Rui Gao presented on model-based design for fuel cell systems using Modelica. The presentation discussed modeling a hybrid SOFC system from a systems perspective using equation-based and object-oriented Modelica models that integrate multi-disciplinary physics. Subsystem tests were conducted on models of the preprocessor and micro gas turbine. Simulation results showed mass balance, fuel cell voltage-current characteristics, thermal losses, and AC power output. Model-based design was identified as a promising approach for smart grid system development to enable bidirectional power flow.

1. MODEL-BASED DESIGN FOR FUEL CELL SYSTEM
Rui GAO Modelon
MECJ-2016, Kyushu University, Fukuoka
1Mechanics Engineering Congress, Japan, 2016
Mechanics Engineering Congress, 2016, Japan
9/14/2016

2. AGENDA
• System perspective to the fuel cell system
• Model-based design for fuel cell system
• Application to smart grid
• Summary
2Mechanics Engineering Congress, Japan, 20169/14/2016

3. SYSTEM PERSPECTIVE TO THE FUEL CELL SYSTEM
• Fuel cell
 Electrolyte
 Cathode
 Anode
• R&D on the
complex fuel
cell system is
mainly by
experimental
method; Few
study is by
Model-based
Design (MBD)
3Mechanics Engineering Congress, Japan, 20169/14/2016

4. SYSTEM PERSPECTIVE TO THE FUEL CELL SYSTEM
• Hybrid SOFC system
 Input:
• Natural gas, water, air
 Preprocessor:
• mix, pre-heat, reform into syngas
 SOFC:
• 5KW stack with 50 cells grouped in
three substacks
• Reformed syngas to anode;
internal reforming reactions.
• Hot air to Cathode
 Micro gas turbine
• Compressor
• Burner
• Turbine
4
Preprocessor
Fuel Cell
Gas Turbine
HX Mix Reform
HX
HX
dd Drain_An Drain_Ca
Exh_gas
NG, Water
Air
Air
Feed_An
Feed_Ca
Mechanics Engineering Congress, Japan, 20169/14/2016

5. SYSTEM PERSPECTIVE TO THE FUEL CELL SYSTEM
5
• System of system
 Traditional power grid
• Single power flow
 Smart power grid
• Bidirectional power flow
http://www.news.gatech.edu/features/building-power-grid-
future
Mechanics Engineering Congress, Japan, 20169/14/2016

6. FUEL CELL MODEL FROM SYSTEM’S DEMAND
6
FC system characteristics
Complex system with
Electro-chemical, Thermo-
fluid, Electrical, Heat
transfer and Control
Engineering
Reaction can be built using
common mechanism;
Specific reactants are
different.
Various system
configurations: PEFC, MCFC,
SOFC, …
Bidirectional power flow
under smart grid paradigm
Demanded model features
Multi-disciplines models
Object oriented model with
partial model and inherited
complete model
Baseline design as template
model, and easy configured
variant design
Acausal model
http://www.2015-2016toyotagroupcars.com/2016-
toyota-mirai/
https://fuelcellsworks.com/archives/2012/06/01/mhi-to-
develop-fuel-cell-triple-combined-cycle-power-generation-
system/l
http://www.theautochannel.com/news/2011/02/09/518063
Mechanics Engineering Congress, Japan, 20169/14/2016

7. MODEL-BASED DESIGN FOR FUEL CELL SYSTEM
• System M&S/1D
CAE
 Design for
electrochemistry
 Design for thermal
 Design for
robustness
 Design for control
• Application
 As plant model
 As functional
model
7
MIL
V&V
SS/Dyn.
V&V
Design
for
Control
Design
for HIL
SIL
V&
V
Lumped/
discretized
models
Design for
Robustness
simplifie
d
models
HIL
V&
V
System
REQs:
System
V&V
Design for
Electrochemistry
Simplifie
d
models
Design for
thermal
Simplifie
d
models
Desig
n
1D
3D
Design
for
Control
CAD/CAE
models
V&
V
System of System
Mechanics Engineering Congress, Japan, 2016
Used as plant model for
controller design;
Used as
specification
definition/validatio
n for 3D design
and analysis.
SS: Steady State
V&V: verification and validation
SIL: software in the loop
HIL: hardware in the loop
9/14/2016

