2009_IEEE-Analysis of Supercapacitor as Second Source Based on Fuel Cell Power Generation

ELECTRIC MACHINERY

Field Computation for an Axial Flux Permanent-Magnet Synchronous Generator . . . . . . . T. F. Chan, L. L. Lai, and S. Xie 1Efficiency Optimization of Two-Asymmetrical-Winding Induction Motor Based on Swarm Intelligence . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. M. A. Amin, M. I. El Korfally, A. A. Sayed, and O. T. M. Hegazy 12Analysis and Real-Time Testing of a Controlled Single-Phase Wavelet-Modulated Inverter for Capacitor-Run Induction

Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. A. Saleh and M.A. Rahman 21Development of a Switched-Reluctance Motor Drive with PFC Front-End . . . . . . . . . . . . . . . . . . . J. Y. Chai and C. M. Liaw 30Online Synchronous Machine Parameter Extraction From Small-Signal Injection Techniques . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Huang, K. A. Corzine, and M. Belkhayat 43Improved Resolution of the MCSA Method Via Hilbert Transform, Enabling the Diagnosis of Rotor Asymmetries at Very

Low Slip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . R. Puche-Panadero, M. Pineda-Sanchez, M. Riera-Guasp, J. Roger-Folch, E. Hurtado-Perez, and J. Perez-Cruz 52

Sensorless Slowdown Detection Method for Single-Phase Induction Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F. Ferreyre, R. Goyet, G. Clerc, and T. Bouscasse 60

Behavior of the Three-Phase Induction Motor With Spiral Sheet Rotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Rosas, O. Boix Aragones, X. Colom Fajula, and A. Rolan Blanco 68

Analysis of Flux Leakage in a Segmented Core Brushless Permanent Magnet Motor . . . . . . . . . M. F. Momen and S. Datta 77Optimization of Multibrid Permanent-Magnet Wind Generator Systems . . . . . . . . . . . . . . . . H. Li, Z. Chen, and H. Polinder 82

ENERGY DEVELOPMENT & POWER GENERATION

A Single-Stage Single-Phase Transformer-Less Doubly Grounded Grid-Connected PV Interface . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Patel and V. Agarwal 93

The Impact of Tower Shadow, Yaw Error, and Wind Shears on Power Quality in a Wind–Diesel System . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Fadaeinedjad, G. Moschopoulos, and M. Moallem 102

Numerical Modeling of Thermoelectric Generators With Varing Material Properties in a Circuit Simulator . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. Chen, L. A. Rosendahl, T. J. Condra, and J. K. Pedersen 112

Short-Term Prediction of Wind Farm Power: A Data Mining Approach . . . . . . . . . . . . . . . A. Kusiak, H. Zheng, and Z. Song 125

(Contents Continued on Back Cover)

Authorized licensed use limited to: King Monkuts Institute of Technology. Downloaded on February 19, 2009 at 22:20 from IEEE Xplore. Restrictions apply.

(Contents Continued from Front Cover)

Microgrid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .M. Shahabi, M. R. Haghifam, M. Mohamadian, and S. A. Nabavi-Niaki 137

Laboratory Studies of a New Stator Slot Wedge Tester for HV Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X. Peng, Z. Jia, S. Gao, L. Wang, Z. Guan, J. Yang, and T. Wang 146

A Coordinated Control Method for Leveling PV Output Power Fluctuations of PV–Diesel Hybrid Systems Connected toIsolated Power Utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. Datta, T. Senjyu, A. Yona, T. Funabashi, and C.-H. Kim 153

Multicriteria Design of Hybrid Power Generation Systems Based on a Modified Particle Swarm Optimization Algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Wang and C. Singh 163

Modulation and control of three phase paralleled Z-source inverters for distributed generation applications . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. M. Vilathgamuwa, C. J. Gajanayake, and P. C. Loh 173

A Synchronous Generator Internal Fault Model Based on the Voltage-Behind-Reactance Representation . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. S. Vilchis-Rodriguez and E. Acha 184

Development of a MATLAB/Simulink Model of a Single-Phase Grid-Connected Photovoltaic System . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .M. E. Ropp and S. Gonzalez 195

Novel Half-Bridge Inductive DC–DC Isolated Converters for Fuel Cell Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Y. Lembeye, V. Dang Bang, G. Lefevre, and J. Ferrieux 203

Extending the Modeling Framework for Wind Generation Systems: RLS-Based Paradigm for Performance Under HighTurbulence Inflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. B. Muhando, T. Senjyu, H. Kinjo, and T. Funabashi 211

A Developed Off-line Model for Optimal Operation of Combined Heating and Cooling and Power Systems . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reza Hashemi 222

Analysis of a Commercial Biogas Generation System Using a Gas Engine–Induction Generator Set . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .L. Wang and P.-Y. Lin 230

Operation of Grid-Connected DFIG Under Unbalanced Grid Voltage Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yi Zhou, P. Bauer, Jan A. Ferreira, and Jan Pier 240

Analysis of Supercapacitor as Second Source Based on Fuel Cell Power Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P. Thounthong, S. Rael, and B. Davat 247

