Power Management of a Stand-Alone Wind/Photovoltaic/Fuel Cell Energy System

IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 23, NO. 3, SEPTEMBER 2008 957

Power Management of a Stand-AloneWind/Photovoltaic/Fuel Cell Energy System

Caisheng Wang, Senior Member, IEEE, and M. Hashem Nehrir, Senior Member, IEEE

Abstract—This paper proposes an ac-linked hybrid wind/photovoltaic (PV)/fuel cell (FC) alternative energy system forstand-alone applications. Wind and PV are the primary powersources of the system, and an FC–electrolyzer combination is usedas a backup and a long-term storage system. An overall powermanagement strategy is designed for the proposed system to man-age power flows among the different energy sources and the storageunit in the system. A simulation model for the hybrid energy systemhas been developed using MATLAB/Simulink. The system perfor-mance under different scenarios has been verified by carrying outsimulation studies using a practical load demand profile and realweather data.

Index Terms—Alternative energy, electrolyzer, fuel cell (FC),hybrid, photovoltaic (PV), power management, stand-alone, wind.

I. INTRODUCTION

THE EVER increasing energy consumption, the soaringcost and the exhaustible nature of fossil fuel, and the

worsening global environment have created increased interest ingreen [renewable and/or fuel celll (FC)-based energy sources]power generation systems. Wind and solar power generation aretwo of the most promising renewable power generation tech-nologies. The growth of wind and photovoltaic (PV) powergeneration systems has exceeded the most optimistic estima-tion [1]–[3]. FCs also show great potential to be green powersources of the future because of many merits they have (suchas high efficiency, zero or low emission of pollutant gases, andflexible modular structure) and the rapid progress in FC tech-nologies. However, each of the aforementioned technologieshas its own drawbacks. For instance, wind and solar power arehighly dependent on climate while FCs need hydrogen-rich fuel.Nevertheless, because different alternative energy sources cancomplement each other to some extent, multisource hybrid alter-native energy systems (with proper control) have great potentialto provide higher quality and more reliable power to customersthan a system based on a single resource. Because of this fea-ture, hybrid energy systems have caught worldwide researchattention [4]–[28].

Manuscript received August 14, 2006; revised December 27, 2006. This workwas supported in part by the National Science Foundation (NSF) Grant ECS-0135229 and in part by the HiTEC fuel cell project at Montana State University,funded by the United States Department of Energy, as a subcontract from Bat-telle Memorial Institute and Pacific Northwest National Laboratory (PNNL)under Award DE-AC06-76RL01830. Paper No. TEC-00399-2006.

C. Wang is with the Division of Engineering Technology, Wayne State Uni-versity, Detroit, MI 48202 USA (e-mail: [email protected]).

M. H. Nehrir is with the Electrical and Computer Engineering Department,Montana State University, Bozeman, MT 59717 USA (e-mail: [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.2007.914200

Many alternative energy sources including wind, PV, FC,diesel system, gas turbine, and microturbine can be used tobuild a hybrid energy system [4]–[28]. Nevertheless, the majorrenewable energy sources used and reported are wind and PVpower [4]–[28]. Due to the intermittent nature of wind andsolar energy, stand-alone wind and PV energy systems normallyrequire energy storage devices or some other generation sourcesto form a hybrid system. The storage device can be a batterybank, supercapacitor bank, superconducting magnetic energystorage (SMES), or an FC–electrolyzer system.

In this paper, a stand-alone hybrid alternative energy systemconsisting of wind, PV, FC, electrolyzer, and battery is proposed.Wind and PV are the primary power sources of the system totake full advantage of renewable energy, and the FC–electrolyzercombination is used as a backup and a long-term storage system.A battery bank is also used in the system for short-time backupto supply transient power. The different energy/storage sourcesin the proposed system are integrated through an ac link bus.The details of the system configuration, system unit-sizing, andthe characteristics of the major system components are alsodiscussed in the paper. An overall power management strategy isdesigned for the system to coordinate the power flows among thedifferent energy sources. Simulation studies have been carriedout to verify the system performance under different scenariosusing practical load profile and real weather data.

The paper is organized as follows. The system configurationand system unit-sizing are discussed in Section II. The systemcomponent characteristics are given in Section III. Section IVdiscusses the overall power management strategy for the system.Section V gives the simulation results. Section VI concludes thepaper.

