Dynamic Modeling and Simulation of a Small Wind-Fuel Cell Hybrid Energy System

M. J. Khan, mjakhan@engr.mun.caFaculty of Engineering & Applied Science

Electrical Engineering

Graduate Student Seminar Symposium, ENGI 9100

December 3, 2003

Outlineo Need for Hybrid energy systemso Wind-fuel cell system analysiso Components of the proposed systemo Layout of the wind-fuel cell systemo Small wind turbineso Fuel cell systemso Auxiliary componentso Matlab/Simulink® modeling o Simulation resultso Conclusions

Need for Hybrid energy systems

Renewable hybrid energy systems are combinations of

o Wind turbineo Solar PVo Micro-hydro turbine, Tidal energy, Biogas planto Batteries, Fuel cells, Ultra-capacitors etc.

Hybrid systems are promising candidates for

o Cleaner performanceo Remote and Standalone operationo Distributed generation and grid connectivity

Wind-fuel cell system analysis

Need for wind-fuel cell system:o Canada has excellent wind energy potentialo Energy from the wind is dependant on windo Hybridization would minimize fluctuationso Wind-fuel cell system is a suitable, clean and

reliable solution

Simulation of a wind-fuel cell system:o Modeling is essential for design, optimization

and performance analysiso Proposed scheme is modeled based on physical

& empirical equationso Simulation is done with Matlab/SimulinkTM

Components of the proposed system

o Primary power: Wind turbine (Southwest Windpower’s AIR403)

o Backup power: PEM fuel cell (Independence 500 of Avista Lab Ltd.)

o Hydrogen production: Electrolyzer (FPM20 of Idatech Ltd.)

o Transient power: Ultra-capacitors Four 435F, 14V units (BMOD 0117 by Maxwell Technologies)

o DC/AC conversion: Single phase 120V 60Hz inverter (TSi power’s Inv 48v VDC series)

Layout of the schemeo Main system specifications : 500watt, 120V, 60Hzo Wind turbine produces electricity depending on availability of windo Excess power is used for hydrogen production by the electrolyzero Hydrogen is kept in the storage tank

o Any deficit in power demand is met by the fuel cell stack

o Sudden changes in the load demand is offset by the ultra-capacitor units

o The inverter converter 48V dc into 120V, 60Hz ac

o A controller controls power flow to and from the components

Small wind turbine

Modeling:Y(s)/X(s)=0.25/(S2+0.7S+0.25)

X(t), Captured powerY(t), Electrical power

Southwest Windpower’s Air 403 specifications:o Rotor Diameter: 1.14 meterso Weight: 6 kgo Start up wind speed: 3 m/so Voltage: 12, 24 and 48 voltso Output: 400 watts at 12.5 m/so Alternator: PM Generator

Fuel cell system basicsBasics:o A Fuel cell generates electricity by electrochemically

reacting hydrogen (H2) and oxygen (O2) and producing water (H2O).

H2+O2 => H2O + Heato A cell contains an anode, cathode and electrolyte. o Several cells are connected to form a stack to deliver

sufficient power

Fuel cells are characterized as:o Very low emitting, Quiet, Highly

scalable and Efficiento Could be used in Transportation,

Distributed & Utility generation and Portable systems

PEM fuel cell systemso Among various types of fuel cells, such as, Alkaline (AFC), Phosphoric

Acid (PAFC), Molten Carbonate (MCFC), Solid Oxide (SOFC), ProtonExchange Membrane fuel cells (PEMFC) are the most promising

o PEM fuel cells are favored for low temperature (~80oC)- low pressure (~3atm) operation, high power density and good transient capability

o A PEM fuel cell system contains auxiliary components such as:o Fuel processoro Compressoro Pumps, Blower, Cooling fanso Filters, Sensorso Power conditioner, Controller etc.

Fuel cell technology challenges and prospectsChallenges for Fuel cell technology:o Fuel processor developmento Hydrogen storage developmento High performance material development o Increasing Energy densityo Cost reduction

Prospects:o Fuel cell technology is expected to

revolutionize power generation scenario

o Worldwide R&D schemes would reduce its cost and increase performance, drastically

PEM fuel cell modelingThe thermodynamic potential:E=1.229 – 0.85x10-3 (T - 298.15) + 4.3085x10-5 .T. (lnPH2 + 0.5 lnPO2)The concentration of dissolved oxygen:cO2 = PO2 /(5.08x106 exp(-498/T))Activation voltage drop:ηact = -0.9514 + 0.00312 T – 0.000187 T ln (i) +7.4x10-5 T ln (cO2)Internal resistance: Rint = 0.01605 – 3.5 x 10 -5 T + 8x10-5 i

Activation resistance: Ra = -ηact/iCell voltage: V = E -vact + ηohmicVoltage transients: dvact/dt=i/C – vact/Ra/COhmic voltage loss: ηohmic = - i RintStack voltage: Vstack = 65 Vcell

Auxiliary components modelingElectrolyzer:nH2 = nF.nc.ie/(2F)nF = 96.5exp(0.09/ie –75.5/ie

2)

Ultra-capacitor:One R-C branch with R=16mohms and C=108.75F

Inverter:PSB model Single phase full bridge inverter for 120V-60Hz output

Controller:PID controller as given by : Gr(s) = Kp(s + Td s2+ 1/Ti)/sO2 flow controller : Kp=2.17, Ti=0.5, Td= 0H2 flow controller : Kp=5.0, Ti=0.5, Td=0

Matlab/Simulink® modeling

Inverter

Electrolyzer

Power flow controller

Reactant flow controllerUltra-capacitor

Fuel cell stack

Wind turbine

Results

Distribution of load demand current among fuel cell stack and wind turbine

DC voltage output with and without ultra-capacitor

Change in wind speed and wind turbine’s power output

Reactant pressures within the fuel cell stack

Conclusions

o A small 500W wind fuel cell hybrid energy system is proposed

o System dynamic modeling, simulation and design of controller are reported

o Transients for the 48V system are found to be between 45V to 53V

o Transient’s duration is between 1 to 5 seconds

o Could be investigated further for similar hybrid systems

Further worko Cost analysis and sizingo Detailed modeling of wind turbine, electrolyzer, fuel

cell peripherals, inverter etc.o Controller design o Studies for efficiency optimization by cogeneration

mode operationo Implementationo Testing

Acknowledgemento Dr. T. Iqbal, Faculty of Engineering & Applied Science, MUNo School of Graduate Studies, MUN & NSERCo Faculty of Engineering & Applied Science, MUN

References

Q & A

o Danish Wind Industry Association: http://www.windpower.orgo Fuel Cells 2000: http://www.fuelcells.orgo National Renewable Energy Laboratory: http://www.nrel.gov

Thank you