Review Article Modeling, Control, and Simulation of a Solar...

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Hindawi Publishing Corporation Advances in Power Electronics Volume 2013, Article ID 352765, 9 pages http://dx.doi.org/10.1155/2013/352765 Review Article Modeling, Control, and Simulation of a Solar Hydrogen/Fuel Cell Hybrid Energy System for Grid-Connected Applications Tourkia Lajnef, Slim Abid, and Anis Ammous Power Electronic Group (PEG), ENIS, BP W, 3038 Sfax, Tunisia Correspondence should be addressed to Tourkia Lajnef; lajne๏ฌ…[email protected] Received 10 January 2013; Revised 18 February 2013; Accepted 18 February 2013 Academic Editor: Jose Pomilio Copyright ยฉ 2013 Tourkia Lajnef et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Di๏ฌ€erent energy sources and converters need to be integrated with each other for extended usage of alternative energy, in order to meet sustained load demands during various weather conditions. e objective of this paper is to associate photovoltaic generators, fuel cells, and electrolysers. Here, to sustain the power demand and solve the energy storage problem, electrical energy can be stored in the form of hydrogen. By using an electrolyser, hydrogen can be generated and stored for future use. e hydrogen produced by the electrolyser using PV power is used in the FC system and acts as an energy bu๏ฌ€er. us, the e๏ฌ€ects of reduction and even the absence of the available power from the PV system can be easily tackled. Modeling and simulations are performed using MATLAB/Simulink and SimPowerSystems packages and results are presented to verify the e๏ฌ€ectiveness of the proposed system. 1. Introduction At present, most of energy demand in the world relies on fossil fuels such as petroleum, coal, and natural gas that are being exhausted very fast. One of the major severe problems of global warming is one of these fuels combustion products, carbon dioxide; these are resulting in great danger for life on our planet [1]. Fossil fuels can have as an alternative some renewable energy sources like solar, wind, biomass, and so; among them on the photovoltaic (PV) generator which converts the solar radiation into electricity, largely used in low power applications. e photovoltaic generator is chosen for its positive points including being carbon free and inexhaustible; moreover, it does not cause noise for it is without moving parts and with size-independent electric conversion e๏ฌƒ- ciency [2]. Nevertheless, the power generated by a PV system is in๏ฌ‚uenced by weather conditions; for example, at night or in cloudy periods, it would not generate any power or application. In addition, it is di๏ฌƒcult to store the power generated by a PV system for future use. e best method to overcome this problem is to integrate the PV generator with other power sources such as an electrolyser, hydrogen storage tank, FC system, or battery due to their good features such as high e๏ฌƒciency response, modular production, and fuel ๏ฌ‚exibility [3, 4]. Its coordination with a PV system could be successful for both grid-connected and stand-alone power applications. anks to the rapid response capability of the fuel cell power system, the photovoltaic fuel cell hybrid system can be able to overcome the inconvenience of the intermittent power generation. Furthermore, unlike a secondary battery, the FC does not only store energy but also produce electricity for unlimited time to support the PV power generator. Hence, the coordination between the FC power system and the photovoltaic generator becomes necessary in order to smooth out the PV power ๏ฌ‚uctuations. is paper focuses on developing a simulation model to design and size the hybrid system for a variety of loading and meteorological conditions. is simulation model is performed using Matlab and SimPowerSystems and results are presented to verify the e๏ฌ€ectiveness of the proposed system. 2. Modeling 2.1. A Dynamic Model of PV Generator. PV arrays are built up with combined series/parallel combinations of PV solar cells, which allow extracting the characteristic parameters of the one-diode equivalent model for a single solar cell.

Transcript of Review Article Modeling, Control, and Simulation of a Solar...

  • Hindawi Publishing CorporationAdvances in Power ElectronicsVolume 2013, Article ID 352765, 9 pageshttp://dx.doi.org/10.1155/2013/352765

    Review ArticleModeling, Control, and Simulation of a Solar Hydrogen/FuelCell Hybrid Energy System for Grid-Connected Applications

    Tourkia Lajnef, Slim Abid, and Anis Ammous

    Power Electronic Group (PEG), ENIS, BP W, 3038 Sfax, Tunisia

    Correspondence should be addressed to Tourkia Lajnef; [email protected]

    Received 10 January 2013; Revised 18 February 2013; Accepted 18 February 2013

    Academic Editor: Jose Pomilio

    Copyright ยฉ 2013 Tourkia Lajnef et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

    Different energy sources and converters need to be integrated with each other for extended usage of alternative energy, in order tomeet sustained load demands during various weather conditions.The objective of this paper is to associate photovoltaic generators,fuel cells, and electrolysers. Here, to sustain the power demand and solve the energy storage problem, electrical energy can bestored in the form of hydrogen. By using an electrolyser, hydrogen can be generated and stored for future use. The hydrogenproduced by the electrolyser using PV power is used in the FC system and acts as an energy buffer.Thus, the effects of reduction andeven the absence of the available power from the PV system can be easily tackled. Modeling and simulations are performed usingMATLAB/Simulink and SimPowerSystems packages and results are presented to verify the effectiveness of the proposed system.