II. SYSTEM CONFIGURATION AND UNIT-SIZING

A. System Configuration

Fig. 1 shows the system configuration for the proposed hy-brid alternative energy system. In the system, the renewablewind and PV power are taken as the primary source while theFC–electrolyzer combination is used as a backup and storagesystem. This system can be considered as a complete “green”power generation system because the main energy sources andstorage system are all environmentally friendly. When there isexcess wind and/or solar generation available, the electrolyzerturns on to begin producing hydrogen, which is delivered to thehydrogen storage tanks. If the H2 storage tanks become full,the excess power will be diverted to the dump load shown inFig. 1. When there is a deficit in power generation, the FC stackwill begin to produce energy using hydrogen from the reservoir

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958 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 23, NO. 3, SEPTEMBER 2008

Fig. 1. System configuration of the proposed multisource alternative hybridenergy system (coupling inductors are not shown).

tanks, or in case they are empty, from the backup H2 tanks. Abattery bank is also used in the system to supply transient powerto load transients, ripples, and spikes. There are several ways tointegrate different alternative energy sources to form a hybridsystem. Each method has its own advantages and disadvantages.In this paper, a 60 Hz ac link is used due to its high reliability,modular and scalable structure, and readiness for grid connec-tion [25], [27]. Different energy sources are connected to the acbus through appropriate power electronic interfacing circuits.The system can be easily expended, i.e., other energy sourcescan be integrated into the system when they are available, asshown in Fig. 1. The main system unit-sizing is discussed in thefollowing section.

B. System Unit-Sizing

The unit-sizing procedure discussed in this section is assumedfor a stand-alone hybrid system with the proposed structure(Fig. 1) for residential electricity supply in the southwesternpart of Montana. The purpose of the study is to properly size thesystem components to assure reliable electricity supply. Hence,the system’s economic aspect is not considered in the paper.Some details on the economics of similar wind/PV/FC systemsare given in another paper by the authors [5].

Fig. 2. Hourly average demand of five typical homes in the Pacific Northwestarea.

The hybrid system is designed to supply power to five homes.A typical hourly average residential load demand for a home inthe Pacific Northwest regions, reported in [29], is used in thissimulation study. The total hourly average load demand of thefive homes is shown in Fig. 2. A 50 kW wind turbine is assumedto be available for the hybrid system. The following unit-sizingprocedure is used to determine the size of the PV array, FCstack, electrolyzer, and the battery.

Before the discussion of unit-sizing, the following concept isapplied for indicating the overall efficiency and the availabilityof a renewable energy source.

Capacity factor (kcf ) of a renewable energy source is definedas

kcf =P

Prated(1)

where P is the actual average output power over a period oftime and Prated is the nominal power rating of the renewableenergy source.

For the wind and solar data reported in [5] and [20], the capac-ity factor of the wind turbine (kcf wtg ) and the PV array (kcf PV )used in the proposed hybrid system for the southwestern part ofMontana are taken as 13% and 10%, respectively.

The purpose of unit-sizing is to minimize the difference be-tween the generated power (Pgen ) from the renewable energysource and the demand (Pdem ) over a period of time T . T istaken as one year in this study:

∆P = Pgen − Pdem

= kcf wtg × Pwtg ,rated + kcf PV × PPV ,rated − Pdem

(2)

where Pwtg ,rated is the power rating of the wind turbine gener-ator and PPV ,rated is the power rating of the PV array.

To balance the generation and demand, the rated power forthe PV array is

PPV ,rated =Pdem − kcf wtg × Pwtg ,rated

kcf PV. (3)

From Fig. 2, the average load demand is 9.76 kW. Then,according to (3), the size of the PV array is calculated to be32.6 kW.


WANG AND NEHRIR: POWER MANAGEMENT OF A STAND-ALONE WIND/PHOTOVOLTAIC/FUEL CELL ENERGY SYSTEM 959

TABLE ISYSTEM COMPONENT PARAMETERS

The FC–electrolyzer combination provides backup for thesystem. The FC needs to supply the peak load demand (Fig. 2)when there is no wind and solar power. Therefore, the size ofthe FC stack is 14.6 kW. To leave some safe margin (20% usedin this paper), an 18 kW FC array is used.

The electrolyzer should be able to handle the excess powerfrom the wind and solar power source. The maximum possibleexcess power is

Pgen, max − Pdem ,min = 50 + 32.6 − 5.85 = 76.75 kW. (4)

However, the possibility that both wind and solar power reachtheir maximum points while the load demand is at its lowestvalue is very small. According to the data reported in [26], theexcess available power normally is less than half of the maxi-mum possible value. And the electrolyzer is also very expensive.Therefore, a 50 kW electrolyzer [over 60% of the maximumavailable given in (4)] is used in this paper.

