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Modeling of a Small Stand-Alone AC System with the Dynamic Models of Fuel Cells and Solar Panels

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Pro. EA Annual Meeting on Eletrostatis 00, Paper G Modeling of a mall tandalone A ystem with the Dynami Models of Fuel ells and olar Panels Kiran K hedella, Lin Zhao and Zhihao Zhang, Dept. of Eletrial
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Pro. EA Annual Meeting on Eletrostatis 00, Paper G Modeling of a mall tandalone A ystem with the Dynami Models of Fuel ells and olar Panels Kiran K hedella, Lin Zhao and Zhihao Zhang, Dept. of Eletrial & omputer Engineering, Gannon University U Power phone: () phone: () phone: () Abstrat his paper presents the preliminary study of the modeling of a small standalone A system with the fuel ells and solar panels as energy resoures. he solar energy will be the main energy soure for eletriity generation during the day and will be omplemented with the fuel ell when needed. he fuel ell and the battery will be responsible to meet the eletriity demand during the night. he dynami imulink models of the fuel ell and the photovoltai ell are implemented and the load harateristis were obtained for both. he system also inludes two D/D onverters to boost the output voltage from both the fuel ell and PV ell to 80V D. he D/A PWM inverter is involved to onverter D to the standard A voltage suitable for general household applianes. he power management strategy and the load sharing ontroller are the two main researh jobs urrently undergoing. I. INRODUION Renewable energy integration with eletri power system is one of the m ajor researh areas t o real ize a green and sm art gri d. he rapi d depl etion of onventional energy resoures al ong wi th t he need t o redue t he envi ronmental i mpats and the tight onstraints over the onstrution of new transmission lines for long distane power transmission leads to the all o f more alternative energy resoures and their effiient utilization. Of partiular interest are renewabl e distributed generation systems with free energy resoures, suh as fuel ells, wind turbines and solar photovoltai (PV) ells [][][]. he output D voltages generated by t he fuel el l and t he PV el l vary i n a wi de range: t he form er (e.g. a proton exhange membrane (PEM ) fuel el l) depends on t he hydrogen flow rate and while the later is highly sensitive to the weather ondition. Although a small power system with a single renewable energy system is possible[][4][5], a small standalone power system with the ombination of more than one renewable energy resoure is m ore appealing due to the availability of the resoures and the sustainable operation of the system[6][7]. he output D voltage generated by the fuel ell and Pro. EA Annual Meeting on Eletrostatis 00 the PV ell is low in magnitude whih needs to be stepup with DD onverters. he DA inverters are required if to support a loads [9][0]. Past researh ativities of the fuel ells and the PV ells for eletriity generat ion foused ei ther on t heir dy nami modeling alo ne [ ][][][] o r th e feas ibility an d th e h arateristis o f th e p ower system with t hem assum ed t o be operat ed under st eady st ate for m ost of t he ases[4][5][6][7][8]. he presented researh work is among the first attempts to inlude dynami models in the system level operation. he proposed small standalone system onsists of t wo energy resoures (PEM fuel ells and PV ells ) and a battery as the energy storage devie as shown in Fig.. When the solar energy is suffiiently high during the day it is used to ompletely meet the load demands. During ni ghts t he fuel el l operat es i ndependently supplying the required power demand of the load. When there is no suffiient solar radiation both photovoltai system and fuel ells operate together to share t he load demand. he battery is used to support this system during transients when the response of the system is not quik enough to meet the hange in load demand. he dynami models of the fuel ells and the PV ells will b e onsidered during the system analysis and simulation. his paper presents the preliminary researh results of the projet inluding detailed dynami models of t he fuel ell and sol ar panel and t he simulation of the system performane under speifi situations. he design and implementation of the power management strategy and the ontroller (as noted with the red dashed l ine in Fig. ) are urrently undergoing. Fig.. proposed small standalone power system with fuel ells and solar panel II. IMULINK DYNAMI MODEL OF PEM FUEL ELL he proton exhange m embrane (PEM) fuel ell also known as t he solid polymer fuel ell was fi rst developed by General Eletri (UA) in 960s for use by NAA. It basially requi res hy drogen as fuel and oxy gen from ambient ai r []. he fuel ell annot immediately respond to hanges in load beause of their slow internal eletrohem ial reations, so a battery is required to meet the load demand during transient state. Fuel ell output voltage and power are i nfluened by the eletrohemial and phy