Evaluation of Total Harmonic Distortion tool for SOFC diagnostics

(1)

!

DIAMOND

DIAMOND

Diagnosis-aided control for SOFC power systems

FCH-JU-2013-1 GRANT AGREEMENT NUMBER: 621208

Evaluation of Total Harmonic Distortion tool for

SOFC diagnostics

Bertrand Morel – André Chatroux

CEA Grenoble

Workshop on Monitoring, Diagnostics and Control for SOFC systems

Improving SOFC-based CHP performance through innovative

diagnosis and control

Naples (I) –

December 16

th

, 2015

(2)

!

DIAMOND

2 DIAMOND – Mid-Term Workshop

• 

Introduc;on: What is Total Harmonic Distor;on (THD)?

• 

Applica;on of THD on small SOFC cell

• 

Transposi;on of THD to 25-cells stack

• 

Conclusions

(3)

!

DIAMOND

Selection of the 3 most critical faults/failures made by all partners in DIAMOND project:

o  Fuel starvation

o  Air starvation

o  O/C & S/C ratio too low

Reasons for the use of THD

Cell voltage measurement is a good sensor but…

Are voltage probes necessary at every stages?

è  Total Harmonic Distortion Analysis could be a way to decrease the number of voltage probes

(4)

!

DIAMOND

THD=Total Harmonic Distortion

A small sinusoidal current signal is superimposed at an operating point

è under ideal operating conditions (linear part of i-V curve) it leads to a sinusoidal voltage response transformed by a linear function (not distorted)

è under critical conditions (like air or fuel starvation) the whole polarization curve shifts and there is an harmonic distortion of the cell voltage response.

(5)

!

DIAMOND

1 2 2

Y

THD

k k

∑

∞ =

=

Then, THD is defined as the ratio of the Euclidean norm of the system response Y of all higher harmonic frequencies (k≥2) to that of the fundamental frequency (k = 1).

è THD = effective method to evaluate nonlinearity of a system: the harmonic content of a waveform is compared to its fundamental.

References:

(6)

!

DIAMOND

THD in the literature

Ramschak, E., Peinecke, V., Prenninger, P., Schaﬀer, T., Hacker, V., 2006. Detec%on of fuel cell cri%cal status by stack voltage analysis. Journal of Power Sources 157, 837–840. doi:10.1016/j.jpowsour.2006.01.009

Kiel, M., Bohlen, O., Sauer, D.U., 2008. Harmonic analysis for iden%ﬁca%on of nonlineari%es in impedance spectroscopy. Electrochimica Acta 53, 7367–7374. doi:10.1016/j.electacta.2008.01.089

Mao, Q., Krewer, U., Hanke-Rauschenbach, R., 2010. Total harmonic distor%on analysis for direct methanol fuel cell anode. Electrochemistry Communica;ons 12, 1517–1519. doi:10.1016/j.elecom.2010.08.022

Mao, Q., Krewer, U., 2012. Sensing methanol concentra%on in direct methanol fuel cell with total harmonic distor%on: Theory and applica%on. Electrochimica Acta 68, 60–68. doi:10.1016/j.electacta.2012.02.018

Mao, Q., Krewer, U., 2013. Total harmonic distor%on analysis of oxygen reduc%on reac%on in proton exchange membrane fuel cells. Electrochimica Acta 103, 188–198. doi:10.1016/j.electacta.2013.03.194

Thomas, S., Lee, S.C., Sahu, A.K., Park, S., 2014. Online health monitoring of a fuel cell using total harmonic distor%on analysis. Interna;onal Journal of Hydrogen Energy 39, 4558–4565. doi:10.1016/j.ijhydene.2013.12.180

Renner, K., Rechberger J., 2015. PEMFC Stack Monitoring with Advanced Total Harmonic Distor%on Analysis. A0801, Proceeding of EFCF 2015, Luzern.

Mosbaek, R.R., DTU Ph.D. Thesis, October 2014. Solid Oxide Fuel Cell Stack Diagnos%cs. Chapter 6 “Fuel starva;on detec;on with THD”.

(7)

!

DIAMOND

SOFC cell/

stack

DC load load AC

+

-

i_DC iAC Cell Voltage Measurements U_cell

Autolab, electronic load,…

Autolab, Hioki,…

Alterna;ve

Voltage Signal Windowing Fast Fourier Transform

Detec;on of Fundamental

Frequency

THD calcula;on

(8)

!

DIAMOND

THD on a SOFC single cell of 9 cm

²

I

+

I

-

V

+

V

-

Autolab PGSTAT302N = generator of sinusoidal current from 104_{to 10}-2_Hz

è I_DC + I_AC

è High sampling rate

(9)

!

DIAMOND

THD on a SOFC single cell

SolidPower single cell with ac;ve surface area=9.08 cm² T=800°C, AU=20% and FU=60% @ i_DC=0.5 A/cm²

è  Frequency range tested: 104->10-2 Hz

è  4 amplitudes tested: 1, 5, 10 and 20% of i_DC

è  5 FU tested: 60, 70, 80, 85 and 90% by varying i_DC

Amplitude, frequency and FU tested for THD analysis

Ex. @ i_DC=0.5 A/cm² 1% è +/- 0.005 A/cm² 5% è +/- 0.025 A/cm² 10% è +/- 0.05 A/cm² 20% è +/- 0.1 A/cm²

FU=60%

FU=70%

FU=80%

FU=90%

FU=85%

(10)

!

