ONLINE PEMFC STACK MONITORING WITH “THDA“...AVL THDA , Trondheim, 23rd – 24th June 2009 8 ON-LINE DETECTION OF CRITICAL WATER ISSUES Extended On-line Diagnosis "AVL-THDA" E.R.,

International Symposium onDIAGNOSTIC TOOLS FOR FUEL CELL TECHNOLOGIES

ONLINE PEMFC STACK MONITORING WITH “THDA“Erich RAMSCHAK, AVL List GmbH

Trondheim, 23rd – 24th June 2009

2AVL THDA, Trondheim, 23rd – 24th June 2009

If defects or critical conditions occur in one or few cells, time variant conditions or local non-linearities in the transfer function distort a superimposed signal and form harmonics

• Extra spectral components (i.e. harmonics) are detectable in thestack voltage – no cell voltage measurement required

• Reduced measurement effort: stack voltage & stack current only

• COST EFFICIENT APPROACH

EFFECTS RESULTING FROM VOLTAGE DRIFTS ARE ANALYZED

INSTEAD OF VOLTAGE DRIFT MEASUREMENT ITSELF

BASICS OF THE APPROACH “AVL THDA”

*AVL patent, registered trademark

““THDATHDA™™”” –– Total Harmonic Distortion Analysis* Total Harmonic Distortion Analysis*


BRIEF BACKGROUND OF HARMONIC DISTORTION

0 2 4 6 8 10 12

-100

-50

0

normalised frequency scale ≡ order of harmonics

am

plit

ude

[d

B]

current spectrum(sinusoidal signal)

voltage spectrum

fundamentalfrequency

3rd order harmonic

5th order harmonic

� Signal distortion forms extra components in the frequency spectrum.Harmonics can be detected at integer multiplies of the fundamental frequency

� Occurrence of extra spectral components is measured

� Quantification: “Klirrfactor” or “THD”, [%] [dB]


battery pack

signal analysis

THDA device

signal

source

de-

coupling

µµCC ≈≈≈≈≈≈≈≈

fuel cell system

M

DC

AC

DC

DC

DC

DC

FC FC controlcontrol

iAC

stack voltage

CAN 2.0

inverters, converters, etc.

stack current

+12V

THDA INSTRUMENTATION PRINCIPLE

� Superimposition of a small AC signal*

� (Spectral-)Analysis of voltage in terms of extra spectral components

i.e. harmonic distortion

* iAC = typ. 1A (�1mV/cell, sinusoidal, low frequency)

STAND ALONE APPROACH


battery pack

fuel cell system

M

DC

AC

DC

DC

DC

DC

FC control

iAC

inverters, converters, ect.

& signal modulation

w/ THDA

≈≈≈≈

iFC

+12V

b.

a.

FULLY INTEGRATED INSTRUMENTATION PRINCIPLE

a. Modulation of specific current signal pattern by converter

b. Embedded signal distortion analysis by existing FC controller (SW function)

COST EFFICIENT APPROACH


THDA OPERATION EXAMPLE (PEMFC SYSTEM)

„THDA level“

is indicating on-line criticalvoltage drifts(somewhere) in

the stack

5kW PEMFC System: Varying Air Supply Conditions Load = 2.5kW, AVL List GmbH 2007

0.0

0.5

1.0

1.5

2.0

200 220 240 260 280 300 320 340 360 380 400

time scale [s]

ce

ll v

olt

ag

e [

V]

air

la

mb

da [

-]

0

15

30

45

60

TH

DA

leve

l

air lambda

THDA

CVM (~100 channels)

5kW PEMFC System: Dead End Operation with Delayed Anode-Purge load = 2.4kW; AVL List GmbH 2007

-2.0

-1.0

0.0

1.0

2.0

25 50 75 100 125 150 175 200 225 250 275 300 325

time scale [s]

ce

ll v

olt

ag

e [

V]

0

12

24

36

48

TH

DA

le

ve

l

H2 purge

THDA

CVM (~100 channels)

H2 purgeH2 purge


On-line determination of causes for detected critical cell voltage drops/drifts:

� Water issues (flooding – drying)