MPPT Scheme for a PV-Fed Single-Phase Single-Stage Grid-Connected Inverter Operating in CCM With Only OneCurrent Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .H. Patel and V. Agarwal 256

Optimal Control of Matrix-Converter-Based WECS for Performance Enhancement and Efficiency Optimization . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Kumar, R. R. Joshi, and R. C. Bansal 264

Guidelines for Protection Against Electric Shock in PV Generators . . . . . . . . . . . . . . . . . . . . J. C. Hernandez and P. G. Vidal 274Modeling and Dynamic Characteristic Simulation of a Proton Exchange Membrane Fuel Cell . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Jia, Q. Li, Y. Wang, Y. T. Cham, and M. Han 283On Load–Frequency Regulation With Time Delays: Design and Real-Time Implementation . . .H. Bevrani and T. Hiyama 292

POWER ENGINEERING LETTERS

Control of the Reactive Power Supplied by a Matrix Converter . . . . . . . . . . R. Cardenas, R. Pena, J. Clare, and P. Wheeler 301


IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 24, NO. 1, MARCH 2009 247

Analysis of Supercapacitor as Second Source Basedon Fuel Cell Power Generation

Phatiphat Thounthong, Member, IEEE, Stephane Rael, and Bernard Davat, Member, IEEE

Abstract—This paper presents the utilization of a supercapaci-tor as an auxiliary power source in a distributed generation system,composed of a polymer electrolyte membrane fuel cell (PEMFC)as the main energy source. The main weak point of fuel cells (FCs)is slow dynamics because one must limit the FC current slope in or-der to prevent fuel starvation problems, to improve its performanceand lifetime. The very fast power response and high specific powerof a supercapacitor can complement the slower power output of themain source to produce the compatibility and performance char-acteristics needed in a load. The FC and supercapacitor character-istics are clearly presented. Experimental results with small-scaledevices (supercapacitor bank: 292-F, 30-V, 400-A; PEMFC: 500-W,40-A) illustrate excellent performance during a motor drive cycle.

Index Terms—Converters, current control, electric vehicles, en-ergy storage, fuel cells (FCs), supercapacitor.

I. INTRODUCTION

E LECTRICAL energy storage is compulsory in numer-ous applications: telecommunication devices (such as cell

phones), stand-by power systems, hybrid vehicles, and new elec-tric hybrid vehicles [1], [2].

Electrochemical capacitors are presently called by a numberof names: supercapacitor, ultracapacitor, or double-layer capac-itor; these terms are used interchangeably. The first high-powersupercapacitors were developed by the Pinnacle Research In-stitute (PRI) for the U.S. military applications such as laserweaponry and missile guidance systems. However, only in the19th century did supercapacitors become well known in the con-text of hybrid electric vehicles promoted by the Department ofEnergy (DOE) [3].

Fuel cell (FC) power sources are expected to be used in agrowing number of applications: in portable applications, intransportation applications [4]–[6], and in stationary power ap-plications [7], [8]. In recent works, an FC/supercapacitor hybrid

Manuscript received September 8, 2006; revised April 22, 2008. Firstpublished January 9, 2009; current version published February 19, 2009. Thiswork was supported in part by a research program in cooperation with theThai-French Innovation Institute, King Mongkut’s University of TechnologyNorth Bangkok with the Institut National Polytechnique de Lorraine under the“Franco-Thai on higher education and research joint project” and in part bythe French National Center for Scientific Research (CNRS) and the NancyResearch Group in Electrical Engineering (GREEN: UMR 7037). Paper no.TEC-00428-2006.

P. Thounthong is with the Department of Teacher Training in Electrical En-gineering (TE), King Mongkut’s University of Technology North Bangkok(KMUTNB), Bangkok 10800, Thailand (e-mail: [email protected]).

S. Rael and B. Davat are with the Groupe de Recherche en Electrotechnique etElectronique de Nancy (GREEN), Institut National Polytechnique de Lorraine(INPL), Nancy 54510, France (e-mail: [email protected];[email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TEC.2008.2003216

source [9], [10] and an FC/battery hybrid source [11], [12]have already been reported. Nonetheless, some research hasonly shown the simulation results in which the FC is consid-ered as an ideal source; some have operated with a small-scaleFC in which FC weak points cannot be observed such as thefuel starvation problem, especially to utilize the FC in dynamicapplications.

Reliability and lifetime are the most essential considerationsin such power sources. Taniguchi et al. [13] clearly demon-strated that hydrogen and oxygen starvation caused severe andpermanent damage to the electrocatalyst of the FC. They haverecommended that fuel starvation must absolutely be avoided,even if the operation under fuel starvation is momentary, in just1 s [13], [14].

For these reasons, the use of the supercapacitor as an auxil-iary source is expected that the very fast power response andhigh specific power can complement the slower power output ofthe main source (particularly the FC generator). Various recentresearches [15]–[17] have documented the subject of superca-pacitor technology, but without its applications, particularly FCapplications.