    1. Introduction

    At present, most of energy demand in the world relies onfossil fuels such as petroleum, coal, and natural gas that arebeing exhausted very fast. One of the major severe problemsof global warming is one of these fuels combustion products,carbon dioxide; these are resulting in great danger for life onour planet [1].

    Fossil fuels can have as an alternative some renewableenergy sources like solar, wind, biomass, and so; amongthem on the photovoltaic (PV) generator which converts thesolar radiation into electricity, largely used in low powerapplications. The photovoltaic generator is chosen for itspositive points including being carbon free and inexhaustible;moreover, it does not cause noise for it is without movingparts and with size-independent electric conversion effi-ciency [2].

    Nevertheless, the power generated by a PV system isinfluenced by weather conditions; for example, at night orin cloudy periods, it would not generate any power orapplication. In addition, it is difficult to store the powergenerated by a PV system for future use. The best methodto overcome this problem is to integrate the PV generatorwith other power sources such as an electrolyser, hydrogenstorage tank, FC system, or battery due to their good features

    such as high efficiency response, modular production, andfuel flexibility [3, 4]. Its coordination with a PV systemcould be successful for both grid-connected and stand-alonepower applications. Thanks to the rapid response capabilityof the fuel cell power system, the photovoltaic fuel cellhybrid system can be able to overcome the inconvenienceof the intermittent power generation. Furthermore, unlikea secondary battery, the FC does not only store energy butalso produce electricity for unlimited time to support thePV power generator. Hence, the coordination between theFC power system and the photovoltaic generator becomesnecessary in order to smooth out the PV power fluctuations.

    This paper focuses on developing a simulation model todesign and size the hybrid system for a variety of loadingand meteorological conditions. This simulation model isperformed using Matlab and SimPowerSystems and resultsare presented to verify the effectiveness of the proposedsystem.

    2. Modeling

    2.1. A Dynamic Model of PV Generator. PV arrays are builtup with combined series/parallel combinations of PV solarcells, which allow extracting the characteristic parameters ofthe one-diode equivalent model for a single solar cell.

  • 2 Advances in Power Electronics

    Anode

    Electrolyte

    Cathode

    Load

    1

    2O

    O

    2 +โˆ’ + 2H+ โ†’ H2O

    H2 โ†’ 2H+ + โˆ’

    2 +1

    2 2โ†’ H2O + heat + electrical enegry

    H2

    O2

    H

    2e

    2e

    Figure 1: Cross-sectional view of a PEMFC.

    The PV cell output voltage is a function of the photocur-rent that is mainly determined by load current depending onthe solar irradiation level during the operation [2]:

    ๐‘‰PV =๐‘๐‘ ๐‘˜๐‘‡

    ๐‘žln[๐ผsc โˆ’ ๐ผPV + ๐ผ0๐‘๐‘

    ๐‘๐‘๐ผ0

    ] โˆ’๐‘๐‘ 

    ๐‘๐‘

    ๐‘…๐‘ ๐ผPV. (1)

    The parameters used in the mathematical model of the PVsystem are shown in the abbreviations section.

    2.2. A Dynamic Model of PEMFC. The PEMFC is an electro-chemical device which allows the electric energy conversionof the chemical energy contained in a reaction between a fuel,the hydrogen, and an oxidizer, the oxygen. The temperatureeffects have been taken into account in the typical range oflow temperature PEM (60โ€“100โˆ˜C) and a thermal behavioursubmodel has been introduced.

    A bias voltage is applied across the electrochemical cell inorder to induce electrochemical reactions at both electrodes.Water is introduced at the anode and dissociated into oxygen,protons, and electrons. The protons are driven by an electricfield through the PEM to the cathode where they combinewith the electrons arriving from the external circuit to formhydrogen gas. The assessment of these two half reactionsproduces water, heat, and electricity as Figure 1 shows.

    Manymodels have been proposed to simulate the fuel cellin the literature [4, 5].Thismodel is built by utilizing the rela-tionship between the output voltage and potential pressureof hydrogen, oxygen, and water. Figure 2 shows the detailedPEMFC model, which is then embedded into the Sim-PowerSystems of MATLAB-controlled voltage source andintegrated into the overall system.

