International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882
Volume 3, Issue 6, September 2014
STUDY OF FUZZY LOGIC AND PID CONTROLLER IN
BUCK-BOOST CONVERTER
PRIYANKA SRIVASTAVA1
ELECTRONICS DESIGN AND
TECHNOLOGY, M.TECH
NATIONAL INSTITUTE OF
ELECTRONICS AND
INFORMATION
TECHNOLOGY (NIELIT)
GORAKHPUR, INDIA
SH. S.K.SINGH2
SCIENTIST-„D‟
NATIONAL INSTITUTE OF
ELECTRONICS AND
INFORMATION TECHNOLOGY
(NIELIT)
GORAKHPUR, INDIA
ABSTRACT
Various controlling schemes are used in dc-dc
converters to control the output voltage, rise time, peak
time and settling time of the response. In this paper,
fuzzy logic and PID control technique are studied on
Buck-Boost converter and the mentioned parameters are
analyzed.
The
model
is
developed
in
MATLAB/Simulink.
Index Terms: PID controller, Fuzzy logic controller,
Buck-Boost converter, MATLAB/Simulink.
I.
SH. NISHANT TRIPATHI3
SCIENTIST-„C‟
NATIONAL INSTITUTE OF
ELECTRONICS AND
INFORMATION
TECHNOLOGY (NIELIT)
GORAKHPUR, INDIA
capacitor C1 and a load resistance R1. When switch S
becomes on, the input voltage source V1 gets connected to
the inductor L1 and therefore inductor current increased
and diode reversed biased. And therefore capacitor
produces output Vo at the load. When the switch is turned
off, the diode gets forward biased and the diode provides
a path for the inductor current. Inductor L1 is connected to
the load R1 and the capacitor C1. Therefore energy
transferred from inductor to the capacitor and then to the
load.
INTRODUCTION
DC-DC converters are basically used for generating
an output voltage at desired level and when a control
technique is used in a dc-dc converter, it produces the
output more efficiently as compared to the converter
when used in open loop. Control systems are designed
and implemented to accomplish the requirements by
providing specified voltage level irrespective of
uncertainties and disturbances occurred in power
semiconductors [1]. And therefore proper and more
efficient technique is used to design control system.
When non linear phenomenon characteristics occur in
DC-DC converters, they make their control and analysis
very difficult [2]. There are many control techniques used
to control these converters for example PI controller, PD
controller, PID controller and Fuzzy Logic Controller.
Here PI, PD, PID controllers are linear controllers and
Fuzzy Logic Controller is a non linear controller. It is
difficult to control the non linear phenomena occurring in
converters with the help of linear controllers i.e. PI, PD
and PID controllers due to limited operating points[3].
And to bring the solution to this problem fuzzy logic
came into picture. Fuzzy logic do not need exact
information about the system and works with
approximate mathematical model. Very easily new rules
can be added into it and it is very robust in nature. And
hence it provides better output with lower rise time, peak
time and settling time.
The converter consists of a dc input voltage source V1,
controlled switch S1, inductor L1, Diode D1, a filter
Fig.1 General Structure of Buck-Boost converter
II.
PROPORTIONAL,INTEGRAL,
DERIVATIVE CONTROLLER
A controller is device which checks and maintains the
operating conditions of a dynamic system. Main
application of controller is to maintain temperature,
speed, flow or pressure. Controllers are used to adjust the
output voltage with the help of a feedback loop. This
feedback loop feedbacks the output voltage to calculate
the difference between reference voltage output voltage
and hence controlling is done to obtain the required
output voltage. Proportional controller is a simple type of
controller in which output voltage is proportional to the
error voltage. Introduction of PI controller helps in
elimination of forced oscillations and reduction of steady
state error because of P control and I control
respectively[4]. The disadvantage of integral mode is that
it has an adverse effect on speed of response and hence
overall stability if the system reduces. D mode has
anticipative nature and therefore it has the ability of
prediction of future errors. PD controllers are used to
control helicopters, aeroplanes, submarines and other
flying and underwater machines.
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998
International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882
Volume 3, Issue 6, September 2014
A controller is obtained by combining the three
modes proportional controller P, integral controller I,
derivative controller D and it is named as PID controller.
It provides better transient and steady state response for
the unit step input and hence gives better results.
rules are designed in the matrix table and these rules are
shown in table1. Defuzzification method used is centroid
of gravity. Triangular membership function is used for
input (error and change in error) and output. The values
are normalized in between [-1,1]with the help of suitable
scaling factors. The two inputs can be written as,
e(k) = Vreference - Voutput
ce(k) = e(k) – e(k-1)
Fig.2 A Proportional-Derivative-Integral controller
PID controllers can be tuned by two popular methods
Good-Gain method and Zieglar Nichols‟ method. Firstly
the process is brought to or close to the specified point
and then proportional controller is assured with Kp = 0 &
then increase in Kp is done till stability is achieved. Hence
the output of PID controller can be written as,
𝑡
𝑈 𝑡 = 𝐾𝑝 𝑒 𝑡 + 𝐾𝑖
𝑒(𝑡)𝑑𝑡 + 𝐾𝑑
0
III.
