Hybrid Wind-Fuel Cell Renewable Energy Utilization Scheme for Village Electricity

8/9/2019 Hybrid Wind-Fuel Cell Renewable Energy Utilization Scheme for Village Electricity

1/6

Proceedings of the 14thInternational Middle East Power Systems Conference (MEPCON10), Cairo University, Egypt, December 19-21, 2010, Paper ID 132.

138

Hybrid Wind-Fuel Cell Renewable Energy UtilizationScheme for Village Electricity

Mohamed A. H. El-Sayed*

Electrical Engineering Department, Kuwait University

[email protected] * on leave from Cairo University

Adel M. Sharaf, Senior Member IEEE

Centre for Energy Studies, University of Trinidad and Tobago

UTTE-mail: [email protected],

Abstract A hybrid wind/fuel cell renewable energy utilizationscheme for electrical energy generation from renewable

resources is digitally simulated and presented in this paper. The

proposed hybrid renewable green energy scheme has four key

subsystems or components to supply the required DC and AC

electric loads. The first subsystem includes the renewable

generation sources from Wind turbine and Fuel Cell. The

second is the interface converters used to connect the renewable

energy generators to the common DC collection bus, where the

generated energy is collected. The third device represents the

added inverter between the common collection DC bus and theadded AC bus interface to feed all AC loads before integration

with the public grid. The fourth subsystem comprises all

controllers including the modulated power filter. The controller

main function is to ensure efficient energy utilization and

dynamic matching between loads and green energy generation

as well as voltage stabilization. The proposed controllers are

coordinated dynamic error driven PI regulators to control the

interfaced converters. The integrated hybrid green energy

system with key subsystems are digitally simulated using the

Matlab/Simulink/Sim-Power software environment and fully

validated for efficient energy utilizations and enhanced interface

power quality under different operating conditions and load

excursions.

KEYWORDS: Wind Renewable energy, Wind Turbine, Fuel cells,Error driven multi loop dynamic control, Modulated Power Filter

compensator.

I. INTRODUCTION

The rapid increase in the demand for electric energy requiresmore installation of energy capacities. The energy capacitiesfrom fossil fuels have been extremely consumed and theirreserves have been rapidly depleted compared to the otherresources. Consequently, there is recently a focus onrenewable energy utilization and development as suitablealternative energy. Among the renewable resources wind,solar and fuel cells are growing in importance and gain theinterest of energy researches. After 1980s, the cost of

electricity provided by wind energy has been drasticallydropping. These cost reductions are due to new technologies,more efficient and more reliable wind turbines [1-4]. Inremote isolated areas and arid communities such as smallislands, diesel generator sets and micro gas turbines are

usually the main source of power supply. Fossil fuel forelectricity generation has several drawbacks: it is costly dueto transportation to the remote areas and it causes globalwarming pollution and green house gases. The need toprovide an economical, viable and environmental safealternative renewable green energy source is very important.As green renewable energy resources such as wind and FuelCells have gained great acceptance as a substitute forconventional costly and scare fossil fuel energy resources.

Stand-alone renewable green energy is already in operation atmany places despite wind and hydrocarbon variations andstochastic nature. Isolated green energy hybrid operation maynot be effective or viable in terms of the cost; efficiency andsupply reliability unless an effective and robust stabilizationof AC-DC interface scheme and effective control strategiesare fully implemented [5,6].

The decline cost of generating electricity $/kWh renewableenergy sources, especially fuel cells due to the industrialdevelopment of the membrane and electrolyte technology. Onthe other hand, the wind speed variation and is dependent onenvironmental conditions. Therefore, an effective approach

is to ensure renewable energy diversity and effectiveutilization by combining more than one renewable energysource to form a coordinated and hybrid integrated energysystem. Integrated green energy system is a valid alternativesolution for small scale micro-grid electrification for remoterural and isolated village/island where the utility gridextension is both costly and geographically difficult. In thispaper, a hybrid renewable green energy system incorporates acombination wind and fuel cell energy sources. A systemusing such diverse combination has the full advantage ofsupply diversity, capacity and system stability that may offerthe strengths of each type [7-11]. The main objective ofintegrated green energy scheme is to provide supply securityfor remote communities. Hybrid integrated green energy

systems are also pollution free, and can provide electricity atcomparatively viable and economic advantages to micro gridor diesel generator set utilized in village/island electricity.The most applications of fuel cell technology are still limitedto hybrid electric vehicles and dispersed electric generation.