Presented here is a hybridization of the supercapacitor asan energy storage device with an FC as a main source. Thenext section contains a description of the FC characteristics,especially the fuel starvation problem. In Section III, the su-percapacitor is presented in detail: a state of the art, a model,a converter, and current regulation. The hybrid control algo-rithm will be explained in Section IV. In the final section, ex-perimental results will show the supercapacitor characteristicsduring operation with a high switching frequency, a constant dis-charging current and an FC hybrid source during a motor drivecycle.

II. FUEL CELL CHARACTERISTICS

A. Fuel Cell Principle

FCs are electrochemical devices that directly convert thechemical energy of a fuel into electricity. Energy is releasedwhenever a fuel (hydrogen) reacts chemically with the oxygenin air. In the case of hydrogen/oxygen FCs, which are the focusof most research activities today, the only by-product is waterand heat [18]–[20]. Polymer electrolyte membrane FCs (PEM-FCs) are promising power sources because of their relativelysmall size, lightweight, and ease to build.

The FC model here is for a type of PEM, which uses thefollowing electrochemical reaction:

H2 +12O2 → H2O + Heat + Electrical Energy. (1)

0885-8969/$25.00 © 2009 IEEE


248 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 24, NO. 1, MARCH 2009

Fig. 1. Simplified diagram of the PEMFC system.

The FC voltage VFC is modeled as [20], [21]:

VFC = E −

Activation loss︷︸︸︷A log

(IFC + in

io

)−

Ohmic loss︷︸︸︷Rm (IFC + in )

+

Concentration loss︷︸︸︷B log

(1 − IFC + in

iL

)(2)

where E is the reversible no loss voltage of the FC (the ther-modynamic potential), IFC the delivered FC current, io the ex-change current, A the slope of the Tafel line, iL the limitingcurrent, B the constant in the mass transfer term, in the internalcurrent, and Rm the membrane and contact resistances.

As developed earlier, the Nernst equation for the hydro-gen/oxygen FC (using literature values [21] for the standard-state entropy change) can be written as:

E =

1.299 − 0.85 × 10−3 (T − 298.15)

+4.3085 × 10−5T

[ln (pH2 ) +

12

ln (pO2 )]

nCell (3)

where T is the cell temperature (in Kelvin), pH2 and pO2 are thepartial pressure of hydrogen and oxygen (in bar), respectively,and nCell is the number of cells in series.

B. Fuel Cell System

Fig. 1 shows a simplified diagram of the PEMFC system,which is also employed for this research. Constructed by theZSW Company (Germany), the FC stack (500 W, 40 A, 13 V)is composed of 23 cells with area of 100 cm2 [22].

When an FC system is operated, its fuel flows are controlledby a “Fuel Cell Controller” (see Fig. 1), which receives anFC current demand (reference), iFCREF , from the user (manualoperation) or from the hybrid control algorithm (in case of auto-matic operation). The fuel flows must be adjusted to match thereactant delivery rate to the usage rate by the FC controller [11].

C. Fuel Starvation of the FC Stack

For clarity about the dynamic limitation of the FC generator,Fig. 2 presents the 0.5 kW PEMFC voltage response to a current.The tests operate in two different ways: current step and currentslope. It shows the drop of the voltage curve in Fig. 2(a), com-

Fig. 2. FC dynamic characteristics to (a) current step (b) current slope: 4 A/s.

pared with Fig. 2(b), because fuel flows (particularly the delayof air flow) have difficulties following the current step, calledthe fuel starvation phenomenon. This condition of operation isevidently harmful for the FC stack [13], [14].

Without any doubt, to use the FC in dynamic applications, itscurrent or power slope must be limited, but some research workhas omitted to do this. One may lack the FC information in whichfailure modes for FC are not well documented, and degradationcauses and mechanisms are not understood. However, recentworks with evidently experimental results have been based onthe control of the FC current slope, for example: 4 A/s for a0.5-kW, 12.5-V PEMFC [9], [11] and 500 W/s for a 2.5-kW,22-V PEMFC [23].

III. SUPERCAPACITOR

A. State of the Art

The concept of the supercapacitor is not recent. Neverthe-less, marketing only began at the end of 1970s. These deviceswere low-sized devices (capacitance of some farads, low spe-cific energy), dedicated to signal applications such as memorybackup [17].

Since the early 1990s, supercapacitors dedicated to high-power industrial applications (capacitance up to some thousandsfarads, specific energy and specific power of several Wh/kgand kW/kg, respectively) have been available. Especially, DOEsupercapacitor development programs of long-term goals arespecific energy >15 Wh/kg, specific power >2.0 kW/kg after2003 [3].


THOUNTHONG et al.: ANALYSIS OF SUPERCAPACITOR AS SECOND SOURCE BASED ON FUEL CELL POWER GENERATION 249

Fig. 3. Specific power versus specific energy of supercapacitor, NiCd, NiMH,and Li-Ion battery technology from the SAFT company.

Finally, the comparison of storage device technologies fromSAFT Company is depicted in Fig. 3. Even though it is true thata battery has the largest energy density (meaning more energyis stored per unit of weight than other technologies), it is impor-tant to consider the availability of that energy. This is the tradi-tional advantage of capacitors. With a time constant of less than0.1 s, energy can be taken from a capacitor at a very high rate.On the contrary, the same size battery will not be able to supplythe necessary energy in the same time period.

