International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
Comparative Analysis of Buck Converter and
Modified Interleaved Buck Converter for
Standalone Wind Energy System
Ashwini A. Patil1, D. S. Chavan2
1,2
Department of Electrical Engineering, Bharati Vidyapeeth Deemed University College of Engineering, Pune, India
ABSTRACT
This paper presents comparative analysis of buck converter and interleaved buck converter for standalone wind energy system.
The comparisons of both converters are on the basis of harmonics, power factor, efficiency and output voltage. As compare to
buck converter the modified interleaved buck converter is better. Because the disadvantages of buck converter are more. In buck
converter switching losses inductor ac losses are more also efficiency is less. Power density is also less. Power factor of buck
converter is less as compare to modified interleaved converter. Also there are disadvantages of conventional interleaved buck
converter like less efficiency, high switching losses, high cost. In Modified interleaved buck converter switches are connected in
series also capacitor provides power path. As the modified interleaved buck converter works in continuous conduction mode so
the current stress is less. The voltage stress across switches is half of input voltage before switch on and switch off conditions. So
the switching losses are less and efficiency is also high. Control logic is implemented for controlling the buck converter.
Proportional integral derivative controller is used in modified interleaved buck converter. Simulation results verify the difference
between buck converters modified interleaved buck converter. By using MATLAB/ SIMULINK the proposed system is modeled.
Keywords: Buck converter, Efficiency, Harmonics, Modified interleaved buck converter and Power factor
I. INTRODUCTION
There are various types of converters like buck, boost, buck boost and interleaved buck converter. Buck converter is used to
step down the voltage i.e. buck converter gives output voltage less than input voltage. In all the devices switch as a power
device used. Suja A et.al [1] Presented modified interleaved buck converter which consist of inferior inductor ripple current
and high step down conversion ratio. When switching frequency is more and duty ratio is less than 50% then proposed buck
converter is used. The benefits of proposed converter are inductor current and output current is very low. Morteza esteki
et.al [2] Presented four phase interleaved buck converter for less voltage stress and high step down ratio . Proposed
converter can be used for reducing switching and conduction losses and efficiency improvement. The benefits of proposed
converter are low output current ripple and uninterrupted input current. D. Lakshmi et.al [3] Presented enhanced step down
interleaved buck converter. There are various advantages of interleaved buck converter like small switching losses, more
efficiency and less switching stress. As compared to conventional interleaved buck converter proposed interleaved buck
converter is better. From simulation and experimental results it is confirmed that proposed interleaved buck converter has
greater step down conversion ratio also inductor ripple current is small. Krishna P.S. [4] presented comparative analysis of
conventional buck converter and modified buck converter. It is concluded that modified interleaved buck converter is better
when the duty ratio is below 50%.Current and voltage ripple are very less in modified interleaved buck converter.
II. BUCK CONVERTER
Fig.1 Buck converter
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
Buck converter is a step down converter which gives output voltage less than input voltage. Buck Converter is simple in
construction but the efficiency of buck converter is less than modified interleaved buck converter. Also the total harmonic
distortion is high in buck converter. To reduce size and weight of the converters must work at high switching frequencies.
But as the switching Frequency increases, switching loss, noise, and stress during turn-on and turn-off transitions also
increase. These drawbacks decrease power conversion efficiency and powering capability, which in turn seriously
deteriorate in system performance.
III. MODIFIED INTERLEAVED BUCK CONVERTER
As shown in fig two active switches are connected in series whereas capacitor provide power path. At 180 phase angle
active switches are driven and by maintaining duty ratio is below 50% at switching frequency output voltage can be
regulated. Current stress is less when interleaved buck converter operates in continuous conduction mode. When converter
is in steady state voltage stress becomes half of input voltage after switch off and before switch on .Capacitor starts
discharging and switching losses decreases.
Figure 2 Modified Interleaved Buck Converter
Figure.3 Operating circuit of modified interleaved buck converter at mode 1
Figure 4 Operating circuit of modified interleaved buck converter at mode 2 or mode 4
Figure 5 Operating circuit of modified interleaved buck converter at mode 3
Mode 1 [t0-t1] At t0 Q1is switched on then mode 1 starts. Current flow through the circuit as shown in fig and capacitor is
charged at voltage VCB. IL2 current flows through diode. Difference between input voltage of coupling capacitor and output
voltage V0 gives voltage across inductor L1.Voltage across inductor gives negative output voltage. Difference between input
voltage and voltage across capacitor gives voltage across diode.
