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Perturb and Observe MPPT Algorithm for

Solar PV Systems-Modeling and Simulation

Jacob James Nedumgatt, Jayakrishnan K. B.,Umashankar S., Vijayakumar D.,

School of Electrical Engineering

VIT University

Vellore, India.

jacob_jned@yahoo.com,

jayakrishnankb007@gmail.com

shankarums@gmail.com, vijayakumar.d@vit.ac.in.

Kothari D P

Director General

Vindhya Institute of Technology and Science

Indore, India

dpk0710@yahoo.com

Abstract-The following paper validates an algorithm for

Maximum Power Point Tracking using Perturb and Observe

technique. The algorithm starts by setting the computedmaximum power PMAX to an initial value (usually zero).

Next the actual PV voltage and current are measured at

specific intervals and the instantaneous value of PV power,

PACT is computed. PMAX and PACT are compared.

PMAX and PACT are compared. If PACT is greater than

PMAX, it is set as the new value of PMAX. At every instant

the PACT is calculated, and the comparison is continuously

executed. Hence the final value of PMAX will be the point at

which maximum power can be delivered to the load. For

maximum power transfer across the load, the input

impedance should be equal to the load impedance. Based on

the mechanism of load matching the duty cycle of the

converter is varied so that the output power will almost be

equal to the input in practical systems. The system will bemodelled with the help of MATLAB/SIMULINK.

Keywords-Photovoltaic; maximum power point tracking;

MPPT; P&O

I. INTRODUCTIONAs people are concerned with the fossil fuel exhaustion

and the environmental problems caused by theconventional power generation schemes present,renewable energy sources, photovoltaic panels and wind-generators, to mention a few are now in great need [2].Among several renewable energy sources, photovoltaicarrays are used in many applications such as water

pumping, battery charging, hybrid vehicles, and gridconnected PV systems. The principal advantagesassociated with photovoltaic arrays are that it consists ofno moving parts. Do not produce any noise andmaintenance costs are minimal. It is also a clean source ofenergy. Amount of energy produced by the sun is so large,that in one hour it can provide more than enough energyfor human population in one year. However, due to the lowefficiency of current solar panels, conversion of sunlightinto electrical power is very poor. This efficiency furtherdecreases if there is no load matching between the inputside (PV array output) and the output side (load). Tomaximize the power derived from the solar panel it is

important to operate the panel at its maximum powerpoint, hence an increase in output efficiency. Maximumpower point changes with the solar irradiation, and cell

temperature. Therefore, an on-line tracking of themaximum power point of a PV array is an essential part of

any PV system. This paper looks at the P&O MPPTtechnique where the instantaneous values of power arecalculated each time, and the maximum power point valueis updated. Having completed all the calculations andcomparisons, the maximum power point is finallydetermined, and the corresponding voltage and current atthe maximum power point is also determined.

II. PVEQUIVALENT CIRCUITA solar cell basically is a p-n semiconductor junction.

When exposed to light, a dc current is generated. Thegenerated current varies linearly with the solar irradiance.The standard equivalent circuit of the PV cell is shown in

Fig. 1.

Figure 1. Equivalent circuit of Solar PV cell

The basic equation that describes the (I-V)characteristics of the PV model is given by the followingequation:

( )

( 1)S

S

q V IR

KTL O

sh

V IRI I I e

R

+

+=

(1)I is the cell current (A).

IL is the light generated current (A).

Io is the diode saturation current.

q is the charge of an electron = 1.6x10-19 (coulombs).

K is the Boltzman constant (j/K).

T is the cell temperature (K).

+

VIL

ISHID

RSH

RS

-

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Rs, Rsh are cell series and shunt resistance (ohms).

V is the cell output voltage (V).

The above equation is valid for a single diode model,where the ideality factor, n, is equal to unity. This factorranges from 1 to 2, if a two diode model is used. Usually

optimization techniques are used to determine a suitablevalue for a particular model. The IO in the equationrepresents the dark saturation, the current which is

produced where there is no light. It will always be present.It is thermally generated. Dark saturation current is alsotemperature dependent. Hence with a change in thetemperature in Kelvin, T, the overall current, I wouldvary. If temperature increases the current I reduces. IL isthe light generated current. It is this parameter which playsthe vital role in a solar cell. Illumination of the cell givesrise to an increase in the minority carrier concentration,more light more excess hole-electron pairs will begenerated. As a result the IL value increases as theirradiance levels rise. Below are the figures which show

the characteristic PV Array curves, voltage versus thepower produced by the PV Array and the current versusvoltage. This is a necessity when determining themaximum power point, if not the PV System will not beefficient.

