International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Design of PI controller for Positive Output Super- Lift LUO
Converter
1
K.Muthuselvi, 2L. Jessi Sahaya Shanthi
1
Department of Electrical &Electronics, SACS MAVMM Engineering College, Madurai, India
2
Department of Electrical &Electronics, Thiagarajar College of Engineering, Madurai, India
Email:rajendran.urban@gmail.com
Abstract: The positive output super- lift LUO converter is
one of the boost converters. It was developed in the year of
2003. The notion of this paper is to design and analyze a
Proportional - Integral (PI) control for Positive Output
Super- Lift LUO converter (POSLLC).Particularly for
Triple-Lift LUO converter is focused. The function of the
proposed converter is to convert positive source voltage to
positive load voltage. The simulation model of the positive
output super- lift LUO converter and its control circuit is
implemented in Matlab/Simulink. The PI control for the
above converter is tested for line voltage variations, load
variations, component variations, steady State region and
Dynamic region.
Keywords: DC-DC converter, Matlab, positive output
super- lift LUO converter, proportional – Integral control,
simulink. Steady state region, dynamic region
I. INTRODUCTION
DC-DC conversion technology has been developing
rapidly and DC-DC converters have been mainly used in
industrial applications such as dc motor drives,
computer peripheral systems, insulation testing and
medical equipments. The output voltage of pulse width
modulation (PWM) based DC-DC converters can be
changed by controlling the duty cycle [1]-[2]. The
voltage lift technique is an important method that is
widely applied in design of electronic circuit. This
technique rejects the influences of parasitic elements and
increases the output voltage greatly. Therefore these
converters perform DC-DC voltage increasing
conversion with large power density, higher efficiency
and very high output voltage with small ripples [3].
Compared with classical DC-DC converters, Super –
Lift LUO converters can provide the output voltages by
increasing stage by stage along a geometric progression
and obtain higher voltage transfer gains. They are
divided into many categories according to their power
stage numbers, such as the elementary circuit (single
power stage), re-lift circuit (two power stages), triple –
lift circuit (three power stages) etc.[4]. Their static and
dynamic behavior becomes highly non-linear, because
of the time variations and switching nature of the power
converters [5]. A good control for DC-DC converters
always ensures stability in any operating point.
Moreover, good response in terms of rejection of load
variations, input voltage variations and even parameter
changes is also required for a perfect control scheme.
The PI control technique offers several advantages
compared to PID control methods: stability, even for
large line and load variations, reduces the steady state
error, robustness, good dynamic response and simple
implementation [2].
In this paper PI control with zero steady state error and
fast response is focused. The static and dynamic
behavior of PI control for positive output super- lift
LUO converter is studied in Matlab/Simulink. For the
purpose of optimizing the stability of positive output
super- lift LUO converter dynamics, while ensuring
correct operation in any working condition, a PI control
is a more reliable approach. The PI control technique is
insisted as a good alternative to the control of switching
power converters [5]-[6]. The main advantage of PI
control schemes is its ability to eliminate the effects of
converter’s parameter variations that leads to invariant
dynamics and static response in the ideal case [2].
II. CIRCUIT DESCRIPTION AND
OPERATION
The proposed Triple lift circuit is shown in Fig.1 and it
consists of only one switch S, three inductors L1, L2 and
L3, Six capacitors C1, C2, C3, C4, C5, C6 and eight
freewheeling diodes. This converter is designed by
implementing super-lift technique. This technique is
more powerful than voltage –lift technique. In voltagelift technique the same converter is designed with two
power switches. The three output voltage levels are
obtained. They are in arithmetic progression. Switching
losses is also high[4].In super-lift technique only one
switching element is used and particular numbers of
diodes, capacitors and inductors are added for obtaining
very high output voltage levels. The three output voltage
levels are in geometric progression.
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ISSN (Online): 2347-2820, Volume -2, Issue-4, 2014
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Average current
ΔiL1=(Vin/L1) kT
(4)
ΔiL2=(V1/L2) kT
(5)
ΔiL3=(V2/L3) kT
(6)
Therefore variation ratio of output voltage v0 is
ε =(Δv0/2V0)=(1-k)/2RfC6
(7)
III. DESIGN OF PI CONTROLLER
Fig.1 Triple- lift circuit
The voltage across capacitor C1 is charged to Vin
.Voltage V1 across capacitor C2 is V1 =((2-k)/(1-k))Vin,
and Voltage V2 across capacitor C4 is V2=((2-k)/(1k))2Vin .
