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International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-6 Issue-2, May 2016
31
Published By:
Blue Eyes Intelligence Engineering
& Sciences Publication Pvt. Ltd.
A High Efficiency DC/DC Boost Converter for
Photovoltaic Applications
Peyman Khazaei, Syyed Mojtaba Modares, Morteza Dabbaghjamanesh, Motab Almousa, Amirhossein
Moeini
Abstract— In this paper, a non isolated interleaved, dc/dc boost
converter with a high efficiency is proposed for using in
photovoltaic system applications. For realizing zero voltage soft
switching (ZVS), two active clamp circuits are used for each
phases of the boost converter. By utilizing a voltage doubler
configuration at the converter’s output terminal and connecting
the secondary side of coupled inductors in series, high conversion
ration can be achieved. The capacitor is also connected in series
with output capacitors to transfer leakage energy to the output.
Interleaved structure is used in input side to minimize current
ripple and reduce magnetic component. So, the converter not
only operates with a higher voltage gain, but also is able to
operate more efficiently and can be used in photovoltaic (PV)
applications.
Keywords-high voltage gain; interleaved DC-DC boost
converter; photovoltaic system; soft switching performance.
I. INTRODUCTION
Chiefly, utilizing high performance dc-dc boost
converters is an essential factor in renewable energy sources
in high power applications. High efficiency, high voltage
gain and being non-isolated are the main features for
renewable energies applications [1]. Ideally, a boost
converter can reach a very high voltage gain with an
unlimited duty cycle, however the turn off period of switches
will be small when the duty cycle gets increased. The ripples
in the current waveform corresponding to power devices get
increased and as a result the power losses increase.
Furthermore, the voltage stresses across for both switch and
diode are identical to the output voltage [2]. The interleaved
structure can be considered as a feasible solution to enhance
the performance, mitigate ripples in the current, reduce the
size of the passive components and also accelerate the
transient response [3-4]. The coupled inductor is utilized to
reduce not only the duty ratio but also the voltage stress
across the switches. Therefore, for applications for which a
high voltage gain is needed, the boost converter with the
coupled inductor can be more efficient compared to the
conventional design [5]. Different active and passive soft
switching interleaved step-up converters in which coupled
inductor is utilized are proposed for loss reduction purposes.
[6-8].
Revised Version Manuscript Received on May 03, 2016.
Peyman Khazaei, Department of Electrical and Computer Engineering,
Louisiana State University, Baton Rouge, LA
Syyed Mojtaba Modares, Department of Electrical and Computer
Engineering, Louisiana State University, Baton Rouge, LA
Morteza Dabbaghjamanesh, Department of Electrical and Computer
Engineering, Louisiana State University, Baton Rouge, LA
Motab Almousa, Department of Electrical and Computer Engineering,
Prince Sattam Bin Abdulaziz University, Saudi Arabia.
Amirhossein Moeini, Department of Electrical and Computer
Engineering, University of Florida, Gainesville, FL.
However, most of them are considered for the Power Factor
Correction (PFC) applications and not an appropriate option
for PV systems for which a DC-DC boost converter with a
high step-up gain is required.
Some interleaved converters are proposed by adding
capacitor cells to the typical interleaved boost converter [9-
10]. However, a considerable number of capacitors are
required to reach a high voltage gain that increases the
complexity in the converter. Different types of interleaved
converters with coupled inductors are well investigated in
[11-13], which can reach high step-up gain by an appropriate
topology. Unfortunately, the maximum numbers of
interleaved phases are only two in these converters and
cannot be designed for any number of phases. Also, the
voltage stress across the diode in the output is greater than
the output voltage.
In this paper, an efficient interleaved converter is
proposed for PV system applications. The interleaved
structure in input side and cascaded configuration in output
side is utilized therefore, there would not be any problem
with a high amount of current and voltage in the input and
output. By utilizing the active clamp design, both the clamp
and main switches work in the zero voltage soft switching
condition. A snubber capacitor in series with output
capacitors is inserted to recycle the leakage energy. So,
switching losses are reduced significantly. When a coupled
inductor is utilized in fly-back condition the other coupled
inductor operates in forwarding condition to transfer energy
to output side, due to interleaved control. The proposed
topology and operational stages are discussed in section ІІ. In
the third section of this paper, the design guidelines of the
converter are given. In section IV the simulation result and
waveforms are illustrated.
