[PPT] - ONLINE PEMFC STACK MONITORING WITH THDA Erich RAMSCHAK, AVL List PowerPoint Presentation

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International Symposium on DIAGNOSTIC TOOLS FOR FUEL CELL TECHNOLOGIES

ONLINE PEMFC STACK MONITORING WITH “THDA“

Erich RAMSCHAK, AVL List GmbH

Trondheim, 23rd – 24th June 2009

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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 the

stack 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

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

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Trondheim, 23rd – 24th June 2009

BRIEF BACKGROUND OF HARMONIC DISTORTION

2 4 6 8 10 12

100
50

normalised frequency scale ≡ order of harmonics amplitude [dB]

Signal distortion forms extra components in the frequency spectrum.

Harmonics can be detected at integer multiplies

f the fundamental frequency
Occurrence of extra spectral components is measured
Quantification: “Klirrfactor” or “THD”, [%] [dB]

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Trondheim, 23rd – 24th June 2009

battery pack

signal analysis

THDA device

signal source de- coupling

µ µC C ≈ ≈ ≈ ≈ ≈ ≈ ≈ ≈ fuel cell system

M

DC AC DC DC DC DC

FC FC control control

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

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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

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Trondheim, 23rd – 24th June 2009

THDA OPERATION EXAMPLE (PEMFC SYSTEM)

„THDA level“ is indicating on- line critical voltage 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] cell voltage [V] air lambda [-]

15 30 45 60

THDA level 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] cell voltage [V]

12 24 36 48

THDA level

H2 purge

THDA

CVM (~100 channels)

H2 purge H2 purge

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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

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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 20 40 60 80 100 120 140 160 500 1000 1500 2000 2500 3000 time [s] intensity of issue [-], temperature [° C] 0.0 0.5 1.0 1.5 2.0 2.5 stoichiometry membrane issue cathode issue water issue temperature air stoichiometry

temperature increase >> dryout high air flow >> dryout too fast air reduction >> blocking through remaining water continous air reduction >> insufficient O2 supply ISSUES:

drying issue liquid water air supply issue

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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 voltage [V] air lambda [-]

10 20 30 40

THDA level

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] cell voltage [V]

12 24 36 48

TH DA level & cathode relevance

H2 purge

THDA

CVM (~100 channels)

H2 purge H2 purge

cathode relevance

cathode relevance cathode relevance

PLUS: “CATHODE RELEVANCE” FOLLOWS “THDA” (cathode issue) OR STAYS CLOSE ZERO (anode issue)

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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 check

wire break, out of range, device overload

EMI

electromagnetically interference

stack voltage stack current

verlapping signals

blower control, motor frequency, valves 2kHz/22bit

signal noise

higher frequency switching signals

load changes

impacting 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

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Trondheim, 23rd – 24th June 2009

ROBUSTNESS: THDA OUTPUT EXAMPLE IN AN AUTOMOTIVE SYSTEM

Automotive FC System: THDA during temporary critical air supply issues

AVL List GmbH, 2007

10 20 30 40 50 60 50 100 150 200 250 time [s] THDA level [-] Voltage & Current 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

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Trondheim, 23rd – 24th June 2009

RELIABILITY: AUTOMATED ERROR DETECTION IN THE THDA CALCULATION

harmonic distortion measurement at two different frequencies: blower controller causes error

(controller uses same frequency as set for THDA)

THDA Index with automated error compensation

THDA Messungen am Range Extender: Einfluss von Lastschwankungen

Lastschwankungen ca. 20A/s; Pe=1.8kW & 3.0kW. 94 Zellen PEMFC Stack, Inverter ist abgeschalten.

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

8 16 24 32 40 48 56 64 25 50 75 100 125 150 175 200 Zeit [s] Klirrfaktor [%] 10 20 30 40 50 60 70 80 Strom [A], Spannung [V] thd1 thd2 V_fc [V] I_fc [A]

THDA Messungen am Range Extender: Einfluss von Lastschwankungen

Lastschwankungen 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] 10 20 30 40 50 60 70 80 Strom [A], Spannung [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 [%] current & voltage

THDA current voltage thd@f1 thd@f2

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Trondheim, 23rd – 24th June 2009

SPIN-OFF EFFECT: ONLINE FAST ELECTRICAL IMPEDANCE MEASUREMENT

Conclusions from this example:

nly 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 Variations

air 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

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 real [Ohm] imaginary* [Ohm]

Z1 Z2 Z3 Z4 Z5 Z1typ Z2typ Z3typ Z1crit. Z2crit. Z3crit.

25Hz 15Hz 5Hz 100Hz 1kHz

Continously EIS scan every 0.5 sec. shows even time variant conditions e.g. during water blocking issues

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Trondheim, 23rd – 24th June 2009

micro-processor board 4 signal inputs (500Volt) analogue alternating current superimposition (3A) CAN 2.0 & RS232 isolated I/O‘s fully isolated 12VDC power supply amplifiere board hall sensor supply

fully equipped & ready for immediate measurment