� Low media supply issues (cathode – anode)

Usage of same hardware and same instrumentation principle

i.e. continuing cost efficient 2 channel approach

EXTENDED DIAGNOSIS FUNCTIONS: CLASSIFICATION OF CRITICAL CONDITIONS


ON-LINE DETECTION OF CRITICAL WATER ISSUES

Extended On-line Diagnosis "AVL-THDA"E.R., AVL List GmbH, Dec.08

0

20

40

60

80

100

120

140

160

0 500 1000 1500 2000 2500 3000

time [s]

inte

ns

ity

of

iss

ue

[-]

, te

mp

era

ture

[°C

]

0.0

0.5

1.0

1.5

2.0

2.5

sto

ich

iom

etr

y

membrane issuecathode issuewater issuetemperatureair stoichiometry

temperature

increase

>> dryout

high air flow

>> dryout

too fast air reduction

>> blocking through

remaining water

continous air reduction

>> insufficient O2 supplyISSUES:

drying issueliquid waterair supply issue


DETERMINATION INTO ANODE – CATHODE ISSUES

“THDA” indicates

critical cell conditions

5kW PEMFC System: Varying Air Supply Conditions Load = 2.5kW, AVL List GmbH 2007

0.0

0.5

1.0

1.5

2.0

200 220 240 260 280 300 320 340 360 380 400

time scale [s]

cell

vo

ltag

e [

V]

air

la

mb

da

[-]

0

10

20

30

40

TH

DA

lev

el

air lambda

THDA

CVM (~100 channels)

cathode relevance

5kW PEMFC System: Dead End Operation with Delayed Anode-Purge load = 2.4kW; AVL List GmbH 2007

-2.0

-1.0

0.0

1.0

2.0

25 50 75 100 125 150 175 200 225 250 275 300 325

time scale [s]

ce

ll v

olt

ag

e [

V]

0

12

24

36

48

TH

DA

le

ve

l &

ca

tho

de

re

lev

an

ce

H2 purge

THDA

CVM (~100 channels)

H2 purgeH2 purge

cathode relevancecathode relevance

cathode relevance

PLUS: “CATHODE

RELEVANCE”FOLLOWS “THDA”(cathode issue) OR STAYS CLOSE

ZERO (anode issue)


SYSTEM VIEW: RELIABILITY & ROBUSTNESS

Criteria for stack monitoring with extended diagnosis functions are

� ROBUST within entire system environment due to special failure detection

and compensation algorithm

� Still detectable without cell voltage monitoring (main criteria are harmonic

distortion based)

THDA index

cathode relevance

plausibility checkwire break, out of range, device overload

EMIelectromagnetically interference

stack voltage stack current

overlapping signalsblower control, motor frequency, valves

2kHz/22bit

signal noisehigher frequency switching signals

load changesimpacting spectral components

2kHz/22bit

criterion #1

criterion #2

criterion #3

criterion #4

~40 parameters

index for critical stack operation

correlation to cathode issues

e.g. thd @f1

…

…

…

water status


ROBUSTNESS: THDA OUTPUT EXAMPLE IN AN AUTOMOTIVE SYSTEM

Automotive FC System: THDA during temporary critical air supply issuesAVL List GmbH, 2007

0

10

20

30

40

50

60

0 50 100 150 200 250

time [s]

TH

DA

level [-

]

Vo

ltag

e &

Cu

rren

t

THDA index

thd w/o compensation

stack voltage

stack current

Within automotive environment usually occur electromagnetic interferences (grey plot).

AVL has developed compensation algorithm for reliable THDA measurement (red plot) � critical issues are clearly indicated


RELIABILITY: AUTOMATED ERROR DETECTION IN THE THDA CALCULATION

harmonic distortion measurementat two different frequencies:

blower controller causes error(controller uses same frequency as set for THDA)

THDA Index

with automatederror compensation

THDA Messungen am Range Extender: Einfluss von LastschwankungenLastschwankungen ca. 20A/s; Pe=1.8kW & 3.0kW. 94 Zellen PEMFC Stack, Inverter ist abgeschalten.

