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PowertrainControl Lab
Control of Fuel Cell Power Systems
Anna Stefanopoulou
Department of Mechanical Engineering
University of Michigan
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)
Work funded by U.S. Army Center of Excellence for Automotive Research (ARC)
and NSF-CMS 0201332 and CMS-0219623
PowertrainControl Lab
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”
1830, C. F. Schonbein discovered the gas cell
Philosophical Magazine1839 (Jan) F. C. Schonbein describes the phenomenon1839 (Feb) W. R. Grove realizes the significance
The gas cell is baptized Fuel Cell
PowertrainControl Lab
Fuel Cells
• Water, electrical energy and heat arise through the controlled combination of hydrogen and oxygen.
• High efficiency, no (locally) harmful emissions, no moving parts—Long-term solution??
1st FCV - Shell’s Daf 44 (1960)heat 22 222 OHOH
PowertrainControl Lab
Fuel Cell Type
PowertrainControl Lab
Fuel Cell Stack
cellcellstackcellstack
AiVnPVnV
MEA
cellVPolarization Curve
i
cellcellstack iAII Fuel Cell Tutorial, Los Alamos National Lab
PowertrainControl Lab
Fuel Cell Characteristics
OxygenHydrogenPressure
Temperature
Humidity
Current drawn fromthe traction motor and auxiliaries
)(),(),(),( 2ttTtptiVV OH
PowertrainControl Lab
Reactant Flow Subsystem
Provide sufficient reactant flow, fast transient response, minimize auxiliary power consumption
Excess Ratio = Supply/Use1.2 for Hydrogen2.0 for Oxygen
Ist
PowertrainControl Lab
Heat & Temperature Subsystem
Fast warm-up, no temperature overshoot, low auxiliary fan and pump power
Ist
PowertrainControl Lab
Water Management Subsystem
Maintaining membrane hydrated, balancing water usage/consumption
Ist
PowertrainControl Lab
Power Management Subsystem
Satisfactory vehicle transient response, assist fuel cell system
auxiliarystacknet PPP
PowertrainControl Lab
Overall Control Problem
PowertrainControl Lab
Literature Review - Model Types
• Multi-Dimensional Fuel Cell Model[Springer, 91, Nguyen, 93, Amphlett, 95, Dutta 01]Model: Pressure, Partial Pressure, Temperature, Humidity EffectsPurpose: Design, Sizing
•Dynamic Fuel Cell System Model[Guzzella, 99, Hauer, 00, Boettner, 01, GCTool]Model: Temperature, Pressure, Humidity DynamicsPurpose: Transient Performance, System Efficiency
• Steady-State Fuel Cell System Model[… many…] Model: Static Power and Efficiency mapsPurpose: Fuel Consumption, Hybridization
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)
PowertrainControl Lab
Reactant Supply System
Goal: During fast current demands, providing sufficient reactant flow to achieve fast transient response, and reduce auxiliary power consumption
PowertrainControl Lab
Compressor and Manifolds Model
Supply Manifold
Compressor
Return Manifold
)(1
cpcmcp
cpcp PP
dt
dJ
smincaoutcpcpsm
asm
incacpsm
TWTWV
R
dt
dp
WWdt
dm
,,
,
outrmoutcarm
rmarm WWV
TR
dt
dp,,
PowertrainControl Lab
• Stack Voltage Model• Cathode Mass Flow Model• Anode Mass Flow Model• Membrane Hydration Model
Fuel Cell Stack Model