Fig. 2 Turn on equivalent circuit
In the description of the converter operation, it is
assumed that all the components are ideal and positive
output triple lift converter operates in a continuous
conduction mode. Fig. 2 and 3 shows the modes of
operation of the converter.
Fig.3 Turn off equivalent circuit
The PI control is designed to ensure the desired nominal
operating point for POSLLC, then regulating POSLLC,
so that it is very closer to the nominal operating point in
the case of sudden load disturbances and set point
variations. In the PI control scheme, proportional gain
(Kp) and integral time (Ti) are designed using Ziegler –
Nichols tuning method [6] In this method by applying
the step test, S- shaped curve of response of POSLLC is
obtained. The S- shaped curve of step response of
POSLLC may be characterized by two constants, delay
time L and time constant T. The delay time and time
constant are determined by drawing a tangent line at the
inflection point of the S-shaped curve and determining
the intersections of the tangent line with the time axis
and line output response c (t). From these values the
proportional gain (Kp) and integral time (Ti) are
calculated. In the proposed control scheme the
proportional gain Kp is taken as 0.1 and integral time Ti
is taken as 1.
IV. SIMULATION OF TRIPLE -LIFT
CONVERTER
The simulations have been performed on the positive
output super- lift LUO converter circuit with parameters
listed in Table I. The static and dynamic performance of
PI control for the positive output super- lift LUO
converter is evaluated in Mat lab/Simulink. Before that a
simple elementary circuit with it’s PI controller is
studied [2].The scheme provides only one output stage.
Topology and control scheme is
also simple. The
proposed triple-lift topology is little bit complex and
their parameters are listed below.
TABLE – I
The voltage across capacitor C5 is charged to V2.The
current flowing through inductor L3 increases with
voltage V2 during switching-on period kT and decreases
with voltage (V0-2V2) during switching-off (1-k) T.
Therefore, the ripple of the inductor current iL3 is
Δ iL3=(V2/L3) kT=(V0-2V2/L3)( 1 -k)T
(1)
Parameter Name
Symbol
Value
Input voltage
V1
12 Volts
Output voltage
V0
324 Volts
V0=((2-k)/(1-k))V2=((2-k)/(1-k))2V1=
((2-k)/(1-k))3Vin
(2)
Inductors
L1, L2 &L3
10 mH
Capacitors
C1, C2,
C3,C4,& C5
2 F
The voltage transfer gain is
Capacitor
C6
20 F
Switching
frequency
fs
450Hz
G= V0/Vin =(2-k/l-k)
3
(3)
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Load resistance
R
30K
Duty cycle
k
0.5
voltage has maximum overshoot of 400 V and 0.75 sec
settling time with designed PI control.
Table I. Circuit parameters
The Matlab/Simulink simulation model is shown in
Fig.4. The difference between feedback output voltage
and set point voltage is given to PI controller and output
of PI controller, changes the duty cycle of the power
switch (n- channel MOSFET)
Fig.6. Input voltage step changes from 12V to 9 V
Fig.4 Simulation model
The POSLLC performance is analyzed in various
aspects. They are performance in transient region,
performance during line variations, load variations,
component variations and performance in constant Kp
with variable Ti, constant Ti with variable Kp.
1.1
Transient region
Fig.5. shows the output voltage of POSLLC with PI
control in the transient region. It can be seen that the
converter output has settled at time of 0.55sec with
designed PI control.
Fig.7 Input voltage step changes from 12 V to 15 V
1.3
Load Variations
Fig.8. shows the output voltage when
changes from 30K  to 27K 
the
load
(-10% load disturbance). The maximum overshoot is
480V and settled at 0.6sec Fig.9 shows the variation of
load from 30K to 33K  (+10% disturbance), the
maximum overshoot of the response is 300V and settled
at 0.65sec.