sial properties of fuel ell, suh as t he apaitane of doubl e layer harge effet, mass diffusion, material onservation, thermodynamis and voltage drops inside the ell. In this a paper a dynami model of PEM fuel ell is adopted [] with the omplete full ell voltage equation given as follows Pro. EA Annual Meeting on Eletrostatis 00 V f = E V V V () at on ohm E R P P = H O E ln () 0 F PH O In () the ativation polarization loss is d ominant at th e low urrent density and an be desribed by the afel equation []: R i f V = at ln () αnf io At high urrent densities, slow transportation of reatants is the main reason for the onentration voltage drop: R il V on = ln (4) nf il i f he ohmi polarization loss varies diretly with urrent and an be expressed as Vohm = i fr int (5) he effets of the thermal dynamis and internal resistane an be expressed as (6) and (7) [] whih are the relations derived from experimental measurement for speifi fuel ell model. t 0 ( 0 ri i f τ = i )( e ) (6) R int = A R e R 0 i f τ R B ln( i ) (7) R f he symbols are defined as follows, V f the output voltage of a fuel ell; E the ideal equilibrium potential and an be onsidered as the open iruit voltage. P X the orresponding partial pressure E 0 the ideal standard potential that is the ideal ell voltage under standard onditions suh as one atmosphere and 5 0 for the ell reation. R universal gas onstant (8.45 kj/mol/k); absolute temperature (K); n number of eletrons partiipating and equal to if hydrogen is the fuel; F Faraday s onstant, harge arried by a mole of eletrons (96485 oulombs/mol); α the eletron transfer oeffiient whih must be in the range from 0 to.0; i f fuel ell urrent (A); i o exhange urrent density i l is the limiting urrent at the eletrode whih has the lowest limiting urrent density R int fuel ell internal resistane (ohm) Pro. EA Annual Meeting on Eletrostatis 00 4 τ and τ R time onstants X, A R, B R and R 0 empirial parameters [] he dy nami m odel of PEM fuel el l governed by equat ions () t o (7) was i mplemented in imulink environment as shown in Fig.. he fuel ell blok represents equations () to (5). Equations (6) and (7) were implemented in bloks thermal dynamis and the fuel ell internal resistane respetively. hree inputs (hydrogen flow rate, oxygen/air flow rate, and the l oad urrent ) and one out put (out put vol tage) onnet t he fuel el l model with the rest of the system as shown in Fig.. Fig. shows the details in the fuel ell subsystem bloks for the ell internal voltage soure, the ativation, ohmi and onentration voltage drops. emp o Workspae H rate qh Eint Vat Load urrent O rate m hermal Dynamis m_deg qo on Vohms ope Rint Fuel ell Internal Resistane Rf Vf Fuel ell ope5 Out Vf o Workspae Fig.. Dynami model of fuel ell implementation in imulink m_deg 7 onstant qh qh_in Eint 4 qo_in qo ell Internal voltage Eo Vat Ativation Polarization Vat Eint K Gain 5 Vf on on onentration Polarization 5 Rf Vohm Rf Ohmi Polarization 4 Vohms Fig.. Fuel ell subsystem Pro. EA Annual Meeting on Eletrostatis 00 5 he load harateristis of the fuel ell based on the proposed imulink model was illustrated in Fig. 4 where both the output voltage and the stak (load) urrent of the PEM fuel ell are normalized to show the general relationship between them. Normalized ell output voltag Normalized ell urrent density Fig. 4. normalized output harateristis of the PEM fuel ell III. D YNAMI MODEL OF PHOOVOLAI ELL he imulink model for t he PV el l was adopt ed [] and m odified to fit in the urrent projet. he output harateristis of a PV ell an be represented by []. Ak = q I I I ph 0 ln RsI I (8) 0 where, q harge of eletron ( ) k Boltzmann onstant (.8 0 J/ o K) I ell output urrent (A) I ph ell photourrent, funtion of irradiation level and juntion temperature (A) I o Reverse saturation urrent of diode R s series resistane of ell (ohm) referene ell operating temperature (0 o ) V ell output voltage (V) Equation (8) is validated for speifi temperature and solar irradiation level. aid so, under a new ell temperature and a new solar irradiation level, the output voltage and the ell photourrent would beome, V new = VVV (9) _ I = ph new II I (0) _ ph where, V, V, I and I are orretion oeffiients whose values are dependent on the ell temperature and the solar irradiation level. hese oeffiients take the forms of Pro. EA Annual Meeting on Eletrostatis 00 6 V V = β Δ, I = β Δ, I γ = = Δ Δ () with Δ as the solar irradiation level hange, Δ as the orresponding ell temperature hange, and the empirial parameters β and γ. Fig 5 display the imulink model represent the PV ell subsystem with equation (8) and Fig. 6 shows the details in the PV subsystem blok representing (9)(). emp Irridiation Ns Produt GND s i I ontrolled Voltage oure ope 6 I PV ubsystem ransport Delay aturation Fig. 5. PV ell system I V Iph Iph ope Produt I ope Iph Produt olar irridiation Photo voltai ell Model & emp Effet Fig. 6. olar irradiation level and temperature effet represented by equations (9)() I Fig. 7. PV ell load harateristis under different irradiane levels and temperature Pro. EA Annual Meeting on Eletrostatis 