2014 Power and Energy Systems: Towards Sustainable Energy (PESTSE 2014)

Model Validation and Maximum Power Point

Tracking of Photovoltaic Module

Alivarani Mohapatra, Byamakesh Nayak, Banishree Misra School of Electrical Engineering, KilT University, Bhubaneswar, India

aliva.priti@gmail.com, electricbkn II@gmail.com, banishreemisra@yahoo.co.in

Abstract-For efficient operation of a photovoltaic (PV) system accurate model of the PV module is required. In this

paper a PV simulation model has been developed and has been validated with experimental results of a commercial PV module, ELDORA-40. Maximum power point tracking (MPPT) must be incorporated in the PV system to get maximum power from the PV system. Maximum power of PV depends on two external parameters, temperature and solar irradiation. Since solar irradiation has faster dynamics than temperature an effort has been given to track maximum power of a PV module using perturb and observe (P&O) MPPT for change of insolation. The study has been carried out in MATLAB-Simulink graphical user interface environment.

Keywords-Photovoltaic(PV)system;Modeling;Maximum

power point tracking (MPPT); Perturb and Observe (P&O)

I. INTRODUCTION

Renewable energy like photovoltaic (PV) energy is more popularly used because it is pollution free, abundant, freely available and inexhaustible. The basic component of a PV system is a PV cell. Numbers of cells are grouped in series and parallel to form modules to meet the energy demand of the load. For large power application a PV array is formed by the series and parallel combination of modules [1]. For practical applications converter circuits needs to be connected to the photovoltaic device to process the electrical power. The basic function of the converter is to regulate the voltage and current to the load and to track the maximum power from the photovoltaic array. It is very important to operate the PV array consistently at maximum power point. Hence the mathematical models of PV array need to be analysed carefully for the dynamic analysis of the converters, and to design different MPP trackers [2].

The maximum power of a PV system changes with environmental condition, and there is only one value of current (Impp) and voltage (V mpp) which defines the maximum power point of a PV module. To increase the efficiency of the system, PV module must work at MPP at all environmental conditions [3-4].So it becomes essential to develop a simplified and comprehensive method to analyse the PV systems under all environmental conditions. In this paper the complete modelling is presented based on the mathematical equations which govern the behaviour of the PV module. Accurate knowledge of the [-V and P-V curve is required for the performance evaluation of the solar PV

978-1-4799-3421-8114/$31.00 ©2014 IEEE

array. Here all the necessary information has been provided to model the PV array and the MPPT techniques are described. The performance of a PV system is evaluated under standard test conditions (STC). Under STC average solar spectrum of 1.5 air mass (AM 1.5) is considered, the irradiance is 1000W/m2, and the cell temperature is taken as 25"C.

II. MODELING OF PHOTOVOLTAIC MODULE

PV modules are usually represented by a simple equivalent circuit model as shown in Fig. 1. [t consists of a current source (Ipv), anti-parallel with a diode with diode current (Id), a series resistance (Rs) and a shunt resistance (Rp).

Rs

D

v

Id

Fig. 1. Equivalent circuit of a PV module

The current-voltage characteristic of a PV module based on single diode model is expressed as [5]

[ (V+RIJ ] V+RI 1=1 -I exp --' -1 ---'-P' () NV R

S la p (1)

where Ipv and 10 are the photovoltaic current and the saturation currents respectively, Vt=kT/q is the junction thermal voltage of the module with Ns number of cells connected in series, q is the electron charge, k is the Boltzmann's constant, T(in Kelvin) is the temperature of the p-n junction, and a(1 <:: a <:: 2) is the diode ideality factor. The I-V curve of the PV module as shown in Fig.2 has three remarkable points: short circuit point (0, [sc), maximum power point (V mpp' Impp) and open-circuit point (Voc, 0).

Since change in temperature and solar irradiation has effect on voltage and current output of PV module, its effect has been taken into consideration in the final PV modeling. The photogenerated current (lpv) depends on both

temperature and sola irradiation according to the following equation [6].

Ipv = [Ipv,n +Kj (T-Tn )J� n

(2)

where Ipv,n is the photo-generated current at nominal condition (usually 2SoC and 1000 W/m2),T is the actual and Tn being the nominal temperature , G is the actual and Gn is the nominal irradiation respectively. The diode saturation current dependent on the temperature may be expressed by Eq.3.