Fig.5. Output voltage in transient region
1.2
Line Variations
Fig.6. shows the output voltage of converter for input
voltage step changes from 12 V to 9 V (-25% supply
disturbance). The converter output voltage has
maximum overshoot of 200V and 0.55sec settling time
with designed PI control. Fig.7 shows the output voltage
variations for the input voltage step change from 12 V to
15 V (+25% supply disturbance). The converter output
Fig.8 Variation of load from 30K  to 27K 
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Fig.9 Variation of load from 30K
1.4
to33 K
Fig.12.Variation of L3 from 10mH to 15mH
Component variations
Fig.10. shows the output voltage when capacitor C6
value changes from 20 F to 25F. The maximum
overshoot is 430V and settled at 0.75 sec.Fig.11.shows
the output response when C6 value changes from 20F
to 15F The response reaches the maximum overshoot
of 500V and settled at 0.48sec.
Fig.13.Variation of L3 from 10mH to 5mH
TABLE – II
Maximu
m
overshoo
t in volts
Settling
time
in
seconds
0.9
480
0.55
0.7
480
0.55
1.5
480
0.55
2.5
480
0.55
4
480
0.55
5.5
480
0.6
7
480
0.6
Parameter Name
Proportion
al gain-Kp
Fig.10.Variation of C6 from 20F to 25F
0.1
Integral
time-Ti
0.6 with
more
ripples
Table II. Performance analysis with constant Kp and
variable Ti
TABLE – III
Parameter Name
Maximum
Settling
Proporti
overshoot
time in
Integral
onal
in volts
seconds
time-Ti
gain-Kp
0.2
480
0.55
1
0.3
480
0.55
0.5
480
0.55
30
Fig.11.Variation of C6 from 20F to 15F
Fig.12. shows the output voltage when inductor L3 value
changes from 10mH to 15mH. The maximum overshoot
is 500V and settled at 0.6 sec.Fig.13.shows the output
response when L3 value changes from 10mH to
5mH.The response reaches the maximum overshoot of
400V and settled at 0.56sec
480
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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0.9
0.7
0.09
0.05
480
480
480
480
0.001
200
REFERENCES
0.55
0.55
0.55
0.55
Signal
oscillates
[1]
F.L.Luo and H.Ye, “Positive output super- lift
converters,” IEEE Trans. Power Electron.,
vol.18, no.1, pp. 105-113, Jan 2003.
[2]
K.RameshKumar and S.Jeevanantham. “PI
control for positive output elementary super- lift
Luo converter,” International Journal of Energy
and Power Engineering, pp.130-135, Mar 2010.
[3]
Fang Lin Luo and Hong Ye, Advanced DC/DC
Converters. London: CRC Press,2003
[4]
N.Dhanasekar, and R.Kayalvizhi. “Design and
simulation of PI control for positive output triplelift Luo converter”, International Journal of
Modern
Engineering
Research,
IJMER.vol.2,issue.6, pp. 4186-4188,Nov-Dec
2012.
[4]
T.S. Saravanan, R. Seyezhai and V. Venkatesh
“Modeling and control of split capacitor type
elementary additional series positive output
super- lift converter”, ARPN Journal of
Engineering and Applied Sciences, vol.7,no.5,
May 2012.
[5]
P. Comines and N. Munro, “PID controllers:
recent tuning methods and design to
specification”, in IEEE Proc. control Theory
applications, vol.149, no.1, pp.46-53, Jan 2002.
Table III. Performance analysis with constant Ti and
variable Kp
V. CONCLUSION
The positive output super- lift LUO converter
(POSLLC) performs the voltage conversion from
positive source voltage to positive load voltage. The PI
control scheme has proved to be robust and it has been
validated with transient region, line and load variations.
The converter performances for constant Kp
and
variable Ti , constant Ti and variable Kp are not
analyzed yet. This work is focused on that aspect also.
The positive output super- lift LUO converter with PI
control is used in applications such as switch mode
power supply, medical equipments and high voltage
projects etc.
VI. ACKNOWLEDGEMENT
The authors would like to acknowledge the management
of SACS MAVMM Engineering College and
Thiagarajar College of Engineering, Madurai.

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