Energy Technology & Policy (2014) 1, 115–122Published with license by Taylor & Francis Group, LLCISSN: 2331-7000 onlineDOI: 10.1080/23317000.2014.979379

Maximum Power Point Tracking (MPPT) Scheme for SolarPhotovoltaic System

AHTESHAMUL HAQUE*

Electrical Engineering, Jamia Millia Islamia University, New Delhi, India

Received July 2014, Accepted October 2014

Abstract: Global energy demand is increasing exponentially. This increase in demand causes concern pertaining to the global energycrisis and allied environmental threats. The solution of these issues is seen in renewable energy sources. Solar energy is considered one ofthe major sources of renewable energy, available in abundance and also free of cost. Solar photovoltaic (PV) cells are used to convert solarenergy into unregulated electrical energy. These solar PV cells exhibit nonlinear characteristics and give very low efficiency. Therefore, itbecomes essential to extract maximum power from solar PV cells using maximum power point tracking (MPPT). Perturb and observe (P&O)is one of such MPPT schemes. The behavior of MPPT schemes under continually changing atmospheric conditions is critical. It leads to twoconditions, i.e., rapid change in solar irradiation and partial shading due to clouds, etc. Also, the behavior of MPPT schemes under changedload condition becomes significant to analyze. This article aims to address the issue of the conventional P&O MPPT scheme under increasesolar irradiation condition and its behavior under changed load condition. The modified MPPT scheme is implemented in the control circuitof a DC–DC converter. The simulation study is done using PSIM simulation software. A prototype unit is tested with artificial light setup ona solar PV panel to simulate the changed solar irradiation condition. The results of the modified MPPT scheme are compared with existingschemes. The modified MPPT scheme works fast and gives improved results under change of solar irradiation. Furthermore, the steady stateoscillations are also reduced.

Keywords: MPPT, photovoltaic, power electronics, perturb and observe, PSIM

1. Introduction

Global energy crisis and climate change threats are among themajor concerns faced by the present civilized world. The limitedreservoirs of fossil fuels and emission of greenhouse gases arethe major identified reasons for the above concern. Renewableenergy sources (RES) such as solar, wind, and tidal are consid-ered the solution to overcome these concerns. Among these RES,solar energy is considered one of the potential sources to solvethe crisis as it is available in abundance and free of cost.1

Solar photovoltaic (PV) cells are used to convert solar energyinto regulated electrical energy using power electronics con-verter.2 These solar PV cells exhibit nonlinear characteristics andvery low efficiency.3 The characteristic of solar cells becomemore complex under changed atmospheric condition such aspartial shading.4 Due to these issues, it becomes essential to

© Ahteshamul HaqueThis is an Open Access article. Non-commercial re-use, distribution,and reproduction in any medium, provided the original work is prop-erly attributed, cited, and is not altered, transformed, or built upon inany way, is permitted. The moral rights of the named author(s) havebeen asserted.*Address correspondence to: Ahteshamul Haque, ElectricalEngineering, Jamia Millia Islamia University, M. M. Ali JauharMarg, Okhla, New Delhi 110025, India. Email: ahaque@jmi.ac.in

researchers to extract maximum power from solar PV cells undervariable atmospheric conditions. Maximum power point track-ing (MPPT) scheme is used to extract maximum power fromsolar PV cells. Various types of MPPT schemes are proposed byresearchers,5−14 namely open circuit, short circuit, perturb andobserve (P&O)/hill climbing, incremental conductance, and soforth.

The P&O method is very popular among all these schemes.It is further classified into various types of P&O MPPT schemesand is adopted by the researchers. The nominal value of capaci-tors connected in parallel with solar PV is taken as a parameterto monitor in extraction of power.5 However, Xiao and Dunfordhave proposed an adaptive scheme to extract the power.6

The P&O method may give false results, i.e., when solar irra-diation is increased, the conventional P&O algorithm moves inthe direction of high power. It fixes the operating point, whichis not maximum power point (MPP). Also, the other issue issteady state oscillations due to the nature of the P&O MPPTscheme. The limitation of the P&O method has been highlightedunder increased solar irradiation condition.8 However, the MPPTbehavior with resistive load change has not been addressedproperly. These issues are addressed properly for other MPPTschemes such as incremental conductance.13,15

The P&O method is evaluated and the duty cycle is decidedby the product of slope (dP/dV) with a constant gain.12

The drawback of this method is high steady state oscillations

116 A. Haque

and longer time to reach steady state under changed powercondition.