    The proportional relationship of the molar flow of gasthrough a valve with its partial pressure can be expressed as

    ๐‘žH2๐‘ƒH2=๐พan

    โˆš๐‘€H2

    = ๐พH2 . (2)

    For hydrogen molar flow, the derivative of the partialpressure can be calculated using the perfect gas equation asfollows [5]

    ๐‘‘

    ๐‘‘๐‘ก๐‘ƒH2 =

    ๐‘…๐‘‡

    ๐‘‰an(๐‘ž

    inH2 โˆ’ ๐‘ž

    outH2 โˆ’ ๐‘ž

    ๐‘Ÿ

    H2) . (3)

    The relationship between the hydrogen flow and the FCsystem current can be written as [5]

    ๐‘ž๐‘Ÿ

    H2

    =๐‘0๐ผ

    2๐น= 2๐พ๐‘Ÿ๐ผ. (4)

    Using (4) and (3), the hydrogen partial pressure can be rewrit-ten in the (s) domain as [5]

    ๐‘ƒH2 =1/๐พH

    2

    1 + ๐œH2๐‘ (๐‘ž

    inH2 โˆ’ 2๐พ๐‘Ÿ๐ผ) , (5)

    where

    ๐œH2 =๐‘‰an๐พH2๐‘…๐‘‡

    . (6)

    Typically, the fuel cell output voltage is obtained from the sumof three effects [5, 6], the Nernst potential, the cathode andanode activation overvoltage, and the ohmic overvoltage dueto internal resistance:

    ๐‘‰cell = ๐ธ + ๐œ‚act + ๐œ‚ohmic, (7)

    where

    ๐œ‚act = โˆ’๐ต ln (๐ถ๐ผ) ,

    ๐œ‚ohmic = โˆ’๐‘…int๐ผ.

    (8)

    Now, the Nernst voltage in terms of gas molarities may beexpressed as [5]

    ๐ธ = ๐‘0[๐ธ0+๐‘…๐‘‡

    2๐นlog [๐‘ƒH2๐‘ƒ

    0.5

    O2 ]] .(9)

    The FC system consumes hydrogen obtained from theon-board high-pressure hydrogen tanks according to thepower demand. A feedback control strategy is used to controlhydrogen flow rate according to the output power of the FCsystem. This feedback control is achieved where FC currenthow the output is taken back into the input while convertingthe hydrogen into molar form [5, 7].

    The quality of hydrogen found from the hydrogen tank isgiven by:

    ๐‘žreqH2

    =๐‘0๐‘๐‘ ๐ผ

    2๐น๐‘ˆ. (10)

    2.3. An Electrolyser Model. Electrolysis of water is the disso-ciation of watermolecules into hydrogen and oxygen gas.Theelectrochemical reaction of water electrolysis is given by

    H2O(liquid) + electrical energy โ‡’ H2(gas)+1

    2O2. (11)

    The rate of hydrogen reacting is directly proportional tothe electrical current in the equivalent electrolysis circuit [8,9], given by

    ๐‘›H2 =๐œ‚๐น๐‘›๐‘๐‘–๐‘’

    2๐น. (12)

  • Advances in Power Electronics 3

    1Fuel cell

    Stack voltage

    Saturation

    1Fuel cell FeedbackCurrent

    +

    +

    +โˆ’

    โˆ’

    โˆ’

    โˆ’

    ๐‘žH2

    ๐‘žO2

    ๐‘ƒH2 ๐‘ƒO2๐‘ƒH2O

    1/๐พH2 1/๐พO21/๐พH2O

    ๐พ๐‘Ÿ ๐‘…int๐‘0โˆ—๐‘๐‘ โˆ—๐‘ข/(2โˆ—๐นโˆ—๐‘ข)

    2โˆ—๐พ๐‘Ÿ

    1/๐‘ŸH O

    ๐‘0โˆ—(๐ธ0 + ((๐‘…โˆ—๐‘‡)/(2โˆ—๐น))โˆ—log 10((๐‘ข(1)โˆ—๐‘ข(3)โˆง(0.5))/(๐‘ข(2))))

    ๐‘‡โˆ˜H2ยท +1 ๐‘‡โˆ˜O2ยท +1

    ๐ตโˆ—log(๐ถโˆ—๐‘ข)

    ๐‘  ๐‘‡โˆ˜H2O ยท +1๐‘  ๐‘ 

    Figure 2: Dynamic model of the FC system.

