Abstract
One of the key problems for a solid oxide fuel cell (SOFC), which is a high-temperature power-generation plant, is the cooperative control of safe operation and system efficiency during load tracking. Within the constraints of thermal safety, the SOFC plant should have the maximum output efficiency under various static conditions. Moreover, the SOFC system can switch between different static working conditions smoothly, safely, and quickly when the external load power changes. To achieve cooperative thermoelectric control, taking a 5-kW stand-alone SOFC system as the research object, according to the optimal static strategy designed based on the optimal operating curves (OOCs), a sliding mode controller (SMC) is designed and the closed-loop responses are discussed for SOFC system power switching during load tracking. The identification results demonstrate that the electrical coupling dynamic model can depict and predict accurately the electrical characteristics of SOFC stacks. And based on the obtained OOCs, the thermoelectric control can be achieved and thermal safety ensured using the designed SMC.
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Abbreviations
- AR :
-
air excess ratio [−]
- BP :
-
bypass valve opening ratio [−]
- C :
-
specific heat capacity [kJ kmol−1 K−1]
- △E 0 :
-
standard electrode potential (V)
- FU :
-
fuel utilization [−]
- F :
-
Faraday’s constant [96,485 C mol−1]
- h :
-
convective heat transfer coefficient [kW cm−2 K−1]
- I :
-
current [A]
- LHV :
-
low heat value [kJ]
- Max. |ΔT PEN|:
-
maximum PEN temperature gradient [K cm−1]
- Max. T PEN :
-
maximum PEN temperature [K]
- N :
-
control volume mole number [kmol]
- \( \dot{N} \) :
-
molar flow rate [kmol s−1]
- N 0 :
-
number of fuel cells [−]
- p :
-
pressure [bar]
- k :
-
thermal conductivity [kW cm−1 K−1]
- P :
-
power [kW]
- \( \dot{Q} \) :
-
heat transfer [kW]
- R :
-
universal gas constant [8.314 kJ kmol−1 K−1]
- A :
-
surface area [cm2]
- T :
-
temperature [K]
- U :
-
voltage [V]
- \( \dot{W} \) :
-
work [W]
- X :
-
species mole fraction
- L :
-
distance between control volume [cm]
- C D :
-
current density [A cm−2]
- i 0 :
-
exchange current [A cm−2]
- S node :
-
area of each node [cm2]
- LSM:
-
lanthanum strontium manganate
- j :
-
the index of discretization units of the cell
- J :
-
the user-defined number of cell nodes
- τ :
-
effectiveness
- γ :
-
specific heat ratio, 1.4
- δ :
-
number of electrons participating in the electro-chemical reaction
- α :
-
charge transfer coefficient, 0.5
- ε :
-
specified tolerance constant, 1e−5
- η :
-
efficiency [%]
- amb:
-
ambient
- act:
-
activation
- B:
-
burner
- bl:
-
blower
- by:
-
bypass
- con:
-
concentration
- dl:
-
diagonal line
- i :
-
species
- in:
-
inlet
- out:
-
outlet
- net:
-
system net output power
- s:
-
stack
- v:
-
volume
- so:
-
solid control volume
- ga:
-
gas control volume
- ca:
-
cathode
- an:
-
anode
- PEN:
-
positive electrode-electrolyte-negative electrode
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Funding
The work was supported by the open fund project of Hubei Province Key Laboratory of Intelligent Information Processing and Real-time Industrial System (No. znxx2018ZD02), the basic research project of Shenzhen (JCYJ20170307160923202), and the National Natural Science Foundation of China (61573162).
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Appendix
Appendix
Detailed expressions of SOFC operating parameters, thermal temperature constraints, and electrical outputs.
Operating parameters
Thermal temperature constraints
Electrical outputs
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Zhang, L., Shi, S., Jiang, J. et al. An optimization and fast load-oriented control for current-based solid oxide fuel cell system. J Solid State Electrochem 22, 2863–2877 (2018). https://doi.org/10.1007/s10008-018-3996-x
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DOI: https://doi.org/10.1007/s10008-018-3996-x