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International Journal of Scientific Research Engineering & Technology (IJSRET)Volume 2 Issue 12 pp 811-814 March 2014 www.ijsret.org ISSN 2278 – 0882

IJSRET @ 2014

SIMULATION OF PI CONTROLLER BASED MAXIMUM

POWER POINT TRACKING FOR A PV SYSTEM

M. S. Sivagamasundari1

, Dr. P. Melba Mary2

, N. K. Jawahar Muthu3

1Assistant Professor, Department of EEE, V V College of Engineering, Tisaiyanvilai2Principal, Department of EEE, V V College of Engineering, Tisaiyanvilai

3Assistant Executive Engineer, TamilNadu Electricity Board

ABSTRACTPhotovoltaic energy conversion becomes main focus

of many researches due to its promising potential as

source for future electricity and has many advantages

than the other alternative energy sources like wind,

ocean, biomass, geothermal etc. Solar energy is

considered among one of the best options forgenerating clean energy. In this paper, a PI controller is

used as an intelligent method for achieving the

Maximum Power Point of a PV system. A buck boost

converter is used in this system. By varying the duty

cycle of the buck boost converter, the source

impedance can be matched to adjust the load

impedance to improve the efficiency of the system.

The performance has been studied by the

MATLAB/Simulink.

Keywords: PI controller, Maximum power point

tracking, MPPT algorithm, Photovoltaic system

1. INTRODUCTION

The Conventional sources of energy are rapidly

depleting. Moreover the cost of energy is rising and

therefore photovoltaic system is a promising

alternative. They are abundant, pollution free,

distributed throughout the earth. However, the

majority of the world's electrical energy came from

conventional sources such as -fossil fuels, coal, natural

gases and oil etc. These fuels are often termed as non-

renewable energy sources. Though, the available

amount of these fossil fuels are extremely large, but

due to decrease in level of fossil fuel and oil level day

by day may be in few years it will end. Hence

renewable energy based source demand increases as it

is environmental friendly and pollution free and it will

also reduce the greenhouse effect.

For many years, researches on the PV power

generation system have received much attention,

particularly, on many terrestrial applications. Another

drawback of PV system is that it does not provide a

constant energy source because its output powerchanges with temperature and insolation level. [1] To

overcome these problems, in this paper, an intelligent

control technique using PI controller is associated to

an MPPT controller in order to increase the efficiency

of the PV system.

2. PHOTOVOLTAIC SYSTEM

A Photovoltaic (PV) system directly converts solar

energy into electrical energy. The basic device of a PV

system is the PV cell. Cells may be grouped to form

arrays. The voltage and current available at the

terminals of a PV device may directly feed small loads

such as lighting systems and DC motors or connect to

a grid by using proper energy conversion devices. This

photovoltaic system consists of main parts such as PV

module, charger, battery, inverter and load. [2]

2.1. Equivalent model

A Photovoltaic cell is a device used to convert solarradiation directly into electricity. It consists of two or

more thin layers of semiconducting material, most

commonly silicon. When the silicon is exposed to

light, electrical charges are generated. A PV cell is

usually represented by an electrical equivalent one-

diode model shown in fig.1.

Fig.1. Single PV cell model

The model contains a current source, one diode,

internal shunt resistance and a series resistance which

represents the resistance inside each cell. The net

current is the difference between the photo current and

the normal diode current is given by the equation. [2]

ID = IO [ -1]………………………… (1)




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I = IL – IO [ – 1]-

…………………… (2)

where

I is the cell current (A).q is the charge of electron (coul).

K is the Boltzmann's constant (j/K).

T is the cell temperature (K).

IL is the photo current (A).

Io is the diode saturation current.(A)

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

V is the cell output voltage (V).

3. BLOCK DIAGRAM OF THE PROPOSED

METHOD

Fig. 2 PV system with MPPT controller

PV system with MPPT controller has been shown

in fig. 2. For any PV system, the output power can be

increased by tracking the MPP (Maximum Power

Point) of the PV module by using a controller

connected to a dc- dc converter (usually buck boost

converter). However, the MPP changes with insolation

level and temperature due to the nonlinear

characteristic of PV modules.

4. BUCK BOOST CONVERTER

The buck – boost converter is a type of DC-DC

converter that has an output voltage magnitude that is

either greater than or less than the input voltage

magnitude. It is a switch mode power supply with a

similar circuit topology to the boost converter and the

buck converter. The output voltage is adjustable based

on the duty cycle of the switching transistor. Also, the

polarity of the output voltage is opposite to the input

voltage. Neither drawback is of any consequence if the

power supply is isolated from the load circuit as the

supply and diode polarity can simply be reversed. The

switch can be on either the ground side or the supplyside. The schematic of a buck – boost converter is

shown in figure.3

Fig.3 Schematic of a buck – boost converter

The conversion ratio given by

(Vo/Vin) = (Iin / Io) = D/ (1-D)

………….............. (3)

Where, D is the duty cycle.

While in the On-state, the input voltage source is

directly connected to the inductor (L). This results inaccumulating energy in L. In this stage, the capacitor

supplies energy to the output load. While in the Off-

state, the inductor is connected to the output load and

capacitor, so energy is transferred from L to C and R.