Fig. 3. Cp –λ characteristics of the WECS at different pitch angles (θ).

Battery capacity can be determined based on the transientpower at the load site. In this study, a 10 kWh battery bankis used. In single-phase systems, a larger size battery may beneeded for reactive power compensation purposes. In three-phase systems, as discussed in this paper, reactive power com-pensation can be achieved by proper control of power electronicswitching devices [39], and only a small size battery is neededfor this purpose [40].

The details of the system component parameters are listed inTable I.

III. SYSTEM COMPONENT CHARACTERISTICS

To develop an overall power management strategy for the sys-tem and to investigate the system performance, dynamic modelsfor the main components in the proposed hybrid system havebeen developed using MATLAB/Simulink [27]. The models arefor the following: wind energy conversion system (WECS), PV,FC, and electrolyzer.

In this section, the characteristics of the aforementioned mainsystem components are discussed. For the details of model de-velopment, the reader is referred to [27].

A. Wind Energy Conversion System

The power Pwind (in watts) extracted from wind is

Pwind =12ρAv3Cp(λ, θ) (5)

where ρ is the air density in kilogram per cubic meter, A is thearea swept by the rotor blades in square meter, and v is the windvelocity in meters per second. Cp is called the power coefficientor the rotor efficiency and is a function of tip speed ratio (TSRor λ) and pitch angle (θ) [30], [31].

A variable-speed pitch-regulated wind turbine is consideredin this paper, where the pitch angle controller plays an importantrole. Fig. 3 shows the groups of Cp– λ curves of the wind turbineused in this study at different pitch angles [31]. It is noted fromthe figure that the value of Cp can be changed by changing thepitch angle (θ). In other words, the output power of the windturbine can be regulated by pitch angle control.

A self-excited induction generator (SEIG) model [27], [37],[38] was developed and used as a part of the WECS model. Theratings of the SEIG are given in Table I.



Fig. 4. Wind turbine output power characteristic.

Fig. 4 shows the output power of the WECS vs. wind speed.It can be observed that the output power is kept constant whenwind speed is higher than the rated wind velocity even thoughthe wind turbine has the potential to produce more power. Thisis done through the pitch angle control to protect the electricalsystem and to prevent over speeding of the rotor. When windspeed is higher than the cutout speed (25 m/s), the system istaken out of operation for protection of its components.

B. Photovoltaic

PV effect is a basic physical process through which solarenergy is converted directly into electrical energy. The physicsof a PV cell, or a solar cell, is similar to the classical p-n junctiondiode [32]. The relationship between the output voltage V andthe load current I of a PV cell or a module can be expressedas [15], [32]

I = IL − I0

[exp

(V + IRs

α

)− 1

](6)

where IL is the light current of the PV cell (in amperes), I0 isthe saturation current, I is the load current, V is the PV outputvoltage (in volts), Rs is the series resistance of the PV cell (inohms), and α is the thermal voltage timing completion factor ofthe cell (in volts).

The I–V characteristic curves of the PV model used in thisstudy under different irradiances (at 25 ◦C) are given in Fig. 5[27]. It is noted from the figure that the higher the irradiance,the larger are the short-circuit current (Isc) and the open-circuitvoltage (Voc). As a result, the larger will be the output PV power.

Temperature plays an important role in the PV performancebecause the four parameters (IL , I0 , Rs , and α) in (6) are allfunctions of temperature. The effect of the temperature on thePV model performance is illustrated in Fig. 6. It is noted from thefigure that the lower the temperature, the higher is the maximumpower and the larger the open circuit voltage.

C. Fuel Cell

Two types of FCs have been modeled for this study. Theyare low-temperature proton-exchange membrane FC (PEMFC)[33] and high-temperature solid oxide FC (SOFC) [34]. Both of

Fig. 5. I–V characteristic curves of the PV model at different irradiances.

Fig. 6. P–V characteristic curves of the PV model at different operating tem-peratures.

them show great potential in hybrid energy system applications.For the purpose of simplicity, only the PEMFC application isdiscussed in this paper.