    1Product 1

    Product

    96.5

    0.09

    75.5

    Mathfunction 1

    Mathfunction

    Gain 1

    Gain

    Fcn

    Divide 2

    Divide 1

    Divide

    1Electrolyser

    current๐‘’๐‘ข

    |๐‘ข|2

    รท

    รท

    รท

    ร—

    ร—

    ร—

    ร—

    ร—

    +โˆ’

    ๐‘ข(1)/2

    -๐พ-

    -๐พ-

    N-H2

    Figure 3: The Simulink diagram of the electrolyser model.

    The relation between the real hydrogen flow rate andthe theoretical one is defined as the Faradayโ€™s efficiency. Ingeneral, it is assumed to be more than 99%. The Faradayefficiency is expressed by [9, 10]

    ๐œ‚๐น= 96.5๐‘’

    (0.09/๐‘–๐‘’โˆ’75.5/๐‘–

    2

    ๐‘’)

    . (13)

    Figure 3 shows the simulation model of the electrolyserimplemented in MATLAB/Simulink.

    2.4. A Hydrogen Storage System. The amount of hydrogenrequired by the PEMFC is sent directly from the electrolyzersystem based on the relationship between the output powerand the hydrogen requirement of the PEMFC system. Theremaining amount of hydrogen is sent to the storage tank [11].The parameters used in the hydrogen storage system are listedin the abbreviations section.

    In this study, the dynamic of the storage is obtained asfollows [10, 11]:

    ๐‘ƒ๐‘โˆ’ ๐‘ƒ๐‘๐‘–= ๐‘

    ๐‘H2๐‘…๐‘‡๐‘

    ๐‘€H2๐‘‰๐‘. (14)

    Neither the compression dynamics nor the compres-sion energy requirements are accounted for in our calcu-lations. All auxiliary power requirements such as pumps,valves were ignored in the dynamic model. The Simulinkversion of the hydrogen storage model is depicted inFigure 4.

    2.5. An Averaged Model of the Converters. The simulationof power electronic systems behavior using semiconductorrefined models gives an accurate, but unaffordable results.The structure of the switch cell is given in Figure 5; it has twobasic switching cells (P-cell and N-cell).

    Each cell consists of one controlled switch and one diode.The two active switches are directly controlled by externalcontrol signals. The diodes are indirectly controlled by thestate of the controlled switches and the circuit conditions.The load is presented by an inductor ๐ฟ and a voltage source(๐‘‰๐‘ ). The DC loop inductance is modeled by an inductor

    ๐ฟ๐‘ ๐‘ก. Depending on the sign of the load current ๐ผ

    ๐ฟ(๐‘ก), only

    two devices (one controlled device and one diode) operatesimultaneously [12โ€“15].

  • 4 Advances in Power Electronics

    Bottle volume

    1Switch

    1

    Divide 3

    1

    H2 molecularmass

    รท

    รท

    ร—

    ร—ร—

    ร—

    ++

    ๐‘‡

    ๐‘‡

    ๐‘ƒbi

    ๐‘‡๐‘ƒ

    ๐‘H2

    -๐ถ-

    -๐ถ-

    -๐ถ-

    Figure 4: The Simulink model of the hydrogen storage system.

    a

    b

    ๐‘‡1

    ๐‘‡2๐ท2

    ๐ท1

    ๐‘†1

    ๐‘‰๐‘ (๐‘ก)

    ๐‘‰๐‘Ž(๐‘ก)

    ๐‘–๐ฟ(๐‘ก)

    ๐‘‰๐‘(๐‘ก)

    ๐‘–๐‘’

    ๐‘ˆ๐‘Ž๐‘ 

    ๐‘ˆ๐‘๐‘ 

    ๐‘†

    ๐ฟ๐‘ ๐‘ก/2

    ๐ฟ๐‘ ๐‘ก/2

    ๐‘‰๐‘’๐ฟ

    I๐‘’1

    I๐‘’2

    (a)

    a

    b

    ๐‘‰๐‘’

    ๐‘‰๐‘

    ๐‘‰1

    ๐ผ1

    +

    โˆ’โˆ’ ๐ผ๐ฟ

    ๐‘‰๐‘Ž

    ๐‘‰๐‘ ๐‘†1

    ๐ฟ

    ๐‘†

    (b)

    Figure 5: (a) The PWM switch, (b) the equivalent circuit of the PWM switch averaged model.

    The proposed averaged model of the PWM-switch ispresented in Figure 5(b). This model contains a controlledvoltage source (๐‘‰

    1) and a controlled current source (๐ผ

    1).

    The PWM-switch is the only nonlinear element which issupposed to be responsible for the nonlinear behavior ofthe converter, Considering ๐‘‡

    ๐‘ as the switching period of the

    controlled switches and (๐‘‘) the duty ratio which is the ratioof the on-time value (๐‘‡on) of the upper controlled switch (๐‘‡1)and the switching period ๐‘‡

    ๐‘ .