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Mode 2 [t1 –t2]: When Q1 is switched off at t1then mode 2 starts. Then, from diode D1 and D2 current
and
flow,
respectively. Both
and
turn into the negative VO, and therefore,
and
reduce linearly. During this
mode, the voltage and current equations are as follows,
(8)
(9)
(10)
(11)
(12)
Mode 3 [t2 –t3 ]: When Q2 is switched on at t2 then mode 3 starts and D2 is switched off. Then
flows through D1 and
from D1, CB, Q2 , and L2
flows. Thus, voltage across CB is discharged. The voltages and currents can be expressed
at mode 3 are as follows.
(13)
(14)
(15)
(16)
(17)
(18)
(19)
IV. SIMULATION
Figure 6 Simulation of standalone wind battery hybrid system by using buck converter
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
Simulation of standalone wind battery hybrid system by using buck converter consists of squirrel cage induction generator,
buck converter, battery for back up. Subsystem consists of wind turbine squirrel cage induction generator and rectifier. As
wind passes through wind turbine, turbine rotate and rotational energy is converted into mechanical energy. Generator
converts mechanical energy into electrical energy. Through the rectifier AC power is converted into DC. Buck converter is
also DC-DC converter gives DC voltage. Constant DC voltage is obtained at load. When the wind is not available the
battery is used as a backup.
Figure 7 Simulation of wind battery hybrid system by using Modified interleaved buck converter
Standalone wind energy system by using interleaved buck converter consists of interleaved buck converter, PID controller
and subsystem. There are various advantages of interleaved buck converter like high efficiency reliable, better thermal
performance and high power density. Subsystem consist of wind turbine, squirrel cage induction generator and rectifier.
V. RESULTS
The results obtained from the MATLAB simulation carried out in sequential manner, are as follows,
Figure 8 Total Harmonic Distortion at 50 Hz by using Buck Converter
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
Total harmonic distortion is 72.49% at 50 Hz by using buck converter. The total harmonic distortion is more in buck
converter.
Figure 9 Total Harmonic Distortion at 50 Hz by using Interleaved Converter
The total harmonic distortion is 31.04% at 50 Hz by using Modified Interleaved Converter as shown in fig 9. As compare to
buck converter the total harmonic distortion is less in Modified interleaved buck converter.
Figure 10 Total Harmonic Distortion at 60 Hz by using Buck Converter
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
Total Harmonic Distortion at 60 Hz by using Buck Converter is 76.32% as shown in fig 10
Figure 11Total Harmonic Distortion at 60 Hz by using Modified interleaved Buck Converter
The total harmonic distortion at 60 Hz by using buck converter is 54.95% as shown in fig 9.6 Power factor
Figure 12 Power Factor of Buck Converter
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
The power factor obtained by using buck converter is 0.8719 as shown in fig 12
Figure 13 Power Factor of Buck Converter
The power factor obtained by using interleaved buck converter is 0.9853
 Buck converter efficiency calculation
For buck converter
Output voltage =60V
Output current= 6.5 A
Input voltage= 250V
Input current= 5A
The efficiency of buck converter is 31%
For Interleaved buck converter
Output voltage =60V
Output current= 6.5 A
Input voltage= 250V
Input current= 3A
The efficiency of modified interleaved buck converter is 52%
CONCLUSION
The comparison of buck converter and modified interleaved buck converter is done on the basis of harmonics, power factor
and efficiency. From simulation and theoretical concepts it is verify that as compare to Buck converter, Modified
interleaved buck converter is better. Because the total harmonic distortion is less in modified interleaved buck converter at
50 Hz and 60 Hz whereas total harmonic distortion is more in buck converter. Power factor is less in buck converter
whereas it is high in interleaved buck converter. Also Efficiency is more in modified interleaved buck converter whereas it
is low in buck converter. In MATLAB/SIMULINK proposed system is implemented
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International Journal of All Research Education and Scientific Methods (IJARESM)
ISSN: 2455-6211, Volume 4, Issue 5, May- 2016
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