2/6

139

Few researches are dealing with the power system applicationof fuel cell and system interactions. Therefore, theinteraction of fuel cell with wind turbine and power systemcomponents as well as switching electronic drives for motors,choppers and controllers are crucial. In this paper windturbine and fuel cell stack supplying power to a common DCbus is considered for transferring the rest of generated

electrical energy to a common AC bus interfaced with thepublic grid [12].

II.

LAYOUTOFTHESTUDIED SYSTEM

The paper presents a hybrid dual Wind/FC generation schemefor supplying remote area with electrical energy. In order toobtain electricity from the hybrid green system at aneconomical price, its topology and control design must beoptimized in terms of coordinated operation and layoutconfiguration. Many topologies are currently available forintegrated green system configurations, depending on the useof interface converters based on common DC/common ACbus interface architecture.

Figure (1) shows the scheme of the studied system withcommon DC/ common AC collection buses interface. Thescheme uses a primary common DC bus collection with anadded secondary common AC bus for feeding any AC loadsand public grid interface. The proposed hybrid green energyscheme is digitally simulated for different operationconditions and load excursions. The developed controlscheme comprises novel multi-loop coordinated dynamicerror driven controllers with supplementary regulation loopsto control the different subsystems [6,7].

Fig.(1) Integrated (Wind-FC) Green Energy UtilizationScheme for Village Electricity

Fuel Cells can be connected in parallel or in series to obtainrequired power rating of the stack. The power obtained bythis way is DC in nature and it should be converted to AC forsome AC type loads. Therefore, DC to AC converters arerequired for such load types. The Electrochemical voltagebehavior of the fuel cell is commonly modeled using thesimple equivalent first order (RC). This circuit consists ofthree passive circuit elements that result in a first orderapproximation of the dynamic response of theelectrochemical capacitor. The circuit includes the double

layer capacitance RC in series with ohmic resistance. Theequivalent series resistance that represents the energy lost dueto the distributive resistance of the electrolyte, electroniccontacts and the porous separator [5, 6]. Hydrogen itself asenergy source of fuel cell is clean, sustainable and emissionfree fuel. Currently hydrogen energy research isconcentrating on the development of efficient and safe fuel

cell technology. Enhancing the output efficiency andimproving the performance of fuel cell are among mainresearch topics.The wind conversion system scheme comprises the windturbine, gear box and electrical AC induction generator.Different types of electric generator are implemented such assquirrel cage induction generator, wound rotor known asdoubly fed induction generator and permanent magnetsynchronous generator [8]. In this study, a self excitedinduction generator is used and modeled together with thewind turbine consisting of three blades to capture the energyof blowing wind.

III.

COORDINATEDERRORDRIVENCONTROLSTRATEGY

Figure (2) shows the general four regulator coordinatedcontrol structure. The hybrid system was digitally simulatedand validated using MATLAB/SimulinkSimPower softwareenvironment in order to test the controller performance forinterfacing devices of FC stack and wind generator underchanging load disturbances. The simulation results show thatthe effects of changing operating conditions are compensatedby controlling the DC-DC chopper, which interfaces the FCstack to the common DC bus. Similarly the effect of windspeed variations is compensated by controlling the AC-DCrectifier converter, which interfaces the wind generator to the

common DC bus. The controller of pulse width modulatedinverter reduces the effect of AC load disturbances. Voltagestabilization is achieved by installing the modulated powerfilter on the AC common bus [6, 12, 13].

Figure (2) Structure of Coordinated four regulators dynamicerror driven controller

The main controller comprises the following four regulators:(1) AC-DC converter regulator for wind turbine.(2) DC-AC inverter regulator to interface DC Bus with

the grid


3/6

140

(3) MPFC regulator for ripple minimization of AC-Bus.(4)

DC-DC converter regulator of Fuel Cell.

Figure (3) shows the detailed regulators mentioned above.

