Perturb and Observe MPPT Algorithm for Solar PV Systems-Modeling ...

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Solar PV Systems-Modeling and Simulation. Jacob James Nedumgatt, Jayakrishnan K. B.,. Umashankar S., Vijayakumar D.,. School of Electrical Engineering.
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. [email protected], [email protected] [email protected], [email protected]. Abstract-The following paper validates an algorithm for Maximum Power Point Tracking using Perturb and Observe technique. The algorithm starts by setting the computed maximum 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 be modelled with the help of MATLAB/SIMULINK.

Kothari D P Director General Vindhya Institute of Technology and Science Indore, India [email protected]

temperature. Therefore, an on-line tracking of the maximum power point of a PV array is an essential part of any PV system. This paper looks at the P&O MPPT technique where the instantaneous values of power are calculated each time, and the maximum power point value is updated. Having completed all the calculations and comparisons, the maximum power point is finally determined, and the corresponding voltage and current at the maximum power point is also determined. II.

PV EQUIVALENT CIRCUIT

A solar cell basically is a p-n semiconductor junction. When exposed to light, a dc current is generated. The generated current varies linearly with the solar irradiance. The standard equivalent circuit of the PV cell is shown in Fig. 1. RS

Keywords-Photovoltaic; maximum power point tracking; MPPT; P&O

+ ISH

ID

I.

INTRODUCTION

As people are concerned with the fossil fuel exhaustion and the environmental problems caused by the conventional power generation schemes present, renewable energy sources, photovoltaic panels and windgenerators, to mention a few are now in great need [2]. Among several renewable energy sources, photovoltaic arrays are used in many applications such as water pumping, battery charging, hybrid vehicles, and grid connected PV systems. The principal advantages associated with photovoltaic arrays are that it consists of no moving parts. Do not produce any noise and maintenance costs are minimal. It is also a clean source of energy. Amount of energy produced by the sun is so large, that in one hour it can provide more than enough energy for human population in one year. However, due to the low efficiency of current solar panels, conversion of sunlight into electrical power is very poor. This efficiency further decreases if there is no load matching between the input side (PV array output) and the output side (load). To maximize the power derived from the solar panel it is important to operate the panel at its maximum power point, hence an increase in output efficiency. Maximum power point changes with the solar irradiation, and cell

V

IL RSH

-

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 following equation:

I = IL − I O ( e

q (V + IR S ) KT

− 1) −

V + IR S R sh

(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).

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 factor ranges from 1 to 2, if a two diode model is used. Usually optimization techniques are used to determine a suitable value for a particular model. The IO in the equation represents 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 also temperature dependent. Hence with a change in the temperature in Kelvin, ‘T’, the overall current, ‘I’ would vary. If temperature increases the current ‘I’ reduces. IL is the light generated current. It is this parameter which plays the vital role in a solar cell. Illumination of the cell gives rise to an increase in the minority carrier concentration, more light more excess hole-electron pairs will be generated. As a result the IL value increases as the irradiance levels rise. Below are the figures which show the characteristic PV Array curves, voltage versus the power produced by the PV Array and the current versus voltage. This is a necessity when determining the maximum power point, if not the PV System will not be efficient.

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

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

Figure 2. Current vs Voltage Characteristic curve

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

Figure 3. Power vs Voltage Characteristic Curve

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

III.

P&O MPPT TECHNIQUE

The problem considered by MPPT methods is to automatically find the voltage VMPP or current IMPP at which a PV array delivers maximum power under a given temperature and irradiance. In P&O method, the MPPT algorithm is based on the calculation of the PV output power and the power change by sampling both the PV Array current and voltage. The tracker operates by periodically incrementing or decrementing the solar array voltage [4]. If a given perturbation leads to an increase (decrease) in the output power of the PV, then the subsequent perturbation is generated in the same (opposite) direction. The duty cycle of the dc chopper is varied and the process is repeated until the maximum power point has been reached. Actually, the system oscillates about the MPP. Reducing the perturbation step size can minimize the oscillation. However, small step size slows down the MPPT. For different values of irradiance and cell temperatures, the PV array would exhibit different characteristic curves. Each curve has its maximum power point. It is at this point, where the corresponding maximum voltage is supplied to the converter.

duty ratio is varied in such a manner that the input power delivered to the converter will almost be equal to the power delivered to the load V.

MATLAB MODELING AND SIMULATION

The PV Array and the PVIV blocks are embedded blocks, where the PV array has been mathematically modelled [4]. These blocks are necessary to calculate the maximum power point, as part of the MPPT technique and also to display the characteristics curves based on different irradiance levels. The same can be implemented for different ambient temperatures.

Figure 10. Simulink block diagram of complete PV system

.

Figure 11. Cuk converter, for a fixed load of 6 ohms 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. The input voltage and current from the PV array is used to calculate the instantaneous power. Based on the MPPT algorithm the maximum power point is identified and the duty ratio of the converter is varied in accordance. The

Cuk Converter is used in this system [5]. It has certain advantages over the buck boost converter. Like the buck boost converter, it can step up or step down the output voltage. Here the capacitor is the main storage element. It helps to ensure continuous current flow, and the inductor which 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 duty ratio is varied to give allow maximum power transfer from the input supply to the load.

A. The following are results shown, with a variation of irradiance levels. The irradiance levels change at fixed intervals of time while maintaining the ambient temperature constant.