8. MODELICA MODELING 1/3: EQUATION BASED MODELING
• Why Modelica?
 Equation-based physics modeling
 Object oriented modeling
 Multi-disciplined
• Electrochemistry
8
∆𝐺𝑓 = ∆𝐺𝑓
0
+ 𝑅𝑇 𝑙𝑛
𝑎 𝐻2 𝑂
𝑎 𝐻2
𝑎 𝑂2
0.5
𝐸 =
−∆𝐺𝑓
2𝐹
∆𝐺𝑓
0
= − 𝑔 𝐻2
𝑜
+ 𝑔 𝐻2 𝑂
𝑜
−0.5 𝑔 𝑂2
𝑜
𝐻2 +
1
2
𝑂2 → 𝐻2 𝑂
(Total) Reaction in the cell
Nernst Potential
Gibbs Free EnergyCell voltage
𝑉𝑐𝑒𝑙𝑙 = 𝐸 + 𝜂 𝑎𝑐𝑡 + 𝜂 𝑜ℎ𝑚𝑖𝑐+ 𝜂 𝑛𝑒
Mechanics Engineering Congress, Japan, 20169/14/2016
Anode
Cathode
𝐻2 + 𝑂2−
→ 𝐻2 𝑂 + 2𝑒−
1
2
𝑂2 + 2𝑒− → 𝑂2−
𝐻2 + 𝐶𝑂
𝐴𝑖𝑟
𝐶𝑂 + 𝐻2 𝑂 → 𝐻2 + 𝐶𝑂2 𝐻2 𝑂 + 𝐶𝑂2
Depleted 𝑂2

9. MODELICA MODELING 2/3: OBJECT ORIENTED MODELING
• Why Modelica?
 Equation-based physics modeling
 Object oriented modeling
 Multi-disciplined
• Membrane example
 connector
 Interfaces to electrical, substance,
heat
9
∆𝑮 𝒇
𝟎
= − 𝒈 𝑯 𝟐
𝒐
+ 𝒈 𝑯 𝟐 𝑶
𝒐
−𝟎. 𝟓 𝒈 𝑶 𝟐
𝒐
connector MassPort
Medium medium;
Pressure p;
flow MassFlowRate m_flow;
SpecificEnthalpy h;
flow EnthalphFlowRate
H_flow;
MassFraction X[n.Xi];
flow MassFlowRate
mX_flow[nXi];
end MassPort;
Mechanics Engineering Congress, Japan, 20169/14/2016

10. MODELICA MODELING 3/3: MULTI-DISCIPLINED
• Why Modelica?
 Equation-based
physics
modeling
 Object oriented
modeling
 Multi-disciplined
10
∆𝑮 𝒇
𝟎
= − 𝒈 𝑯 𝟐
𝒐
+ 𝒈 𝑯 𝟐 𝑶
𝒐
−𝟎. 𝟓 𝒈 𝑶 𝟐
𝒐
Mechanics Engineering Congress, Japan, 20169/14/2016

11. MODEL MANAGEMENT：1/2
• Ex. Property models
 Ideal gases
 Condensed gases
 Two phases water
• Electro-chemistry
 Reactions
 Fuel cell
 Reformer
 Pre-treatment
• Heat transfer
• Electrical
• Control
11Mechanics Engineering Congress, Japan, 20169/14/2016

12. MODEL MANAGEMENT：2/2
• Interface and Template
 Ex. Fuel cell
 Replaceable & re-declare
12
Interface Templates Components
Mechanics Engineering Congress, Japan, 20169/14/2016

