Implementation of High Step-up Interleaved
Converter with VSI Akshaya.S.R
1, R.Niranjan Kumar
2, D.Vinodini
3, M.Pradeep
4
1234Assistant professor, Department of Electrical and Electronics Engineering, Veltech, Chennai
[email protected] , [email protected]
3,
Abstract— The Interleaved converters are widely employed
in photovoltaic systems. The main advantage is low
conduction losses, low cost and high voltage gain. The high
step up interleaved converter with VSI proposed in this
project is used to boost the output power from the PV source
to the load with high step-up gain without operating at
extreme duty ratio. High voltage is obtained by the voltage
multiplier module of interleaved converter composed of
switched capacitors and coupled inductors. The boosted
output voltage is fed to the R load through single phase
voltage source inverter. The simulation of interleaved
converter is carried out in MATLAB/Simulink.
Keywords—PV system, Interleaved Converter, Voltage multiplier module, Voltage Source Inverter.
I. INTRODUCTION
The renewable energy is increasing demand that is collected from the various resources like solar, tides,
waves, wind and geothermal energy. These resources are
obtained naturally and can be considered to be
inexhaustible instead of using conventional resources. Renewable energy sources are known to be much cleaner
and produce energy without the harmful effects of
pollution unlike their conventional counterparts [3]. Renewable energy are clean sources of energy that have a
much lower environmental impact than conventional
energy technologies [1]. Each source of renewable energy
has unique benefits and cost. The major problem in solar PV is to track the maximum power from the solar PV cell.
To extract the maximum power from the solar panel
introduced MPPT technique (voltage feedback method).
The input supply get from sun light through solar panel
is fed to the integrated boost fly-back converter to
enhance the voltage [2]. The interleaved converter
operated with two switches, different phase shift can be
given to operate the converter. The two switches are
conduct parallel to each other to reduce the conduction
losses. The voltage stress across the switch will be
alleviated and reduction of conduction losses. Fig. 1
shows a typical block diagram for proposed system which
consists of solar photo voltaic system, a interleaved boost
fly-back converter and voltage source inverter for ac
application. The converter connected as two stage
converters with cascaded structure [5].
Figure 1. Block diagram for proposed system
Fig. 1 shows a typical block diagram for proposed
system which consists of solar photo voltaic system, a
interleaved boost fly-back converter and voltage source
inverter for ac application. The converter connected as
two stage converters with cascaded structure [5]. Now a day’s a conventional step up converters like
boost converter and fly-back converter cannot obtain high step-up conversion due to leakage inductance and high
stress on switch [6]. The step-up converters with single
switch are not suitable to obtain high voltage. The low
conduction losses will increases the lifetime of renewable
energy sources and suitable for high power applications.
The above mentioned disadvantages are limited by using
conventional interleaved boost converter to obtain high
power. Switched capacitors are integrated with interleaved
boost converter to make high voltage gain. A voltage
multiplier module in converter can be used in a converter
to multiple the output voltage [8]. The two switches
operated parallel, when one of the switch turn off then the
energy stored in the inductor will transfer to respective
paths and current distribution Voltage multiplier module
consist of switched capacitors and coupled inductors. For
ac power application single phase voltage source inverter
will be used.
International Journal of Pure and Applied MathematicsVolume 119 No. 15 2018, 3779-3784ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/
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II. PV MODULE AND CONVERTER OPERATION
A. Mathematical Model of PV Module
The modeling techniques of PV array will represent the
photovoltaic array as an equivalent electrical circuit. Fig.1
represents the equivalent circuit of PV module [4].
The thermal voltage Vt of the module for Ns cells connected
in series is given as NskT/q. RS and Rsh are the equivalent
series resistance and shunt resistance of the photovoltaic cell. v,cell is the current generated by the incident light (it is directly proportional to the Sun irradiation).