I =

Isc,n + KjAT

o exp[ Voe,n + KvAT ]

_l NsVt,na

(3)

where AT = T -Tn' K] and Kvare short-circuit

current/temperature coefficient and open-circuit voltage/temperature coefficient of solar cell respectively.

2.5fi=1 ===========::::;.;;:::::=--:-;.;;ppr-i 2

« ::-1.5 c Q) � 1

C> 0 .5

00

sc

5

Current Source region

10 Voltage (V)

15 20

Fig. 2. Characteristic I-V curve of PV module with short circuit, open circuit and maximum power points

III. MODEL BASED ON SIMULINK

The complete simulink model of a PV module is given in Fig. 3. Each block contains sub models to build the complete model. For the model two types of tags are used: From tag and the Goto tag. The model developed is based on the basic equation of a PV cell given in Eq.1. For Ipy and 10 calculation Eq.2 and Eq.3 has been used respectively. Various stages for developing the model are discussed. Internal datasheet parameters provided by manufacturer and unknown parameters extracted [7-8] are given through Matlab m-file. External parameters like temperature (T) and solar irradiation (G) must be provided to evaluate the characteristics of PV module at particular temperature and irradiation.

IV. MAXIMUM POWER POINT TRACKING AND THE

P&O METHOD

The PV characteristics changes with environmental condition and are non linear in nature, requiring an identification of the optimal maximum operating power point. The MPPT controller is a power electronic converter inserted between PV module and load to operate the PV module at MPP point in all condition by controlling the duty cycle of the converter as shown in Fig.5. The MPPT control methodology presented in this paper is P&O method.

IPv

Vo l ta g e Me�urement

Subsystem

Fig.3 Matlab/Simulink block diagram of the PV module

Modeling stage 1 (calculation of 10)

Thermal_voltage1

Modeling stage 2(calculation of Ipv)

Modeling stage 3(calculation of I)

Fig.4 Photovoltaic subsystem model built with Matlab/Simulink

Solar Array

Pulse from control unit

v Buck dc-dc converter

Fig.S Block diagram of MPPT simulation model

I---V O-,-� R,

For PV module to deliver maximum power, the internal resistance of the PV module must be equal to the equivalent load resistance. In this method a perturbation in the duty ratio of dc-dc converter involves perturbation in equivalent load resistance, which perturbs the PV array current and consequently perturbs the PV array voltage to match the solar array internal resistance equal to equivalent load resistance. This perturbation technique is used to track the MPP voltage or current. It can be seen from Fig. 6 that the increment or decrement of the voltage increases or decreases the power when operating point is on the left of the MPP, and decreases or increases the power when the operating point is on the right of MPP. Fig.7 shows the flowchart of the algorithm. Under this condition the system starts oscillating around the MPP. The oscillation can be minimized by reducing the perturbation size. However, the system is sluggish due to reduction of the perturbation size.

40,--------,---------,---------,--------�--, -G=1000 W/m2

5 10 15 20 Voltage in volts

Fig.6. Simulated P-V curve of ELDORA-40 PV module influenced by different insolation level with constant temperature of 2SoC

V. R ESULTS AND DISCUSSION

From the PV module Matlab/Simulink model discussed in Fig.3 and FigA the voltage and current of the PV module noted down for different values of load resistance at 2SoC of temperature and 220W/m20f solar irradiation. At the same temperature and solar irradiation, experiment has been conducted on ELDORA-40 PV panel to measure set of voltage and current at different load condition ranging from no load to full load. The experimental set-up of ELDORA-40 PV panel is shown in Fig.8.Simulated I-V and P-V characteristics of the ELDORA-40 PV �anel at temperature of 2SoC and solar radiation of 220W/m compared with the experimental results at above mentioned temperature and solar radiation. Figs.9-1O shows excellent agreement

between the experimental and simulated result for both I-V and P-V characteristic.

