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