Control of Fuel Cell Power Systems

1
Control of Fuel Cell Power Systems

• Anna Stefanopoulou
• Department of Mechanical Engineering
• University of Michigan

Work funded by U.S. Army Center of Excellence
for Automotive Research (ARC) and NSF-CMS 0201332
and CMS-0219623
Thanks to Prof. Huei Peng and Jay Pukrushpan
(UMICH) Scott Bortoff and team (UTRC) Woong-Chul
Yang and Scott Staley (Ford) Herb Dobbs and Eric
Kalio (US-Army NAC)
2
Historical Perspective
1894, W. Ostwald in the 2nd annual conference
of the German Society of Electrotechnologists
declares that the fuel cell is greater
achievement than the steam engine
and predicts the Siemens steam generator will
end up soon in the museum
3
Fuel Cells

• Water, electrical energy and heat arise through
  the controlled combination of hydrogen and
  oxygen.
• High efficiency, no (locally) harmful emissions,
  no moving partsLong-term solution??

4
Fuel Cell Type
5
Fuel Cell Stack
MEA
Fuel Cell Tutorial, Los Alamos National Lab
6
Fuel Cell Efficiency Characteristics
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Fuel Cell Characteristics
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Reactant Flow Subsystem
Excess Ratio Supply/Use 1.2 for Hydrogen 2.0
for Oxygen
Ist
Provide sufficient reactant flow, fast transient
response, minimize auxiliary power consumption
9
Heat Temperature Subsystem
Ist
Fast warm-up, no temperature overshoot, low
auxiliary fan and pump power
10
Water Management Subsystem
Ist
Maintaining membrane hydrated, balancing water
usage/consumption
11
Power Management Subsystem
Satisfactory vehicle transient response, assist
fuel cell system
12
Overall Control Problem
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Literature Review - Model Types

• Estimates of time constants for Subsystems
• Electrochemistry O(10-19sec)
• Electrode Membrane RC System O(Unknown)
• Membrane Water Content O(Unknown)
• Hydrogen Air manifolds O(0.1 sec)
• Flow Control Supercharge Device O(1 sec)
• Vehicle Dynamics O(100 sec)
• Cell Stack Temperature O(100sec)

• Multi-Dimensional Fuel Cell Model
• Springer, 91, Nguyen, 93, Amphlett, 95, Dutta
  01
• Model Pressure, Partial Pressure, Temperature,
  Humidity Effects
• Purpose Design, Sizing
• Dynamic Fuel Cell System Model
• Guzzella, 99, Hauer, 00, Boettner, 01, GCTool
• Model Temperature, Pressure, Humidity Dynamics
• Purpose Transient Performance, System Efficiency
• Steady-State Fuel Cell System Model
• many
• Model Static Power and Efficiency maps
• Purpose Fuel Consumption, Hybridization

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Reactant Supply System
Goal During fast current demands, providing
sufficient reactant flow to achieve fast
transient response, and reduce auxiliary power
consumption
15
Compressor and Manifolds Model
Compressor
Supply Manifold
Return Manifold
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Fuel Cell Stack Model
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Stack State Equations
Cathode
Electrochemistry
Anode
Membrane mass transport
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Membrane Hydration Model
Water flow across membrane from anode to
cathode
(Electro-osmotic drag) (Back-diffusion)
Current density
Water molar flow rate through membrane
Water Concentration
mol/sec
Diffusion coefficient
Electro-osmotic coefficient
Membrane water content
19
Voltage Model(Polarization)
SAE 98C054 and personal communications with the
authors W-C Yang and J.A. Adams
Pressure
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Stack Voltage Model (Polarization)
Pukrushpan et al, IMECE 2002
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Control Objectives
pressure
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Optimal Operating Points
Steady-state lO2 and Pnet for different Ist
(using model)
Net Power
Oxygen Excess Ratio
Gelfi et al, ACC 2003
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Transient Interactions
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Performance Tradeoff
Varigonda et al, AICHE 2003
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Performance Tradeoff (cont.)
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Nonlinear Simulation Results
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Transients and Coordination with Power Electronics
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Outline

• Overview --- How FC work?
• Modeling of Fuel Cell System
• Control of Oxygen Reactant
• Control of Fuel Processor for Hydrogen Reactant
• Experimental Setup

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ProblemHydrogen Supply

• On-board storage (direct)
• Cryogenic (liquid) hydrogen
• Liquifying hydrogen is expensive and storing this
  
• extremely cold fuel on a vehicle is difficult.
• Pressurized (gaseous) hydrogen
• Requires significant energy for compression,
• stringent safety precautions and bulky,
• heavy and expensive storage tanks.
• Metal hydride or Carbon nanofiber storage
• New technology
• far from commercial development.
• Onboard fuel processors (reformer)
• Convert hydrocarbon fuel, such as methanol or
  gasoline, to a H2 rich gas.

