Dcdc Converter Simulations

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Avaibable online at: www.sci-journals.com

International Journal of Advanced

Power Electronics

www.sci-journals.com

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Science-International Journal of Advanced Power Electronics

SIMULATION OF BUCK, BOOST AND BUCK-BOOST POWER

CONVERTERS FOR SOLAR PANEL

Chandani Sharma1

, Anamika Jain2

1Department of Electronics and Communication Engg. Research Scholar, Graphic Era University, Dehradun2Department of Electronics and Communication Engg. Professor, Graphic Era University, Dehradun

e-mail: [email protected], [email protected]

Abstract: Power systems design, layout and computation for Photovoltaics forms the basis of nationalaction plan for Solar India. Power switching converters are used in numerous solar based appli cations.The rapid increase in standalone and gr id based structures employ cir cuit regulation using Buck, Boost and

Buck-Boost Converters. I n th is perspective, electri city generation and supply is requir ed to adapt changes

relat ive to duty cycle for continuous and discrete time systems. An eff ort is made in thi s paper to visual ize

potential of converters in meeting global energy requi rements. Analysis of power electronic converters iscarr ied out in continuous and discrete Simu li nk envir onment considering eff ect of phase delay. Duty cycle

and effi ciency calculations for 60W panel using 36 solar cell s are compared.

Keywords: Solar India, Power switching converters, standalone and grid structures, Duty cycle,

Efficiency, Simulink.

1.INTRODUCTION

Solar being abundant, distributed, pollution less and

recyclable appear as primary source of energy to

meet global demand in power engineering. However,

converters form an important interface between panel

and load for applications. Since direct connection ofpanel with load raises installation costs, converters

are used. There is therefore a need to systematically

analyze and understand how solar and converters

operate together as an optimal system.

DC/DC converters are described as power electronic

switching circuits since they convert one form ofvoltage to other. These may be applicable for

conversion of different voltage levels. Generally

three basic types of converters are accountable as per

their use. They either step up by boosting voltage at

output known as Boost converter or by stepping

down reducing voltage known as Buck converters.

There is another class of converters used for both


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Chandani Sharma/ Science Journals 08(2014) , 1408-1(1)

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stepping up or down the voltage output described as

Buck-Boost converters. Buck-Boost converters

reverse polarity of output voltage, as such they are

sometimes known as inverters.

Unlike AC we cannot step up or step down DCdirectly. Power flow through components need to be

determined. The nonlinear components connected in

the network produce harmonic components at output

of waveform. These may affect efficiency and duty

cycle. Expressions may be given by following

assumptions for ideal case,

PIN= POUT+ PLOSS (1)

VOUT/VIN= IIN/IOUT (2)

(%) = POUT/PIN (3)

VOUT/VIN= D, (4)

Where,

Power fed into Converter from panel: PIN

Power output of Converter: POUT

Power lost into Converter: PLOSS

Voltage input from panel to Converter: VIN

Voltage output from Converter: VOUT

Current input from panel to converter: IIN

Current output from Converter: IOUT

Efficiency: Duty cycle: D

Efficiency of converters is about 80-90%. The DC

output voltage that appears across the load is an

integral value or a fraction of the input voltage which

turns out to be equal to the duty cycle. Duty cycle is

also defined as ratio of TON/T, where T is complete

time period described by inverse of the operatingfrequency.

2.SIMULINK MODELING OF CONVERTERS

The equations of PV cell are simulated using

simulink MATLAB software [6], [7]. Output of PV

panel is fed to converter and used to drive gate

voltage. Four main components are used in designing

converters. These include switching power MOSFET

symbolically Q, flywheel diode D, inductor L and

filter capacitor at output C. MOSFET gate is

connected to PV panel. A control circuit is used to

monitor the output voltage from converter and

maintain it at the desired level. This is done by

switching MOSFET on and off at a fixed rate known

as converters operating frequency. By varying duty

cycle based on proportion of each switching period Q

is turned on and operation of system can beidentified.

Various simulated circuits for continuous and

discrete GUI blocks showing waveforms for with and

without phase delay are determined for three

different converters. The Power GUI simulink blocks

help to run circuit for variable solver using

continuous GUI or find a solution for fixed time steps

using discrete GUI. However to vary duty cycle

prior to switching MOSFET on and off states phase

delay block is used. Outputs are presented for

different converters in succeeding sections.

2.1 BUCK CONVERTER

Buck converters are used to buck or reduce output

from solar panel. Panel output voltage is fed into gate

of MOSFET. On switching MOSFET, current flows.

As inductor starts building up oscillations by

developing magnetic field across it due to which

voltage is buck up or reduced. When MOSFET is

turned off, EMF is suddenly reversed in the inductor

that opposes further drop in current. It supplies

current to the load itself via Diode.

The basic circuit configuration used in the buckconverter for continuous GUI is shown in Fig.1.

Fig. 1 Buck Converter without Phase Delay forContinuous GUI Circuit

To determine output ti input voltage fraction, duty

cycle is calculated given by expression,

VOUT/VIN= D, (5)

or VOUT = VINx D (6)


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Thus Buck Converter output voltage can be varied in

proportion to input voltage varying the switching

duty cycle. Resulting output is represented by

following waveform.

Fig. 1.1 Buck Converter Output without PhaseDelay for Continuous GUI Circuit

The circuit is simulated with phase delay that causes

more oscillations in output.