Fig.4 Plot of membership function for error e
𝑑𝑒(𝑡)
𝑑𝑡
FUZZY LOGIC CONTROLLER
Fuzzy logic controller is a digital approach to control
the dc-dc converters and proves to be a better method as
compared to the classical analog methods. It is designed
depending on the expert information and knowledge
about the system and exact model is not a question of
concern[5]-[7]. The two input terms are error and change
in error which are given at input of controller.
Fig.5 Plot of membership function for change in error
Fig.3 Fuzzy logic controller in Buck-Boost converter
Fuzzifier converts the crisp sets into fuzzy sets. A
mamdani type inference method is used for the design of
controller. A group of seven fuzzy subsets are used, these
are PB,PM,PS,ZE,NS,NM,NB. Using IF-THEN rule, 49
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Fig.6 Plot of membership function for output
999
International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882
Volume 3, Issue 6, September 2014
TABLE I. Fuzzy logic table rules
PID controller has rise time below 0.0029sec and
Fuzzy logic controller has rise time below 0.0021sec.
Fig.9 Peak time in Buck mode
IV.
RESULTS AND DISCUSSION
In this section results are derived and discussed. A
Fuzzy logic controller and Proportional-IntegralDerivative controller is studied for the Buck-Boost
converter and its simulink model is designed. The two
models using fuzzy logic and PID controller are tested for
both buck mode and boost mode.
PID controller has peak time below 0.0047sec and
Fuzzy logic controller has peak time below 0.0041sec.
(A) Buck mode: Output voltage is calculated for
Vreference = 10 volt and Vinput = 12 volt. Rise time,
peak time and settling time are analyzed for
reference voltage varying from 2 volt to 10 volt.
Fig.10 Settling time in Buck mode
PID controller has settling time below 0.304sec and
Fuzzy logic controller has peak time below 0.298sec.
(B) Boost mode: Output voltage is calculated for
Vreference = 30 volt and Vinput = 12 volt. Rise time,
peak time and settling time are analyzed for
reference voltage varying from 14 volt to 30 volt.
Fig.7 Output voltage for reference voltage = 10 volt
Fig.11 Output voltage for reference voltage = 30 volt
Fig.8 Rise time in Buck mode
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1000
International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882
Volume 3, Issue 6, September 2014
PID controller has settling time below 0.1345sec and
Fuzzy logic controller has settling time below 0.1336sec.
V.
Fig.12 Rise time in Boost mode
PID controller has rise time below 0.1041sec and
Fuzzy logic controller has rise time below 0.1038sec.
Fig.13 Peak time in Boost mode
PID controller has peak time below 0.108sec and
Fuzzy logic controller has peak time below 0.1076sec.
CONCLUSION
It can be concluded that Fuzzy logic controller has
good transient state response. It provides lower rise time,
peak time and settling time with higher output voltage.
Mathematical model needed to be exact in PID controller
which is a difficult task in non linearity and during
variation and disturbances. And therefore fuzzy logic
controller is a better method as compared to PID
controllers as mathematical model not need to be exact
and provides non linear control to converters.
REFERENCES
[1] I.Eker and Y.Torun, “Fuzzy logic control to be be
conventional method,”Energy Conversion and
Management, vol.47 pp.377-394,3//2006
[2] K.Guesmi, N.Essounbouli,A.Hamzaoui, J.Zaytoon,
and N.manamanni,”Shifting nonlinear phenomenon
in a DC-DC converter using a Fuzzy logic
controller,” Mathematics and Computers in
simulation, vol.76,pp.398-409,1/7/2008
[3] A.Khaligh and A.Emadi,”Suitability of the pulse
adjustment technique to control single DC/DC
choppers feeding vehicular constant power loads in
parallel with conventional loads,”International
Journal of Electricand Hybrid Vehicles, vol.1,
pp.20-25,//2007
[4] Karl Johan Astrom and Tore Hagglund ,PID
controllers theory design and tuning 2nd Edition ,
Instrument Society of America, 1995
[5] Liping
Guo,
J.Y.H.a.R.M.N.,
comparative
Evaluation of Linear PID and Fuzzy Control for a
Boost Converter.
[6] Paolo Mattavelli, L.R., Giorgio Spiazzi and Paolo
Tenti General-Purpose Fuzzy Controller for DC–DC
Converters. IEEE Trans. Vol. 12. Issue 1.79-86,
1997.
[7] Dr.K.Thanushkodi, N.R.a., Bi-directional DC–DC
Converter with Adaptive Fuzzy Logic Controller.
2009 No. 1(89)
Fig.14 Settling time in Boost mode
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