Figure 3. Block diagram for proposed system
All PV array datasheets bring basically the following
information: the nominal open-circuit voltage (Voc,n ), the
nominal short-circuit current (Isc,n ), the voltage at the
MPP (Vmp), the current at the MPP (Imp), the open-circuit
voltage/temperature coefficient (Kv), the short circuit
current/temperature coefficient (Ki) and the maximum
experimental peak output power (Pmax,e). This information is always provided with reference to the nominal condition or Standard Test Condition (STC),
where the temperature is 25oC and solar irradiation is
1000 W/m2.
B. Converter Operating Principles
The interleaved converter with voltage multiplier module is composed of switched capacitor and coupled inductor connected with boost converter to form a boost fly-back converter with interleaved structure [5]. The step-up interleaved converter with interleaved structure is shown in Fig. 3. The fly-back converter has primary
windings of coupled inductors with Np turns and
secondary winding of coupled inductors with Ns turns are connected to increase voltage [6]. The interleaved fly-back converter consists of two MOSFETs. When one switch get turn OFF then it performs as a fly-back converter, and other switch will be turned off to perform as a forward converter [5]-[8]. Different phase shift can be given to control both the switches.
Mode I: The power switch S2 in ON condition then S1 begin to turn on. All the diodes are reverse biased and stored energy is quickly released to output terminal via
Df2.
Mode II: The power switches S1 and S2 are in ON state
and all the diodes are reverse biased.
Mode III: The switch S1 will be in On state where S2
will be in OFF state. The energy released to output
terminal and Vc1 obtain double output voltage of the
boost converter.
Figure 3. Interleaved boost fly-back converter
Mode IV: In this mode the operating condition will be
same as that of the previous condition. Mode V: The power switch S1 remains in ON state, and
the other power switch S2 begins to turn on. The store
energy is released through the output terminal via fly-back
– forward diode Df1. Mode VI: Both of the power switches S1 and S2 remain
in ON state, and all diodes are reversed biased. Current through both the leakage inductor will increase linearly.
Mode VII: The power switch S2 remains in ON state, and
the other power switch S1 begins to turn off. The current through series leakage inductors flow through the output
capacitor C2 via fly-back–forward diode Df2. Here Vc1 obtains double times the output voltage of the boost
converter. Mode VIII: In this mode the operating condition will be
same as that of the previous condition except the clamped
diode Dc1.
III. CONVERTER CONFIGURATION AND
SIMULATION DIAGRAM
A. Step-up Voltage gain
The voltage on clamp capacitor can be regarded as an output voltage of the boost converter; thus, voltage VCc can be derived from
VCc =
𝑣𝑖𝑛
(1 −𝐷)
(2)
When one of the switch get turned off then Vc1
obtains double output voltage of the boost converter and
derived from
VCc = 𝑣𝑖𝑛
(1−𝐷)+ Vcc (3)
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The output filter capacitors C2 and C3 are charged by energy transformation from the primary side. When S2 is in ON state and S1 is in OFF state, Vc2 is equal to the
induced voltage of Ns1 plus the induced voltage of Ns2, and when S1 is in ON state and S2 is in OFF state, Vc3 is
also equal to the induced voltage of Ns1 plus the induced
voltage of Ns2.
Vc1 =
𝑣𝑖𝑛
(1 − 𝐷)
+ + 𝑣𝑖𝑛
(1−𝐷) (4)
Vc1 =
2𝑣𝑖𝑛
(1 − 𝐷)
(5)
Thus the voltages Vc2 and Vc2 can be derived from
Vc2 = Vc3 =
𝑛 𝑣𝑖𝑛
(1 − 𝐷)
(6)
The output voltage can be derived from
V0 = Vc1 + Vc2 + Vc3
V0 = 2𝑣𝑖𝑛
(1−𝐷) +
𝑛 𝑣𝑖𝑛
(1−𝐷) +
𝑛 𝑣𝑖𝑛
(1−𝐷)
V0 = 𝑣𝑖𝑛
(1−𝐷) (2 + 2n)
V0 =
2 + 2𝑛 𝑣𝑖𝑛
(1 − 𝐷)
(7)
The step-up voltage of interleaved boost converter
is derived it as
as to be always capable of defining the ac output voltage [16]. It can be observed that the ac output voltage can take
values up to the dc link value Vi, which is twice that
obtained with half-bridge VSI topologies. Several modulating techniques have been developed that are applicable to full-bridge VSI.
Figure 4. Simulation diagram for Interleaved boost fly-back converter
with VSI
IV. SIMULATION RESULTS
The Fig. 5 represent the voltage and current waveforms
for interleaved boost fly-back converter. The output
voltage obtained is 220V and output current obtained is
0.42A.
