ISSN 2319-8885
Vol.04,Issue.43,
October-2015,
Pages:9462-9469
www.ijsetr.com
A Soft-Switching Push–Pull Based DC-DC Converter Fed with PV
for Utility Grid Connected Application
G. BHARATH KUMAR1, SURESH. MIKKIL2
1
PG Scholar, Dept of EEE, Sri Mittapalli College Of Engineering, Tummalapalem, Guntur (Dt), AP, India.
Associate Professor, Dept of EEE, Sri Mittapalli College Of Engineering, Tummalapalem,Guntur (Dt), AP, India.
2
Abstract: Building a DC-DC converter with high step-up, low cost and high efficiency from low DC voltage is the requirement
in many applications. It is achieved by employing a front-end push pull converter based full-bridge inverter. In conventional push
pull converter during device turn-off, voltage overshot occurs across the semiconductor devices. So, an additional snubber or
voltage clamping is required to limit the overshoot voltage. It increases the component’s count and losses making the converter
less efficient. The above problem is eliminated by operating the converter with soft-switching achieved by using secondary
modulation technique. This paper presents one of the imperative applications of renewable vitality i.e residential photovoltaic
power system. The series connected configuration of PV modules are not popular compared to parallal-connected configuration.
It is because of the protection needs and making complete use of the PV generated power for the PV residential generation system
with utility grid connected. As the Push-pull converter has just two essential devices with common ground to supply and it results
in basic and decreased gating requirement. The simulation results are presented by using Matlab/simulink software.
Keywords: Current-Fed Converter, Push–Pull, Residential Photovoltaic (PV) Power System, Soft Switching, Utility Grid.
I. INTRODUCTION
The conventional power generation method faces
problems like depletion of fossil fuels and polluting the
environment. Also because of the increasing demand and
energy crisis, world’s power production has shifted hugely
towards renewable energy systems. Additionally, the source
is freely available and is pollution free. Solar PV is one of the
fast growing methodologies among the renewable energy
systems accounting for 1/3 of the world’s power production
by 2030. In solar PV the major factor to be overloaded is the
low DC voltage produced from the solar panel and also the
non-uniform nature of the source. The power production is
also affected due to partial shading and panel mismatch.
Hence the project lies to provide a DC-DC converter with
high step-up, low cost and high efficiency [1-5]. The boost
converter is the preferred choice in earlier days because of its
high voltage gain and simple circuit structure. But the power
level is limited due to hard switching operation which also
increases switching losses leading to less efficiency. To
increase the power level, power device parallel technology is
one of the solutions. However, this method cannot reduce the
input and output current ripples. Interleaved structure is
another effective solution to increase the power level which
can minimize the current ripple, can reduce passive
component size, can improve the transient response and can
realize the thermal distribution.
However, the power devices still operate at hard switching
leading to less efficiency [6-8]. Soft-switching current-fed
half-bridge frontend isolated DC-DC converter base inverter
for AC module applications was proposed. By using the
converter clamping of the device voltage by secondary
modulation is achieved, thus eliminating the need of snubber
or active clamp. This paper is used as a reference for
understanding the benefits of soft-switching and the method
of attaining it. [11] Safety enhanced high step-up DC-DC
converter for AC photovoltaic module application was
proposed. To protect installers and users from electrical
hazards Chen proposed a converter that employs floating
active switch to isolate energy from the PV panel when the
AC module is off. This paper is used as a reference for
achieving high step-up voltage conversion ratio, without
extreme duty ratio and the numerous turns- ratios of a
coupled inductor. [12]. The development of a high efficiency
bidirectional converter for power sources with great voltage
diversity was focused [14].
II. CONVENTIONAL PUSH-PULL CONVERTER
The Push-Pull converter is utilized in PV ac module
systems because of the fact that it has only few components
and isolation between the PV modules and the ac utility grid
line. Using a voltage-fed source in the primary side of the
transformer in the circuit is not a good idea which should
have high step-up ratio due to low input voltage and the high
output voltage. Therefore, the push-pull converter is used
with a current source which can decrease the turn ratio of the
transformer. In the secondary side of the transformer, the
conventional push-pull converter is designed using center tap
or full-bridge types as shown in Fig.1. In the center-tap, the
voltage stress across diodes is higher than the voltage stress
Copyright @ 2015 IJSETR. All rights reserved.