Additionally, the main drawback of the batteries is a slowcharging time, limited by a charging current; in contrast, thesupercapacitor can be charged in a short time, depending on theavailability of a high charging current (power) from the mainsource. The capacitor voltage vC (t) can then be found using thefollowing classical equation:

vC (t) =1C

∫ tn

t0

iC (t) dt. (4)

For example, an SAFT supercapacitor module (583 F, 15 V,400 A) can be charged from zero voltage (zero of charge) to themaximum voltage in 22 s at a constant current of 400 A. Moreadvantageous, unlike batteries, supercapacitors can withstand avery large number (thousands to millions) of charge/dischargecycles without degradation [24].

B. Supercapacitor Model

The supercapacitor model is very complex because of thedistributed-parameter model. Many different models have beenproposed for the double-layer effect [17]. Recent works [10],[17] have proposed that the reduced order model (as portrayedin Fig. 4) for a supercapacitor cell is presented because of itssimplicity and its operating times on the order of a few seconds.It is comprised of three ideal circuit elements: a capacitor CCell ,a series resistor RS called the equivalent series resistance (ESR),and a parallel resistor Rp . The parallel resistor Rp models theleakage current found in all capacitors. This leakage current isequal to a few milliamps in a big supercapacitor.

Fig. 4. Simplified equivalent circuit of a supercapacitor cell including Rp .

Fig. 5. Discharge profile for a supercapacitor under constant current.

Many applications require the capacitors to be connected to-gether, in series and/or parallel combinations, to form a “bank”with a specific voltage and capacitance rating. Normally, theyare always connected in series.

Capacitance variations affect the voltage distribution duringcycling, and voltage distribution during sustained operation ata fixed voltage is influenced by leakage current variations. Forthis reason, an active voltage balancing circuit is employed toregulate the cell voltage.

It is common to choose a specific voltage, and thus, calculat-ing the required capacitance. In analyzing any application, onefirst needs to determine the following system variables affectingthe choice of supercapacitor:

1) maximum voltage, VCMax ;2) working (nominal) voltage, VCNom ;3) minimum allowable voltage, VCMin ;4) current requirement, IC , or the power requirement, PC ;5) time of discharge, td ;6) capacitance per cell, CCell;7) cell voltage, VCell .Connecting many cells in series to form a bank, this does lead

to an increase in total ESR and to a decrease in total capacitance.Defining nS as the number of capacitors connected in series, themaximum capacitor voltage VCMax , total ESR, and capacitanceCSuperC of the capacitor bank can be estimated as:

VCMax = nS VCell

ESR = nS RS

CSuperC =CCell

nS

⎫⎪⎪⎬⎪⎪⎭ . (5)

The discharge profile for a supercapacitor bank under a con-stant current is shown in Fig. 5. A constant discharging current



Fig. 6. Discharge profile for a supercapacitor under constant power.

IC is particularly useful when determining the parameters ofthe supercapacitor. Nevertheless, Fig. 5 should not be used toconsider sizing supercapacitors for constant power applicationssuch as a general power profile (drive cycle) used in electricvehicle. Worst case scenarios from drive cycle determine sizeof the storage devices. For example, Mitchell et al. [25] pre-sented that the Renault fuel cell automobile (SCENIC II, ratedpower of 70 kW of a PEMFC) needs a supplementary constantpower (from battery) of around 30 kW for a 3 s for transientpower (vehicle acceleration). Then, the discharge profile for asupercapacitor under a constant power PC is shown in Fig. 6.

To estimate the minimum capacitance requirement CMin , onecan write an energy equation without losses (ESR neglected)under a discharging constant power PC as:

12CMin

(V 2

C Nom − v2SuperC (t)

)= PC t (6)

where vSuperC (t) is the supercapacitor terminal voltage. Then,

CMin =2PC td

V 2C Nom − V 2

C Min. (7)

Since the power being delivered is constant, the minimumvoltage VC Min and maximum current IC Max can be determinedbased on the current conducting capabilities of the supercapac-itor. Equations (6) and (7) can then be rewritten as:

VC Min =√

V 2C Nom − 2PC td

CMin

IC Max =PC√

V 2C Nom − (2PC td/CMin)

⎫⎪⎪⎬⎪⎪⎭ . (8)

The variables VC Max and CSuperC are related by the numberof cells in series. Voltage rating is important, but the capacitorwill also fail if the current is too high. The assumption is that thecapacitors will never be charged above the combined maximumvoltage rating of all the cells. Generally, VC Min is chosen asVC Max/2, from (6), resulting in the remaining energy of 25%.

