dynamic modeling and simulation of a small wind-fuel cell...
TRANSCRIPT
Dynamic Modeling and Simulation of a Small Wind-Fuel Cell Hybrid Energy System
M. J. Khan, [email protected]. T. Iqbal, [email protected]
The 28th Annual Conference of the Solar Energy Society of Canada
August 18 to 20, 2003Queen's University, Kingston, Canada
Outline
o Need for Hybrid energy systemso Wind-fuel cell system analysiso Small wind turbineo Fuel cell system basicso Components of the proposed systemo Specificationso Simulationo Resultso Conclusions
Need for Hybrid energy systems
Renewable hybrid energy systems are suitable combinations of
o Wind turbineo Solar PVo Micro-hydro turbine, Tidal energy, Biogas planto Batteries, Fuel cells, Ultra-capacitors etc.
Hybrid systems are promising sources, owing to
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 wind speedo 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/Simulink®
Components of the proposed systemo 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 are: 500watt, 120V, 60Hzo Wind turbine produces electricity depending 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
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 Efficient
o 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), Proton Exchange 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 modeling
The 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 modeling
Electrolyzer: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 controller Ultra-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
Further worko Cost analysis and sizingo Controller design with detailed modeling of wind
turbine, electrolyzer, fuel cell peripherals, inverter etc.o Studies for efficiency optimization in cogeneration mode
operationo Implementationo Testing
References
Q & A