G. BHARATH KUMAR, SURESH. MIKKIL
across the diodes in full-bridge type. Therefore the center-tap
To simplify the analysis, the following assumptions are
type is not suitable for a topology with a high secondary
made: 1) boost inductor L is large enough to maintain
voltage of the transformer.
constant current through it; 2) all the components are ideal;
L
3) series inductors Llk1 and Llk2 include the leakage
D1
inductances of the transformer; the total value of Llk1 andLlk2
+
is represented as LlkT; and 4) magnetizing inductance of the
+
transformer is infinitely large. The steady-state operating
np
C
ns
R
waveforms are shown in Fig.3. The primary
switchesS1andS2are operated with identical gating signals
phase shifted with each other by 180◦ with an overlap using
fixed-frequency duty cycle modulation. The overlap varies
np
ns
with duty cycle, and the duty cycle should be kept above
50%. Steady-state operation of the converter during different
D2
Vg
intervals in a one half HF cycle is explained using equivalent
circuits shown in Fig. 3. For the rest half cycle, the intervals
Q1
Q2
are repeated in the same sequence with other symmetrical
devices conducting to complete the full HF cycle.
Fig.1. Main circuit of the conventional Push-Pull
Converter.
The conventional push-pull converter is composed of
switching devices (Q1, Q2), a boost inductor (L), and a high
frequency transformer. The primary-side voltage (Np) of the
transformer is the sum of the input voltage Vg and L voltage
VL.
III. OPERATION AND ANALYSIS OF THE
CONVERTER
In this paper, a dual-stage dc/ac inverter as shown in Fig.2.
is proposed that is composed of high step-up snubber less
current fed push–pull front-end converter and standard fullbridge inverter. Voltage doubler is selected to reduce number
of the switches and the transformer turns ratio. A novel
secondary modulation technique is proposed to clamp the
voltage across the primary side devices and therefore
eliminates the necessity for snubber. Switching losses are
decreced considerably owing to zero-current switching (ZCS)
of primary side switches and zero voltage switching (ZVS) of
secondary side switches. With the soft switching when the
primary switches are turned On and Off Switching loss can
be reduced. switches turn ON at the zero voltage switching
condition , Turn OFF at the zero current switching condition
through parallel resonance between leakage inductance and
resonant capacitor. Soft switching is inherent, load
independent, and is maintained with wide variation of input
voltage and power, and thus is suitable for PV applications.
In this segment, enduring-state operation and examination of
proposed high step-up front-end current-fed converter have
been explained.
FRONT END CONVERTER
FULL BRIDGE INVERTER
i in
D5
D3
i lk1
L
cin
vin
A
s1
C1
D7
s5
LF
s7
c7
c5
cF
D6
D2
S2
C3
c 01
- lk1+
- lk2+
B
D1
S3
D8
VO
i lk2 1:1:n
C2
D4
HF Tr
S4
c02
s6
c6
s8
RL
c8
C4
Fig.2. Proposed inverter with snubber less high step-up
current-fed push–pull dc/dc converter.
Fig.3. Operating waveforms of proposed high step-up
ZCS current-fed push–pull isolated dc/dc converter
shown in Fig. 2.
Interval 1 (see Fig. 4(a); to <t<t1): In this interval, primary
side switch S2 and anti parallel body diodeD3 of the
secondary side switch are conducting. Power is transferred to
the load through HF transformer. The non conducting
secondary deviceS4is blocking output voltage VDC and the
non conducting primary deviceS1 is blocking reflected output
voltage VDC/n. The values of current through various
components are: iS1 = 0, iS2 =Iin, ILlk1=0, iLlk2 =Iin, iD3 =Iin/n
voltage across the switch S1: VS1 =VDC/n. Voltage across the
switch S4: VS4 =VDC.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
A Soft-Switching Push–Pull Based DC-DC Converter Fed with PV for Utility Grid Connected Application
naturally. Current through all primary devices reaches
Final values are:iLlk1 =iLlk2 =Iin/2,iS1 =iS2 =Iin/2, and iD3=0.
(a)
Interval 2 (see Fig. 4(b); t1 <t<t2): At t=t1, primary switchS1
is turned-ON. The corresponding snubber capacitor C1
discharges in a very short period of time. At the end of this
interval, S1is fully conducting andC1is completely
discharged.
Lin/2.
Interval 4(see Fig. 4(d); t3 <t<t4): In this interval, secondary
deviceS3 is turned-ON with ZVS. Currents through all the
switching devices continue increasing or decreasing with the
same slope as interval 3. At the end of this interval, the
primary deviceS2 commutates naturally with ZCC and the
respective current S2 reaches zero obtaining ZCS. The full
current, i.e., input current is taken over by other deviceS1.
Final values are:iLlk1 =iS1 =Iin,iLlk2 =iS2=0, andiS3 =I in/n.
(d)
(b)
Interval 3 (see Fig. 4(c); t2 <t<t3): Now all two primary
switches are conducting. Reflected output voltage appears
across series inductorsLlk1andLlk2, diverting/transferring the
current through switchS2 toS1. It causes current through
previously conducting deviceS2 to reduce linearly.