In this article, the P&O MPPT scheme is modified consid-ering increase in solar irradiation, steady state oscillations, andload changing condition. The results of the modified schemeare compared with the existing P&O MPPT scheme, and theimprovements are highlighted. The new MPPT scheme is imple-mented in the control circuit of a buck DC–DC converter.A prototype hardware model is made and tested in the lab. Themicrocontroller is used to implement the proposed MPPT algo-rithm. The solar simulation and its changing irradiation conditionhave been carried out with flooded artificial lighting on solar PVpanel. PSIM simulation software is used for simulation study.

2. Modeling and Characteristics of Solar Photovoltaic(PV) Cell

The basic element of a solar PV system is PV cells. These cellsare connected to form modules. It is further expanded in the formof arrays as per the power requirement. These PV cells exhibitnonlinear characteristic. The output of the PV cell varies withsolar irradiation and the ambient temperature. The characteristicequations of PV cell are given in Equations 1, 2, and 3.3

I = Iph − Ios {exp [(q/AKT) (V + IRs)] − 1} − (V + I ∗ Rs)/Rp

(1)

Ios = Ior exp [qEGO/Bk ((1/Tr) − (1/T))] [T/Tr]3 (2)

Iph = S [Isc + KI (T − 25)] /100 (3)

Where I is the PV cell output current; V, the PV cell output volt-age; Rp, the parallel resistor; and Rs, the series resistor. Ios, isthe PV module reversal saturation current. A and B are idealityfactors; T, the temperature (◦C); k, the boltzmann’s constant;Iph, the light-generated current; q, the electronic charge; and KI,the short-circuit current temperature coefficient at ISC. S is solarirradiation (W/m2); ISC, the short-circuit current at 25◦C and1000 W/m2, EGO, the band gap energy for silicon; Tr, refer-ence temperature and Ior, the saturation current at temperature Tr.Figure 1 shows that the power varies nonlinearly with the varia-tion in solar irradiation, and maximum power point (MPP) varies,too. However, the modeling of solar PV under partial shadingcondition gives the results differently.4 The MPP point varieswith ambient conditions. It is the task of researchers to makethis moving point as the operating point to extract the maximumpower.

3. Conventional Perturb & Observe/Hill ClimbingMPPT Scheme

The other name of the P&O method is hill climbing method.In fact, the hill climbing and P&O methods are different waysto achieve the MPP. Hill climbing MPPT is achieved by perturb-ing the duty cycle of the power converter. In the P&O method,the perturbation is applied either in the reference voltage or in the

MPP with increase in solar irradiation

Fig. 1. Solar PV power characteristics with different solar irradiationlevel.

reference current signal of the solar PV. The flow chart of the con-ventional P&O method is shown in Figure 2. In this flow chart, Yis shown as the reference signal. It could be either solar PV volt-age or current. The main aim is to achieve the MPP. To achieveit, the system operating point is changed by applying a smallperturbation (�Y) in solar PV reference signal. After each per-turbation, the power output is measured. If the value of powermeasured is more than the previous value, then the perturbationin reference signal is continued in the same direction. At anypoint, if the new value of solar PV power is measured less thanthe previous one, then the perturbation is applied in the oppositedirection. This process is continued till MPP is achieved.8

4. Issue Related to the Conventional P&O MPPTScheme

The main issue with the conventional P&O MPPT scheme isits failure to give the correct MPP under fast changing atmo-spheric conditions as shown in Figure 3 and is also discussedin Esram and Chapman.8 Figure 3 shows that the operating pointA under one atmospheric condition; a perturbation in referencesignal (which is voltage in the figure) brings the operating pointat B. This algorithm is reversed back to operating point A due tothe decrease in power. However, if the solar irradiation changes,the power curve shifted from P2 to P1 in one sampling period.

