03-05-2011, 02:58 PM
KEYWORDS
Fuzzy PID controllers, PID controllers, intelligent
hybrid controllers, simulation.
ABSTRACT
In this study, a design methodology is introduced that
blends the classical PID and the fuzzy controllers in an
intelligent way and thus a new intelligent hybrid
controller has been achieved. Basically, in this design
methodology, the classical PID and fuzzy controller
have been combined by a blending mechanism that
depends on a certain function of actuating error.
Moreover, an intelligent switching scheme is induced
on the blending mechanism that makes a decision upon
the priority of the two controller parts; namely, the
classical PID and the fuzzy constituents. The
simulations done on various processes using the new
hybrid fuzzy PID controller provides ‘better’ system
responses in terms of transient and steady-state
performances when compared to the pure classical PID
or the pure fuzzy controller applications. The controller
parameters are all tuned by the aid of genetic search
algorithm.
INTRODUCTION
As PID is regarded as the standard control structures of
the classical control theory, and fuzzy controllers have
positioned themselves as a counterpart of classical PID
controllers on the same dominant role at the knowledgerich
spectrum (Åström and Hagglund 1995, Oh et al. 2004).
PID controllers are designed for linear systems and they
provide a preferable cost/benefit ratio. However, the
presences of nonlinear effects limit their performances.
Fuzzy controllers are successful applied to non-linear
system because of their knowledge based nonlinear
structural characteristics. Hybridization of these two
controller structures comes to ones mind immediately to
exploit the beneficial sides of both categories. Naturally
various hybrid controller structures have been arisen in
literature (Kwok et al. 1990, Brehm and Rattan 1993, Li
1998, Li et al. 1999, Xiaoyin and Belmin 1993, Reznik et
al.2000). In some applications, these two control
structures are combined by a switch (Ketata et al. 1995,
Matsunaga and Kawaji 1991, Otsubo et al. 1998,
Parnichkun and Ngaecharoenkul 2001). In (Er and Sun
2001) a fuzzy switching method between fuzzy
controller and conventional PID controllers is used to
achieve smooth control during switching.
The intent of this study is to design a new hybrid fuzzy
PID controller so that a further improved system
response performance in both the transient and steady
states have been achieved as compared to the system
response obtained when either the classical PID or the
fuzzy controller has been implemented. Here, the
classical PID and fuzzy controller have been combined
by a blending mechanism that depends on a certain
function of actuating error. An intelligent switching
scheme is induced on the blending mechanism that
makes a decision upon the priority of the two controller
parts. Simulations are performed on
MATLAB®/Simulink toolbox to illustrate the efficiency
of the proposed method.
INTELLIGENT HYBRID FUZZY PID
CONTROLLER STRUCTURE
Fuzzy PID controllers in literature can be classified into
three major categories as direct action type, fuzzy gain
scheduling type, and hybrid type fuzzy PID controllers
(Yesil et al. 2003, Akbiyik et al. 2005). The direct
action type can also be classified into three categories
according to number of inputs as single input, double
input, and triple input direct action fuzzy PID
controllers
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