Interval 5 (see Fig. 4(e); t4 <t<t5): In this interval, the
leakage inductance currentiLlk1increases further with the same
slope and anti parallel body diodeD2 starts conducting
causing extended zero voltage to appear across commutated
switch S2 to ensure ZCS turn-off. Now, the secondary device
S3 is turned-OFF. At the end of this interval, current through
switch S1 reaches its peak value. This interval should be very
short to limit the peak current though the transformer and
switch reducing the current stress and kVA ratings.
(e)
(c)
It also results in conduction of switch S1 with zero current
which helps reducing associated turn on loss. The currents
through various components are given by
The currents through operating components are given by
(4)
(1)
(5)
(2)
(6)
(3)
Where LlkT=Llk1+Llk2. Before the end of this interval t=t3, the
body diodeD3is conducting. Therefore,S3 can be gated on for
ZVS turn-on. At the end of this interval, D3 commutates
Interval 6 (see Fig. 4(f); t5 <t<t6): During this interval,
secondary switchS3 is turned-OFF. Anti parallel body diode
of switch S4 takes over the current immediately. Therefore,
the voltage across the transformer primary reverses polarity.
The current through the switchS1 and body diodes D2 also
start decreasing.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
G. BHARATH KUMAR, SURESH. MIKKIL
IV. PHOTOVOLTAIC (PV) SYSTEM
The crystalline silicon PV module, the model of the PV
unit can be represent by the corresponding electrical circuit
shown in Fig. 5. For that corresponding circuit, a set of
equations have been derived, based on the standard theory,
which allow the operation of a single solar cell to be
simulated using data given from manufacturers or field
experiments.
IL
I
(f)
The currents through operating components are given by
RS
ISH
(7)
RSH
D
DC
(8)
(9)
At the end of this interval, current through D 2 reduce to zero
and is commutated naturally. Current through S1reaches Iin.
Final values: iLlk1 =iS1 =Iin,iLlk2 =iD2=0, andiD4 =Iin/n.
Interval 7(see Fig. 4(g); t6 <t<t7): In this interval, snubber
capacitorC2charges to vDC/n in a short period of time. Switch
S2is in forward blocking mode now.
Fig.5 Equivalent electrical circuit of a PV module.
The series resistance RS speaks to the interior misfortunes
because of the current flow. Shunt resistance R sh, in parallel
with diode, this compares to the spillage current to the
ground. The single exponential mathematical statement
which models a PV cell is separated from the material
science of the PN intersection and is broadly concurred as
reverberating the conduct of the PV cell
(10)
(g)
Interval 8(see Fig. 4(h);t7 <t<t8): In this interval, currents
through S1 and transformer are constant at input current I in.
Current through anti parallel body diode of the secondary
switch D4 is at Iin/n. The final values are: iLlk1 =iS1 =Iin,iLlk2 =
iS2 =0, andiD4 =Iin/n. Voltage across the switch S2 VS2 =VDC/n.
In this half HF cycle, current has transferred from switch S 2
to S1, and the transformer current has reversed its polarity.
The number of PV modules connected in series and
parallal in PV array are used in expression. The Vt is also
stated in terms of the ideality factor of PN junction (n),
Boltzmann’s constant (KB), temperature of photovoltaic
array (T), and the electron charge (q). Applied a dynamical
electrical array reconfiguration (EAR) approach on the
photovoltaic (PV) produced of a utility grid-tied PV system
based on a plant-situated setup, keeping in mind the end goal
to enhance its vitality generation when the working states of
the sun powered boards are distinctive.. The EAR procedure
is done by embeddings a controllable exchanging network
between the PV generator and the focal inverter, which
permits the electrical reconnection of the accessible PV
modules.
V. UTILITY GRID CONNECTED
Limited fossil energy and increased air pollution have
spurred researchers to develop clean energy sources. One of
these sources is the photovoltaic (PV) power generation
system, which is a clean, quiet and an efficient method for
generating electricity. In practical applications. PV arrays can
be used in battery charging, water pumping, PV vehicles,
satellite power systems, utility grid connected power systems,
standalone power systems, and so on. Due to the low
conversion efficiency of PV arrays, on way to reduce the cost
of the overall system is by using high efficiency power
processors. The power processor usually adopts a dc/dc
converter as its energy processing system.
