Download Total Harmonic Distortion Analysis-based

Total Harmonic Distortion
Thank You for Your Attention
Analysis-based
diagnostics
for PEMFC
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StefanPofahl(AVL)–DanielRitzberger(TUVienna)
DIAMONDMid-termexploitaDonWorkshop
WorkshoponMonitoring,DiagnosDcsandControlforSOFCsystems
ImprovingSOFC-basedCHPperformancethroughinnovaDvediagnosisandcontrol
16thDec2015,Napoli,Italy
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Total Harmonic Distortion Analysis-based
diagnostics for PEMFC
Outline
o 
o 
o 
o 
o 
Fuel Cell Stack Monitoring: State of the Art / Requirements
Principles of THDA-based PEMFC Diagnostics
FFT & Concept of Harmonic Distortion Analysis
Features of THDA Methodology
Generalized Frequency Response Function
(Daniel Ritzberger / TU Vienna) o  Model-based Calibration
(Daniel Ritzberger / TU Vienna)
o  Summary & Discussion
2005:v0.0
2015:v1.0
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Fuel Cell Stack Monitoring
STATEOFTHEARTFORPEMFCMONITORING
•  Measuringofindividualsinglecellvoltagesorcellvoltagepairs
analysisintermsofvoltagedriWs(CellVoltageMonitoring/CVM)
•  HighinstrumentaDoneffortand
elaboratedwiringconceptsforreliableoperaDon
•  Drawback:
DeterminaDonoffailurecausesorlifeDmeesDmaDonsarenotpossible
REQUIREMENT
•  RealDmeindicaDonofcriDcalfuelcellcondiDons,i.e.onlinemonitoring
•  DetecDonofcellvoltagedropsanditsreasons
àiniDatecounteracDons
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AVL PEMFC stack monitoring
battery
pack
voltage
measurement
signal analysis on stack level
inverters,
fuel cell system
FC Stack
diagnostic algorithms on stack level
stack
current
FC control
iAC
current superimposition
stack
voltage
CAN 2.0
dryout low media liquid water
THDAon
device
stack level
µC
signal
analysis
≈
signal
source
decoupling
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PRINCIPLE OF FC-MONITORING WITH AVL-THDA
“THDA™” – Total Harmonic Distortion Analysis*
*patented, registered trademark
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Concept of Harmonic Distortion Analysis
FFT:TransiDonTimeDomainàFrequencyDomain
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Concept of Harmonic Distortion Analysis
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Theoretical Example for THDA
o Healthy condition
THDA INPUT:
FC OUTPUT:
AC stack voltage response
FFT:
signal frequencies can be identified
noisy
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Theoretical Example for THDA
o Critical condition
THDA INPUT:
FC OUTPUT:
FFT
2nd harmonic of 50Hz
2nd harmonic of 120Hz
AC stack voltage response
harmonics can be detected
noisy, harmonics are formed
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Theoretical Example for THD calculation
no 2nd harmonic of 50Hz
no 2nd harmonic of 120Hz
healthy condition
noharmonics
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Theoretical Example for THD calculation
2nd harmonic of 50Hz
2nd harmonic of 120Hz
critical condition
harmonics
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MATRIX EXAMPLE FOR CLASSIFICATION
(SIMPLIFIED)
criteria: measured physical parameter
effect
e.g. thd@f1, imaginary@f1, phase@f3, real@f5 etc.
criterion #1
criterion #2
criterion #3
criterion #4
low media supply
+
+
+++
o
liquid water droplets
o
+
+++
++
membrane dry out
o
o
o
o
…
criterion #12
o
+
o
+++
sensitivity of effects to criteria:
o = none, + = sensible, ++ = moderate influence, +++ = high influence
rule
low media
water issue
membrane issue
(#1 & #2 & #3) and not #4
(#3 & #2 & #4) and not #1
#12 (only)
METHODOLOGY
•  DifferentoperaDngcondiDons
àtypicalchangesofelectr.characterisDcs(collecDonofseveralcriteria*)
•  InterpretaDonofchangesincriteriaandcorrelaDontooperaDngcondiDons
àdescripDonwithmathemaDcalformulas
* criteria
are…
•  derived from FC voltage & current at four different frequencies, analysed in time or frequency domain
•  total 12-15 different criteria implemented in detection algorithms
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THDA INSTRUMENTATION PRINCIPLE
Demonstration & Testing Phase
battery pack
inverters, converters, etc.