membrvgenvoutcavincavcaw
outNinNN
reactOoutOinOO
WWWWdt
dm
WWdt
dm
WWWdt
dm
22
2
222
2
,,,,,,,
,,
,,,
PowertrainControl Lab
Stack State Equations
membrvgenvoutcavincavcaw
outNinNN
reactOoutOinOO
WWWWdt
dm
WWdt
dm
WWWdt
dm
,,,,,,,
,,
,,,
22
2
222
2
membrvoutanvinanvanw
reactHoutHinHH
WWWdt
dm
WWWdt
dm
,,,,,,
,,, 222
2
Cathode
AnodeF2
nIMW
F2
nIMW
F4
nIMW
stvgen,v
stHreact,H
stOreact,O
22
22
),,I(fW ancastvmembr,v
Electrochemistry
Membrane mass transport
PowertrainControl Lab
= (Electro-osmotic drag) – (Back-diffusion)
Water flow across
membrane from
anode to cathode
m
an,vca,vwdmembr,v t
ccD
F
inN
mol/sec
Membrane Hydration Model
Water molar flow ratethrough membrane
Water Concentration
Electro-osmotic coefficient
Diffusion coefficient
Current density
2
)caan(m
Membrane water content
PowertrainControl Lab
Voltage Model(Polarization)
3
1
max20 1
c
ohmic
a
concohmact
i
iciiReVVE
VVVEV
),(),,(),,,(),,,(2222 OconcmohmOcaactOH pTVTVppTVppTE
SAE 98C054 and personal communications with the authors: W-C Yang and J.A. Adams
Pressure
PowertrainControl Lab
31
c
max2ohm
ica0 i
iciiRe1VVEV
2c ,10c ,2.2i
p12.0
pp
atm 2pfor )54.0T106.1(p)068.0T1066.8(
atm 2pfor )68.1T1045.1(p)62.0T1016.7(c
)T
1
303
1(350exp00326.0005139.0
tR
)057.0T108.5(p)17.0T108.1(p)1062.1T1062.1(V
013.1
)pp(12.0ln
2
1
013.1
pplnT1031.4)15.298T(105.828.0V
013.1
pln
2
1
013.1
plnT1031.4)15.298T(105.823.1E
31max
sat,vO
x
x4
x5
x3
x4
2
m
mohm
4x
42x
25a
sat,vcasat,vca540
OH54
2
22
Stack Voltage Model (Polarization)
Pukrushpan et al, IMECE 2002
PowertrainControl Lab
Ist
Power
pressure
2OnetP
z
Control Objectives
Vcm
cmVstI
uw
reactO
inOO W
W
,
,
2
2
2 reactedoxygen
suppliedoxygen
Oxygen Excess Ratio
CMFCnet PPP Net Power
PowertrainControl Lab
Optimal Operating PointsSteady-stateO2 and Pnet
for different Ist (using model)
Desired
set-point
ref
O
refnetref
2
Pz
2OnetP
z
)I(W
)V(W
reacted oxygen
supplied oxygen
streact,O
cmin,OO
2
22
Oxygen Excess Ratio
CMFCnet PPP Net Power
Gelfi et al, ACC 2003
PowertrainControl Lab
uz
wzc
2
2
G
GK
KcCancelation Controller
Transient Interactions
uzwz
uzwz
22
11
GG
GGwu z
P
2O
net
(Pnet)=z1
(Ist)=w
wz1G
(Vcm)=u uz2G O2)=z2
wz2G
uz1G
PowertrainControl Lab
0
dtqQqRuuzQzJ qTT
zT
Performance Tradeoff
Varigonda et al, AICHE 2003
Voltage should be used in the feedback
PowertrainControl Lab
Performance Tradeoff (cont.)Closed Loop Bode Plots for Different Control Gains
Power transients faster than 10 rad/s cause severe compromise to the FC Stack life due to O2 starvation
PowertrainControl Lab
Nonlinear Simulation Results
PowertrainControl Lab
Transients and Coordination with Power Electronics
PowertrainControl Lab
Outline
• Overview --- How FC work?• Modeling of Fuel Cell System• Control of Oxygen Reactant
• Control of Fuel Processor for Hydrogen Reactant • Experimental Setup
PowertrainControl Lab
Problem—Hydrogen 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) hydrogenRequires significant energy for compression, stringent safety precautions and bulky, heavy and expensive storage tanks.
