1. ©SJA 2007 1 Søren Juhl Andreasen and Søren Knudsen Kær Aalborg University Institute of Energy Technology Dynamic Model of High Temperature PEM Fuel Cell Stack Temperature

2. ©SJA 2007 2 Presentation outline ∙HTPEM features ∙Experimental fuel cell system setup ∙Previous work ▫Stack temperature profile identification ∙Governing equations ▫Energy balance ▫Fuel cell power input ▫Convection ▫Conduction ∙Model definitions ∙Model assumptions ∙HTPEM FC stack temperature control ▫Current feedforward ▫PI controller ∙Model validation ▫Heating ▫Operation ▫Pulsating air flow

3. ©SJA 2007 3 HTPEM PBI(H 3 PO 4 )-membrane features Operating conditions ▫FC operating conditions 120-200 o C, preferred range (160-180 o C) ▫Allowable CO content 1-3% (10000-30000 ppm) ▫No humidification of anode- and cathode flows ▫Fast response to load changes due to high temperatures (even with CO) Advantages ▫No humidification of cathode or anode => Very simple FC system and stack design ▫No liquid water should be present in FC membranes=> Simple stack design ▫Large CO-tolerance (1-3%), LTPEM is typically 10-100ppm ▫Possible system integration with simple reformer, due to high CO tolerance ▫Storing hydrogen as a liquid hydrocarbon => methanol, ethanol etc. ▫Avoiding and extra cooling circuit, by using extra cathode air Disadvantages (Challenges) ▫Lower cell voltage = Lower efficiency (not as low as DMFC though) ▫Start-up time is often long because of high operating temperatures (min 100 o C) to avoid water condensation. ▫High demands for materials at these elevated temperatures

4. ©SJA 2007 4 Performance of HTPEM fuel cell ©SJA 2007

5. 5 HTPEM FC System- pure hydrogen

6. ©SJA 2007 6 Previous work – Initial experimental results Stack temperature profile identification

7. ©SJA 2007 7 Fuel cell stack energy balance Energy balance : Fuel cell heat input : External heat input : Forced Convection : Heat Conduction : Natural Convection :

8. ©SJA 2007 8 Manifold and gas channel temperature

9. ©SJA 2007 9 Model assumptions ∙Quasi-steady-state : Constant surface temperature. ∙Fuel cell stack modelled as three lumps. ∙Constant U rev of 1.2V. ∙Fuel cell heat generation calculated at steady-state. ∙No axial and in-plane heat conduction between lumps. ∙Additional heating in inlet plate and BPP junction modelled as small constant gain. ∙Heat transfer in the MEA is neglected. ∙Hydrogen heating and cooling effects neglected. ∙Constant air mass flow in channels, consumption subtracted. ∙Small natural convection term added.

10. ©SJA 2007 10 HTPEM FC stack temperature control SystemController T measured T reference U blower I reference I->m Air FC air flow – PI controller with Current feedforward Stack temperature 160-180 o C, what T measured should be used? + + - +

11. ©SJA 2007 11 Typical stack temperature control case Middle temperature controlledEnd temperature controlled Initial heating followed by 20 A load step.

12. ©SJA 2007 12 Model validation - Electrical heating Experiment : 400 W heating Simulation : 350 W heating

13. ©SJA 2007 13 Model validation – Constant current Experiment : 20 A load Simulation : 1500 W heating, 20 A load

14. ©SJA 2007 14 Model validation – Pulsating air flow Operation : small current ramp, 20 A load air flow pulsing no controls

15. ©SJA 2007 15 Example of experimental data

16. ©SJA 2007 16 Conclusions and future work Conclusions ∙Developed model can with good agreement predict fuel cell stack temperature dynamics. ∙Developed model can within acceptable ranges predict the steady-state values of the fuel cell stack temperatures. ∙The modelled exhaust temperature must be improved for use as a direct control feedback. ∙Minimization of measured temperatures should be examnied using model based control. Furture Work ∙Manifold and channel temperature dynamics ∙Air flow subtraction along the channel ∙Discrete (at cell level) model ∙Model validation on 1 kW HTPEM stack with other geometry

17. ©SJA 2007 17 Thank you for your attention!