In applications where high currents are drawn, the effect of theESR has to be taken into account. The energy dissipated Elossin the ESR, as well as in the cabling, connectors, and converter,could result in an undersizing of the number of capacitors re-quired. For this reason, one can theoretically calculate the losses

Fig. 7. Two-quadrant supercapacitor converter.

in the ESR as:

Eloss =∫ td

0i2SuperC (τ) ESRdτ

= PC ESRCMin ln(

VC Nom

VC Min

)⎫⎪⎪⎬⎪⎪⎭ . (9)

To calculate the required capacitance CSuperC , one canrewrite (6) as:

12CSuperC

(V 2

C Nom − V 2C Min

)= PC td + Eloss . (10)

From (6) and (10), one obtains:

CSuperC = (1 + χ) CMin

χ =Eloss

PC td

⎫⎬⎭ (11)

where χ is the defined energy ratio.

C. Supercapacitor Converter

The supercapacitor bank is connected to the dc bus by meansof a 2-quadrant dc/dc converter (bidirectional converter). Theconverter studied here is the circuit, as shown in Fig. 7 [26].L1 represents the inductor used for energy transfer and currentfiltering. The inductor size is classically defined by switchingfrequency and current ripple. Note here that since it is beyondthe scope of this paper to discuss converter circuit topologies,a simple circuit has been selected. The supercapacitor current,which flows across the storage device, can be positive or nega-tive, allowing energy to be transferred in both directions.

The supercapacitor converter is driven by means of com-plementary pulses, applied on the gates of two insulated-gatebipolar transistors (IGBTs): S1 and S2 . The gate drive com-mands are generated by a hysteresis controller coming from thehybrid control algorithm. It is realized in order to control thesupercapacitor current. This controller is selected because ofthe simplicity to implement it and its fastest response to currentreference [27].

IV. HYBRID CONTROL ALGORITHM

Fig. 8 depicts the hybrid source control strategy [22]. It lies inusing the supercapacitor bank, which is the fastest energy source



Fig. 8. FC/supercapacitor hybrid control algorithm, where vBus is the dc bus voltage, VBusREF the dc bus voltage reference, EBusREF the dc bus energyreference, EBusM ea the filtered dc bus energy, vSup erC the supercapacitor voltage, VSup erCREF the supercapacitor voltage reference, vSup erCM ea the filtereddc bus voltage, vFC the FC voltage, iSup erC the supercapacitor current, iSup erCREF the supercapacitor current reference, iFC the FC current, iFCREF theFC current reference, iFCM ea the filtered FC current, pSup erCREF the supercapacitor power reference, and GSL the absolute value for the FC current slopelimitation.

of the system, for supplying the energy required to achieve thedc bus voltage regulation, as if this device were a standardpower supply. Therefore, the FC, although obviously the mainenergy source of the system, may be seen as the device thatsupplies energy to supercapacitor bank to keep them charged.Consequently, the supercapacitor converter is driven to realizea classical dc link voltage regulation, and the FC converter isdriven to maintain the supercapacitor bank at a given state ofcharge. For reasons of safety and dynamics, these convertersare primarily controlled by inner current loops. These currentloops are supplied by two reference signals, iSuperCREF andiFCREF , generated by the dc link voltage regulation loop andthe supercapacitor voltage regulation loop, respectively (iFCREFalso supplies the “fuel cell controller” to adjust fuel flows to thedesired current) [11].

For the dc bus voltage control loop, supercapacitor powerreference pSuperCREF is generated by means of a proportional–integral (PI) regulator. This signal is then divided by the su-percapacitor voltage, and limited to maintain supercapacitorvoltage within an interval [VC Min , VC Max ]. This results in su-percapacitor current reference iSuperCREF . This reference mustalso be limited within an interval (maximum charging, maxi-mum discharging), as depicted in the block “SuperC LimitationFunction” [9].

For the supercapacitor voltage control loop, it consists of aproportional (P) controller limited in level and slope, to respectconstraints associated with the FC. The reference iFCREF thatdrives the FC converter through the FC current loop is thenkept within an interval [IFCMin , IFCRated ]. The upper value ofthis interval corresponds to the rated FC current, and the lowervalue should be zero. Moreover, slope limitation to a maximum

Fig. 9. Test bench of FC/supercapacitor hybrid power source.

absolute value (GSL ) of some amperes per second enables safeoperation of the FC (refer to “FC Current Slope Limitation,”even during transient power demand).

V. EXPERIMENTAL VALIDATION

A. Test Bench Description

To validate the supercapacitor as a second source to assistthe main source, a small-scale test bench is realized as shownin Fig. 9. The dc bus studied here is 42 V (PowerNet), a newstandard voltage in automotive systems [28]–[31].

The SAFT supercapacitor bank (292 F, 30 V, 400 A) iscomposed of two supercapacitor modules connected in series



Fig. 10. SAFT supercapacitor bank: 292 F, 30 V, 400 A.

(see Fig. 10). A module is six cells connected in series (singlecell: 3500 F, 2.5 V, 400 A, ESR = 1 mΩ). One chooses: VC Max =30 V; VC Nom = 25 V; VC Min = VC Max/2 = 15 V. From (7)without losses, the energy storage (discharging from VC Nom toVC Min ) is equal to 58.4 kJ or 16.2 Wh. The current ripple ∆Iof the hysteresis current controller is set at 3 A.

