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below a suitable value, the oxygen starvation would occur. In several studies,
controlling the oxygen excess ratio is proposed to prevent the oxygen starvation
phenomenon [4]. The proposed control strategies include feedforward control [5,
6], Linear Quadratic Regulator (LQR) [7], dynamic matrix predictive control
[8], model predictive control [9] and adaptive control [10]. These control meth-
ods have achieved well control effect. However, some of them are not suitable for
the requirements of model parameters with time varying in the real system, and
some strategies are more complex that it is dicult to apply. A simple control
strategy has been appropriated in this work to regulate the oxygen excess ratio
based on the fuzzy control and fuzzy inference.
The proposed control strategy in this paper is fuzzy double model control
which is used to regulate the oxygen excess ratio at a desired level when the
load current changes. And this control strategy contains the fuzzy control, PID
control and the switching strategies between these two control methods within
the adjusting process. The fuzzy logic control plays a major role at the beginning
of regulation so as to increase the system response speed and enhance the system
robustness, and then the PID control will play the leading role to achieve the
purpose of eliminating the system steady state error when the system is above
to reaching the steady state.
This paper is organized as follows: Section 2 presents a description of the
PEM fuel cell and the mathematical definition of the oxygen excess ratio. Sec-
tion 3 gives a detailed description of the fuzzy control, PID control and switching
method based on the fuzzy inference of the fuzzy double model control. In section
4, the simulation results obtained with the proposed fuzzy double model con-
trol are shown and compared to the fuzzy PID control. In section 5 the major
conclusions are drawn.
2 System Description
This section gives a brief introduction of the PEM fuel cell we studied in this
work and exact mathematical definition of oxygen excess ratio process, and then
an optimal control object is specified.
2.1 PEM Fuel Cell System
The PEM fuel cell can convert the chemical energy of hydrogen and oxygen
into electricity through electrochemical reaction. A PEM fuel cell power system
requires the integration of many components beyond the fuel cell stack itself,
to allow ecient performance under different operating conditions. The PEM
fuel cell system should include the fuel supply and air supply subsystems, the
temperature regulation subsystem, the power conversion subsystem which is used
to convert the generated DC power to regulated DC or grid quality AC power.
And it is also necessary to require a controller to maintain eciency and avoid
degradation of available fuel cell voltage.
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