constant output voltage for grid connected photovoltaic
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Constant Output Voltage for Grid Connected Photovoltaic Application
System using oscillator and varactor diode
Abstract:
There are so many advantages of using non-
conventional energy sources over
conventional energy sources. The widely
used energy source is the sun. nowadays
people are using solar panels in wide range.
Even government is providing subsides for
installing solar panels. The output DC
voltage of solar panel is not constant due to
clouds. To get the output constant, we
require an electric circuit to get constant
output. There are many devices such as
microcontroller, microprocessor, Arduino to
make controlling circuit.
1. Introduction Non renewable sources are going to vanish
in few years. In addition they make noise
and atmosphere polluted. The solution is to
use solar or wind energy which is free of
cost. The solar panel is the best option as it
is available most of the time and almost
everywhere. Only disadvantage is that, the
output is not constant. Here we are
introducing group of circuit to make this
output at constant level. Here DC to DC
boost converter is used along with oscillator
and varactor diode. Here we used dual
circuit to get almost constant output.
Feedback loop is provided to the varactor
diode to make oscillator frequency constant.
Block diagram of the system is shown in
fig1
2. DC-DC boost converter
This is the first stage of the circuit. It gives
boosted constant output. Boost converter is
performed by a combination of four
components which are inductor, electronic
switch, diode and capacitor [1]. The
connection of circuit is as shown in fig2.
DC out
Fig 1 Block diagram of system
Fig 2 DC-DC boost converter [1]
VARACTOR
DIODE
SOLAR
PANEL
DC-DC BOOST
CONVERTER
OSCILLATOR RECTIFIER
JASC: Journal of Applied Science and Computations
Volume VI, Issue V, May/2019
ISSN NO: 1076-5131
Page No:680
Kishan Patel
Assistant Professor, Department of Electrical Engineering, Chandubhai S Patel Institute Of Technology, Charusat University, Changa
Email: kishanpatel.ee@charusat.ac.in
When the input current which rises flows
through inductor L and switch SW, energy is
stored in the inductor and load is supplied by
capacitor current. When the switch is turned
off at t = kT. The current that was flowing
through the switch would now flow through
inductor L, diode D, output capacitor C, and
load R. The inductor current falls until the
switch is turned on again in the next cycle.
During this time, energy stored in the
inductor is transferred to the load together
with the input voltage. In this way we get
constant output. This output is given to
oscillator circuit to make it more constant.
3. Varactor diode
Varactor Diode is a reverse biased p-n
junction diode, whose capacitance can be
varied electrically. Varactor diode is also
called as voltage variable capacitor diodes.
The operation of the p-n junction depends
on the bias applied which can be either
forward or reverse in characteristic. The
width of the depletion region is seen to
increase with an increase in the applied
voltage for the reverse bias. Under such
condition, the p-n junction can be
considered to be analogous to a capacitor,
where the p and n layers represent the two
plates of the capacitor while the depletion
region acts as a dielectric separating them.
The mathematical expression for varactor
diode is given by, C = €A / D. This type of
diode is widely used in VCO (Voltage
Controlled Oscillators), to get constant
frequency output.
4. Oscillator circuit
Here we are using colpitts oscillator to
generate frequency. The Colpitts Oscillator
uses two centre- tapped capacitors in
series with a parallel inductor to form its
resonance tank circuit producing
sinusoidal oscillations. Oscillator is an
amplifier with the positive feedback and it
converts DC input signal into AC output
waveform with certain variable frequency
drive and certain shape of output waveform
by using the positive feedback instead of
input signal. The tuned tank circuit consists
of an LC resonance sub-circuit connected
between the collector and the base of a
single stage transistor amplifier producing a
sinusoidal output waveform. The Colpitts
oscillator uses a capacitive voltage divider
network as its feedback source. The two
capacitors, C1 and C2 are placed across a
single common inductor, L. here C1 is
varactor diode or we can say capacitor that
varies with voltage. Fig 3 shows colpitts
oscillator.
vcc
Fig 3 Colpitts oscillator
5. Proposed system
The complete system is given in fig 1 . The
output from solar panel is given to boost
converter. This output is further given to
oscillator circuit with varactor diode. This
DC output is used as power supply to
oscillator. The frequency output of oscillator
is given rectifier to get average DC output.