Adams et al., The Development of Ford's
P2000 Fuel Cell Vehicle, SAE 2000-01-1061
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Hydrogen-on-Demand
Direct H2 Electrolyser
Fuel Processor
Regenerative
Source Nature 414, 2001
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On-Board Reforming

• Advantage Widely Available, Inexpensive,
  Consumer Acceptance, Fuel Flexibility
• Liquid Fuels From Petroleum and/or Other Sources
  (e.g, Ethanol)
• Natural gas
• Large potential reserves, distributed worldwide
• H2 From Catalytic Partial OXidation (CPOX)
• Partial Oxidation CH4 0.5O2 Heat CO 2 H2
  (at 700o )
• Total Oxidation CH4 2O2 Heat CO2 2 H2O
• Water-Gas Shift CO H2O CO2 H2
• Autothermal point balances heat input/output
• 0.25-0.5 (2500-5000 ppm) of CO remains in the
  feed
• Unacceptable performance if CO is 0.001
  (10ppm)
• Preferential Oxidation (PrOX) is needed!!
• Precise Control of O2 feed for the CO oxidation
• Any extra O2 will react with H2 (loss of fuel)

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From Direct Hydrogen to Hydrogen-on-Demand
When direct (stored) hydrogen is not
available.... the Fuel Processor Control System
becomes critical for efficiency, responsiveness
and reliability.
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From Direct Hydrogen to Reformate Hydrogen
H2 generation from Catalytic Partial OXidation
(CPOX) Partial Oxidation CH4 0.5O2 Heat
CO 2 H2 (at 700o ) Total Oxidation CH4 2O2
Heat CO2 2 H2O
Goals Coordinate fuel (methane) and air flow to
achieve -- high conversion of H2 (regulate CPOX
Temperature) -- maximize H2 utilization
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Integrated FPSFCSCBrn
Burn the excess H2 (Catalytic burner) use the
heat for (i) heating (or vaporizing) the fuel
(ii) recover power throughTC Highly coupled
system with non-minimum phase response ? very
slow start-up
Varigonda et al, AIChE 2003
35
Baseline Controller
Ist
ublo
uvlv
Tcpox
VH2
36
Multivariable Controller
Ist
ublo
uvlv
Tcpox
VH2
Pukrushpan et al, ACC 2003
37
Analysis of MIMO Controller
VH2
C12 term is important
Closed-loop step response
Closed-loop frequency response
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Multivariable Controller ? Coordination
Ist
ublo
uval
Tcpox
VH2
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Analysis of the FPSFC Interaction
Tcpox
ublo
S
C11
S
S
S
C22
S
uvalve
VH2
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Analysis of the FPSFC Interaction (cont.)
and causes a disturbance to the Tcpox through
the P12 plant interaction
Ist

Tcpox
S
S
C22
S
uvlv
VH2
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Adding Measurements from FPS ? RobustnessPerforma
nce
Ist
ublo
uval
...
Pprox
Tcpox
Pa
VH2
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Outline

• Overview --- How it works?
• Modeling of Fuel Cell
• Control of Oxygen Reactant
• Control of Fuel Processor for Hydrogen Reactant
• Experimental Setup

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Estimation of Hydrogen Starvation
Question Can we use the Fuel Cell Voltage to
predict the hydrogen and oxygen content during
typical flow, pressure, current transients?
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Fuel Cell Control Test Station
Designed by The Schatz Energy Research Center
(SERC) Humboldt State University, Arcata, CA
1082 WE Lay Auto Lab
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PEM Fuel Cell (2.4 kW)
Water
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Fuel Cell Control Test Station
1082 WE Lay Auto Lab
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Summary

• Control of Fuel Cells
• -- Stringent tradeoffs between net power response
  and oxygen supply
• -- Estimation of hydrogen utilization with
  conventional sensors
• Control of Fuel Processor (Hydrogen reformer)
• -- Multivariable Control of Natural Gas and Air
  Flow

Thanks to -- Scott Bortoff and Shubro Ghosh
(UTRC and UTC-FC) -- W-C Yang and Scott Staley
(Ford SRL and Th!nk) -- Charles Chamberlin,
Peter Lehman (SERC)
Sponsors NSF and ARC (TACOM)
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Thanks!!!
Graduate Students Jay Pukrushpan Ardalan Vahidi
UnderGraduate St. Marietsa Edje Dave Nay
Visiting Students Sylvain Gelfi Denise McKay
Thanks to Professor Peng