Figure 2. Current vs Voltage Characteristic curve

Figure 3. Power vs Voltage Characteristic Curve

Figure 4. MPP changes with Temperature (I-V Curves)

Figure 5. MPP changes with Temperature (P-V Curves)

Figure 6. MPP changes with Irradiance levels(I-V Curves)

Figure 7. MPP changes with Irradiance levels (P-V Curves)

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III. P&OMPPTTECHNIQUEThe problem considered by MPPT methods is to

automatically find the voltage VMPP or current IMPP atwhich a PV array delivers maximum power under a giventemperature and irradiance. In P&O method, the MPPTalgorithm is based on the calculation of the PV output

power and the power change by sampling both the PVArray current and voltage. The tracker operates by

periodically incrementing or decrementing the solar arrayvoltage [4]. If a given perturbation leads to an increase(decrease) in the output power of the PV, then thesubsequent perturbation is generated in the same (opposite)direction. The duty cycle of the dc chopper is varied andthe process is repeated until the maximum power point has

been reached. Actually, the system oscillates about theMPP. Reducing the perturbation step size can minimize theoscillation. However, small step size slows down theMPPT. For different values of irradiance and celltemperatures, the PV array would exhibit differentcharacteristic curves. Each curve has its maximum power

point. It is at this point, where the corresponding maximumvoltage is supplied to the converter.

.

Figure 8. Flowchart of P&O MPPT Technique

IV. PV SYSTEM MODELLING

Figure 9. General block diagram of P&O MPPT Technique

The above figure is a generalized block diagram. Theinput voltage and current from the PV array is used to

calculate the instantaneous power. Based on the MPPTalgorithm the maximum power point is identified and theduty ratio of the converter is varied in accordance. The

duty ratio is varied in such a manner that the input powerdelivered to the converter will almost be equal to the

power delivered to the load

V. MATLAB MODELING AND SIMULATIONThe PV Array and the PVIV blocks are embedded

blocks, where the PV array has been mathematicallymodelled [4]. These blocks are necessary to calculate themaximum power point, as part of the MPPT technique andalso to display the characteristics curves based on differentirradiance levels. The same can be implemented fordifferent ambient temperatures.

Figure 10. Simulink block diagram of complete PV system

Figure 11. Cuk converter, for a fixed load of 6 ohms

Cuk Converter is used in this system [5]. It has certainadvantages over the buck boost converter. Like the buck

boost converter, it can step up or step down the outputvoltage. Here the capacitor is the main storage element. Ithelps to ensure continuous current flow, and the inductorwhich is placed at the load side also reduces the ripple in

the output current. Based on the value of the input voltage,which is the voltage at the maximum power point, the dutyratio is varied to give allow maximum power transfer fromthe input supply to the load.

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A. The following are results shown, with a variation ofirradiance levels. The irradiance levels change at fixed

intervals of time while maintaining the ambient

temperature constant.

Figure 12. Variation ofirradiance levels to the pv array while keepingthe ambient temperature constant.

Figure 13. Pulses to the gate

Figure 14. Voltage across Inductor L1 and Capacitor C1

Figure 15. Variation in Output Voltage and Input Voltage

Figure 16. Variation in Input Power and Output Power

Figure 17. Variation in Output Current and Input Current

Figure 18. Variation in duty cycle

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B. The following are results shown, with a variation ofambient temperature. The ambient temperature

changes at fixed intervals of time maintaining a

constant irradiance level.

Figure 19. Variation of ambient temperature tacon

pv array while G is constant (G=1)

Figure 20. Variation in output voltage and input voltage

Figure 21. Variation in output power and input power

Figure 22. Variation in output current and input current

Figure 23. Variation in duty cycle

The simulation results show that the duty ratio varies insuch a manner that the output voltage across the load isconstant. There are loads that are sensitive to voltage,hence a constant output voltage is a requirement.

VI. CONCLUSIONThe PV Array has been mathematically modelled. The

programmes implemented in the MPPT technique achievethe maximum power point. It has been shown that for the

particular irradiance levels the maximum power deliveredby the PV Array is delivered to the load. The same iscarried out if there is a variation in temperature. It is asimple MPPT setup resulting in a highly efficient system.In conclusion, non-conventional energy sources willdominate the conventional sources of energy in the nearfuture and here one uses the greatest renewable energy ofall, the suns energy.