    In Figure 5(b), the current source (๐ผ1) and the voltage

    source (๐‘‰1) are given by

    ๐‘‰1= โŸจ๐‘‰๐‘Ž๐‘ โŸฉ ,

    ๐ผ1= โŸจ๐‘–๐‘’2

    โŸฉ ,

    (15)

    where โŸจ๐‘ˆ๐‘Ž๐‘ โŸฉ and โŸจ๐‘–

    ๐‘’2

    โŸฉ are the time averaged values of theinstantaneous terminal waveforms ๐‘ˆ

    ๐‘Ž๐‘ (๐‘ก) and ๐‘–

    ๐‘’2

    (๐‘ก), respec-tively, over one cycle ๐‘‡

    ๐‘ .

  • Advances in Power Electronics 5

    L (inductor)

    n-H1

    Step1Eclairement

    Irรฉf

    Amp Irรฉf

    VAC

    Perte2

    Rapp cyc

    Irรฉf

    Amp Irรฉf

    Electrolysercurrent

    ๐‘‰๐‘ 

    ๐‘‰๐‘’

    ๐‘‘

    ๐ผout

    ๐ผin ๐ผele

    ctro

    ๐ผ PV

    ๐‘žH2

    ๐‘žO2

    ๐ผpem

    Courant mesureฬ

    Puissance

    ๐‘žH2

    ๐‘–+

    +

    โˆ’

    โˆ’

    DCbusH2

    ๐ผpem๐‘‰pem

    ๐‘–pemO2

    ๐‘†

    ๐‘‰cell

    ๐‘–out

    ๐‘–out1

    Out1

    ๐‘‘

    ๐‘‰๐‘ 

    Iond

    Vond

    Vond

    ๐ผ FC

    Vond1Iond

    ๐ผpv

    ๐ผpv

    ๐‘‰pv

    ๐‘‰pv

    ๐‘‰ac

    ๐ผ๐ฟ

    ๐‘ƒpv

    N-H2

    ๐‘‡๐‘ƒ

    PV

    eฬIReฬseau

    P diode

    P switch

    Figure 6: Schematic drawing of the PVFC hybrid system.

    In this paper we have chosen MOSFETโ€™s devices for thecontrolled switch and the PIN devices for diodes. We noticethat the load current ๐‘–

    ๐ฟis considered constant and equal to

    the averaged value of the real current ๐‘–๐ฟ(๐‘ก) in the load over

    the switching period ๐‘‡๐‘ . During devices turn-on and turn-off

    phases, the different voltage magnitudes are given by

    ๐‘‰๐‘ฅ= โˆ’(๐ฟ

    ๐‘ ๐‘ก(๐‘‘๐ผ๐น

    ๐‘‘๐‘ก+๐‘‘๐ผ๐‘…

    ๐‘‘๐‘ก) โˆ’ ๐‘‰๐‘‘) ,

    ๐‘‰RM = โˆ’(๐‘‰๐‘’ + ๐ฟ ๐‘ ๐‘ก๐‘‘๐ผ๐‘…

    ๐‘‘๐‘กโˆ’ ๐‘‰๐‘ก) ,

    ๐‘‰๐‘ ๐‘ก= ๐ฟ๐‘ ๐‘ก

    ๐‘‘๐ผ๐น

    ๐‘‘๐‘ก, ๐‘‰

    ๐‘ž= ๐‘‰๐‘’+ ๐‘‰๐‘‘โˆ’ ๐ฟ๐‘ ๐‘ก

    ๐‘‘๐ผ๐น

    ๐‘‘๐‘ก.

    (16)

    The averaged values of the voltage across the device of thevoltage source ๐‘‰

    1and current ๐ผ

    1are obtained by integrating

    the voltage and the current evolutions over one cycle ๐‘‡๐‘ .

    2.6. The PV System Model and Integration to the OverallHybrid Model. As shown in Figure 6, the majority of thePVFC system comprises a solar-cell model, a PEM fuel cellgenerator, and a water electrolyser. The parameters of the PVsystems are listed in Table 1. The PEMFC system parametersare given in Table 2.

    DC-DC converters are widely used in PV generatingsystems as an interface between the PV generator and thewater electrolyser. An optimized controller for the DC-DC

    Table 1: PV system model parameters.