13. SUB-SYSTEM TESTS
• Sub-system
 Preprocessor
 Micro gas turbine
13Mechanics Engineering Congress, Japan, 2016
microGasTurbine
GC T
Combustor
feedFuel
mT
.
drainAir
pT
feedAir
mT
.
ground
combustorcombustor
isBurning
true
inertia
J=J
air_loss
summary
generator
groundExc
idealCheckValve
drain
heat_port
feedFuel
feedAir
pin_p
pin_n
0 100 200 300 400 500 600 700 800 900 1000
0.0
0.5
1.0
1.5
2.0
2.5
feedFuel.fluidPort.p feedAir.fluidPort.p
0 100 200 300 400 500 600 700 800 900 1000
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
0.005
feedFuel.m_flow feedAir.fluidPort.m_flow
0 100 200 300 400 500 600 700 800 900 1000
-200
-150
-100
-50
0
50
100
150
200
250
resistor.i[1] resistor.i[2] resistor.i[3]
0 200 400 600 800 1000
-4000
-2000
0
microGasTurbine.generator.flange.tau
Test model
Test model
flowSource_Water
mT
.
flowSource_NG
mT
.
flowSource_AirATR
mT
.
Boundary_hotgas
p T
flowSource_Hotgas
mT
.
flowSource_ATRHeat
mT
.
Boundary_ATRHeat
pT
Boundary_Reformate
pT
turbulentLoss
preprocessor
0.0H2
CH4 0.0
CO 0.0
CO2 0.0
H2O 0.0
Mole %
N2 0.0
O2 0.0
0.0 0.0
0.0 0.0
p(bar)h(kJ/kg)
T(degC)(g/s)
reformer
steamMix_TZ
AirHeater
Geometry_Record Initialization_Record summary
FuelHeater
fuelLoss
gasMix
NGMix
NGLoss
drain_Reformate
feed_NG
drain_NGHeat feed_SteamHeat feed_ATRHeatdrain_ATRHeat
feed_Water
feed_ATRAir
9/14/2016

14. HYBRID SOFC SYSTEM SIMULATION RESULT
• Analysis
 Mass balance
 Fuel cell
voltage-current
density relation
 Thermal loss
 Power-current
density relation
 AC power
14Mechanics Engineering Congress, Japan, 2016
0 400 800 1200 1600 2000 2400 2800 3200 3600 4000
0.0E0
4.0E-5
8.0E-5
1.2E-4
1.6E-4
2.0E-4
checkMassBalanceSystem.mH_in
checkMassBalanceSystem.mH_out
checkMassBalanceSystem.mC_in
checkMassBalanceSystem.mC_out
Voltage [V] Power [W]
Stack
flowCathode
mT
.
ground
current
stack
summary
WaterSource
mT
.
NGSource
mT
.
ATRAirSource
mT
.
exhaustSink
p T
preprocessor
anLoss anVolume
cathVolume
microGasTurbine
GC T
Combustor
MGT_volOut
groundMGT
compMix
checkMassBalanceSystem
44.8 4478
0 1000 2000 3000 4000
0
50
100
150
current.i
0 1000 2000 3000 4000
35
40
45
50
55
current.v
500 1000 1500 2000 2500
40
42
44
46
48
50
stack.subStack[1].summary.j_external [A/m2]
current.v
0 400 800 1200 1600 2000 2400 2800 3200 3600 4000
0E0
1E5
2E5
3E5
4E5
resistor.resistor[1].LossPower
Mass balance
Fuel cell characteristic
Load current
AC power
0 400 800 1200 1600 2000 2400 2800 3200 3600 4000
750
760
770
780
790
800
810
stack.stackHeatLosses.topWall[1].T
stack.stackHeatLosses.topWall[2].T
stack.stackHeatLosses.topWall[3].T
stack.stackHeatLosses.topWall[4].T
Temperature of the stack top
500 1000 1500 2000 2500
40
42
44
46
48
50
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
stack.subStack[1].summary.j_external [A/m2]
current.v stack.summary.PStkElec*
Voltage, power/current density relatio
9/14/2016

15. APPLICATION TO SMART GRID: CONTEXT EVOLUTION
15Mechanics Engineering Congress, Japan, 20169/14/2016
http://www.news.gatech.edu/f
eatures/building-power-grid-
future

16. SUMMARY
• FC model features are summarized from the system perspective
• Hybrid SOFC system is modeled using Modelica
 Equation based modeling
 Object-oriented modeling
 Flexible architecture
 Multi-discipline physics model
 Model management
• Modelica model-based design is a promising approach for smart grid
system development
 Modelica models enable bidirectional power flow in smart grid.
 In the future, many aspects need to modeled for smart grid systems
• Design for operability, reliability, maintainability, cost, …
16Mechanics Engineering Congress, Japan, 20169/14/2016

17. THANK YOU FOR YOUR ATTENTION
www.modelon.com
9/14/2016 Mechanics Engineering Congress, Japan, 2016 17