Powertrain Control Lab Control of Fuel Cell Power Systems Anna Stefanopoulou Department of...

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


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


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


Fuel Cell Type


Fuel Cell Stack

cellcellstackcellstack

AiVnPVnV

MEA

cellVPolarization Curve

i

cellcellstack iAII Fuel Cell Tutorial, Los Alamos National Lab


Fuel Cell Characteristics

OxygenHydrogenPressure

Temperature

Humidity

Current drawn fromthe traction motor and auxiliaries

)(),(),(),( 2ttTtptiVV OH


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


Heat & Temperature Subsystem

Fast warm-up, no temperature overshoot, low auxiliary fan and pump power

Ist


Water Management Subsystem

Maintaining membrane hydrated, balancing water usage/consumption

Ist


Power Management Subsystem

Satisfactory vehicle transient response, assist fuel cell system

auxiliarystacknet PPP


Overall Control Problem


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)


Reactant Supply System

Goal: During fast current demands, providing sufficient reactant flow to achieve fast transient response, and reduce auxiliary power consumption


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,,


• 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

,,,,,,,

,,

,,,


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


= (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


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


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


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


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


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


0

dtqQqRuuzQzJ qTT

zT

Performance Tradeoff

Varigonda et al, AICHE 2003

Voltage should be used in the feedback


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


Nonlinear Simulation Results


Transients and Coordination with Power Electronics


Outline

• Overview --- How FC work?• Modeling of Fuel Cell System• Control of Oxygen Reactant

• Control of Fuel Processor for Hydrogen Reactant • Experimental Setup


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


Hydrogen-on-Demand

Direct H2

Electrolyser

Solar

Regenerative

Fuel Processor

Source: Nature 414, 2001


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)


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


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


Tcpox VH2

Ist

uvlv

ublo

Baseline Controller

Tcpox

VH2


Tcpox VH2

Ist

uvlv

ublo

Multivariable Controller

VH2

Tcpox

Pukrushpan et al, ACC 2003


Analysis of MIMO Controller

2HVcpoxT

22C21C12C11C

valveublou

C12 term is important

Closed-loop step response Closed-loop frequency response

VH2


Tcpox VH2

Ist

uval

ublo

Multivariable Controller Coordination


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


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!!


TcpoxVH2

Ist

uval

ublo

Adding Measurements from FPS Robustness+Performance

...Pprox Pa


Outline

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

• Experimental Setup


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:


Fuel Cell Control Test Station

1082 WE Lay Auto Lab

Designed by The Schatz Energy Research Center (SERC)Humboldt State University, Arcata, CA


PEM Fuel Cell (2.4 kW)

Air

Current

Hydrogen

Water


Fuel Cell Control Test Station

Data-Acquisitionwith LabView

ThermalManagement Mass Air

Controllers

Hydrogen Sensor

HydrogenStorage and Pressure Regulation

ControllableLoad

1082 WE Lay Auto 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)


Thanks!!!

Graduate StudentsJay PukrushpanArdalan Vahidi

UnderGraduate St.Marietsa EdjeDave Nay

Visiting StudentsSylvain GelfiDenise McKay

Thanks to Professor Peng

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