Thank You for Your Attention

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Stefan Pofahl (AVL)Principles of THDA™ Methodology

Total Harmonic Distortion

Analysis-based diagnostics

for PEMFC

Total Harmonic Distortion Analysis-based

diagnostics for PEMFC

Outlineo Fuel Cell Stack Monitoring: State of the Art / Requirements

o Principles of THDA-based PEMFC Diagnostics

o FFT & Concept of Harmonic Distortion Analysis

o Features of THDA Methodology

o Summary & Discussion

2015: v1.02005: v0.0

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Fuel Cell Stack Monitoring

STATE OF THE ART FOR PEMFC MONITORING

• Measuring of individual single cell voltages or cell voltage pairs analysis in terms of voltage drifts (Cell Voltage Monitoring / CVM)

• Drawbacks:

• High instrumentation effort and elaborated wiring concepts for reliable operation

• Determination of failure causes or lifetime estimations are not possible

REQUIREMENT

• Real time indication of critical fuel cell conditions, i.e. online monitoring

• Detection of the route cause of cell voltage drops and its reasons initiate counteractions

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AVL PEMFC stack monitoring

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

current superimposition

voltage measurement signal analysis on stack level

diagnostic algorithms on stack level

dry-out low media liquid water

on stack level

FC Stack

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PRINCIPLE OF FC-MONITORING WITH AVL-THDA

*patented, registered trademark

“THDA™” – Total Harmonic Distortion Analysis* 5

Concept of Harmonic Distortion Analysis

FFT, Transition: Time Domain Frequency Domain

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Concept of Harmonic Distortion Analysis

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Theoretical Example for THDA

oHealthy condition

THDA INPUT: FC OUTPUT: FFT:

AC stack voltage response noisy signal frequencies can be identified

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Theoretical Example for THDA

oCritical condition

THDA INPUT: FC OUTPUT: FFT

AC stack voltage response noisy,

harmonics are formed

harmonics can be detected

2nd harmonic of 50Hz

2nd harmonic of 120Hz

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Theoretical Example for THD calculation

no 2nd harmonic of 50Hz

no 2nd harmonic of 120Hz

healthy condition

no harmonics

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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)

criterion #1 criterion #2 criterion #3 criterion #4 criterion #12

low media supply + + +++ o o

liquid water droplets o + +++ ++ + o

membrane dry out o o o o +++

…

sensitivity of effects to criteria: o = none, + = sensible, ++ = moderate influence, +++ = high influence

effe

ct

criteria: measured physical parametere.g. thd@f1, imaginary@f1, phase@f3, real@f5 etc.

membrane issue#12 (only)

water issue(#3 & #2 & #4) and not #1

low media(#1 & #2 & #3) and not #4

rule

* criteria are… • derived from FC voltage & current at four different frequencies, analyzed in time or frequency domain

• total 12-15 different criteria implemented in detection algorithms

METHODOLOGY

• Different operating conditions typical changes of electr. characteristics (collection of several criteria*)

• Interpretation of changes in criteria and correlation to operating conditions description with mathematical formulas

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THDA INSTRUMENTATION PRINCIPLE

Demonstration & Testing Phase

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

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 (1mV/cell, sinusoidal, low frequency)

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

output data

1

23

13

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.

THDA INSTRUMENTATION PRINCIPLE

Product Embedded

COST EFFICIENT APPROACH:

full integration of THDA functions

(no additional devices are needed

for THDA)

a. Modulation of specific current

signal pattern by power inverter

small modification of inverter is

needed (by inverter company)

b. Signal measurement and analysis by existing FC

controller (ECU) small modification of ECU in terms of

signal input filter is needed (by ECU company);

implementation of THDA SW module in to the ECU code

1. THDA algorithm is integrated to the fuel cell system contoller

2. Signal processing can be integrated into the existing power electronics!

THDA doesn‘t add HW costs to fuel cell systems, only licence agreement with AVL required!

1. THDA algorithm is integrated to the fuel cell system contoller

2. Signal processing can be integrated into the existing power electronics!

THDA doesn‘t add HW costs to fuel cell systems, only licence agreement with AVL required!

DESCRIPTION OF FC-MONITORING WITH “AVL-THDA”

*patented, registered trademark

“THDA™” – Total Harmonic Distortion Analysis*

• 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

Reduced measurement effort:

• stack voltage & stack current only

cost efficient 2 channel instrumentation

easy set-up

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ADVANTAGES OF FC-MONITORING

WITH “AVL-THDA”

*patented, registered trademark

“THDA™” – Total Harmonic Distortion Analysis*

• 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

Decreasing of RH by 10% at a current density of 0.1A/cm² causing a voltage drop of 8mV per cell. THDA-indicator “dry-out” detects and identifies even small performance losses.

EXAMPLE

Decreasing of RH by 10% at a current density of 0.1A/cm² causing a voltage drop of 8mV per cell. THDA-indicator “dry-out” detects and identifies even small performance losses.

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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

Visualization of Harmonics

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Summary

THDA is intended to monitor fuel cell stacks in real product applications

like FCEV, CHP, mCHP, APU,…

THDA gives online info on state of dry out, low media, liquid water

THDA offers fast EIS

Laboratory instrumentation product THDA™ is a commercial product

AVL THDA™ validated by 7 major automotive OEMs

and >10 fuel cell system integrators from other industries.

No additional hardware required for product application THDA

THDA algorithm can run in existing control HW

Outlook:

“State of Health (SoH)”-Rating

Distinguish between “Low Fuel” and “Low Air”

Monitor SOFC Stacks (Projects will start in 2016)

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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