    PV system model parameters ValueThe number of parallel cells per strings (๐‘

    ๐‘) 36

    The number of series cells per strings (๐‘๐‘ ) 1

    The number of parallel modules 6Ideality or completion factor (๐‘Ž) 1.9Boltzmannโ€™s constant (๐‘˜) 1.3805๐‘’ โˆ’ 23 [j/โˆ˜K]PV cell temperature (๐‘‡) 298 [โˆ˜K]Electron charge (๐‘ž) 1.6๐‘’ โˆ’ 19CShort-circuit cell current (representinginsolation level) (๐ผsc) (A)

    2.926

    PV cell reverse saturation current (๐ผ0) (A) 0.00005

    Series resistance of PV cell (๐‘…๐‘ ) (ฮฉ) 0.0277

    must find the optimum duty cycle which leads the PVgenerator as close as possible to its MPPT and ensure that theworking point at the water electrolyser is a safety point. Sincethe fuel cell stack operates at a lowDC voltage range (102V inthis paper), the DC-DC converter must boost the DC voltageand invert it to the AC grid frequency (230V/50Hz here)for grid-connected operations. To keep the DC buses fixedat 400V, we chose to use a hysteresis regulator.

    Hence, the fuel cell control problem is translated intoan output current control requirement, to be realized by theDC/DC converter, in order to ensure optimal operation for

  • 6 Advances in Power Electronics

    Table 2: FC system model parameters.

    FC system model parameters ValueActivation voltage constant (๐ต) 0.04777 [Aโˆ’1]Activation voltage constant (๐ถ) 0.0136Conversion factor (CV) 2Faradayโ€™s constant (๐น) 96484600 [C/kmol]Hydrogen time constant (๐œH2 ) 3.37 [s]Hydrogen valve constant (๐พH2 ) 4.22 โˆ— 10

    โˆ’5 [kmol/(atms)]Hydrogen-oxygen flow ratio (๐‘ŸHโ€“O) 1.168๐พ๐‘Ÿconstant =๐‘

    0/4 โˆ— ๐น 2.2802 โˆ— 10โˆ’7 [kmol/(atms)]

    Number of cells (๐‘0) 88

    Number of stacks (๐‘๐‘ ) 1

    Oxygen time constant (๐œo2 ) 6.74 [s]Oxygen valve constant (๐พo2 ) 2.11 โˆ— 10

    โˆ’5 [kmol/(atms)]FC system internal resistance (๐‘…int) 0.00303 (ฮฉ)FC absolute temperature (๐‘‡) 343 [K]Universal gas constant (๐‘…) 8314.47 [j/(kmol K)]Utilization factor (๐‘ˆ) 0.8Water time constant (๐œH2O) 18.418 [s]Water valve constant (๐พH2O) 7.716 โˆ— 10

    โˆ’6 [kmol/(atms)]

    1

    3

    Puissance2

    11

    ๐‘ขร— +โˆ’

    Courant mesureฬ

    ๐‘‰pile-ref PI๐‘‘

    Figure 7: Inner control loop insuring fast dynamics of PEMFC.

    a given fuel flow rate. Under these conditions, the cell outputpower is directly related to its fuel consumption at the selectedoptimum operating point of the V-I characteristic.

    Operating the fuel cell at different output power levelsrequires suitable variation of its input flow rate, to be realizedby the overall control system of the cell. The power demandrequirement of the fuel cell is translated into a currentdemand input by dividing with stack output voltage:

    ๐ผdemand =๐‘ƒdemand๐‘‰fc

    . (17)

    2.7. Control Strategy of the Hybrid Power System. The pro-posed control strategy is based on a power decouplingstrategy in the frequency domain of the power source. Thisenergy-management strategy fulfills the fast energy demandsif the load respects the integrity of each source. The innercontrol loop is tuned to drive the PEMFC current. ๐‘‰Bus canbe considered constant during current regulation. With thisassumption, a classical proportional-integral (PI) controlleris proposed (Figure 7).

    3

    2

    Duty cycle1

    Product

    0 Angle rรฉactifSignal Irรฉf

    Boost control

    5

    4

    3

    2

    1

    ๐ผpv

    ๐‘‰pv

    ๐‘‰pv

    ๐‘ƒvp

    ๐‘‰ac๐‘‰ac

    ๐‘ƒpv

    ร—

    ๐ผload

    ๐‘‡1

    ๐‘‡2

    ๐‘‡3

    ๐‘‡4

    ยดยด

    ยด

    ยดCaracteฬristique Reฬseau

    Amp Ireฬf

    Reฬgulation

    Regulation de Vondet determination de Iref

    VondVond

    Iref

    Figure 8: Current regulation implementation.

    0 0.5 1 1.5 20

    500

    1000

    1500

    2000

    2500

    3000

    Figure 9: Power drawn from solar system.

    The implementation structure of the loop regulationwith hysteresis is given in Figure 8 scheme. This cascadedcontrol structure shows that it could satisfy the differentrequirements of the hybrid system both from the point ofview of the feed load and from the point of view of thecomponent limits.