The PEMFC system is 500 W, 40 A, 13 V (see Fig. 1).The FC stack is connected to the dc bus by a classical boostconverter [11]. The FC maximum (rated) current is set at 40A with a controlled current slope of 4 A/s (absolute value),as already presented in Fig. 2. The hybrid control algorithm isimplemented in the real-time card dSPACE DS1104, throughthe mathematical environment of Matlab-Simulink.

B. Supercapacitor Characteristics to Constant CurrentDischarging

Fig. 11 presents the transient response of supercapacitor con-verter interfacing between the dc bus and the supercapacitorbank. The initial voltage of the supercapacitor bank is 30 V. Thecurrent reference iSuperCREF is Ch2 and the measured currentiSuperC is Ch4. One can observe that the hysteresis controllerfunctions well with a current ripple of 3 A and the high dynamicresponse of the supercapacitor auxiliary source (from 0 to 50 Ain 0.4 ms).

Fig. 12 illustrates the constant discharging current with acurrent step from 0 to 50 A, and vice versa. The initial voltageof the supercapacitor bank is 30 V. It can be observed that theinitial voltage of the storage device instantaneously droppedwhen stepping current because of ESR effect, which can becalculated as:

ESR =30 V − 28 V

50 A=

18 V − 20−50 A

= 40 mΩ. (12)

This value is over the theoretical value of 12 mΩ (12∗1 mΩ).After studying with SAFT engineers who designed the prototypesupercapacitor cells, we may conclude that the aged cells may

Fig. 11. Supercapacitor current response to a step 0–50 A.

Fig. 12. Supercapacitor current response to a step 0–50 A, and vice versa.

lead to increasing oxide connection and total ESR, but we arestill waiting for demonstrations of this.

From (4), one can also calculate the total capacitance as,

CSuperC =50 A × 60 s28 V − 18 V

= 300 F. (13)

This value is closed to the theoretical value of 292 F. More-over, one may investigate that during a constant dischargingcurrent, the supercapacitor voltage waveform is virtually linear;then the reduced order model presented in Fig. 4 is sufficient forthe supercapacitor impedance model with a small leakage cur-rent. From (9) to (11), if we know the constant discharging powerprofile of the system, we can now estimate energy losses in ESRand the useful energy provided to the dc bus. Unquestionably,from these tests, the fast response of the supercapacitor power



Fig. 13. Hybrid source response during motor drive cycle.



source can be operated with the FC main generator in order toimprove the slow dynamics of the FC system.

C. Performances of Fuel Cell/Supercapacitor Hybrid Source

The experimental tests shown later were carried out by con-necting the dc link to an active load composed of a two-quadrantconverter, loaded by a dc motor coupled with a dc generator.Fig. 13 presents waveforms obtained during the motor drivecycle: the dc bus and FC voltages; FC, supercapacitor, andload (motor) powers; motor speed; FC and supercapacitor cur-rents; and supercapacitor state-of-charge (voltage). The initialstate is no-load power and the storage device full-of-charge,VSuperC = 25 V; as a result, zero for both the FC and superca-pacitor currents. At t = 10 s, the motor speed accelerates to thefinal speed of 1000 r/min; synchronously the final FC currentincreases with a limited slope of 4 A/s to a rated current of 40 A.Thus, the supercapacitor, which supplies most of the power re-quired during motor acceleration, remains in a discharge stateafter the motor start. The final supercapacitor current is 8 Abecause the steady-state load power (approximately 0.6 kW) isgreater than the FC rated power (0.5 kW), and the peak loadpower is about 1 kW, which is about two times that of the FCrated power.

After that, at t = 40 s, the motor speed decelerates to stopwith a peak load power of about −0.5 kW. The supercapac-itor is deeply charged, demonstrating three phases. First, thesupercapacitor recovers the energy supplied to the dc bus bythe FC (0.5 kW) and the motor. Second, the supercapacitor ischarged only by the FC. Third, the supercapacitor is nearly full-of-charge, then reducing the charging current. After that, boththe FC and supercapacitor currents reduce to zero when VSuperCreaches VC Nom of 25 V. Fortunately, only small perturbationson the dc bus voltage waveform can be seen, which is of majorimportance in using supercapacitors to improve the dynamicperformance of the whole system.

VI. CONCLUSION

The main objective of this paper is to present the supercapac-itor characteristics for energy storage applications, particularlyfor future FC power generations. The slow dynamics of an FCgenerator can be ameliorated by using a very fast power re-sponse and the high specific power of the supercapacitor source.During motor starts/stops or other significant steps in load, thesupercapacitor provides the balance of energy needed duringthe momentary load transition period, and also, absorbs excessenergy from regenerative braking.

Experimental results (with small-scale devices of a superca-pacitor bank and a PEMFC) authenticate the excellent perfor-mance of the whole system during a motor drive cycle.

ACKNOWLEDGMENT

The authors would like to thank Dr. I. Sadli for operating theFC system during experimentations.

REFERENCES

[1] S. M. Lukic, J. Cao, R. C. Bansal, F. Rodriguez, and A. Emadi, “Energystorage systems for automotive applications,” IEEE Trans. Ind. Electron.,vol. 55, no. 6, pp. 2258–2267, Jun. 2008.

