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Int. J. Elec&Electr.Eng&Telecoms. 2015 Karthik Shetty and Deepesh S Kanchan, 2015

ANALYSIS OF PHOTOVOLTAIC SYSTEMS TOACHIEVE MAXIMUM POWER POINT TRACKING

WITH VARIABLE INDUCTOR

Karthik Shetty1* and Deepesh S Kanchan1

*Corresponding Author: Karthik Shetty,[email protected]

Photovoltaic (PV) system is the most promising source of energy and a new concept in use,which is obtaining popularity due to increasing importance to research for alternative sources ofenergy over exhaustion of customary fossil fuels worldwide. This systems are developed todraw energy from the sun, in the most competent manner. In this project Buck converter basedPV system with resistive load is considered. The converter topology uses a variable inductorwhich provides adequate harmonic reduction. Employing the theorem that matching impedanceyields maximum power transfer, a number of algorithms have been developed for MaximumPower Point Tracking (MPPT). In this paper Incremental Conductance with integral regulatorMPPT algorithm has been used. The proposed system is simulated using Matlab/Simulinkenvironment.

Keywords: PV, MPPT, Incremental Conductance (IC) algorithm

INTRODUCTIONThe demand for energy is increasingparticularly worldwide. Although theunavailability of fossil fuels had pushed us totowards finding the alternative sources ofenergy. Solar energy is the most important andsustainable energy system. Solar energysystems has a major role in distributedgeneration network. There are many otherrenewable sources of energy such as wind,tidal, biomass, etc. But the solar energy is

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1 Department of Electrical and Electronics, St. Joseph Engineering College, Vamanjoor, Mangalore, India.

present everywhere which makes readilyavailable than other renewable sources ofenergy that can be easily extracted and utilized.With the help of solar panel which is made upof silicon photovoltaic cells the solar energycan be converted into electrical energy. Theefficiency of the solar systems depends onmany factors such as insolation, temperatureand spectral characteristics, dust, shadingwhich results in poor performance. Currentlymore research has been focused on how to

Research Paper

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extract effective power form solar cells [1].There are two ways such as MPPT and solartracking systems. Literature survey shows thatthere will be a 30-40% increase in thepercentage of energy as compared to PVsystems with MPPT. Maximum Power Pointtracking is the online control strategy to trackthe maximum output power point underdifferent operation conditions such asinsolation and Temperature. This MPPT isused to increase the efficiency Of PV systems.According to maximum power point theoremthe output power can be maximized byadjusting the source impedance equal to theload impedance. Presently the most commonalgorithm used is the Perturbation andObserve (P&O) method, IncrementalConductance (IC) method and hill climbing.P&O and hill climbing are widely applied inMPPT controller due to their easyimplementation and simplicity. Meanwhile inboth methods the steady state oscillationappear due to perturbation, which may lead toincrease in power loss. The MPPT algorithmused in this paper is Incremental Conductance(IC) algorithm. Incremental conductancemethod is based on the fact that under rapidlyvarying conditions the slope of the PV arraypower curve versus voltage curve is zero atmaximum power point which in turn improvesthe tracking efficiency [2]. The block diagramof PV system with DC-DC converter andMPPT is shown in Figure 1.

The Simulink model of a PV system issimulated under different insolation. TheSimulink model with PV system and MPPT withDC-DC converter will be implemented inMatlab/Simulink.

MODELLING OF APHOTOVOLTAIC SYSTEMPhotovoltaic cell generates electricity from thesun. PV panel works under the principle ofPhotoelectric effect which directly convertssunlight into electricity. The most commonmodel used to foretell the energy productionin modelling of a photovoltaic cell is the singlediode circuit model. The ideal photovoltaicmodel consist of a single diode connected inparallel with the light generated current source.Solar cells are connected in series and parallelto set up a solar array. Figure 2 shows theequivalent model of a solar cell.