VII. REFERENCES[1] N. Femia, et. Al. Optimization of Perturb and observe Maximum

PowerPoint tracking Method, IEEE Trans. Power Electron., Vol.20, pp.963-973, July 2005.

[2] E. Koutroulis; et. al , Development of a Microcontroller-basedphotovoltaic maximum power tracking control system, IEEETrans. Onpower Electron., Vol. 16, No. 1, pp. 46-54, 2001.

[3] J.A.Jianget. Al. , Maximum Power Tracking for PhotovoltaicPowerSystems, Tamkang Journal of Science and Engineering,Vol. 8, No. 2,pp. 147-153, 2005.

[4] Thesis-Akihiro Oi,Design and simulation of photovoltaic waterpumping system,September 2005

[5] Ned Mohan, Tore M. Undeland, William P. Robbins, PowerElectronics, Converters, Applications and Design, Third Edition,New Delhi,Wiley India (P.) Ltd.

[6]

Stuart Bowden and Christiana Honsberg,http://www.pveducation.org/pvcdrom

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VIII. BIOGRAPHIESJacob James Nedumgatt was born inKollam, Kerala. He is currently pursuing

Masters Degree in Power Electronics at

VIT University, Vellore. He received his

Bachelor Degree in Electrical andElectronics Engineering in the year 2009 at

Rajagiri School of Engineering andTechnology, affiliated to Mahatma Gandhi.

University, Kerala. His research interests are

Power Electronics applications in Solar PVsystems and Multilevel Inverters.

Jayakrishnan K B was born in ErnakulamKerala. He is currently pursuing Masters

Degree in Power Electronics & Drives at

VIT University, Vellore. He received his

Bachelor Degree in Electrical and

Electronics Engineering in the year 2009

from TKM College of Engineering ,affiliated to University of Kerala. His

research interests are Power Electronicsapplications in Renewable Energy Systemsand Power System protection.

Umashankar. S (M11) received hisBachelor Degree in Electrical andElectronics Engineering and Master Degreein Power Electronics in the year 2001 and2004 respectively. Currently he is Asst.Professor-Senior in the School of ElectricalEngineering at VIT University, Vellore. Heworked as Senior R&D Engineer and SeniorApplication Engineer in the powerelectronics and Drives field for more than 6years. He has published/presented many

national and international journals/conferences. He has also co-

authored/co-edited many books/chapters on wind power/energy andallied areas. His current areas of research activities include renewableenergy, real time digital simulator, HTS generator, FACTS, andpower quality.

D. P. Kothari (F10) received the B.E.degree in electrical engineering, the M.E.degree in power systems, and the Ph.D.degree in electrical engineering from theBirla Institute of Technology and Science(BITS), Pilani, India. Currently, he isAdvisor to Chancellor of the VIT University,

Vellore, Tamil Nadu, India. He was Head,Centre for Energy Studies, lIT Delhi (1995-97), and Principal, Visvesvaraya Regional

Engineering College, Nagpur (1997-98). He has been Director i/c, lITDelhi (2005) and Deputy Director (Administration), lIT Delhi (2003-06). He has published/presented around 600 papers in national andinternational journals/conferences. He has also co-authored/co-edited22 books on power systems and allied areas. His activities includeoptimal hydrothermal scheduling, unit commitment, maintenancescheduling, energy conservation, and power quality. He has guided 28Ph.D. scholars and has contributed extensively in these areas asevidenced by the many research papers authored by him. He was aVisiting Professor at the Royal Melbourne Institute of Technology,Melbourne, Australia, in 1982 and 1989. He was a National ScienceFoundation Fellow at Purdue University, West Lafayette, IN, in 1992.He is a Fellow of the IEEE, Indian National Academy of Engineering(INAE) and Indian National Academy of Sciences (FNASc). He hasreceived the National Khosla award for Lifetime Achievements inEngineering for 2005 from lIT Roorkee. The University GrantsCommission (UGC) has bestowed UGC National SwamiPranavananda Saraswati award for 2005 on Education for outstandingscholarly contribution.

D. Vijayakumar received his BachelorDegree in Electrical and ElectronicsEngineering and Master Degree in PowerSystems in the year 2002 and 2005respectively. He worked as a Lecturer inPallavan College of Engineering from 2005to 2006. He received his Doctorate in 2010at Electrical Department in Maulana AzadNational Institute of Technology (MANIT),Bhopal, India. Presently, He is an Associate

Professor in the School of Electrical Engineering, VIT University,

Vellore. His current areas of research interest are power systemprotection, and Renewable energy sources.