[2] A. Kusko and J. Dedad, “Stored energy—Short-term and long-term energystorage methods,” IEEE Ind. Appl. Mag., vol. 13, no. 4, pp. 66–72,Jul./Aug. 2007.

[3] P. Thounthong, B. Davat, and S. Rael, “Drive friendly: Fuelcell/supercapacitor hybrid power source for future automotive power gen-eration,” IEEE Power Energy, vol. 6, no. 1, pp. 69–76, Jan./Feb. 2008.

[4] P. Corbo, F. Migliardini, and O. Veneri, “An experimental study of aPEM fuel cell power train for urban bus application,” J. Power Sources,vol. 181, pp. 363–370, Jul. 2008.

[5] K. Rajashekara, J. Grieve, and D. Daggett, “Hybrid fuel cell power inaircraft,” IEEE Ind. Appl. Mag., vol. 14, no. 4, pp. 54–60, Jul./Aug. 2008.

[6] S. Jemeı, D. Hissel, M. C. Pera, and J. M. Kauffmann, “A new modelingapproach of embedded fuel-cell power generators based on artificial neuralnetwork,” IEEE Trans. Ind. Electron., vol. 55, no. 1, pp. 437–447, Jan.2008.

[7] P. C. Buddingh, V. Scaini, and L. F. Casey, “Utilizing waste hydrogenfor energy recovery using fuel cells and associated technologies,” IEEETrans. Ind. Appl., vol. 42, no. 1, pp. 186–194, Jan./Feb. 2006.

[8] M. D. Lukas, K. Y. Lee, and H. Ghezel-Avagh, “Development of a stacksimulation model for control study on direct reforming molten carbonatefuel cell power plant,” IEEE Trans. Energy Convers., vol. 14, no. 4,pp. 1651–1657, Dec. 1999.

[9] P. Thounthong, S. Rael, and B. Davat, “Control strategy of fuelcell/supercapacitors hybrid power sources for electric vehicle,” J. PowerSources, vol. 158, pp. 806–814, Jul. 2006.

[10] M. Uzunoglu and M. S. Alam, “Modeling and analysis of an FC/UChybrid vehicular power system using a novel-wavelet-based load sharingalgorithm,” IEEE Trans. Energy Convers., vol. 23, no. 1, pp. 263–272,Mar. 2008.

[11] P. Thounthong, S. Rael, and B. Davat, “Control algorithm of fuel celland batteries for distributed generation system,” IEEE Trans. EnergyConvers., vol. 23, no. 1, pp. 148–155, Mar. 2008.

[12] M. Kim, Y. J. Sohn, W. Y. Lee, and C. S. Kim, “Fuzzy control basedengine sizing optimization for a fuel cell/battery hybrid mini-bus,” J.Power Sources, vol. 178, pp. 706–710, Apr. 2008.

[13] A. Taniguchi, T. Akita, K. Yasuda, and Y. Miyazaki, “Analysis of elec-trocatalyst degradation in PEMFC caused by cell reversal during fuelstarvation,” J. Power Sources, vol. 130, pp. 42–49, May 2004.

[14] P. Thounthong, S. Rael, and B. Davat, “Test of a PEM fuel cell with lowvoltage static converter,” J. Power Sources, vol. 153, pp. 145–150, Jan.2006.

[15] J. M. Rosolen, E. Y. Matsubara, M. S. Marchesin, S. M. Lala, L. A. Mon-toro, and S. Tronto, “Carbon nanotube/felt composite electrodes withoutpolymer binders,” J. Power Sources, vol. 162, pp. 620–628, Nov. 2006.

[16] K. Liu, Z. Hu, R. Xue, J. Zhang, and J. Zhu, “Electropolymerizationof high stable poly(3,4-ethylenedioxythiophene) in ionic liquids and itspotential applications in electrochemical capacitor,” J. Power Sources,vol. 179, pp. 858–862, May 2008.

[17] R. M. Nelms, D. R. Cahela, and B. J. Tatarchuk, “Modeling double-layercapacitor behavior using ladder circuits,” IEEE Trans. Aerosp. Electron.Syst., vol. 39, no. 2, pp. 430–438, Apr. 2003.

[18] S. Y. Choe, J. W. Ahn, J. G. Lee, and S. H. Baek, “Dynamic simulatorfor a PEM fuel cell system with a PWM dc/dc converter,” IEEE Trans.Energy Convers., vol. 23, no. 2, pp. 669–680, Jun. 2008.

[19] F. C. Wang, H. T. Chen, Y. P. Yang, and J. Y. Yen, “Multivariable robustcontrol of a proton exchange membrane fuel cell system,” J. PowerSources, vol. 177, pp. 393–403, Mar. 2008.

[20] I. Sadli, P. Thounthong, J. P. Martin, S. Rael, and B. Davat, “Behaviourof a PEMFC supplying a low voltage static converter,” J. Power Sources,vol. 156, pp. 119–125, May 2006.