Out1

1

Vr

1

Transport

Delay 1

Transfer Fcn 2

1

10e-3s+1

Transfer Fcn 1

1

10e-3s+1

Scope 1 Saturation

PWM Generator 1

Signal(s)Pulses

Gain 4

-K-

Gain3

0.6

Gain 2

0.4

Gain 1

-K-

Discrete

PI Controller

PI

IDC

2

VDC1

Fig. (3-a) AC-DC Converter Regulator for the Wind EnergyConversion Scheme

Out1

1

Vr

1

Transport

Delay 1

Transfer Fcn 2

1

10e-3s+1

Transfer Fcn 1

1

10e-3s+1

Scope1 Saturation

PWM Generator 1

Signal(s)Pulses

Gain 4

-K-

Gain3

0.6

Gain 2

.4

Gain 1

-K-

Discrete

PI Controller

PI

IDC

2

VDC

1

Fig. (3-b) DC-DC Converter Regulator of Fuel Cell BatterySource

Out2

2

Out1

1

Transport

Delay 1

Transfer Fcn 3

1

10e-3s+1

Transfer Fcn 2

1

10e-3s+1

Scope1

Saturation

RMS

RMS

PWM Generator 1

Signal(s)Pulses

Gain4

-K-

Gain3

.5

Gain 2

1

Discrete

PI Controller

PI

Abs

|u|

VAC

1

Fig. (3-c) DC-AC Inverter Regulator for DC-AC Interface

Out2

2

Out1

1

Transport

Delay 1

Transfer Fcn 3

1

10e-3s+1

Transfer Fcn 2

1

10e-3s+1

Scope1

Saturation

RMS

RMS

PWM Generator 1

Signal(s)Pulses

Gain4

-K-

Gain3

.5

Gain 2

1

Discrete

PI Controller

PI

Abs

|u|

VAC

1

Fig. (3-d) Modulated Power Filter Regulator for AC-BusStabilization

The AC-DC converter regulator compensates for anydynamic oscillations in DC-bus voltage together with theregulator of the induction generator voltage. The inverter andmodulated power filter regulate the AC-Bus. The loopweighing factors are assigned to ensure loop time scaling anddominant control action. In each regulator the total errorsignal is the summation of the separate control loops and isfed into PI controller. The total error signal to ensuremaximum power utilization of the multi-loop is driventhrough PI controller that is used to compensate the dynamictotal error in order to provide control signal, which is thenconverted to degrees as phase angles. This phase angles arethen sent to the Pulse Width Modulated (PWM) generatorthrough saturation to adjust the sequence of the twoIGBT/Diode switch triggering. The coordinated controlscheme is able to guarantee the tracking of a time-varyingtrajectory with minimum steady state error.

IV.

DIGITALSIMULATIONRESULTS

The integrated AC-DC system driven by wind turbine and FCstack was digitally simulated using MATLAB/ Simulink/SimPower software environment to validate the coordinatedcontroller effectiveness under varying PV array parametersand load excursions. The integrated system model issubjected to a number of load excursions and wind speedvariations. The system static DC load is increased by 50% att= 6 s and the AC load is doubled at t=10 s. This system iscontrolled using the described two basic dynamicindependent controllers regulating the operation of theelectronic interface converters, namely DC-DC choppers andswitching stages of the DC-AC inverter which arecoordinated for regulated DC and AC-bus voltage control andvoltage stabilization in case of sudden load excursions andwind speed changes.

Figures (4- 6) show the digital simulation of the integratedsystem dynamic responses of DC-bus voltage and AC-busvoltage and current using multi-loop dynamic error driven PIcontrol strategy. The Wind driven induction generator and FC


4/6

141

voltage and current are drawn in Figures (7, 8). The digitalsimulation using the Matlab/Simulink/Simpower SoftwareEnvironment indicated that the excursions in system loads arecompensated by the error driven controller of the DC-DCchoppers, DC-AC inverter and modulated power filter. Thechange in AC load has a small impact of the system variablesas the AC grid compensates this change. The effect of wind

speed change from 12 m/s to 10 m/s is investigated and thesystem response of common DC-bus voltage and current ofwind induction generator and fuel cell are drawn in Figures(9-11). The controller error response of DC Common bus isdrawn in Fig. (12). Figures (13, 14) show the voltage currentrelation of wind generator and fuel cell, respectively. The 3-Drelation current, voltage and power of wind generator andfuel cell are drawn in figures (15, 16). In addition thesimulation results validate the robustness of the novelcoordinated hybrid Wind/FC scheme. It is clearly shown thatthe proposed dynamic error driven error PI controller canensure maximum utilization and voltage stabilization withacceptable steady state error. Moreover, the common DC andAC bus current is ripple free with minimum inrush currentsand ripple excursion. The multi-loop control strategy can befurther modified to ensure combined voltage stabilization andloss reduction in different green energy powered systems.