Figure 15. Variation in Output Voltage and Input Voltage

Figure 12. Variation of irradiance levels to the pv array while keeping the ambient temperature constant.

Figure 16. Variation in Input Power and Output Power

Figure 13. Pulses to the gate

Figure 17. Variation in Output Current and Input Current

Figure 14. Voltage across Inductor L1 and Capacitor C1

Figure 18. Variation in duty cycle

B. The following are results shown, with a variation of ambient temperature. The ambient temperature changes at fixed intervals of time maintaining a constant irradiance level.

Figure 22. Variation in output current and input current

Figure 19. Variation of ambient temperature tacon pv array while G is constant (G=1)

Figure 23. Variation in duty cycle

The simulation results show that the duty ratio varies in such a manner that the output voltage across the load is constant. There are loads that are sensitive to voltage, hence a constant output voltage is a requirement. VI. Figure 20. Variation in output voltage and input voltage

CONCLUSION

The PV Array has been mathematically modelled. The programmes implemented in the MPPT technique achieve the maximum power point. It has been shown that for the particular irradiance levels the maximum power delivered by the PV Array is delivered to the load. The same is carried out if there is a variation in temperature. It is a simple MPPT setup resulting in a highly efficient system. In conclusion, non-conventional energy sources will dominate the conventional sources of energy in the near future and here one uses the greatest renewable energy of all, the sun’s energy. VII. REFERENCES [1]

Figure 21. Variation in output power and input power

[2]

[3]

[4] [5]

[6]

N. Femia, et. Al. “Optimization of Perturb and observe Maximum PowerPoint tracking Method,” IEEE Trans. Power Electron., Vol. 20, pp.963-973, July 2005. E. Koutroulis; et. al , “ Development of a Microcontrollerbasedphotovoltaic maximum power tracking control system”, IEEE Trans. Onpower Electron., Vol. 16, No. 1, pp. 46-54, 2001. J.A.Jianget. Al. , “Maximum Power Tracking for Photovoltaic PowerSystems”, Tamkang Journal of Science and Engineering, Vol. 8, No. 2,pp. 147-153, 2005. Thesis-Akihiro Oi,”Design and simulation of photovoltaic water pumping system”,September 2005 Ned Mohan, Tore M. Undeland, William P. Robbins, “Power Electronics, Converters, Applications and Design”, Third Edition, New Delhi,Wiley India (P.) Ltd. Stuart Bowden and Christiana Honsberg, http://www.pveducation.org/pvcdrom

VIII. BIOGRAPHIES Jacob James Nedumgatt was born in Kollam, Kerala. He is currently pursuing Master’s Degree in Power Electronics at VIT University, Vellore. He received his Bachelor Degree in Electrical and Electronics Engineering in the year 2009 at Rajagiri School of Engineering and Technology, affiliated to Mahatma Gandhi. University, Kerala. His research interests are Power Electronics applications in Solar PV systems and Multilevel Inverters. Jayakrishnan K B was born in Ernakulam Kerala. He is currently pursuing Master’s 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 Electronics applications in Renewable Energy Systems and Power System protection. Umashankar. S (M’11) received his Bachelor Degree in Electrical and Electronics Engineering and Master Degree in Power Electronics in the year 2001 and 2004 respectively. Currently he is Asst. Professor-Senior in the School of Electrical Engineering at VIT University, Vellore. He worked as Senior R&D Engineer and Senior Application Engineer in the power electronics and Drives field for more than 6 years. He has published/presented many national and international journals/conferences. He has also coauthored/co-edited many books/chapters on wind power/energy and allied areas. His current areas of research activities include renewable energy, real time digital simulator, HTS generator, FACTS, and power quality.

D. P. Kothari (F’10) received the B.E. degree in electrical engineering, the M.E. degree in power systems, and the Ph.D. degree in electrical engineering from the Birla Institute of Technology and Science (BITS), Pilani, India. Currently, he is Advisor to Chancellor of the VIT University, Vellore, Tamil Nadu, India. He was Head, Centre for Energy Studies, lIT Delhi (199597), and Principal, Visvesvaraya Regional Engineering College, Nagpur (1997-98). He has been Director i/c, lIT Delhi (2005) and Deputy Director (Administration), lIT Delhi (200306). He has published/presented around 600 papers in national and international journals/conferences. He has also co-authored/co-edited 22 books on power systems and allied areas. His activities include optimal hydrothermal scheduling, unit commitment, maintenance scheduling, energy conservation, and power quality. He has guided 28 Ph.D. scholars and has contributed extensively in these areas as evidenced by the many research papers authored by him. He was a Visiting Professor at the Royal Melbourne Institute of Technology, Melbourne, Australia, in 1982 and 1989. He was a National Science Foundation 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 has received the National Khosla award for Lifetime Achievements in Engineering for 2005 from lIT Roorkee. The University Grants Commission (UGC) has bestowed UGC National Swami Pranavananda Saraswati award for 2005 on Education for outstanding scholarly contribution. D. Vijayakumar received his Bachelor Degree in Electrical and Electronics Engineering and Master Degree in Power Systems in the year 2002 and 2005 respectively. He worked as a Lecturer in Pallavan College of Engineering from 2005 to 2006. He received his Doctorate in 2010 at Electrical Department in Maulana Azad National 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 system protection, and Renewable energy sources.