II.
PROPOSED
CONVERTER
TOPOLOGY
The topology of the proposed converter is shown in Fig.
1. The main switches S
1
and S
2
work in the interleaved
control. The active clamp circuits are composed of auxiliary
switches S
C1
and S
C2
, and clamp capacitors C
C1
and C
C2
,
which are utilized to recycle the leakage energy and suppress
the turn-off spike voltage on the main switches, and realize
zero voltage soft switching. There are two coupled inductors,
which L
1a
and L
2a
with n
1
turns which have been coupled
with their corresponding inductors L
1b
and L
2b
with n
2
turns.
The L
m1
and L
m2
are the magnetizing inductors, and L
k1
and
L
k2
are the leakage inductances of coupled inductors. N
represents the turn ratio n
2
/n
1
. The couples reference are
marked by "*" and "•". The C
o1
, C
o2
and C
o3
are the output
capacitors and D
o1
, D
o2
, D
o3
and D
o4
are the output diodes.
Moreover, the capacitor C
o3
works as snubber capacitor, to
recycles the leakage energy in the coupled inductor. There
are 16 main stages in one switching period. Because of the
A High Efficiency DC/DC Boost Converter for Photovoltaic Applications
32
Published By:
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symmetrical structure of the converter, only half of 16 stages
are considered. The steady state profiles are depicted in Fig.
2. In Fig.3 corresponding circuit of each stage is illustrated.
Figure 1. proposed ZVT boost converter.
Figure 2. Key waveforms of proposed converter.
Time interval [t
0
, t
1
]: the main switches S
1
and S
2
conduct, and the clamp switches S
C1
and S
C2
are in OFF state.
All diodes are in reverse biased. The current flowing though
the magnetizing inductors L
m1
and L
m2
increases by input
voltage linearly.
)()()(
0
11
011
tt
LL
V
tIti
km
in
mLmL
−
+
+=
(1)
)()()(
0
22
022
tt
LL
V
tIti
km
in
mLmL
−
+
+=
(2)
Time interval [t
1
, t
2
]: at the beginning of this time
interval, the main switch S
2
goes to the OFF state, then the
corresponding capacitor C
S2
is energized by the current i
Lm2
.
Capacitor C
S2
causes the main switch S
2
gets OFF with ZVS
condition. At t
2
, voltage of main switch S
2
becomes equal to
clamp capacitor C
C2
.
)(
)(
)(
1
2
12
2
tt
C
tI
tv
s
mL
sd
−=
(3)
Time interval [t
2
, t
3
]: at t
2
, charging of switch S
2
leads to
diode D
o1
and the inverse-parallel diode of the switch S
C2
begin to conduct, and the leakage energy transfer to output.
The coupled inductor L
1
works as transformer and forward
mode and the coupled inductor L
2
works as flyback converter
to supply energy to the load in the output. The leakage
inductance L
k2
and the capacitor C
C2
, make a resonance
circuit. The circuit operation at this stage is according to the
following formula:
)(cos)()(
21222
tttIti
mLkL
−ω= (4)
)(sin)()(
212032
tttIZVtv
kLOCC
−ω+= (5)
1111
)(
oDmLkLs
iNtIii +== (6)
Where
22
1
.
1
Ck
CL
=ω
Time interval [t
3
, t
4
]: at t
3
, the switch S
C2
conducts in
ZVS condition, as its inverse-parallel is conducting. The
voltage across the capacitor C
C2
will be equal to the voltage
across the output capacitor C
o3
. Therefore, the diode D
o4
begins to conduct.
Time interval [t
4
, t
5
]: at t
4
, the current of diode D
o4
falls to
zero and then the current of clamp capacitor C
C2
becomes
equal to the current leakage inductance L
k2
[33].
Time interval [t
5
, t
6
]: at the beginning of this time period,
the clamp switch S
C2
gets OFF. While the voltage across the
capacitor C
S2
drops, the voltage across the S
C2
rises with a
same degree. Thus, the switch S
C2
gets off with ZVS
performance. The capacitor C
C2
is disconnected from
converter and the L
k2
starts to resonance with the C
S2
.
