ws well supported by the dvnced th nd science courses he hd tken, including AP Courses in Biology, Cheistry, nd Physics (e.g., Newtonin Mechnics, Electricity, nd Mgnetis), s well s th courses up to Clculus (AP BC Clculus) nd Coputer Science. In ddition, this student ws rnked in the top 1-2% of his clss. These fctors contributed to the success of the ipleenttion of the developed teching odule. It y tke longer tie for the high school students who hven t good STEM preprtion in ipleenting the teching odule. However, the student prticipting in the work believed tht there were good ount of people in his school (e.g., top 25% rnked junior or senior students) who would be ble to ccoplish the se work if they hd the se trining opportunity. Since extr ttention ust be tken to ke sure high school students understnd the trining terils, it y be chllenging to tech ore thn few students t tie. Hving ultiple students work on one project together is one wy to get ore high school students trined in this teching odule. All the students will hve the benefit of lerning the teril, but lso lerning to work with peers. In ddition, recording the teching odules in videos nd ipleenting the flipped-clssroo teching fort y be helpful to iprove the teching efficiency, s the students cn follow the videos to input their progrs in MATLAB step by step. The recorded videos lso llow the students to wtch ultiple ties. This y help the students to understnd the concepts nd odeling processes. Nevertheless, it is possible for lrger nuber of high school students to lern concepts such s process control nd siultions, possibly through suer session or s

11 clss offered during the school yer. Conclusion High school students in USA fll behind the students of soe other countries in Mth nd Science. This work presents n exple project in which high school student ws educted with the skills in process siultion nd control. Upon the trining in Siulink nd the introduction of bsic concepts in ODE odels nd process control, the student ws ble to crete Siulink odel representing the opertions within icrobil fuel cell. The student lso investigted the influence fro the proportionl nd integrl coponents on the perfornce of PID controllers tht regulte the current production of the MFC by controlling the substrte inlet flow-rte. The developed Siulink odel ws vlidted by the instructor nd the reserch results were presented t poster session. Overll, this work deonstrtes the possibility of introducing ore dvnced STEM topics to high school students by designing interesting projects, using softwre with friendly user interfce, pplying interctive teching strtegies such s breking coplex probles into sll pieces to encourge the student s ctive prticiption nd lerning. References 1 Logn, B., Generting electricity fro wstewter tretent, Wter Environ Res, 2005, 77 (3), Ross, D. E., J. M. Flynn, D. B. Bron, J. A. Grlnick, D. R. Bond, Towrds electrosynthesis in Shewnell: energetics of reversing the Mtr pthwy for reductive etbolis, PLoS One, 2011, 6 (2). 3 Pinto, R. P., B. Srinivsn, M. F. Mnuel, B. Trtkovsky, A two-popultion bio-electrocheicl odel of icrobil fuel cell, Bioresource Technol, 2010, 101 (14), Wng, H. M., Z. Y. J. Ren, A coprehensive review of icrobil electrocheicl systes s pltfor technology, Biotechnol Adv, 2013, 31 (8), Seborg, D. E. E., Edgr T.F., D.A. Mellichp, F. Doyle, Process Dynics nd Control. 3 ed.; Wiley, John & Sons: Cleent Ekputr Cleent Ekputr is 16 yer old senior t Gret Vlley High School in Mlvern, PA. During suer internship in the Deprtent of Cheicl Engineering t Villnov University, he used MATLAB to odel nd control the processes within icrobil fuel cells. He is now plnning to study engineering in college. Zuyi (Jcky) Hung Zuyi (Jcky) Hung is n Assistnt Professor in the Deprtent of Cheicl Engineering t Villnov University. He teches Cheicl Process Control (for senior students) nd Systes Biology (for grdute students) t Villnov. His reserch is focused on developing dvnced odeling nd systes nlysis techniques to nipulte icrobil biologicl systes for generting biofuels fro wstewter nd for cobting biofil-ssocited pthogens. His group (the Biologicl & Environentl Systes Engineering lb (BESEL)) hs developed the first odel for icrobil deslintion cells nd the first etbolic odeling pproch for quntifying the biofil fortion of pthogens.