    3. Results and Discussion

    In this section we present simulation results for the couplingbetween the PV/FC and the PEM electrolyser through theDC-DC converter controller. The PV generator is a 2880Wpower plant at 1000 (w/m2) solar radiation. From Figures 9and 10, we observe that the current and the available powerfrom the PV generator decreases because of radiation varia-tion.

    Initially, the total power generated by the PV generatoris sent to the electrolyser through a DC-DC converter togenerate hydrogen. The hydrogen produced by the electrol-yser causes the pressure of the storage tank to vary as shownin Figure 11. These results are obtained for two values ofsolar radiation 1000 (w/m2) and 800 (w/m2). We notice thatthe final value of pressure is used as initial condition in thefollowing simulation.

  • Advances in Power Electronics 7

    0 0.5 1 1.5 20

    5

    10

    15

    20

    25

    30

    Figure 10: The current variation for the PV solar system.

    0.5 1 1.5 21

    2

    3

    4

    5

    6ร—10โˆ’6

    Figure 11: Amount of hydrogen produced by electrolyser.

    After this, the total power generated by the PV systemis sent to grid via a DC/AC converter. At 1000 (w/m2) solarradiation, the PV generator used in this study is capable ofdelivering 2880W while the FC delivers 200W, but at 800(w/m2) solar radiation (at 1 s) the power produced by the PVsystem tends to 2300W. So the generated power by the PVis less than the demand; power will be supplied from the FCsystem.Thepower produced by the FC system tends to 500Wat 1 s of time simulation.

    The internal voltage of the FC system decreases when theFC output power increases. This relation between power andthe voltage of the FC system authenticates the reliability of theFC model. The transient response of the FC system voltageto the load changes varies according to the amount of powersupplied by the FC system as shown in Figure 12. The powerproduced by the FC system is given in Figure 13.

    The amount of hydrogen moles consumed by the FCsystem is proportional to the power drawn from the FCsystem. The hydrogen flow to the FC system per second isdepicted in Figure 14.

    Figure 15 shows the hydrogen storage tank pressurevariation corresponding to the amount of hydrogen extracted

    0 0.5 1 1.5 2108

    108.2

    108.4

    108.6

    108.8

    109

    Figure 12: Voltage of the fuel cell.

    0 0.5 1 1.5 20

    100

    200

    300

    400

    500

    600

    Figure 13: Power produced by the FC system.

    0 0.5 1 1.5 20

    0.5

    1

    1.5

    2

    2.5

    3

    3.5 ร—10โˆ’5

    Figure 14: The molar flow of hydrogen consumed by FC.

  • 8 Advances in Power Electronics

    0 0.5 1 1.5 240

    50

    60

    70

    80

    90

    100

    110

    120

    Figure 15: The pressure variation of the hydrogen storage tank.

    0 0.5 1 1.5 20

    5

    10

    15

    20

    Figure 16: The pressure variation of storage hydrogen.

    from the storage tank. It is evident that the hydrogenstorage tank pressure decreases with time as more and morehydrogen is extracted from the storage tank. The pressurevariation of storage hydrogen is as illustrated in Figure 16.

    4. Conclusion

    In this paper, a PV/FC generator and PEM electrolyserhave been described for a PV/FC system intended for grid-connected operations. Special attention has been paid to themodeling of temperature dependence, concentration overpotential, and limiting current in the PEMelectrolysermodel.Then, the power conditioning system, including the DC/DCand DC/AC converters, is presented and typical waveformsare shown from its simulation in MATLAB/Simulink.

    Abbreviations

    ๐‘Ž: Ideality or completion factor๐ผ0: PV cell reverse saturation current [A]

    ๐ผPV: PV cell output current [A]๐ผsc: Short-circuit cell current (representing

    insolation level [A])๐‘˜: Boltzmannโ€™s constant [j/โˆ˜K]๐‘€V: Voltage factor๐‘๐‘: The number of parallel strings

    ๐‘๐‘ : The number of series cells per string

    ๐‘ž: Electron charge [C]๐‘…๐‘ : Series resistance of PV cell [ฮฉ]๐‘‡: PV cell temperature [โˆ˜K]๐‘‰MP: PV cell voltage corresponding to maximum

    power [V]๐‘‰oc: Open-circuit voltage [V]๐‘‰PV: Terminal voltage for PV cell [V]๐‘€H2 : Molar mass of hydrogen [kg kmol

    โˆ’1]๐‘H2 : Hydrogen moles per second delivered to the

    storage tank [kmol/s]๐‘ƒb: Pressure of tank [pascal]๐‘ƒbi: Initial pressure of the storage tank [pascal]๐‘…: Universal (Rydberg) gas constant [j/(kmol K)]๐‘‡๐‘: Operating temperature [โˆ˜K]๐‘‰๐‘: Volume of the tank [m3]๐‘: Compressibility factor as a function of pressure.