(h)
Fig..4 Equivalent circuits during different intervals of the
operation of the proposed converter (see Fig. 2) for the
steady-state operating waveforms illustrated in Fig. 3.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
A Soft-Switching Push–Pull Based DC-DC Converter Fed with PV for Utility Grid Connected Application
VI. OPERATION AND ANALYSIS OF THE
CONVERTER WITH THREE PHASE INVERTER
The topology of the push pull converter with three phase
inverter for utility grid connected PV systems is depicted in
Fig 6.The proposed circuit concist of two decoupled power
processing stages. The conventional push pull converter is
modified by splitting the output dc capacitor into two
separate ones And Cin and Lin denote the input capacitor and
push pull inductor, respectively. The center taps of the
switches (S3 and S4) and the two output capacitors (Co1 and
(a)
Co2) are connected to the secondary terminals of the
transformer Tr. The transformer leakage inductance is
reflected to the primary is represented by Lin and the
transformer turns proportion is 1: 1:n. A voltage doubler
made out of two diodes (D3 and D4) and two capacitors (C3
and C4) is joined to correct transformer auxiliary voltage to
the inverter dc link. A three phase inverter composed of six
IGBTs (S5–S10) using synchronized as the dc–ac conversion
stage. The inverter connected to utility grid is the energy
storage device.
(b)
Three Phase Inverter
Fig.8. Simulation results of Vin = 22 V (a) Current
iin
Fromd end converter
through input inductor iL and (b) Voltage VAB.
IL
D
I
9
D
D
5
7
D3
i l k1
L
S3
c
01
S7 S 9
S5
C3
RS
C9
C
C
-l
k
1+
D
-lk2+
ci n A B
Utility
DC
grid
D6
D1 D2
D8
ilk2 1:1:n
D10
S1 S 2
D4 c02
C 1 C 2 HF Tr
S1
S
S
7
ISH
RSH
5
S4
6
C4
C
6
8
10
C8
C
10
Fig.6. the Push- Pull Converter With PV And Three
Phase Inverter Utility Grid Connected Topology.
(a)
VII.MATLAB/SIMULINK RESULTS
Simulation results of this paper is as shown in bellow
Figs.7 to 17.
(b)
Fig.9.Simulation results of (a) Primary switches currents
iS1 and iS2 and (b) secondary switches currents iS3 and iS4.
Fig.7. Matlab/simulink model of snubber less high stepup current-fed push–pull dc/dc converter.
(a)
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
G. BHARATH KUMAR, SURESH. MIKKIL
(b)
Fig.13.Scaled voltages across capacitors VCo1, VCo2 and
Vco1+Vco2.
(c)
Fig.10.Simulation results of (a) Output voltage VO and
voltages across output capacitors (b) VCo1 (c) VCo2.
Fig.11. Simulation results at Vin = 41 V and 20% power
through input inductor iL
Fig.14. Matlab/Simulink Model of Snubber Less High
step-up current-fed push–pull dc/dc converter with full
bridge inverter.
(a)
(b)
Fig. 12.Simulation results of (a) Primary switches
currents iS1 and iS2 (b) secondary switches currents iS3 and
iS4.
Fig.15.Output voltage Vo, output current Io, and inverter
output voltage Vinv at peak power.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
A Soft-Switching Push–Pull Based DC-DC Converter Fed with PV for Utility Grid Connected Application
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VIII.CONCLUSION
2002.
In this paper, the soft switching technique has been used
[12]H. C. Shu, ―Design and analysis of a switched-capacitorin order to reduce the switching losses. The boost rectifier
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secondary modulation achieves the soft-switching of all
1, pp. 65–73, Jan. 2003.
semiconductor devices (ZCS of primary side and ZVS of
secondary devices) without modifying the topology. It solves
the basic problem of device turn-off in current-fed converter
and is absolutely new and innovative. Proposed modulation
achieves zero current commutation and natural voltage
clamping of the devices without snubber or any auxiliary
circuit. It relieves the need of extra reactive snubber or active
clamping circuit making it novel and snubber less. In this
paper Push–Pull Based DC-DC Converter fed with PV for
Utility grid Connected Application is employed.
IX. REFERENCES
[1]current-fed soft-switching push-pull front end converter
based bidirectional inverter for residential photo voltaic
power system.
Author’s Profile:
Gaviriboina Bharath Kumar, pursuing
M.Tech power electronics and electrical
drives in department of Electrical and
Electronics
Engineering
from
Sri
Mittapalli College Of Engineering
affiliated to jntu Kakinada and received
B.Tech degree in 2013 from Nalanda
Institute Of Engineering and Technology. His interested
areas are power electronic converters, multilevel inverters,
and renewable energy sources.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469
G. BHARATH KUMAR, SURESH. MIKKIL
Suresh Mikkili is Working as Associate
Professor in Sri Mittapalli College Of
Engineering . he received his B.Tech
degree from Narasaraopeta Engineering
College Narasaraopeta and M.Tech from
NIT Warangal.he has 11 years of teaching
experience.he specialized in power
electronics and drives and areas of intrests
are switching converters, and reluctance motors, and
multilevel inverters.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.43, October-2015, Pages: 9462-9469