22-09-2012, 01:11 PM
A FUZZY LOGIC CONTROLLED THREE-PHASE NEUTRALPOINT
CLAMPED BIDIRECTIONAL PFC RECTIFIER
1A FUZZY LOGIC.pdf (Size: 780.03 KB / Downloads: 48)
Abstract
In this paper, a fuzzy logic controlled three-phase neutralpoint
clamped power factor correction (PFC) bidirectional
rectifier is proposed. The fuzzy logic control is based on the
linguistic description and does not require a mathematical
model of the system. The outer loop PI voltage controller and
the inner loop PI current controllers are replaced respectively
by the fuzzy PI voltage controller and fuzzy PI current
controllers. The performance of the fuzzy logic controller
based converter is compared with the conventional PI
controller based converter. The fuzzy controller based
converter is relatively more robust than the conventional PI
controller and gives better dynamic response of the converter.
The MATLAB Fuzzy Logic Toolbox is used for
implementing the fuzzy logic control scheme. Various
simulation results are presented under steady-state and
transient conditions to validate the utility of fuzzy logic
controllers.
Introduction
Recently for medium and high power applications at high
voltages, multilevel converters have been found a viable
solution. They are gaining widespread popularity among the
power factor correction converters because of their excellent
performance like sinusoidal input currents with negligible
THD, nearly unity supply power factor, reduced-rippled and
regulated dc output voltage, reduced voltage stress, reduced
dv/dt stresses and low EMI emissions [1],[4],[7],[8],[11].
Among the modulation techniques, space vector modulation
has recently grown as a very popular PWM method because
it offers the advantages of improved power quality at the line
as well as the load side of the rectifier at relatively reduced
switching frequency, higher efficiency and better harmonic
spectrum [7],[8],[11]. The controller is the heart of converter
operation and has been a subject of intense research in recent
years.
Basic fuzzy algorithm
In a fuzzy logic controller, the control action is determined
from the evaluation of a set of simple linguistic rules. The
development of rules requires a thorough understanding of
the process to be controlled, but it does not require the
mathematical model of the system. The membership
functions (MFs) of the associated input and output linguistic
variables are generally predefined on a common universe of
discourse. To convert the numerical variables into linguistic
variables, the following seven fuzzy levels or sets are chosen
[3]: NB (Negative Big), NM(Negative Medium),
NS(Negative Small), ZE(Zero), PS(Positive Small),
PM(Positive Medium) and PB(Positive Big), as shown in Fig.
4 which depicts the membership function of the fuzzy logic
controller inputs.
Conclusion
A fuzzy logic controlled three-phase NPC bidirectional
rectifier is proposed which gives excellent line-side and loadside
power quality like the sinusoidal line currents with
negligible THD, near unity input power factor, reducedrippled
and well- regulated load voltage. Both the outer-loop
PI voltage controller and two inner-loop PI current
controllers are replaced by the properly designed fuzzy PI
voltage controller and fuzzy PI current controllers. It is found
that the fuzzy-logic controlled NPC converter gives a better
steady-state and dynamic performance both in rectification as
well as inversion modes.