    References

    [1] K.-S. Ro and S. Rahman, โ€œTwo-loop controller for maximizingperformance of a grid-connected photovoltaic-fuel cell hybridpower plant,โ€ IEEE Transactions on Energy Conversion, vol. 13,no. 3, pp. 276โ€“281, 1998.

    [2] Y. Sukamongkol, S. Chungpaibulpatana, and W. Ongsakul, โ€œAsimulation model for predicting the performance of a solarphotovoltaic system with alternating current loads,โ€ RenewableEnergy, vol. 27, no. 2, pp. 237โ€“258, 2002.

    [3] J. J. Hwang, D. Y. Wang, N. C. Shih, D. Y. Lai, and C. K. Chen,โ€œDevelopment of fuel-cell-powered electric bicycle,โ€ Journal ofPower Sources, vol. 133, no. 2, pp. 223โ€“228, 2004.

    [4] J. J. Hwang, W. R. Chang, F. B. Weng, A. Su, and C. K. Chen,โ€œDevelopment of a small vehicular PEM fuel cell system,โ€International Journal of Hydrogen Energy, vol. 33, no. 14, pp.3801โ€“3807, 2008.

    [5] M. Y. El-Sharkh, A. Rahman, M. S. Alam, P. C. Byrne, A. A.Sakla, and T. Thomas, โ€œA dynamic model for a stand-alonePEM fuel cell power plant for residential applications,โ€ Journalof Power Sources, vol. 138, no. 1-2, pp. 199โ€“204, 2004.

    [6] J. Padulleฬs, G. W. Ault, and J. R. McDonald, โ€œIntegrated SOFCplant dynamic model for power systems simulation,โ€ Journal ofPower Sources, vol. 86, no. 1, pp. 495โ€“500, 2000.

    [7] J. Hamelin, K. Agbossou, A. Laperrieฬ€re, F. Laurencelle, and T. K.Bose, โ€œDynamic behavior of a PEM fuel cell stack for stationaryapplications,โ€ International Journal of Hydrogen Energy, vol. 26,no. 6, pp. 625โ€“629, 2001.

    [8] M. J. Khan andM. T. Iqbal, โ€œDynamicmodeling and simulationof a small wind-fuel cell hybrid energy system,โ€ RenewableEnergy, vol. 30, no. 3, pp. 421โ€“439, 2005.

    [9] O. Ulleberg, Stand-alone power systems for the future: optimaldesign, operation and control of solar-hydrogen energy systems[Ph.D. thesis], NorwegianUniversity of Science andTechnology,1998.

  • Advances in Power Electronics 9

    [10] K. Sapru, N. T. Stetson, S. R. Ovshinsky et al., โ€œDevelopment ofa small scale hydrogen production-storage system for hydrogenapplications,โ€ in Proceedings of the 32nd Intersociety EnergyConversion Engineering Conference, pp. 1947โ€“1952, August 1997.

    [11] H. Goฬˆrguฬˆn, โ€œDynamic modelling of a proton exchange mem-brane (PEM) electrolyzer,โ€ International Journal of HydrogenEnergy, vol. 31, no. 1, pp. 29โ€“38, 2006.

    [12] H. J. N. Spruijt, D. M. Oโ€™Sullivan, and J. B. Klaassens, โ€œPWM-switch modeling of DC-DC converters,โ€ IEEE Transactions onPower Electronics, vol. 10, no. 6, pp. 659โ€“664, 1995.

    [13] J. Chen, R. W. Erickson, and D. Maksimovicโ€™, โ€œAveraged switchmodeling of boundary conduction mode DC-to-DC convert-ers,โ€ in Proceedings of the 27th Annual Conference of the IEEEIndustrial Electronics Society (IECON โ€™01), vol. 2, pp. 844โ€“849,Denver, Colo, USA, November 2001.

    [14] A. Ammous, K. Ammous, M. Ayedi, Y. Ounajjar, and F. Sellami,โ€œAn advanced PWM-switch model including semiconductordevice nonlinearities,โ€ IEEE Transactions on Power Electronics,vol. 18, no. 5, pp. 1230โ€“1237, 2003.

    [15] S. Abis, K. Ammous, H. Morel, and A. Ammous, โ€œAdvancedaveraged model of PWM-switch operating in CCM and DCMconduction modes,โ€ International Review of Electrical Engineer-ing, vol. 2, no. 4, pp. 544โ€“556, 2007.

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