TABLE I POWER SPECIFICATIONS
𝑣0
𝑣𝑖𝑛 =
(2+2𝑛)
(1−𝐷) (8)
B. Simulation Diagram for Interleaved Converter
The boost converter with interleaved structure is shown
in Fig. 3. The switches are controlled by sinusoidal pulse
width modulation technique. A high step-up interleaved
converter, which is suitable for renewable energy system,
is proposed in this paper [9]. Through a voltage multiplier
module composed of switched capacitors and coupled
inductors, a conventional interleaved boost converter
obtains high step-up gain without operating at extreme
duty ratio [10]-[13]. The converter not only reduces the
current stress but also constrains the input current ripple,
which decreases the conduction losses and lengthens the
lifetime of the input source [14]. By operating at less duty
cycle ratio the switching conduction losses will be
reduced which will be advantage for power electronics
circuits [15]. The voltage source inverter is similar to the half-bridge
inverter; however, a second leg provides the neutral point
to the load. As expected, both switches S3 and S6 (or S5
and S4) cannot be on simultaneously because a short
circuit across the dc link voltage source Vi would be produced. The undefined condition should be avoided so
System parameters Values
PV module rated power 100 W
Open circuit voltage 22.41 V
Short circuit current 6.2 A
Switching frequency of converter 50 KHz
Fly-back converter transforms N1/N2 = 1/1
turns ratio
Switching frequency of inverter 50 Hz
Output voltage 220 V
Input voltage 17 V
Inductor 500 µH
Capacitor 200 µH
Duty cycle ratio 0.7
The PV array has been assumed to be comprising a
combination of Ns cells in series and Np cells in parallel in order to achieve the required voltage, current and power
capacity. Vp, Vo and the internal resistance Rin for the array have been calculated from the values of the open
circuit voltage (Voc), maximum power voltage (Vpm) and
maximum power current (Ipm) of each cell [4]. The Fig. 6. represents the power waveform for interleaved boost fly-back converter. The output power obtained is 90W. All PV array datasheets bring basically the following
information: the nominal open-circuit voltage (Voc,n ), the
nominal short-circuit current (Isc,n ), the voltage at the
MPP (Vmp), the current at the MPP (Imp), the open-circuit
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voltage/temperature coefficient (Kv), the short circuit
current/temperature coefficient (Ki) and the maximum
experimental peak output power (Pmax,e). The amount of
incident light directly affects the generation of charge carriers, and consequently, the current generated by the device. The information is always provided with reference to the nominal condition or Standard Test Condition
(STC), where the temperature is 25oC and solar
irradiation is 1000 W/m2.
Figure 5. Output voltage and current for interleaved converter
Figure 6. Output power for interleaved converter
The modulation technique is multiple number of output
pulse per half cycle and pulses are of different width. The
width of each pulse is varying in proportion to the amplitude of a sine wave evaluated at the center of the
same pulse [14]. The gating signals are generated by
comparing a sinusoidal reference with a high frequency
triangular signal. Whenever the carrier wave greater than the reference wave switch pulse is generated [15]. The
single phase full bridge voltage source inverter is
connected with interleaved converter to get AC waveform. The inverter is operated by turning on the
cross switches to avoid short circuit. The Fig. 7.
Represents the switch pulse for inverter which has
sinusoidal in nature [16]. Analogy PWM control requires the generation of both
reference and carrier signals that are feed into the comparator and based on some logical output, the final
output is generated. The reference signal is the desired signal output maybe sinusoidal or square wave. There are
various types of PWM techniques and so it can get different output and the choice of the inverter depends on
cost, noise and efficiency.
Figure 7. Switch pulse for Inverter
The Fig. 8. represent the voltage and current waveform
for interleaved boost fly-back converter with VSI. The
output voltage obtained is 220V and output current obtained is 0.4A. The inverter power rating is 100W.
Figure 7. Output voltage and current waveforms for interleaved
converter with VSI in closed loop
The power output of the interleaved boost fly-back
converter is shown in Fig. 9.
Figure 8. Output power for interleaved converter with VSI
V. CONCLUSION
The Interleaved converter for solar photovoltaic system
is utilized in this project, in two different topologies such
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as interleaved converter without single phase full bridge
VSI and interleaved converter with single phase full bridge VSI for PV system. Typical features like high step-
up voltage and low conduction losses are obtained with the proposed system. The DC-DC converter consists of
boost converter connected in interleaved structure with fly-back rectifier, which boosts up the output of the solar
cell array. The single phase full bridge VSI generated the
sinusoidal output voltage that is smoothened with the R load.
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