[21] J. M. Correa, F. A. Farret, V.A Popov, and M. G. Simoes, “Sensitivityanalysis of the modeling parameters used in simulation of proton exchangemembrane fuel cells,” IEEE Trans. Energy Convers., vol. 20, no. 1,pp. 211–218, Mar. 2005.

[22] P. Thounthong, S. Rael, and B. Davat, “Control strategy of fuel cell and su-percapacitors association for distributed generation system,” IEEE Trans.Ind. Electron., vol. 54, no. 6, pp. 3225–3233, Dec. 2007.

[23] P. Corbo, F. E. Corcione, F. Migliardini, and O. Veneri, “Experimentalassessment of energy-management strategies in fuel-cell propulsion sys-tems,” J. Power Sources, vol. 157, pp. 799–808, Jul. 2006.



[24] J. R. Miller and D. A. Evans, “Performance characteristics of high relia-bility double layer capacitor components,” in Proc. 35th IEEE Int. PowerSources Symp., Cherry Hill, NJ, Jan. 22–25, 1992, pp. 302–305.

[25] W. Mitchell, B. J. Bowers, C. Garnier, and F. Boudjemaa, “Dynamicbehavior of gasoline fuel cell electric vehicles,” J. Power Sources, vol. 154,pp. 489–496, Mar. 2006.

[26] A. Khaligh, “Realization of parasitics in stability of dc–dc convertersloaded by constant power loads in advanced multiconverter automotivesystems,” IEEE Trans. Ind. Electron., vol. 55, no. 6, pp. 2295–2305, Jun.2008.

[27] O. Wasynczuk, S. D. Sudhoff, T. D. Tran, D. H. Clayton, and H. J. Hegner,“A voltage control strategy for current-regulated PWM inverters,” IEEETrans. Power Electron., vol. 11, no. 1, pp. 7–15, Jan. 1996.

[28] B. Fahimi, A. Emadi, and R. B. Sepe, Jr., “Switched reluctance machine-based starter/alternator for more electric cars,” IEEE Trans. Energy Con-vers., vol. 19, no. 1, pp. 116–124, Mar. 2004.

[29] J. Garnier, A. De Bernardinis, M. C. Peera, D. Hissel, D. Candusso, J.M. Kauffmann, and G. Coquery, “Study of a PEFC power generator mod-ular architecture based on a multi-stack association,” J. Power Sources,vol. 156, pp. 108–113, May 2006.

[30] A. Emadi, Y. J. Lee, and K. Rajashekara, “Power electronics and motordrives in electric, hybrid electric, and plug-in hybrid electric vehicles,”IEEE Trans. Ind. Electron., vol. 55, no. 6, pp. 2237–2245, Jun. 2008.

[31] T. A. Keim, “Systems for 42 V mass-market automobiles,” J. PowerSources, vol. 127, pp. 16–26, Mar. 2004.

Phatiphat Thounthong (M’09) received the B.S.and M.E. degrees from King Mongkut’s Institute ofTechnology North Bangkok (KMITNB), Bangkok,Thailand, in 1996 and 2001, respectively, and thePh.D. degree from the Institut National Polytech-nique de Lorraine (INPL), Nancy-Lorraine, France,in 2005, all in electrical engineering.

From 1997 to 1998, he was an Electrical Engi-neer with E.R. Metal Works, Ltd. (EKARAT Group),Thailand. From 1998 to 2002, he was an AssistantLecturer at KMITNB, where he is currently an Assis-

tant Professor. His current research interests include power electronics, electricdrives, and electrical devices (fuel cell, batteries, and supercapacitor).

Stephane Rael received the M.E. degree in electri-cal engineering from the Ecole Nationale Superieuredes Ingenieurs Electriciens de Grenoble (ENSIEG),Grenoble, France, in 1992, and the Ph.D. degree inelectrical engineering from the Institut National Poly-technique de Grenoble (INPG), Grenoble, in 1996.

Since 1998, he has been with the Institut Na-tional Polytechnique de Lorraine, Nancy, France,where he was earlier an Assistant Professor, and cur-rently, a Professor. His current research interests in-clude power electronic components, supercapacitors,

batteries, and fuel cells.

Bernard Davat (M’89) received the Engineer degreefrom Ecole Nationale Superieure d’Electrotechnique,d’Electronique, d’Informatique, d’Hydraulique etdes Telecommunications (ENSEEIHT), Toulouse,France, in 1975, and the Ph.D. and Docteur d’Etatdegrees in elecrical engineering from the Institut Na-tional Polytechnique de Toulouse (INPT), Toulouse,in 1978 and 1984, respectively.

From 1980 to 1988, he was a Researcher at FrenchNational Center for Scientific Research (CNRS),Laboratoire d’Electrotechnique et d’Electronique In-

dustrielle (LEEI). Since 1988, he has been a Professor at the Institut Na-tional Polytechnique de Lorraine, Nancy, France. His current research inter-ests include power electronics, drives, and new electrical devices (fuel cell andsupercapacitor).


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2009_IEEE-Analysis of Supercapacitor as Second Source Based on Fuel Cell Power Generation