Fig. 1.2 Buck Converter with Phase Delay for

Continuous GUI Circuit

Fig. 1.3 Buck Converter Output with Phase Delay

for Continuous GUI CircuitTo determine steady state behavior under regulated

time intervals converter circuit was experimented

using discrete GUI as detailed below for delay and no

delay circuits,

Fig. 1.4 Buck Converter without Phase Delay For

Discrete GUI Circuit

Fig. 1.5 Buck Converter Output without Phase

Delay for Discrete GUI Circuit

Fig. 1.6 Buck Converter with Phase Delay for

Discrete GUI Circuit

When above circuit is simulated, outputs obtained

from Discrete GUI matches exactly similar tocontinuous GUI using no phase delay. However,

introduction of phase delay results more oscillations

in output waveforms giving reduced output for

discrete circuit in comparison to continuous. The

delay factor incorporates this change as represented

in Fig. 1.7.


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Fig. 1.7 Buck Converter Output with Phase Delay

for Discrete GUI Circuit

2.2 BOOST CONVERTER

The components arrangement appears different for

boost converter as in Fig.2.

Fig. 2 Boost Converter without Phase Delay for


This is used to step up the voltage. It consists of highspeed switch MOSFET, with output voltage control

by variation of switching duty cycle. Current flows

via inductor L and MOSFET Q when connected from

the input source. The energy is stored in Magnetic

field developed across L. There is no current flowingpresently through D. However load current is

supplied by the charge in C. L opposes current by

immediately reversing EMF when Q is turned off.

Thus inductor voltage adds i.e., boosts the source

voltage, and through L current is directed to flow

across D and the load, recharging C.

The voltage step-up ratio for circuit is,

VOUT/VIN= 1/ (1-D) (7)

Where 1-D is actually the proportion of the switching

cycle when Q is off, rather than on. So the step-upratio is also,

VOUT/VIN= T/TOFF (8)

Working of circuit is given through waveforms

plotted in Fig 2.1.

Fig. 2.1 Boost Converter Output without Phase

Delay for Continuous GUI Output

When simulating diagrams in Matlab scope for delay

using GUI model, outputs result higher overshoot

with increased responses as in Fig 2.2 and 2.3.

Fig. 2.2 Boost Converter with Phase Delay for


Fig 2.3 Boost Converter with Phase Delay for


Performing different orientations for discrete GUI

circuits, results match performances of boost

converter circuit using no phase delay but with


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slightly raised outputs. These are shown below,

Fig. 2.4 Boost Converter without Phase Delay for

Discrete GUI Output


Delay for Discrete GUI Output

Discrete GUI formulate reduced outputs for delay

circuits with sloping stretches as indicated in

diagrams to follow.


Discrete GUI Output

Fig. 2.7 Boost Converter Output with Phase Delay

for Discrete GUI Output

2.3 BUCK-BOOST CONVERTER

The configuration of Buck and Boost converters is

implemented in a different way as in Fig 3.

Fig. 3 Buck-Boost Converter without Phase Delay

for Continuous GUI Circuit

The voltage could be either step up or step down,

depending on the duty cycle. Inductor L directly

stores energy by developing magnetic field whenMOSFET is in on state. Diodes being reverse biased

results in no current flow through load. Capacitor C

works during this Ton phase. But as MOSFET is

turned off, L is disconnected from the source. It

opposes current to drop by instantly reversing EMF.

Hence output is available for phase delay making

circuit functional on and off frequently and not for

circuit without delay. This switching generates a

voltage that forward biases Diode and current flows

into the load charging C. But this occurs for phase

delay circuit causing variations in waveforms as in

Figures below.

Fig. 3.1 Buck-Boost Converter Output without

Phase Delay for Continuous GUI Circuit


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Fig. 3.2 Buck-Boost Converter with Phase Delay

for Continuous GUI Circuit

Fig. 3.3 Buck-Boost Converter Output with Phase

Delay for Continuous GUI Circuit

With this configuration, ratio between the output and

input voltages can be expressed as,

VOUT/VIN= - D/ (1-D) (9)

This equates to

VOUT/VIN= - TON/TOFF (10)

So buck-boost converter can be concluded to step

down voltage when the duty cycle is less than 50%

(i.e., Ton < Toff). For step up duty cycle is greater

than 50% (Ton > Toff). Further results are

determined using discrete GUI that results output forno phase delay condition too in Fig. 3.5.

Fig. 3.4 Boost Converter without Phase Delay for

Discrete GUI Output


Delay for Discrete GUI Output

On introducing delay in circuit outputs appear

inverse to origin just similar to continuous GUI

model. Succeeding Figures highlight modeling andsimulations using delay.


Discrete GUI Output

Fig. 3.7 Boost Converter Output with Phase Delay

for Discrete GUI Output


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3.COMPARISONS

The modelling performance of three different

converters is studied based on four modelling

constraints. It can be concluded that prior to voltage

boosting, reducing or both actions Boost, Buck orBuck-Boost converter is selected. Phase delay affects

the results by introduction of oscillations. Since for

variable step solver in continuous systems output is

not available the behaviour of circuits in discrete

steps becomes compulsory. By analyzingperformance it can be determined that Buck

converter output is almost same for delay or no delay

circuit for 36 cells solar panel. Boost converter

reduces output of phase delay circuit. Buck-Boost

converter can help in achieving dual purpose with

inverted outputs. Thus while choosing converter for a

specified application, choice of model must beselective to achieve appropriate responses.

4.

FUTURE WORK

Solar Converters work as best renewable power

sources for charging battery or operation of

appliances. Studies could be made prior to analyse

efficiency and determine losses in converters. Designand development of advanced lossless converters

with appropriate duty cycle can be considered for

further research in varying panel sizes.

5.ACKNOWLEDGEMENTS

Acknowledgements may be made to those

individuals or institutions not mentioned elsewhere inthe paper that made an important contribution.

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Dcdc Converter Simulations