The waveforms of current and voltage in a buck – boost

converter operating in continuous mode and

discontinuous mode are shown in figure 4 and 5.

Fig.4 Waveforms of current and voltage in a buck – boost converter operating in continuous mode

Fig.5 Waveforms of current and voltage in a buck – boost converter operating in discontinuous mode




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5. MPPT ALGORITHMS

To obtain the maximum power from a

photovoltaic array, a maximum power point tracker

(MPPT) is used. Many different algorithms have beenproposed for tracking MPP in the past. Commonly

used algorithms are Perturb and observe method,

Incremental conductance method, Constant voltage

method, Constant Current method etc. The

Perturbation and observation is one of the most

commonly used MPPT methods for its simplicity and

ease of implementation. The P&O works well when

the irradiance level change slowly but it presents

drawbacks such as slow response speed, oscillationaround the MPP in steady state, and even tracking in

not working properly under rapidly changing

atmospheric conditions. [3]-[8]

Fig.6 Simulink model of the proposed system

6. SIMULATION RESULTS

In this paper, the simulation model is developed

with MATLAB/SIMULINK. The simulation model of

the proposed method is shown in figure.6.Theproposed circuit needs independent dc source which is

supplied from photovoltaic cell. The inputs are fed by

voltage and current of the PV terminals, while the

output provides duty cycle for the buck boost

converter. The input voltage is 24V and the output

voltage after being buck boosted up is 48.2V and

shown in fig.6. Buck Boost converter controls the

output voltage by varying the duty cycle k, of the

switch and the value of k is 0.67 which is calculated

using the formulae Vo = Vs*k / 1- k. If we vary the

pulse width of the pulse generator various voltage

ranges at the output can be obtained. Once the buck

boost converter injected the power from the PV panel

and the PI controller starts function, it varies the value

of duty cycle which will change the input value that is

sensed by the PI controller. By using the PI controller

the error has been minimized in the system and the

efficiency is improved. The various parameter valuesare

Inductance of the buck boost converter is L=1mH

Resistance = 60 ΩInput Capacitance = C = 4.7μF

Proportional gain Kp=0.012

Integral gain Ki = 129.26

Output voltage = 48.2V

Output current = 4.82A

Output Power = 232.32W

Efficiency = 90.8%

The waveforms for output voltage and output

current of buck boost converter are shown in figure 7

and 8. The response of PI controller based MPPT is




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shown in figure 9 .The response of PI controller is

better since it takes more settling time. Therefore the

PI control algorithm is capable of improving the

tracking performance.

Fig. 7 Output current for buck boost converter

Fig. 8 Output voltage for buck boost converter

Fig. 9 PI Controller based MPPT

7. CONCLUSION

In this paper, the proposed method is by

implementing a maximum power point tracker

controlled by PI controller using buck boost DC/DC

converter to keep the PV output power at the

maximum point all the time. By varying the duty cycle

of the buck boost converter, the source impedance can

be matched to adjust the load impedance which

improves the efficiency of the system. The response of

PI controller is better since it takes more settling time.

Therefore the PI control algorithm is capable of

improving the tracking performance. The performance

has been studied by the MATLAB/Simulink.

REFERENCES

[1]. Kimiyoshi Kobayashi, Hirofumi Matsuo andYutaka Sekine, “A novel optimum operatingpoint tracker of the solar cell power supply

system” ,IEEE Conference on Power Electronics,Volume 3, 20-25 June 2004.

[2]. M. G. Villalva, J. R. Gazoli, and E. R. Filho

“Comprehensive Approach to Modeling andSimulation of Photovoltaic Arrays” IEEETrans. Power Electr., vol. 24.

[3]. Y.Kuo-“Maximum Power Point Trackingcontroller for photovoltaic energy conversion

system”-IEEE Trans Ind. Electron-Volume 48-

2001.

[4]. Nicola Femia, Giovanni Petrone, Giovanni

Spagnuolo, Massimo Vitelli “Optimization of Perturb and Observe Maximum Power Point

Tracking Method” IEEE transactions on power electronics, vol. 20, no. 4, July 2005.

[5]. D. P. Hohm and M. E. Ropp, “ComparativeStudy of Maximum Power Point Tracking

Algorithms”, Progress in photovoltaics:research and applications Prog. Photovolt: res.

Appl. 2003.

[6]. Xuejun Liu and Luiz A. C. Lopes, “AnImproved Perturbation and Observation

Maximum Power Point Tracking Algorithm

for PV Arrays”, 2004 35th Annual IEEEPower Electronics Specialists Conference.

[7]. Chung-Yuen Won, Duk-Heon Kim, Sei-Chan

Kim “A New Maximum Power Point Tracker of Photovoltaic Arrays Using Fuzzy

Controller”, IEEE transaction 1994.

[8]. S. Armstrong and W.G Hurley “Investigatingthe Effectiveness of Maximum Power Point

Tracking for a Solar System”, IEEE

Conference on Power Electronics, 2005.