• Metal hydride or Carbon nanofiber storageNew technologyfar 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 P2000Fuel Cell Vehicle,” SAE 2000-01-1061
PowertrainControl Lab
Hydrogen-on-Demand
Direct H2
Electrolyser
Solar
Regenerative
Fuel Processor
Source: Nature 414, 2001
PowertrainControl Lab
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 feedUnacceptable 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)
PowertrainControl Lab
Fuel Cell Stack
SFuelTank
HumidifierHEX
CoolingSystem
Blower
Energy Storage(Battery)
PowerConditioning
& Control
LOAD
Fuel Processor
Air from
Vaporizer/Desulfurizer
Reformer High-TempWGS
Low-TempWGS PROX
Fuel Processor
Air
Air
Water
Water Water
Hydrogen-richgas
When direct (stored) hydrogen is not available....the Fuel Processor Control System becomes critical for efficiency, responsiveness and reliability.
From Direct Hydrogen to Hydrogen-on-Demand
PowertrainControl Lab
From Direct Hydrogen to Reformate Hydrogen
Goals: Coordinate fuel (methane) and air flow to achieve-- high conversion of H2 (regulate CPOX Temperature)-- maximize H2 utilization
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
PowertrainControl Lab Varigonda et al, AIChE 2003
Integrated FPS+FCS+CBrn
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-minimumphase response very slow start-up
PowertrainControl Lab
Tcpox VH2
Ist
uvlv
ublo
Baseline Controller
Tcpox
VH2
PowertrainControl Lab
Tcpox VH2
Ist
uvlv
ublo
Multivariable Controller
VH2
Tcpox
Pukrushpan et al, ACC 2003
PowertrainControl Lab
Analysis of MIMO Controller
2HVcpoxT
22C21C12C11C
valveublou
C12 term is important
Closed-loop step response Closed-loop frequency response
VH2
PowertrainControl Lab
Tcpox VH2
Ist
uval
ublo
Multivariable Controller Coordination
PowertrainControl Lab
Analysis of the FPS+FC Interaction
Tcpox
VH2
ublo
uvalve
C11
C22
Ist…The current commandaffects hydrogen…
The error in hydrogen is detected by the controller through the C22 (typically a PI controller).
The fuel valve tries to compensate for the detected hydrogen error
… and causes a disturbance to the Tcpox through the P12 plant interaction
PowertrainControl Lab
Analysis of the FPS+FC Interaction (cont.)
Tcpox
VH2
Ist
uvlv
The Tcpox pertrubationIs detected by the PI controller in C11
That energizes the blower signal whicheventually rejects the P12 disturbance.
ublC11
C22
…… and causes a disturbance to the Tcpox through the P12 plant interaction
C12
… for faster response, one can use a direct command to the blower signal based on the fuel valve excursion. This is accomplished by the C12 term!!
PowertrainControl Lab
TcpoxVH2
Ist
uval
ublo
Adding Measurements from FPS Robustness+Performance
...Pprox Pa
PowertrainControl Lab
Outline
• Overview --- How it works?• Modeling of Fuel Cell • Control of Oxygen Reactant • Control of Fuel Processor for Hydrogen Reactant
• Experimental Setup
PowertrainControl Lab
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?
Answer: is between the ODE and the PDE world
Attempt:
PowertrainControl Lab
Fuel Cell Control Test Station
1082 WE Lay Auto Lab
Designed by The Schatz Energy Research Center (SERC)Humboldt State University, Arcata, CA
PowertrainControl Lab
PEM Fuel Cell (2.4 kW)
Air
Current
Hydrogen
Water
PowertrainControl Lab
Fuel Cell Control Test Station
Data-Acquisitionwith LabView
ThermalManagement Mass Air
Controllers
Hydrogen Sensor
HydrogenStorage and Pressure Regulation
ControllableLoad
1082 WE Lay Auto Lab
PowertrainControl Lab
• 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
Summary
Sponsors: NSF and ARC (TACOM)
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)
PowertrainControl Lab
Thanks!!!
Graduate StudentsJay PukrushpanArdalan Vahidi
UnderGraduate St.Marietsa EdjeDave Nay
Visiting StudentsSylvain GelfiDenise McKay
Thanks to Professor Peng