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Total Harmonic Distortion Thank You for Your Attention Analysis-based diagnostics for PEMFC ! DIAMOND StefanPofahl(AVL)–DanielRitzberger(TUVienna) DIAMONDMid-termexploitaDonWorkshop WorkshoponMonitoring,DiagnosDcsandControlforSOFCsystems ImprovingSOFC-basedCHPperformancethroughinnovaDvediagnosisandcontrol 16thDec2015,Napoli,Italy 1 DIAMOND ! 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 2 ! DIAMOND Fuel Cell Stack Monitoring STATEOFTHEARTFORPEMFCMONITORING • Measuringofindividualsinglecellvoltagesorcellvoltagepairs analysisintermsofvoltagedriWs(CellVoltageMonitoring/CVM) • HighinstrumentaDoneffortand elaboratedwiringconceptsforreliableoperaDon • Drawback: DeterminaDonoffailurecausesorlifeDmeesDmaDonsarenotpossible REQUIREMENT • RealDmeindicaDonofcriDcalfuelcellcondiDons,i.e.onlinemonitoring • DetecDonofcellvoltagedropsanditsreasons àiniDatecounteracDons 3 DIAMOND ! 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 4 DIAMOND ! PRINCIPLE OF FC-MONITORING WITH AVL-THDA “THDA™” – Total Harmonic Distortion Analysis* *patented, registered trademark 5 DIAMOND ! Concept of Harmonic Distortion Analysis FFT:TransiDonTimeDomainàFrequencyDomain 6 DIAMOND ! Concept of Harmonic Distortion Analysis 7 DIAMOND ! Theoretical Example for THDA o Healthy condition THDA INPUT: FC OUTPUT: AC stack voltage response FFT: signal frequencies can be identified noisy 8 DIAMOND ! 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 9 DIAMOND ! Theoretical Example for THD calculation no 2nd harmonic of 50Hz no 2nd harmonic of 120Hz healthy condition noharmonics 10 DIAMOND ! Theoretical Example for THD calculation 2nd harmonic of 50Hz 2nd harmonic of 120Hz critical condition harmonics 11 DIAMOND ! 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 12 DIAMOND ! 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) 13 DIAMOND ! 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 14 DIAMOND ! 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 15 DIAMOND ! 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 16 DIAMOND ! Generalized Frequency Response Function IntermodulaDon: ExemplaryGFRF: FromtheUniversityofSheffield: www.dflybrain.org/GFRFResults.html 17 ! DIAMOND 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. 18 ! 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 DIAMOND ! DIAMOND Thank You for Your Attention! 2005 – 2015: HW and GUI available as serial device 20 ! Volterra series Polynomial expansion of the linear convolution 21 DIAMOND ! 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 DIAMOND ! 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 23 DIAMOND ! DIAMOND Volterra series Volterra serias with bitonal excitation: Kernel 2. order: (excerpt) 24 Output consists of: first harmonic, constant bias, Intermodulated frequency ! Volterra series Kernels described the nonlinear system Generalized Frequency Response Functions: 25 DIAMOND