)](sin1)[()(
52522
tttIti
LkLk
−ω−=
(7)
)](cos1[
.)(
)()(
52
22
5
522
tt
CtI
tVtv
S
Lk
sSdSd
−ω−
ω
−=
(8)
Where
22
2
.
1
sk
CL
=ω
L
2a
L
1
a
L
1b
L
2b
International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-6 Issue-2, May 2016
33
Published By:
Blue Eyes Intelligence Engineering
& Sciences Publication Pvt. Ltd.
(2)
(1)
(4)
(3)
(6)
(5)
(8)
(7)
Figure 3. Different stages of the converter: (1) interval 1 (t
0
- t
1
), (2) interval 2 (t
1
- t
2
), (3) interval 3 (t
2
-t
3
), (4) interval
4 (t
3
- t
4
), (5) interval 5 (t
4
- t
5
), (6) interval 6 (t
5
- t
6
), (7) interval 7 (t
6
- t
7
), (8) interval 8 (t
7
- t
8
)
Time interval [t
6
, t
7
]: Initially, the voltage across the
switch S
2
is zero. Therefore, the corresponding diode of the
switch S
2
starts to operate in the conducting mode. The
current through L
k2
increases linearly, which controls
declining rate of the output diode D
o1
.
)(
)()(
21
2
1
611 kk
oC
oDoD
LLN
V
titi +
−=
(9)
Time interval [t
7
, t
8
]: at the beginning of this interval, the
main switch S
2
will be ON with ZVS soft switching
performance due to its inverse-parallel diode which conducts.
At t
8
, the leakage current L
k2
reaches zero and the diode D
o1
goes to the OFF state while the current is zero. The input
voltage will charge two main inductors. A same pattern
occurs in the rest of the switching time.
A High Efficiency DC/DC Boost Converter for Photovoltaic Applications
34
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III. DESIGN
GUIDELINES
If the leakage inductance is zero (ideal condition),
conduction resistance as well as the voltage drop are
negligible. The voltage of the clamp and output capacitors
can be acquired using equations (10) and (11):
D
V
VV
in
oCcC
−
==
1
3 (10)
D
VN
VV
in
oCoC
−
==
1
21 (11)
Where D is the duty cycle for the main switch. The
output voltage is summation of the output capacitors.
Therefore, the voltage gain is:
D
N
V
V
M
in
out
−+
== 1
1.2
(12)
Equation (13) indicates the equality of the voltage across
the clamp capacitors and the voltage stress across the power
switches.
121
&_
+
=
−
=N
V
D
V
V
outin
clampmainstress
(13)
The voltage stress across the switches is proportional to
the coupled inductor’s turn ratio. Therefore, by selecting a
proper turn ratio the voltage switch stress can be reduced. All
active switches are turned off with ZVS due to parallel
capacitors C
S1
and C
S2
.
The clamp switches are in the ON state under ZVS
condition as their corresponding inverse-parallel diodes are
conducting when switches S
C1
and S
C2
turn on. To meet the
ZVS ON state of main switches, all the energy in parallel
capacitor of the main switch has to be transferred to leakage
inductance. Therefore, when the main switch is in the ON
state, the stored energy in the leakage inductance has to be
greater than the amount of energy in the parallel capacitor.
Therefore, the zero voltage switching-ON performance of
main switches is obtained from energy consideration:
2
1
2
)
12
(
4
2+
≥N
V
C
I
L
out
S
in
K
(14)
As a result:
22
2
)12(
2
in
outS
K
IN
VC
L+
≥
(15)
The relationship of leakage inductance versus input
current in different turn ratio is plotted in Fig. 4. The required
leakage inductance in ZVS condition decreases as the input
current increases. Equation (16) shows the proper
determination of the clamp capacitor [14]:
2
2
2
2
)1(
sK
C
fL
D
Cπ−
≥
(16)
The magnetizing inductor and the output capacitor are
determined by considering a permissible percentage of ripple
in the inductor current and proper voltage ripple on the
output capacitor voltage [15].
Figure 4. Relation of leakage inductance, and input
current, and turns ratio.
IV.