DC
fuel cell system
DC
DC
DC
DC
2
3
stack
voltage
output data
1
stack
current
FC control
CAN 2.0
+12V
AC
iAC
THDA device
µC
signal
analysis
M
≈
signal
source
decoupling
HARDWARE PRINCIPLE
1.  Superimposition of a small alternating current signal burst* during operation
2.  (Spectral-)Analysis of signal response = voltage (thd measurement,
impedance spectroscopy, statistical parameters, …)
3.  Results via CAN or RS232 interface to FC controller or GUI
* iAC = typ. 1A (à1mV/cell, sinusoidal, low frequency)
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DESCRIPTION OF FC-MONITORING WITH “AVL-THDA”
•  Defects or critical conditions
• 
local non-linearity in the transfer function
• 
distort a superimposed signal
• 
form harmonics
•  Extra spectral components (i.e. harmonics) are detectable in the
entire stack sum voltage
à
Reduced measurement effort:
• 
stack voltage & stack current only
cost efficient 2 channel instrumentation
easy set-up
“THDA™” – Total Harmonic Distortion Analysis*
*patented, registered trademark
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ADVANTAGES OF FC-MONITORING
WITH “AVL-THDA”
•  On basis of THDA HW approach:
variety of electrical stack characteristics are additionally available
i.e. electrochemical impedance spectroscopy (EIS) on stack level
•  Quick response time
•  Good detection resolution
EXAMPLE
DecreasingofRHby10%atacurrentdensityof0.1A/cm²causingavoltagedropof8mV
percell.
àTHDA-dryoutdetectsandidenDfiesevensmallperformancelosses.
“THDA™” – Total Harmonic Distortion Analysis*
*patented, registered trademark
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EXTENDED DIAGNOSIS FUNCTIONS
Determination of causes in case of critical cell voltage drifts i.e.
classification into
•  Water issues (liquid water droplets in flow field)
•  Media supply issues (cathode – anode)
•  Dry out (membrane)
Constraint:
Usage of same hardware and same instrumentation
VisualizaDonofHarmonics
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Generalized Frequency Response Function
IntermodulaDon:
ExemplaryGFRF:
FromtheUniversityofSheffield:
www.dflybrain.org/GFRFResults.html
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Model-based Calibration
Nonlinear system identification of fuel cells
o  NARMAX model in time domain
o  Generalized Frequency Response Function (GFRF) in frequency domain
NARMAX model identified under normal operating conditions used for output
prediction
è significant deviation suggest change of operation point (e.g. fault)
EIS, THDA and intermodulation of multi-tone excitation described by GFRF.
NARMAX Model and GFRF allow for a holistic model analysis in time and
frequency domain for nonlinear systems.
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Summary
è  THDA is intended to monitor fuel cell stacks in real product applications
like FCEV, CHP, mCHP, APU,…
è  THDA gives online info on state of dry out, low media, liquid water
è  THDA offers fast EIS
è  Laboratory instrumentation product THDA™ is a commercial product
è  AVL THDA™ validated by 7 major automotive OEMs
and >10 fuel cell system integrators from other industries.
è  No additional hardware required for product application THDA
THDA algorithm can run in existing control HW
Outlook:
è  “State of Health (SoH)”-Rating
è  Distinguish between “Low Fuel” and “Low Air”
è  Monitor SOFC Stacks (Projects will start in 2016)
è  Automated Calibration / Self-adaptive Calibration
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Thank You for Your Attention!
2005 – 2015:
HW and GUI
available as serial device
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Volterra series
Polynomial expansion of the linear convolution
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Volterra series
Volterra series with harmonic excitation:
Kernel 1. order:
Response of the 1. order kernel is the linear system response with the same
frequency but different amplitude and phase
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Volterra series
Volterra series with harmonic excitation:
Kernel 2. order:
Response of the 2. order kernel has doubled frequency (1. harmonic) and a
constant bias
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Volterra series
Volterra serias with bitonal excitation:
Kernel 2. order:
(excerpt)
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Output consists of:
first harmonic,
constant bias,
Intermodulated frequency
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Volterra series
Kernels described the nonlinear system
Generalized Frequency Response Functions:
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