DIAMOND

T=800C, AU=20%

EIS performed between 104_{and 0.01 Hz}

@ i_DC=0.5 A/cm² +/-5% è +/- 0.025 A/cm² @ i_DC=0.584 A/cm² +/-5% è +/- 0.029 A/cm² @ i_DC=0.667 A/cm² +/-5% è +/- 0.033 A/cm² FU=60% FU=70% FU=80% FU=90% FU=85% @ i_DC=0.708 A/cm² +/-5% è +/- 0.035 A/cm² @ i_DC=0.750 A/cm² +/-1% è +/- 0.007 A/cm²

(11)

!

DIAMOND

THD on a SOFC single cell @ FU=60%

T=800°C, AU=20% @ i_DC=0.5 A/cm² i(DC)=0.5 A/cm² è FU=60%

+/- i_AC=1%, 5%, 10%, 20% i_DC

(12)

!

DIAMOND

T=800°C, AU=20% @ i_DC=0.5 A/cm² i_DC=0.5 A/cm² è FU=60%

+/- i_AC=1%, 5%, 10%, 20% i_DC

è  THD analysis impacted by noise

when a small amplitude (1%) is used

è  %THD increases at low

frequency (0.01 Hz) and when AC amplitude is increased

(13)

!

DIAMOND

T=800°C, AU=23.3% @ i_DC=0.584 A/cm² i(DC)=0.584 A/cm² è FU=70%

+/- i_AC=1%, 5%, 10%, 20% i_DC

è  Distorsion of EIS diagram only with

(14)

!

DIAMOND

T=800°C, AU=23.3% @ i_DC=0.584 A/cm² i(DC)=0.584 A/cm² è FU=70%

+/- i_AC=1%, 5%, 10%, 20% i_DC

è  Idem, THD analysis impacted

by noise when a small amplitude (1%) is used

è  %THD increases signiﬁcantly

at low frequency (0.01 Hz) and when AC amplitude is increased

(15)

!

DIAMOND

T=800°C, AU=26.6% @ i_DC=0.667 A/cm² i_DC=0.667 A/cm² è FU=80%

+/- i_AC=1%, 5%, 10%, 20% i_DC

è  Distorsion of EIS diagram starts with an AC

(16)

!

DIAMOND

T=800°C, AU=26.6% @ i_DC=0.667 A/cm² i_DC=0.667 A/cm² è FU=80%

+/- i_AC=1%, 5%, 10%, 20% i_DC

è  %THD increases also at 0.1 Hz

è  An addi;onal phenomena is

imposed at low frequency by a 20% AC amplitude that could be reoxida;on of Ni

(17)

!

DIAMOND

+/- i_AC=1%, 5%, 10% i_DC

è  Distorsion of EIS diagram starts with an AC

(18)

!

DIAMOND

+/- i_AC=1%, 5%, 10% i_DC

è  %THD increases also at 0.1 Hz

(19)

!

DIAMOND

è  Huge distorsion of EIS diagram at

AC amplitude of 5% T=800°C, AU=30% @ i_DC=0.75 A/cm²

i_DC=0.75 A/cm² è FU=90% +/- i_AC=1%, 5% i_DC

(20)

!

DIAMOND

+/- i_AC=1%, 5% i_DC

(21)

!

DIAMOND

THD results - Summary : effect of amplitude, frequency and

FU on THD analysis

è  Usefull range of frequency to be studied: 1->0.01 Hz

è  With a 5% AC amplitude it’s possible to detect FU>80% between 0.01 Hz and 0.1 Hz. A reoxida;on

phenomena seems to be detected with THD analysis at FU=90%.

è  With a 10% AC amplitude it’s easier to detect FU>80% between 0.01 Hz and 0.1 Hz.

FU=60, 70, 80, 85 et 90%

(22)

!

DIAMOND

THD on a 25-cells stack

25-cells stack Autolab PGSTAT302N = generator of sinusoidal current from 104_{to 10}-2_Hz è I_DC + I_AC

Hioki = portable data logger

è Simultaneous acquisi;on

of 25 cell voltage measurements

è High sampling rate = 20 ms

è High resolu;on = 50 µV

+

(23)

!

DIAMOND

THD on a faulty 25-cells stack

è  With i-V curves, it’s easy to make a diagnos;c!

è  Is THD abble to detect cell 21?

THD performed @ -i_DC=40 mA/cm²

-i_AC=4 mA/cm² (10% of i_DC) -fq=0.1, 0.031 and 0.01 Hz

(24)

!

DIAMOND

THD on a faulty 25-cells stack

è  THD value is high for the cell 21 and also for the cell 15

è  This value is increasing when frequency is decreased

è  @ 0.01 Hz, diﬀerence of THD value between a ‘good’ cell and a ‘bad’ cell is a 10 factor

THD performed @ -i_DC=40 mA/cm²

-i_AC=4 mA/cm² (10% of i_DC) -fq=0.1, 0.031 and 0.01 Hz

(25)

!

DIAMOND

THD on a faulty 25-cells stack @ i=40 mA/cm

²

è  Ra;o between Standard Devia;on and Mean value indicates that a higher sensibility is obtained

(26)

!

DIAMOND

Conclusions and perspectives

è  THD analysis is adapted for fuel/air starva;on detec;on at single cell level

Usefull range of frequency to be studied: 1->0.01 Hz

è  Transposi;on of THDA has been done on a 25-cells stack

è  It appears that detec;on of fault like high FU will be more accurate with mean value of THD than

mean value of cell voltage measurements.

è  Decreasing the number of cell voltage probes seems to be realis;c