Log-Datei="lastschwankungen.txt"; E.R. 25.Juni 2007

0

8

16

24

32

40

48

56

64

0 25 50 75 100 125 150 175 200

Zeit [s]

Klirr

fak

tor

[%]

0

10

20

30

40

50

60

70

80

Str

om

[A

], S

pa

nn

un

g [

V]

thd1

thd2

V_fc [V]

I_fc [A]

THDA Messungen am Range Extender: Einfluss von LastschwankungenLastschwankungen ca. 20A/s; Pe=1.8kW & 3.0kW. 94 Zellen PEMFC Stack, Inverter ist abgeschalten.

Log-Datei="lastschwankungen.txt"; E.R. 25.Juni 2007

25 50 75 100 125 150 175 200

Zeit [s]

0

10

20

30

40

50

60

70

80

Str

om

[A

], S

pa

nn

un

g [

V]

thd

V_fc [V]

I_fc [A]

cut

cut

dynamic load test of stationary PEMFC system with THDA Monitoring

time [s] time [s]

thd

[%]

cu

rre

nt&

vo

lta

ge

THDA

current

voltage

thd@f1

thd@f2


SPIN-OFF EFFECT: ONLINE FAST ELECTRICAL IMPEDANCE MEASUREMENT

Conclusions from this example: only imaginary fraction changes at lower frequencies

� douple layer capacity = constant & not important � membrane characteristics not changed � activation resistance to be considered � harmonic distortion effects for air supply issues below ~20Hz

Niquist Plot for Air Supply Variationsair lambda varies from 2.1 to 1.6; frequencies=6/14/26/96/1000Hz; P=500W

AVL List GmbH, July 2008

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

real [Ohm]

ima

gin

ary

* [O

hm

]

Z1

Z2

Z3

Z4

Z5

Z1typ

Z2typ

Z3typ

Z1crit.

Z2crit.

Z3crit.25Hz

15Hz

5Hz

100Hz

1kHz

Continously EIS scan every 0.5 sec.

shows eventime variantconditions e.g. during waterblocking issues


micro-processorboard

4 signal inputs(500Volt)

analogue alternatingcurrent super-

imposition (3A)

CAN 2.0 & RS232 isolated I/O‘s

fully isolated12VDC power supply

amplifiere board

hall sensor

supply

fully equipped & ready forimmediate measurment

micro-processorboard

4 signal inputs(500Volt)

analogue alternatingcurrent super-

imposition (3A)

CAN 2.0 & RS232 isolated I/O‘s

fully isolated12VDC power supply

amplifiere board

hall sensor

supply

fully equipped & ready forimmediate measurment

HW & SW EQUIPPMENT

CAN 2.0RS232

AVL PUMA FC TESTBENCHGUI for logging and visualisation

FC CONTROLLER


OUTLOOK: LIFETIME MEASUREMENT

Online STATE OF HEALTH MEASUREMENT on

basis of THDA approach including interpretation of

certain electrical impedance parameters

TARGET is a powerful online monitoring

technology including

� detection of critical cell conditions

� determination of failure causes

� SOH measurement

for increasing system efficiency,

fuel cell lifetime and reliability on

cost efficient HW approach

Cooperative project with partners

supported by

Evolution of the fuel cell state of health as a function of timeN.Fouquet et al /Journal of Power Sources, Volume 159, Issue 2,

22 September 2006, Pages905-913


AVL THDA is an ONLINE STACK MONITORING TECHNOLOGY based on

analyzing harmonic distortion effects of voltage drifts instead of single cell

voltage measurement

Standard THDA routines together with extended criteria give the EXTRA

INFORMATION FOR CLASSIFICATION into cathode, anode or membrane

effects

Two channel measurement (VFC, IFC) with COST EFFECTIVE HARDWARE

components significantly reduces the instrumentation effort

THDA includes special algorithm for ROBUSTNESS & RELIABILITY within

practical system application

SUMMARY

Documents

ONLINE PEMFC STACK MONITORING WITH “THDA“...AVL THDA , Trondheim, 23rd – 24th June 2009 8 ON-LINE DETECTION OF CRITICAL WATER ISSUES Extended On-line Diagnosis "AVL-THDA" E.R.,