Figure 1: Block Diagram of ProposedScheme

Figure 2: Equivalent Model of a Solar Cell

The use of the simplified circuit model inthis work makes it suitable for power

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electronics designer to have a simple andeffective model for the simulation ofphotovoltaic devices with power converters.The single diode model is used in this paper.In Figure 2 Iph refers to the photocurrent andRp and Rs refers to the intrinsic parallel andseries resistance. The photocurrent of thephotovoltaic module depends linearly on thesolar irradiation and t is also influenced by thetemperature. It is given by

Iph = (Isc + ki(Tk – Tref))*/1000 ...(1)

where Iph is the photocurrent at nominalconditions (25 °C), Isc is the short circuit current,ki is the short circuit current temperaturecoefficient, and Tref and Tk are the referenceand actual temperatures in kelvin respectively.On the other hand cell’s saturation currentvaries with the cell’s temperature and is givenby:

Is = Irs*(Tk/Tref)^3*exp(q*Eg(1/Tref – 1/Tk)/K*A) ...(2)

where Irs is the cell’s reverse saturation currentat a reference temperature and solarirradiation. Eg is the band gap energy of thesemiconductor used in the cell and A is theideality factor. The reverse saturation currentis given by:

Irs = Isc/exp(q*Voc/Ns*K*A*Tk)–1) ...(3)

where Voc is the cell’s open circuit voltage, Kis the Boltzmann’s constant, Ns is the no cell inseries. The I-V and P-V characteristics of asolar cell is shown.

INCREMENTALCONDUCTANCE ALGORITHMThe output power of a PV module changes withthe change in the solar insolation andtemperature. In the PV characteristics there isa maximum power point for the PV module tooperate, it is preferred that PV moduleoperates close to this point. The voltage atwhich PV module produces maximum poweris called maximum power point. The mostcommon algorithm are P&O and Incrementalconductance. The advantage of IncrementalConductance is that it provides high efficiencyunder rapidly changing atmosphericconditions. In this paper the maximum powerpoint is achieved by Incremental Conductancealgorithm with an integral regulator [3]. Thetheory of Incremental Conductance algorithmis determining the variation of terminal voltageof PV modules by comparing and measuringthe incremental conductance andinstantaneous conductance of PV module. Thepower will be maximum at a point when thevalue of incremental conductance is equal tothat of instantaneous conductance. Thismaximum power point can be obtained fromthe voltage and current measurements, thealgorithm calculates the duty cycle required tomaximize the flow of power.

Figure 4 shows the basic concept ofIncremental conductance on P-V curve of asolar module. In the above figure the slope ofthe P-V curve is zero. If the PV module

Figure 3: I-V and P-V Characteristicsof a Solar Cell

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operating to the left of the MPP on PV curve,the PV voltage must be increased in order toreach the MPP. If the PV module operating tothe right of the MPP on P-V curve, the PVvoltage must be reduced in order to reach theMPP. The basic equations of this method areas follows:

at MPP ...(4)

Left of MPP ...(5)

Right of MPP ...(6)

where I and V are the PV module output currentand voltage respectively. By using the factor

which is defined as the Maximum powerpoint identifier factor, the IC method isrecommended to efficiently track the MPP ofPV array [7]. The right hand side of the equationrepresents the instantaneous conductance andleft hand side of the equation represents theincremental conductance of the PV module.When the ratio of change in outputconductance is equal to negative outputconductance, the PV module will operate atmaximum power point. In order to operate a

PV system within its maximum power point andconsidering the temperature variation andirradiance a maximum power point trackingalgorithm is needed to track and maintain thepeak power. In this paper the algorithm ismodified which includes integral regulator. Thisintegral regulator minimizes the error wherethe output of the integral regulator will be equalto the duty cycle. This implementation can bedone by adding a controller which improvesthe incremental conductance method byminimizing the error between the actualconductance and incremental conductance.This controller can reduce the rippleoscillations caused during steady states. Wehave,

P = V*I ...(7)

Maximum power point is obtained when

...(8)

Applying chain rule to the derivative ofproduct yields to

...(9)

The above equation can be written in termsof voltage and current as

...(10)

The maximum power point trackingregulates the PWM output of the DC-DCconverter until the condition: isobtained. The flowchart of the incrementalalgorithm is shown in Figure 5.

