online pemfc stack monitoring with “thda“...avl thda , trondheim, 23rd – 24th june 2009 8...
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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*
3AVL THDA, Trondheim, 23rd – 24th June 2009
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]
4AVL THDA, Trondheim, 23rd – 24th June 2009
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
5AVL THDA, Trondheim, 23rd – 24th June 2009
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
6AVL THDA, Trondheim, 23rd – 24th June 2009
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
7AVL THDA, Trondheim, 23rd – 24th June 2009
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
8AVL THDA, Trondheim, 23rd – 24th June 2009
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
9AVL THDA, Trondheim, 23rd – 24th June 2009
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)
10AVL THDA, Trondheim, 23rd – 24th June 2009
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
11AVL THDA, Trondheim, 23rd – 24th June 2009
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
12AVL THDA, Trondheim, 23rd – 24th June 2009
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
13AVL THDA, Trondheim, 23rd – 24th June 2009
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
14AVL THDA, Trondheim, 23rd – 24th June 2009
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
15AVL THDA, Trondheim, 23rd – 24th June 2009
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
16AVL THDA, Trondheim, 23rd – 24th June 2009
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