The economic analysis show that the revenue due to sellingavoided natural gas and CO

2in the international market has a

great impact on the feasibility of implementing WECS. Theincrease of WECS investment cost could be compensated ifthe avoided natural gas can be sold in the international market

at price ranging between 0.032 and $0.042/m3

while CO2

price ranging between 3 and 8$/ton respectively. Theinvestment can be covered over 10 years (50% of WTGs life

time) if the avoided natural gas can be sold at $0.075/m 3 andCO

2at $8/ton.

The current fuel cell cost is about 4000$/kW and themanufacturers have the goal to reduce this cost throughhigher production rates and continued improvement in designand technology. As fuel cell operates efficiently and cleanly,economical incentives include sale of carbon credit. Theseincentives could reduce the generation cost of fuel cellssignificantly. As a result, Fuel cell based hybrid system couldsubstitute the traditional power sources in near future.

V.

CONCLUSION

The paper presents a hybrid wind/FC renewable energyutilization scheme for electrical energy supply toVillage/Island or remote areas. The integrated renewablescheme utilized a multi regulator error driven coordinatedcontroller to ensure effective energy utilization, common DCand AC bus stabilization, enhanced power quality and nearmaximum energy utilization under varying operatingconditions and/ or load excursions. The integrated DC-AC

system is digitally simulated and validated using theMatlab/Simulink/Sim-power Software environment. Thesample study system comprises the fuel cell battery, windenergy conversion system with DC-DC converters and DC-AC interface inverter and modulated power filtercompensator for AC bus stabilization. The operation of thenovel error driven multi-regulator controller scheme for

hybrid green renewable energy utilization is validated undersudden load excursions and wind speed variations. A novelmodulated power filter compensator was used as voltagestabilization at the AC common bus. Novel dynamic errordriven regulators were coordinated to ensure a stabledecoupled common DC and AC bus interfaces with minimumcurrent ripple and near maximum utilization.

VI- REFERENCES

[1] M. A. H. El-Sayed, "Substitution Potential of WindEnergy in Egypt", International Journal of Energy Policy,vol. 30, pp. 681-687, 2002.

[2] Nafeh, E. Sweelem, F. Fahmy, M. El-Sayed,"Comparative Cost Analysis between PEM Fuel Cell andDiesel in Transportation Applications, Al-AzharUniversity Engineering Journal (AUEJ) Vol. 9, No.3, July2006, pp.821-831, Cairo, Egypt.

[3] M. A. El-Sayed, Effat Mousa, Effect of Large ScaleWind Farms on the Egyptian Power System DynamicsICREPQ 08, 12-14 March 2008, Santander, Spain.

[4] Nafeh, E. Sweelem, F. Fahmy, M. El-Sayed, "Modelligand Control of PEM Fuel Cell System in Transportation,Scientiufic Bulletin of the Faculty of Engineering, Ainshams University, Part II, Electrical Engineering, Vol. 40,

No. 4, Dec. 2005, pp. 807-821, Cairo, Egypt.[5] A. Sharaf, R. Chhetri, A novel dynamic capacitor

compensator/green plug scheme for 3-phase 4-wireutilization loads, Proceeding IEEE-CCECEconference, Ottawa, Ontario, Canada 2006.

[6] Mohamed A. H. El-Sayed, Adel M. Sharaf, AnEfficient Hybrid Wave/Photovoltaic Scheme for EnergySupply in Remote Areas , accepted for publication ininternational journal of Renewable Energy Technology.

[7] H. Fargali, F. Fahmy, M. A. El-Sayed, Control andoptimal sizing of PV-Wind powered rural zone in EgyptAl-Azhar Engineering 10 th International conference,Cairo, Dec. 24-26, 2008.