DC-DC CONVERTER WITHVARIABLE INDUCTORDc-Dc converters can be used as switchedmode regulators to convert an unregulated Dcvoltage to a regulated Dc output voltage. In this

Figure 4: Basic Idea of IncrementalConductance on P-V Curve

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paper the converter used is Buck converter. Inbuck converter, for a correct operation theoutput voltage must be less than the PVmodule voltage. The switch operates at highfrequency to produce the chopped voltage.The power flow is controlled by adjusting theduty cycle. In this buck converter variableinductor has been introduced. This use ofvariable inductor has an advantage ofincreasing the load range [5]. The minimuminductance is given by:

Lmin= ...(11)

where D is the duty ratio, Vp is the panelvoltage, Ip is the panel current, fs is the switchingfrequency.

SIMULATION RESULTS ANDDISCUSSIONThe Simulation has been implemented inMatlab/Simulink. Simulation has been carriedout for 10 W 18 V Solar panel with the switchingfrequency of 10 KHz. The insolation is variedfrom 200 W/m2 to 800 W/m2. The parametersof the PV module are obtained from thedatasheet [4]. The Simulink model of PVmodule with MPPT of Buck converter is shownbelow.

Figure 5: Flowchart of IncrementalConductance MPPT

Figure 6: Simulink Model of a PV Modulewith MPPT of Buck Converter

Figure 7: Simulink Model of a PV Module

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The Simulink model of a PV module and I-V characteristics is shown below.

Figure 8: I-V Characteristicsof a PV Module

800 14.1 0.47 0.480 179.7

700 12.4 0.41 0.487 184.1

600 10.6 0.35 0.490 185.4

500 8.85 0.29 0.490 186.8

400 7.08 0.23 0.491 188.4

300 5.3 0.17 0.491 190.8

200 3.5 0.12 0.491 178.5

Table 1: Parameters Under DifferentConditions

Insolation(W/M2)

Voltage(Vp)

Current(Ip)

DutyRatio (D)

Lmin(µH)

Figure 9: Simulink Model of IncrementalConductance Algorithm with Integral

Regulator

Figure 10: Waveform of Current AfterSwitch with Harmonics for 800 W/m2

Figure 11: Waveform of Current AfterVariable Inductor for 800 W/m2

Figure 12: PV Module Power and OutputPower at 800 W/m2

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CONCLUSIONThe Simulation of PV module with MPPT hasbeen successfully implemented in Matlab/Simulink. This paper intends a MPPT methodwith an integral regulator which requires onlymeasurements of Incremental conductancemethod. The variable inductor provides goodharmonic reduction. The proposed method hasadvantages like good tracking efficiency, highresponse.

ACKNOWLEDGMENTOn completion of this work I would like extendgratitude and sincere thanks to my guide, HODand Principal of St. Joseph EngineeringCollege for constant motivation and support.

REFERENCES1. Abdulkhadir M, Samosir A S, Yatim A H

M and Yusuf S T (2013), “A New Approachof Modelling and Simulation of MPPT forPhotovoltaic System in Simulink Model”,ARPN Journal of Engineering andApplied Sciences, Vol. 8, No. 7.

2. Hiren Patel and Vivek Agarwal (2008),“Maximum Power Point Tracking Schemefor PV Systems Operating Under PartiallyShaded Conditions”, IEEE Trans. on

Industrial Electronics, Vol. 55, No. 4,pp. 1689-1698.

3. Hussein K H Murta, Hoshino I T andOsakada M (1995), “MaximumPhotovoltaic Power Tracking: AnAlgorithm for Rapidly ChangingAtmospheric Conditons”, IEEEProceedings of Generation,Transmission and Distribution, Vol. 142,No. 1.

4. Kuo Y and Al E T (2001), “MaximumPower Point Tracking Controller forPhotovoltaic Energy Conversion System”,IEEE Trans. Ind. Electron, Vol. 48,pp. 594-601.

5. Kuo Y C and Liang T J (2001), “NovelMaximum Power Point Tracking Controllerfor Photovoltaic Energy ConversionSystem”, IEEE Transactions on IndustrialElectronics, Vol. 48, No. 3, pp. 94-601.

6. Wolfle W H and Hurley W H (2003), “QuasiActive Power Factor Correction with aVariable Inductor Filter: Theory, Designand Practice”, IEEE Tarns. on PowerElectronics, Vol. 18, No. 1, pp. 248-255.

7. 10W 18V solar panel datasheet.

analysis of photovoltaic systems to achieve maximum …

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