SIMULATION RESULTS
A PV array is used instead of the dc source of proposed
converter in simulation. The parameters of PV modules are
presented in table І. Four PV modules are connected in series
and parallel to obtain high power level. Table ІІ shows
converter parameters. In order to achieve maximum power
from PV array, average current control and maximum power
point tracking (MPPT) control have been used. The voltage
in MPP is computed by using IncCon MPPT method
described in [16] and it is compared with extracted PV
voltage. The difference between them is used as an input for
voltage controller [17-24]. By comparing the output of
current controller with carrier wave, appropriate pulse for the
gate of main switch is generated. The phase difference
between each gate signal is 180°, because there are two
phases in proposed interleaved boost converter [25-32].
Fig. 5 illustrates control algorithm of the converter topology.
The gate signals of the clamp switches S
C1
and S
C2
are
complement with the gate signals for main switches S
1
and
S
2
. Fig. 6 shows the voltage, current and power profiles of
output PV array without and with MPPT and with irradiance
change. The currents of leakage inductances and input
current are illustrated in Fig. 7. The ripple in the input current
is not considerable because of the interleaved design. The
voltage and current of clamp capacitor are shown in Fig. 8.
Fig. 9 indicates the switching transition of the main and the
clamp switches. It is shown that all power switches of
converter are operating with zero voltage soft switching
performance for the entire switching period that mitigates the
power losses. The voltage and current profiles of the diode
D
o1
are depicted in Fig. 10.
TABLE I.
PV
M
ODULE CHARACTERISTICS
Model: RECAE220-us
Max. output power, P
max
(W) 220
Open circuit voltage, V
OC
(V) 36.6
International Journal of Soft Computing and Engineering (IJSCE)
ISSN: 2231-2307, Volume-6 Issue-2, May 2016
35
Published By:
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MPPT voltage, V
MPPT
(V) 28.7
Short circuit current, I
SC
(A) 8.2
MPPT current, I
MPPT
(A) 7.7
TABLE II.
K
EY PARAMETERS OF THE CONVERTER
Input Voltage, V
in
(V) 59 Magnetizing inductor, L
m
(uH) 130
Output voltage, V
out
(V) 520 Output capacitors, Co
(uF) 50
Output power, P
out
(W) 880 Turns ratio, N 1:1
Main switches frequency,
f
s
(KHz) 100 Leakage inductances, L
k1
and L
k2
(uH) 1.5
Clamp Capacitors, C
C1
and C
C
2
(uF) 3 Parallel capacitors, C
S1
and C
S
2
(nF) 1
Figure 5. Control algorithm of the proposed converter
Figure 6.Voltage, current and Power of PV at without
and with MPPT and irradiance change.
Figure 7. Input current i
Lk1
, i
Lk2
, and I
in
Figure 8.Voltage and current of the clamp circuit.
Figure 9. ZVT performance of (a) main switch, (b) clamp
switch.
Figure 10.Voltage and current of diod D
o1
.
The voltage stress across the diode is
out
V
NN122+, which
is less than the output voltage. The declining rate of the
current through diode is controlled by leakage inductance. A
comparison of measured efficiency at different levels of load
for this proposed converter and the converter introduced in
[13], is given in Fig. 11. There is approximately 3%
A High Efficiency DC/DC Boost Converter for Photovoltaic Applications
36
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improvement in efficiency compared with the converter
proposed in [13] at 880W full load under the same testing
scenario. The efficiency is enhanced with a less complicated
configuration in comparison to the converter in [13].
Figure 11. Measured efficiency comparison at different
percent loads.
V. CONCLUSION
An efficient high voltage gain ZVS non-isolated
converter with interleaved structure in input and voltage
doubler structure in output of for PV system has been
proposed in this paper. Zero voltage soft switching
performance is realized by active clamp circuit to mitigate
the power losses. The proposed converter also uses switches
with low turn on resistance and voltage rate. Furthermore,
due to interleaved operation the input current ripple can be
mitigated. The steady state waveforms and stages analysis
and design guidelines are discussed. At last, simulation
results of converter with PV array 880W, 59V, 520V are
presented. Simulation results confirm that the proposed
interleaved converter is an appropriate option for conversions
in which the high voltage gain and efficiency are two
important factors.
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