The operating point will move from A to C. It is to be notedthat C is not the MPP of power curve P1. But the power at Cis more than the power at A; however, the perturbation is keptsame. Consequently, this phenomenon of divergence from MPPis continued, if solar irradiation increases continuously.

The high ripple content in the power at steady state is the otherissue, which may be due to the nature of the P&O method asevaluated.12

5. Proposed P&O MPPT Scheme

The P&O MPPT technique depends on the change in power sup-plied by solar PV. This supplied power level depends on solar

Maximum Power Point Tracking Scheme 117

V.

Measure and record P(t)

Compare P(t) – P(t–1)>0

Yes

CompareY(t) – Y(t–1)>0

CompareY(t) – Y(t–1)>0

No

Y(t+1) = Y(t) – ΔY Y(t+1) = Y(t) + ΔYY(t+1) = Y(t) – ΔY Y(t+1) = Y(t) + ΔY

Yes

No No

Yes

Return

Start

Fig. 2. Flowchart of conventional perturb and observe MPPT method.

Fig. 3. Issue in P&O MPPT scheme under changing atmosphericcondition.

irradiation, ambient temperature, and resistive load. The refer-ence signal is either incremented or decremented periodically,comparing the power obtained in the present cycle. The referencesignal is considered as PV voltage in this work. Table 1 presentsthe summary of the P&O MPPT method, and Table 2 describesthe change in power with the change in solar irradiation and loadresistance.

Once the solar irradiation is increased, the PV power isincreased, and if it decreases, the power is decreased. The PVpower varies differently with resistive load.

Table 1. Summary of the perturb and observe MPPT method.

Perturbation Change in power Next perturbation

Positive Positive PositivePositive Negative NegativeNegative Positive NegativeNegative Negative Positive

Table 2. Summary of change in power with the change in solarirradiation and load resistance.

Cause Change Power Voltage

Solar irradiation Increase Increase IncreaseDecrease Decrease Decrease

Load resistance Increase Decrease IncreaseDecrease Increase Decrease

The flowchart of the modified P&O MPPT is shown inFigure 4. The perturbation in the reference is dependent on theslope dP/dV. The slope dP/dV is measured, and the thresholdvalue is shown in Equation 4.

∣∣∣∣

dP

dV

∣∣∣∣= 0.05 (4)

During the stage, when the slope is high, the perturbation step ismore, and when the slope is less, the perturbation step is small.The change in PV current along with PV voltage is also mea-sured. The slope calculation gives the improved and fast MPP,

118 A. Haque

Record V(t), I(t)

Record Power P(t)

Start

dP>0

No Yes

No Yes

0.05<dV

dP

Yes No Yes No

dV > 0

V(t+1) = V(t) +β.V(t)

YesNo

Yes

Update V(t) = V(t+1) I(t) = I(t+1)

Return

dV= V(t) – V(t–1) dI = I(t) – I(t–1)

dP = P(t) – P(t–1)β = 0.005 γ = 0.08

dV > 0

dI > 0

Yes

Yes 0.05<

dV

dP

V(t+1) = V(t) +γ.V(t)

V(t+1) = V(t) –β.V(t)

V(t+1) = V(t) – γ.V(t)

dI > 0

No

0.05<dV

dP

No

V(t+1) =V(t) –β.V(t)

No

V(t+1) = V(t) – γ.V(t)

0.05<dV

dP

V(t+1) = V(t) +β.V(t)

V(t+1) = V(t) +γ.V(t)

NoYes

Fig. 4. Flowchart of the proposed perturb and observe MPPT method.

when operating under increased solar irradiation condition. Theearlier work is done by multiplying slope with constant gainthroughout the operation.12 Also, the load change is another areawhere the proposed algorithm gives reliable results.