[8] Wind power in power systems, edited by T. Ackermann,John Wiley &Sons, 2005

[9] E. Muljadi and C.P. Butterfield, Dynamic Model forWind Farm Power Systems, Global Wind PowerConference, Chicago, Illinois, March/April 2004.

[10] Naik, R.; Mohan, N.; Rogers, M.; Bulawka, A., A novelgrid interface, optimized for utility-scale applications ofphotovoltaic, wind and fuel-cell systems , IEEETransactions on Power Delivery, Volume 10, Issue 4,Oct. 1995 Page(s):1920 1926.


5/6

142

[11] J.J. Brey, A. Castro, E. Moreno and C. Garcia,"Integration of Renewable Energy Sources as anOptimized Solution for Distributed Generation," 28thAnnual Conference of the Industrial Electronics Society2002, vol. 4, 5-8 Nov. 2002.

[12] Adel M. Sharaf, Mohamed A. H. El-Sayed, DynamicControl of Fuel Cell Powered Water Pumping Station,

Renewable Energies and Power Quality Journal(RE&PQ) ,No. 7, April 2009.

[13] Mohamed A. H. El-Sayed, Adel M. Sharaf, A NovelFACTS Dynamic Stabilization Scheme for Stand-aloneTidal Energy Conversion Systems, accepted forpublication in International Journal of RenewableEnergy Technology.

Appendix for Simulated System ParametersWind Turbine Induction Generator :Vr= 480 V Sr= 275 kVA N= 1800 r.p.mFuel Cell Battery:R1= resistance of first parallel (RC) circuit =0.496 C1= capacitance of first parallel (RC) circuit =1.55 E-3 FRm = Ohmic resistance of the fuel cell equivalent circuit=0.08074 R2= resistance of second parallel (RC) circuit =1.508 C2= capacitance of second parallel (RC) circuit =18.12 E-3 FEa=nominal fuel cell induced voltage=270 VStatic DC-Bus Load parameters:DC Load: Heating= 100 kW, Lighting=50 kWStatic AC-Bus Load parameters:AC load = 100 kWSwitchable AC load =100 kWModulated Power Filter at AC Bus:C1=C2= 85 f Rf= 0.05 Lf= 0.1 HPI controller parameters:

PV and Wind DC-DC Chopper Regulators : Kp =5, KI=1Inverter and Modulated Power Filter Compensator : Kp =4.5and KI=1.25

Fig.(4) Common DC bus voltage dynamic Response undervarying load Conditions (increasing DC load by 50% at t=6

s, doubling AC load at t=10 s)

Fig.(5) Common AC bus current dynamic Response undervarying load Conditions ( doubling the AC load at t=10 s)

Fig.(6) Common AC bus voltage dynamic Response undervarying load Conditions ( doubling the AC load at t=0.5 s)

Fig.(7) Fuel Cell current dynamic Response under varyingload Conditions (increasing DC load by 50% at t=6 s,doubling AC load at t=10)

Fig.(8) Induction generator current dynamic Response undervarying load Conditions (increasing DC load by 50% at t=6s, doubling AC load at t=10)

Fig.(9) Common DC bus voltage dynamic Response undervariable wind speed ( Changing in Wind speed=12m/s for theperiod from 0-5s, and then wind speed= 10 m/s for the periodfrom 5-10s)

Fig.(10) Fuel Cell current dynamic Response under variablewind speed (Change in Wind speed=12m/s for the periodfrom 0-5s, and then wind speed= 10 m/s for the period from 5to 10s)


6/6

143

Fig.(11) Induction generator current dynamic Responseunder variable wind speed (Change in Wind speed=12m/s forthe period from 0-5s, and then wind speed= 10 m/s for theperiod from 5 to 10s)

Fig. (12) Control Error of the DC-Common Bus Controller

Fig.(13) Dynamic Voltage-Current V-I characteristic of WindGenerator

Fig. (15) Power-Voltage-Current, 3-D Relationship for WindGenerator

Fig. (16) Power-Voltage-Current, 3-D Relationship for FuelCell Stack

Fig. (14) Dynamic Voltage-Current Relationship for Fuel CellStack

Documents

Hybrid Wind-Fuel Cell Renewable Energy Utilization Scheme for Village Electricity