If power supply of oscillator increases, then
the frequency of oscillation also increases.
So DC output of rectifier increases. This Dc
output is given to varactor diode. As voltage
JASC: Journal of Applied Science and Computations
Volume VI, Issue V, May/2019
ISSN NO: 1076-5131
Page No:681
increases the capacitance of varactor diode
also increases. This capacitance is connected
to the tank circuit. So increase in
capacitance of tank circuit causes frequency
of oscillation to decrease. So average output
of oscillator also decrease.
If power supply of oscillator decreases, then
the frequency of oscillation also decreases.
So DC output of rectifier decreases. This Dc
output is given to varactor diode. As voltage
decreases the capacitance of varactor diode
also decreases. This capacitance is
connected to the tank circuit. So decrease in
capacitance of tank circuit causes frequency
of oscillation to increase. So average output
of oscillator also increase.
5. Simulation
Fig 4 Voltage vs time
Fig 5 Current vs time
The simulation of the system was carried out
in ELECTRONICS WORKBENCH (EWB)
and MATLAB. Boost converter was
simulated in EWB. This output was given to
different programs of MATLAB. Oscillator
programs were design in MATLAB. As
shown in fig 4, the output voltage is constant
at value around 24V. Fig 5 shows the
current is also constant. As shown in fig 6,
the graph of efficiency decreases as output
voltage tends to increase. This is because
limitations of transistor used in oscillator.
Fig 6 Graph of efficiency
6. Conclusions
As the simulation shows, it is proved that
output is constant as particular voltage
levels. The current is also constant. So we
do not get variations in output power, and
our device gets constant power from solar
panel. In these way, solar panel advantages
are utilized.
7. References
[1] Pui-Weng Chan, Syafrudin Masri, “DC-
DC Boost Converter with Constant Output
Voltage for Grid Connected Photovoltaic
Application System”
[2] E. Koutroulis, K. Kalaitzakis and N. C.
Voulgaris, “Development of a
microcontroller based photovoltaic
maximum power point tracking system,”
IEEE Trans. On Power Electronics, vol. 16,
no. 1, pp. 46-54, 2001.
JASC: Journal of Applied Science and Computations
Volume VI, Issue V, May/2019
ISSN NO: 1076-5131
Page No:682
[3] Ahmad Al Nabulsi, Muneer Al Sabbagh,
Rached Dhaouadiand Habib-ur Rehman, “A
300 watt cascaded boost converter design
for solar energy systems,” International
Conf. on Electric Power and Energy
Conversion Systems, pp. 1-4, 2009.
[4] A. Hajimiri and T. H. Lee, A general
theory of phase noise in electrical
oscillators, IEEE J. Solid-State Circuits 33
(1998) 179–194
[5] Ahmad Al Nabulsi, Muneer Al Sabbagh,
Rached Dhaouadiand Habib-ur Rehman, “A
300 watt cascaded boost converter design
for solar energy systems,” International
Conf. on Electric Power and Energy
Conversion Systems, pp. 1-4, 2009.
[6] Razavi, B. Design of Analog CMOS
Integrated Circuits. McGraw-Hill. 2001.
[7] Ulrich Rohde, Ajay Poddar, and Georg
Bock, 2005. The Design of Modern
Microwave Oscillators for Wireless
Applications: Theory and Optimization,
540-543 John Wiley & Sons, ISBN 0-471-
72342-8.
JASC: Journal of Applied Science and Computations
Volume VI, Issue V, May/2019
ISSN NO: 1076-5131
Page No:683
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