6. DC–DC Converter Topology and MPPT WorkingZone

The MPPT operating zone for solar PV is dependent on DC–DC converter topology and restricts the value of resistive loadfor which MPPT become effective. The MPPT scheme is

DC – DC

Converter

Rin Ro

Fig. 5. Block diagram of DC–DC converter.

implemented in the control of DC–DC converter, i.e., it variesthe duty cycle. The basic principle of adjusting the duty cycle isto match load impedance with input impedance seen by the DC–DC converter, i.e., impedance of solar PV as shown in Figure 5.Rin (the input impedance seen by the converter) and Ro (theoutput impedance connected with converter) are related with

Maximum Power Point Tracking Scheme 119

characteristic equation. This mathematical equation varies withDC–DC converter topologies, which are summarized in Figure 6.Figures 6 and 7 show the operating and non-operating zone ofMPPT. The MPPT is working in the entire range of characteristic

curve in the case of Buck-Boost and SEPIC (single-ended pri-mary inductor converter) DC–DC converter. Since these convert-ers are complex, they exhibit more cost in comparison to buck orboost converters.

INPUT OUTPUT RELATIONSHIP

6.1 – Characteristic Equation of Buck Converter 6.2 – Characteristic Equation of Boost Converter

6.3 – Characteristic Equation of Buck-Boost Converter 6.4 – Characteristic Equation of Sepic Converter

D – Duty Cycle

RoRin

Rin = Ro/D2

Rin vs Duty Cycle

INPUT OUTPUT RELATIONSHIP

D – Duty Cycle

RoRin

Rin = Ro(1–D)2

Rin vs Duty Cycle

INPUT OUTPUT RELATIONSHIP

D – Duty Cycle

RoRin

Rin vs Duty Cycle

Rin = (1–D)2*Ro/D2

INPUT OUTPUT RELATIONSHIP

D – Duty Cycle

RoRin

Rin = (1–D)2*Ro/D2

Rin vs Duty Cycle

Fig. 6. Characteristic equations of commonly used DC–DC converters.

V – I Characteristic Curve of Solar PV

DC – DCCONVERTER TYPE

MPP ZONE

WORKING ZONE NO WORKING ZONE

BUCK A-B B-CBOOST B-C A-B

BUCK-BOOST A-B, B-C NONE

SEPIC A-B, B-C NONE

RLoad << RMPP

RLoad = RMPP

RLoad >> RMPP

A

B

C

Fig. 7. MPPT working zone with DC–DC converter topology.

120 A. Haque

++

MOSFET

VinDIODE

–

Vo/p

Lbuck

Cbuck

–

Fig. 8. Schematic: DC–DC buck converter.

7. Design of Buck DC–DC Converter and Solar PVParameters

The DC–DC buck converter is used to implement the modi-fied MPPT scheme (Fig. 8). The input voltage of DC–DC buckconverter is the output voltage of solar PV. Equation 5 gives therelationship between input and output voltage of buck converter.2

Vo = d.Vin (5)

where Vo is the output voltage, d is the duty cycle and Vin isthe input voltage of buck converter. The parameters of buckconverter are calculated for the design work (Table 3). Theparameters of solar PV model: ELDORA40 poly crystalline islisted in Table 4.

8. Experimental Setup and Results

The block diagram of experimental setup for testing of the modi-fied MPPT algorithm is shown in Figure 9. The solar PV panel inthe lab is flooded with artificial light (halogen lamp). The inten-sity of artificial light is controlled to simulate the fast-changingsolar irradiation. The solar PV is connected with the buck DC–DC converter. The DC load is connected at the output of the buck

Table 3. Parameters of DC–DC buck converter.

S. No.Name of theParameter Values

1 Vin VMPP when MPP is workingVcell in NO MPP Zone

2 MOSFET 20A, 600V3 DIODE 20A, 1000V, Fast Recovery4 Lbuck 1mH, 15A Saturation5 Cbuck 1000 uF6 Vo d∗VMPP

d∗Vcell

7 Frequency 20 kHz8 Power Output 35W

Table 4. Parameters of solar PV.