The PEMFC model is based on the validated dynamic modelfor a PEMFC stack reported in [33]. It is an autonomous modeloperated under constant channel pressure with no control onthe input fuel flow into the FC. The model was validated byexperimental data measured from an Avista Labs (ReliOn now)SR-12 500 W PEMFC stack. The FC will adjust the input fuelflow according to its load current to keep the channel pressureconstant. Fig. 7 shows the output voltage vs. load current (V–I)characteristic curve of the 500 W PEMFC model comparedwith the experimental data [33]. This characteristic curve canbe divided into three regions. The voltage drop across the FCassociated with low currents is due to the activation loss insidethe FC; the voltage drop in the middle of the curve (which isapproximately linear) is due to the ohmic loss in the FC stack;and as a result of the concentration loss, the output voltage at theend of the curve will drop sharply as the load current increases.



Fig. 7. PEMFC V–I characteristic: comparison of model response with exper-imental data.

D. Electrolyzer

An electrolyzer is a device that produces hydrogen and oxy-gen from water. Water electrolysis can be considered a reverseprocess of a hydrogen-fueled FC. In contrast to the electro-chemical reaction occurring in an FC to produce dc electricity,an electrolyzer converts dc electrical energy into chemical en-ergy stored in hydrogen. From electrical circuit point of view, anelectrolyzer can be considered as a voltage-sensitive nonlineardc load [15]. For a given electrolyzer, within its rating range, thehigher the dc voltage applied, the larger is the load current. Thatis, by applying a higher dc voltage, more H2 can be generated.Of course, more electrical power is consumed at the same time.The model of an electrolyzer stack developed for this study isbased on the empirical I–V equation reported in [15] and [26],described as

Velec,cell = Vrev +r1 + r2T

AI

+ kelec ln(

kT 1 + kT 2/T + kT 3/T 2

AI + 1

)(7)

where Velec,cell is the cell terminal voltage (in volts), Vrev isthe reversible cell voltage, r1 (in ohms square-meter) and r2 (inohms square-meter per degree Celsius) are the parameters for theohmic resistance inside the electrolyzer, kelec (in volts), kT 1 (insquare meters per ampere), kT 2 (square-meter degrees Celsiusper ampere), and kT 3 (square-meter degree Celsius square perampere) are the parameters for the overvoltage, A is the area ofthe cell electrode (in square-meters), I is the electrolyzer current(in amperes), and T is the cell temperature (in degrees Celsius).

The V–I characteristics of the electrolyzer model used in thisstudy at different cell temperatures are given in Fig. 8. At agiven current, the higher the operating temperature, the lower isthe terminal voltage needed.

Fig. 8. V–I characteristics of the electrolyzer model under different tempera-tures.

IV. OVERALL POWER MANAGEMENT STRATEGY

An overall control strategy for power management among dif-ferent energy sources in a multisource energy system is needed.Fig. 9 shows the block diagram of the overall control strategyfor the proposed hybrid alternative energy system. The WECS,controlled by a pitch angle controller, and a PV electricity gen-eration unit, controlled by a maximum power point tracking(MPPT) controller (not discussed in this paper) [27], are themain energy sources of the system. The power difference be-tween the generation sources and the load demand is calculatedas

Pnet = Pwind + PPV − Pload − Psc (8)

where Pwind is the power generated by the WECS, PPV is thepower generated by the PV energy conversion system, Ploadis the load demand, and Psc is the self-consumed power foroperating the system. The system self-consumed power is thepower consumed by the auxiliary system components to keepit running, for example, the power needed for running the cool-ing systems, the control units, and the gas compressor. For thepurpose of simplification, only the power consumed by the com-pressor (Pcomp ) is considered in this study.

The governing control strategy is that, at any given time, anyexcess wind and PV-generated power (Pnet > 0) is supplied tothe electrolyzer to generate hydrogen that is delivered to thehydrogen storage tanks through a gas compressor. Therefore,the power balance equation given in (8) can be written as

Pwind + PPV = Pload + Pelec + Pcomp , Pnet > 0 (9)

where Pelec is the power consumed by the electrolyzer to gener-ate H2 and Pcomp is the power consumed by the gas compressor.

When there is a deficit in power generation (Pnet < 0), theFC stack begins to produce energy for the load using hydrogenfrom the storage tanks. Therefore, the power balance equationfor this situation can be written as

Pwind + PPV + PFC = Pload , Pnet < 0 (10)

where PFC is the power generated by the FC stack.



Fig. 9. Block diagram of the overall control scheme for the proposed hybrid alternative energy system.

Dynamic models have been used for all the components ofthe system shown in Fig. 9. The details of these models can befound in [27].