Fig.7. Flowchart of the P&O Algorithm

Fig. 8. Experimental set-up of ELDORA-40 PV panel

0.8,-------,-------,---------,-------,----------,

�O.6

� r----=--=-===#=->-__

:::0.4 c � ::::J uO.2

5 10 15 Voltage in Volts

25

Fig.9. Comparison of simulated I-V characteristic of ELDORA-40 PV panel with that of experimentally obtained I-V characteristic at 2SoCof temp and 220W/m2of solar radiation

c .;:: 4 OJ � (1-2

o 5 10 15 Voltage in Volts

20

Fig. 10. Comparison of simulated P-V characteristic of ELDORA-40 PV panel with that of experimentally obtained P-V characteristic at 25()Cof temp and 220W/m20f solar radiation

The data Datasheet parameters of the ELDORA-40 PV panel at STC is given in Table l .

TABLE-lDATASHEET PARAMETERS OF THE ELDORA-40 PV PANEL AT STC

Isc,n 2.4A Voc,n 21.8V Vmp,n 17.2V Imp,n 2.20A

Ns 36 Kv -0.0032V/K K] 0.0004 A/K

The Matlab/Simulink model of the P&O algorithm is shown in Fig. 1l .

Fig.II.Matlab/Simulink block model of P&O MPPT

Step variation of solar irradiation from 1000W/m2 to 600W/m2 at fixed temperature of 2SoC at instant of 1 second has been considered to verify the tracking capability of P&O MPP tracker. The maximum power of the ELDORA-40 PV module at different insolation is given in table2.The result shown in Fig.12 confirms the tracking capability of the P&O method.

TABLE-2 MAXIMUM POWER OF ELDORA-40 PV PANEL AT DIFFERENT INSOLATION AND FIXED TEMPERATURE OF 25()C

Solar irradiation in W/m2 Maximum Power in Watt 1000 37.841 600 22.192

40,-------�--------�------�--------�

30

o

o 0.5 1 1.5 2 Time in seconds

Fig.12. Maximum power point tracking using P&O method with change in solar irradiation

VI. CONCLUSION

Matlab/Simulink model of the PV module has been explained in details. The simulated I-V and P-V characteristics have been compared with the experimental results. The results show the accuracy of the model. An attempt has been carried out to track the maximum power of the PV module with change of solar irradiation using P&O MPPT algorithm. The result shows that, this method can well track the maximum power point with variation of irradiation.

REFERENCES

[I] Villalva, M.G. ; Gazoli, J.R. ; Filho, E.R., "Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays," Power Electronics,

IEEE Transactions on, vo1.24, no.5, pp.1l98-1208, May 2009.

[2] Xiao Weidong, N. Ozog, W.G. Dunford, "Topology Study of Photovoltaic Interface for Maximum Power Point Tracking", IEEE

Transactions on Industrial Electronics, vol. 54, no. 3, pp.1696-1704,2007.

[3] Subudhi, B. ; Pradhan, R., "A Comparative Study on Maximum Power Point Tracking Techniques for Photovoltaic Power Systems," Sustainable Energy, IEEE Transactions on, volA, no.l, pp.89-98, Jan. 2013.

[4] T. Esram, P. L. Chapman, "Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques", IEEE Transactions on Energy Conversion, vol. 22, no. 2, pp. 439 - 449, June 2007.

[5] Villalva, M.G. ; Gazoli, J.R. ; Filho, E.R., "Modeling and circuit-based simulation of photovoltaic arrays," Power Electronics Conference, 2009. COBEP '09. Brazilian, pp.l244-1254, Sept. 27 2009-0ct. 1 2009.

[6] Alqahtani, AH., "A simplified and accurate photovoltaic module parameters extraction approach using matlab," Industrial Electronics

(ISlE), 2012 IEEE International Symposium on , pp.1748-1753, 28-31 May 2012.

[7] Mohapatra, A; Nayak, B.K. ; Mohanty, K.B., "Comparative study on single diode photovoltaic module parameter extraction methods," Power,

Energy and Control (ICPEC), 2013 International Conference on ,pp.30-34, 6-8 Feb. 2013.

[8] Sera, D.; Teodorescu, R. ; Rodriguez, P. , "PV panel model based on datasheet values," Industrial Electronics, 2007. ISlE 2007. IEEE International Symposium on , pp.2392-2396, 4-7 June 2007.