S. No. Name of the Parameter Values

1 Name of the Vendor of solar PV Vikram SolarModel: ELDORA40

2 PV Type PolyCrystalline3 No. of Cells: Connected in series 364 Rated Maximum Power: PMPP 40W5 Open Circuit Voltage: VOC 21.9 V6 Short Circuit Current: ISC 2.45 A7 Voltage at MPP: VMPP 17.4 V8 Current at MPP: IMPP 2.3 A

converter. The PV voltage and current is sensed by using sensorsand given as input to the microcontroller [Model: PIC- 16F887].The microcontroller processes the proposed MPPT and gives out-put as pulse width modulated [PWM] signal to the gate of buckconverter. The opto-coupler driver IC [TLP-250] is used to drivethe power Mosfet of the converter. The data logger is connectedto record the solar PV power, current, and voltage. The gate sig-nal is monitored using digital CRO. A voltmeter and an ammeterare connected at the load end.

DC–DC BuckConverter

Microcontroller PWM(PIC-16F887)

MPPT Controller

Opto-Coupler IC: TLP250

DATA LOGGER

Voltage Sensor

Current Sensor

Digital CRO

LOAD

Voltmeter

A

Solar PV

FloodedwithArtificialLights

Fig. 9. Block diagram of experimental setup.

Maximum Power Point Tracking Scheme 121

Fig. 10. Simulation results: Power (P)-Voltage (V) curve.

Fig. 11. Experimental results with full artificial light.

The rating of solar PV used is 40W @ 1000 w/m2 solar irra-diation. The simulated Power-Vcell characteristic is shown inFigure 10. Since the PV is flooded with artificial lighting, there-fore, power generated is not 40W—rather, it is around 6–7 Watts.But the purpose to test the effectiveness of MPPT scheme isachieved. The Power-Vcell curve of solar PV from the exper-imental setup with artificial light source, i.e., 1000 W/m2, isshown in Figure 11.

Figure 12 shows the experimental results under changed solarirradiation levels. Figure 13 presents the experimental resultsobtained under similar conditions to that of simulation. It can beseen that the time taken to reach MPP is approximately 0.21 sec,and even if the solar irradiation is changed, the MPP schemeis not giving false results. Also, the experimental and simula-tion results are almost similar, except the steady state oscillation

Fig. 12. Simulation results: Power vs. time.

Fig. 13. Experimental results: Power vs. time.

Fig. 14. Experimental results: Solar PV power vs. time at differentload conditions.

is invisible in simulation. It is due to the fact that dP/dV ismuch less.

Figure 14 shows the experimental results under different loadconditions. It is evident that if RLoad is less than RMPP, the MPPworks and restores the power to MPP level. The moment RLoad

is greater than RMPP, the proposed MPP fails, which is obviouslyexpected. Figures 15 and 16 shows the experimental results forvariable duty cycle.

Table 5 presents a comparison of the result between the gainmethod and the proposed method. It is evident that time to reachMPP, peak to peak steady state oscillations, and step load changeresponse time is improved.

122 A. Haque

Fig. 15. Experimental results: PWM gate signal.

Fig. 16. Experimental results: PWM gate signal.

Table 5. Comparative results of gain and proposed method.

S. No. Name of the parameterGain

methodProposedmethod

1 Time to reach MPP from zero 0.4 sec 0.192 sec2 Peak to peak steady state

oscillation2.0 watt 0.500 watt

3 Step load change - responsetime

2.5 sec 1.800 sec

9. Conclusions

The correct and fast tracking of MPP under change solar irra-diation and change load conditions are challenging tasks forresearchers. The proposed MPPT scheme provides a solutionto improve the existing methods. The proposed scheme mayhelp in achieving accurate and fast response in standalone andgrid-connected solar PV energy conversion systema. It can beapplied in fast-changing solar irradiation areas where solar PVis used. The limitation of the proposed method is that it is notevaluated under partial shading conditions.

Appendix: Nomenclature

MPPT – Maximum power point trackerPV – PhotovoltaicRp – Parallel resistorIos – PV module reversal saturation currentT – Temperature in degree CelsiusIsc – Short circuit currentRES – Renewable energy sourcesP&O – Perturb and observeRs – Series resistorA, B – Ideality factork – Boltzmann’s constantS – Solar irradiation

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