V. SIMULATION RESULTS

Using the component models discussed in Section IV, asimulation system test bed for the proposed wind/PV/FC–electrolyzer energy system has been developed usingMATLAB/Simulink. In order to verify the system performanceunder different situations, simulation studies have been carriedout using practical load demand data and real weather data(wind speed, solar irradiance, and air temperature). As dis-cussed in Section II, the system is designed to supply electricpower demand of five houses in the southwestern part ofMontana. A typical hourly average load demand for a house inthe Pacific Northwest regions, reported in [29], is used in thissimulation study. The total hourly average load demand profileof five houses over 24 h is shown in Fig. 2. The weather data areobtained from the online records of the weather station at DeerLodge, Montana, affiliated with the Pacific Northwest Coopera-tive Agricultural Weather Network (AgriMet) [35]. Simulationstudies are carried out for power management during a typicalwinter day and a summer day. The load demand is kept thesame for the two cases. Simulation results for the winter andsummer scenarios are given and discussed in the followingsection.

A. Winter Scenario

1) Weather Data: The weather data for the winter scenariosimulation were collected on February 1, 2006. The wind speeddata were collected at the height of 2 m, corrected to the turbinehub height (assumed to be 40 m) using the following expression[20], [36]:

Ws1 = Ws0

(H1

H0

)α

(11)

where Ws1 (in meters per second) is the wind speed at the hubheight H1 (in meters), Ws0 (in meters per second) is the windspeed at the height H0 (in meters), and α is the wind speedcorrection exponent. The exponent α is taken as 0.13 in thisstudy, as suggested and used in [20] and [36].

Fig. 10 shows the corrected hourly wind speed profile over24 h on the day (February 1, 2006) the data were collected. Thehourly solar irradiance data and air temperature collected on thesame day are shown in Figs. 11 and 12, respectively.

2) Simulation Results: The system performance under theload profile given in Fig. 2 and the weather data shown inFigs. 10–12 is evaluated and discussed later.

The output power from the wind energy conversion unit in thehybrid energy system over the 24 h simulation period is shownin Fig. 13. When the wind speed is over 14 m/s, the output poweris limited to 50 kW by the pitch angle controller (discussed inSection III). When the wind speed is less than the wind turbinecutin speed (3 m/s), there is no wind power generated.



Fig. 10. Wind speed data for the winter scenario simulation study.

Fig. 11. Solar irradiance data for the winter scenario simulation study.

Fig. 12. Air temperature data for the winter scenario simulation study.

The output power from the PV array in the system over the24 h simulation period is shown in Fig. 14. As shown in Fig. 9,the PV array output power is controlled by an MPPT controllerto give maximum power output under different solar irradiances.It is noted that the PV output power curve, shown in Fig. 14,

Fig. 13. Wind power for the winter scenario study.

Fig. 14. PV power for the winter scenario.

has a wave shape similar to that of the solar irradiance profileshown in Fig. 11.

As discussed in Section III (Fig. 6), temperature plays an im-portant role in the PV module’s performance. Fig. 15 shows thePV temperature response over the simulation period. Two mainfactors for determining the temperature of the PV module are thesolar irradiance (Fig. 11) and the surrounding air temperature(Fig. 12). It is noted from Fig. 6 that the higher the temperature,the lower is the maximum power value. Figs. 14 and 15 alsoshow the effect of temperature upon the PV performance.

When Pnet> 0 [see (8) and (9)], there is excess power avail-able for H2 generation. Fig. 16 shows the available power profileover the 24 h simulation period. The available power is used bythe electrolyzer to generate H2 . Fig. 17 shows the H2 gener-ation rate over the simulation period. The corresponding dcvoltage applied to the electrolyzer and the electrolyzer currentare shown in Fig. 18. It is noted from Figs. 16–18 that the morepower available for storage, the higher is the dc input voltage tothe electrolyzer, and as a result, the more is the generated H2 .

When Pnet < 0, the sum of wind and PV-generated power isnot sufficient to supply the load demand. Under this condition,



Fig. 15. PV temperature response over the simulation period for the winterscenario.

Fig. 16. Power available for H2 generation of the winter scenario.

Fig. 17. H2 generation rate for the winter scenario study.

the FC turns on to supply the power shortage. Fig. 19 shows theactual power delivered by the FC stack.

B. Summer Scenario

1) Weather Data: The weather data collected in Dear Lodge,MT, on June 21, 2005, are used for the summer scenario study[35]. The wind speed data, corrected to the height of 40 m, isshown in Fig. 20. The solar irradiance and air temperature dataat the same site on the same day are shown in Figs. 21 and 22,respectively.