00 7 Fig. 7 provides the output harateristis of a single PV ell under different solar irradiation levels and different temperature. he nonlinearity at ell high voltage range is evidened. IV. OVERALL YEM IMULAION he overall system was shown in Fig. 8 with the main omponents represented as bloks. wo D/D onverters boost the output voltage of fuel ell module (47 el ls) and t he PV module (7 ells) to 80V. Eah module is proteted from the bakflow urrent with a diode. he 80V D bus is onneted with a PW M inverter (three legs/six pulses) to get balaned threephase. Filters are installed to deal with the harmonis and the threephase transformer is for isolation purpose. W ith the power management ontroller not in plae urrently, manual adjustment is involved to assign the load sharing. Fig. 9 displays the waveform of the threephase load voltage H pressure Vf Vf Vd s i qo O pressure 5 emp qh Fuel ell dynami Irridiation Vf Vd D/D s I I Diode i D/A g A B A Pulse generator 6pulses ontrol ontrol isolation ransformer A a B b B Filter A B Load v Vab v Vb v a ope PV ell dynami D/D Diode Fig. 8. Overall model of a small standalone A system Fig. 9. Output threephase voltage waveform Pro. EA Annual Meeting on Eletrostatis 00 8 V. DIUION he model of a small standalone A system with fuel ell and solar panel was implemented and simulated with imulink. he preliminary result shows the feasibility of inluding dynami models of the renewable energy resoures in the analysis of the system performane. he researh of the power management strategy and ontroller is urrently undergoing. It will monitor the availability of the renewable energy to determine the swithing on or off of the resoures to balane the supply and demanding. When both energy resoures are involved in eletriity generation at the same time, the ontroller will determine the load share. he ontroller also an ontrol the angle of the PV ells to trak the sun and the flow rate of the hydrogen to meet the power needs. REFERENE [] L. Freris and D. infield, Renewable energy in power system, Wiley, 009. [] M. Hashem Nehrir and aisheng W ang, Modeling and ontrol of fuel ells distributed generation appliations, Wiley, 009. [] Z. Zhang, Modeling, analy sis and ontr ol of a PE M fuel ell based m iro gr id power sy stem, Ph. D. dissertation, he University of Western Ontario, London, Ontario, June 007. [4] Akihiro Oi, Design and sim ulation of photovoltai water pum ping sy stem, M.. thesis, alifornia Polytehni tate University, an Luis Obispo, A, ept 005. [5] M. Y. Elharkh, N.. isworahardjo,. Yalinoz and M.. Alam, Portable diret hydrogen fed PE M fuel ell model and experimental verifiation, Int. J. Energy Res, 009. [6]. Rahman and K.s. am, Feasibility study of photovoltaifuel ell hybrid energy system. IEEE rans. on Energy onversion, (), pp. 5055, 988. [7]. Busquet, J. Labbe and R. Metk emeijer, tand alone power system oupling a PV field and a fuel ell: desription of the seleted system and advantages, Proeedings of the PV in Europe onf erene, Rome, Italy, 7 Ot., pp , 00. [8] L. Wei, Modeling, ontrol and sim ulation of a small photovoltai fuel ell hy brid generation system, omputational Intelligene and software engineering, 009 [9] M. H. odorovi, L. Palm a and P. E njeti, Design of wide input r ange d d onver ter with a r obust power ontrol shem e suitable for fuel ell power onversion, presented in Nineteenth annual IEEE applied power eletronis onferene and exposition, vol., pp. 7479, 004 [0] J. W. Jung and A. Key hani, ontr ol of a fuel ell based Z soure onver ter, IEEE rans. of Energy onversion, Vol., No.. June 007. [] H. Altas and A. M. haraf, A photovoltai array simulation mode for MALABimulink GUI environment, IEEE international onferene on lean eletrial power, pp. 445, 007 [] O. hekoofa and M. aherbaneh, Modeling of silion solar panel by MALAB/imulink and evaluating the importane of its parameters in a spae appliation, rd international onferene on reent advanes in spae tehnologies, pp. 7974, 007. []. A. David and N. A. Gounden, imulation of photovoltai array driven eletri mahines with power eletroni interfaes, imulation onlinefirst, 00. [4] R.. Jagaduri and G. Radman, Modeling and ontr ol of distr ibuted generation systems inluding PE M fuel ell and gas turbine, Eletri Power ystems Researh, vol. 77, pp. 89, 007 [5]. aux, J. Lahaize, M. Fadel, P. hott and L. Niod, Modeling and ontr ol of a f uel ell system and storage elements in transport appliations, J. of proess ontrol vol. 5, pp.4849, 005. [6] K. edghisigarhi and A. Feliahi, Dynami and tr ansient analysis of power distribution systems with fuel ells Part I: Fuel ell dynami model, IEEE rans. Energy onversion, vol. 9, 004 [7] K. edghisigarhi and A. Feliahi, Dynami and tr ansient analysis of power distribution systems with fuel ells Part II: ontrol and stability enhanement, IEEE rans. Energy onversion, vol.9, 004 [8]. Wang, Modeling and ontr ol of hy brid wind/photovoltai/fuel ell distr ibuted gener ation sy stems, Ph.D. dissertation, Montana state university, Bozeman, Montana, July 006.
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