Fig. 18. Electrolyzer voltage and current for the winter scenario study.

Fig. 19. Power supplied by the FC stack of the winter scenario study.

Fig. 20. Corrected wind speed data for the summer scenario simulation study.

By comparing the winter solar irradiance data shown inFig. 11 and the summer solar irradiance data given in Fig. 21,it is obvious that the daily time frame when solar energy isavailable is wider in the summer than in the winter.

2) Simulation Results: In this section, the system perfor-mance under the same load demand profile given in Fig. 2 andthe weather data shown in Figs. 20–22 is evaluated. The outputpower from the WECS and the PV array in the hybrid energysystem over the 24 h simulation period are shown in Figs. 23 and24, respectively. The spikes in Fig. 24 are due to the MPPT con-trol, which tries to keep the PV array operating at its maximum



Fig. 21. Irradiance data for the summer scenario simulation study.

Fig. 22. Air temperature data for the summer scenario simulation study.

Fig. 23. Wind power generated for the summer scenario study.

power points under different temperatures and solar irradiances.The time range of the spike is small (about 1 s).

When Pnet > 0, there is excess power available for H2 gen-eration. Fig. 25 shows the H2 generation rate over the simu-lation period. When Pnet < 0, the sum of the wind and thePV-generated power is not sufficient to supply the load demand.Under this scenario, the FC stack turns on to supply the powershortage by using the H2 stored in the storage tank. Fig. 26shows the corresponding H2 consumption rate.

Fig. 24. PV power generated for the summer scenario study.

Fig. 25. H2 generation rate for the summer scenario study.

Fig. 26. H2 consumption rate for the summer scenario study.

The H2 storage tank pressure varies as H2 flows in and out. Itis apparent that the storage tank pressure will go up when thereis excess power available for H2 generation and will decreasewhen the FC stack turns on (consuming H2) to supply powerto the load. Fig. 27 shows the tank pressure variations over the24 h simulation period for the summer scenario study.



Fig. 27. Tank pressure over the 24 h for the summer scenario study.

VI. CONCLUSION

In this paper, an ac-linked stand-alone wind/PV/FC alterna-tive energy system is proposed. The system configuration andunit-sizing are discussed; the characteristics of the main compo-nents in the system, namely, the WECS, PV, FC, and electrolyzerare given; and the overall control and power management strat-egy for the proposed hybrid energy system is presented. Thewind and PV generation systems are the main power genera-tion devices, and the electrolyzer acts as a dump load using anyexcess power available to produce H2 . The FC system is thebackup generation and supplies power to the system when thereis power deficit. The simulation model of the hybrid system hasbeen developed using MATLAB/Simulink. Simulation studieshave been carried out to verify the system performance underdifferent scenarios using the practical load profile in the PacificNorthwest regions and the real weather data collected at DeerLodge, MT. The simulation results, given for a winter and asummer scenario, show the effectiveness of the overall powermanagement strategy and the feasibility of the proposed hybridalternative energy system.

ACKNOWLEDGMENT

The authors thank Dr. D. Pierre at Montana State Universityfor his comments and suggestions.

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Caisheng Wang (M’02–SM’08) received the B.S.and M.S. degrees from Chongqing University,Chongqing, China, in 1994 and 1997, respec-tively, and the Ph.D. degree from Montana StateUniversity, Bozeman, in 2006, all in electricalengineering.

From August 1997 to May 2002, he was an Elec-trical Engineer at Zhejiang Electric Power Test andResearch Institute, Hangzhou, China. Since August2006, he has been a faulty member in the Divisionof Engineering Technology, Wayne State University,

Detroit, MI. His current research interests include modeling and control of powersystems and electrical machinery, alternative/hybrid energy power generationsystems, and fault diagnosis and online monitoring of electric machines.

M. Hashem Nehrir (S’68–M’71–SM’89) receivedthe B.S., M.S., and Ph.D. degrees from OregonState University, Corvallis, in 1969, 1971, and 1978,respectively, all in electrical engineering.

Since 1987, he has been with the Electrical andComputer Engineering Department, Montana StateUniversity, Bozeman, where he is currently a Pro-fessor. His current research interests include controland modeling of power systems, alternative energypower generation systems, and application of intelli-gent controls to power systems. He is the author of

two textbooks and an author or coauthor of numerous technical papers.


Documents

Power Management of a Stand-Alone Wind/Photovoltaic/Fuel Cell Energy System