IJEEE, Vol. 1, Issue 5 (October, 2014)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
SIMULATION MODEL FOR PV ARRAY & ITS CHARACTERISTICS 1
Ekta, 2Maninder Kaur
1,2
Electrical Department, Baba Banda Singh Bahadur Engineering College, Punjab, India 1
ekku14@gmail.com, 2maninder.thakur@bbsbec.ac.in
Abstract—This paper presents the implementation of a photovoltaic model using Matlab software, which can be representative of PV cell module, and array for easy use on simulation. The proposed model is designed with a user-friendly icon and a dialog box like Simulink block libraries. This makes the PV model easily simulated and analyzed in conjunction with power electronics for a maximum power point tracker. Taking the effects of sunlight irradiance and cell temperature into consideration, the output power and current characteristics of PV model are simulated. This enables the dynamics of PV power system to be easily analyzed, simulated and optimized. Index Terms-photovoltaic model, Matlab-Simulink. I. INTRODUCTION With increasing concerns about fossil fuel deficit, sky rocketing oil prices, global warming, and harm to ecosystem and environment, the promising incentives to develop alternative energy resources with high efficiency and low emission are imperative. Among the renewable energy resources, the energy through the photovoltaic (PV) effect can be considered the most essential and pre requisite sustainable resource because of the easy and unending availability, and sustainability of solar energy[1]. Regardless of intermittency of the sunlight, solar energy is widely available in the environment and completely free of cost. Recently, photovoltaic array system is likely recognized and widely utilized to the forefront in electric power applications. It can generate DC electricity without environmental impact and contamination when is exposed to solar radiation. Being a semi conductive device, the PV system is static, quite, and no moving parts, and these make it have little operation and maintenance costs. Even though the PV system is having high capital fabrication cost and low conversion efficiency, the sky rocketing oil prices make solar energy naturally viable energy supply with potentially long-lasting benefits. PV module represents the main power conversion unit of a PV generator system. The output characteristics of a photovoltaic module depends on the solar insolation, cell temperature and output voltage of PV module as we know that PV module has nonlinear characteristics, it is beneficial to model it for the design and simulation of maximum power point tracking (MPPT)[9,10] for PV system applications. Almost all welldeveloped PV models describe the output characteristics mainly affected by the solar insolation, load voltage and cell temperature. However, the equivalent circuit models are implemented on simulation. However, the SimPowerSystem tool in Matlab-Simulink package offers International Journal of Electrical & Electronics Engineering
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wind turbine models but no PV model to integrate with current electronics simulation. Thus, it is difficult to simulate and analyse in the modeling of PV power system. This motivated me to develop a model for PV cell, array[1,2], and module using Matlab-Simulink. The main feature of this paper is the implementation of a PV model in the form of masked block, which has a user-friendly dialog and icon in the same way of Matlab block libraries. Recent works done by Ciobotaru (2007), Pandiarajan (2012) and Jamri (2010), respectively [2], [3] and [4], revealed some basic aspects of photovoltaic cell modelling. They have adopted similar model of solar cell and carried out some simulation works on their output characteristics including power vs voltage and current vs voltage using MATLAB/Simulink[10,11]. The output characteristics[8] are similar showing a power that increases proportionally to the voltage from an initial stage up to a certain threshold after which it decreases rapidly down to zero. II. PHOTOVOLTAIC MODEL AND ITS GOVERNING EQUATIONS Solar Energy is a good choice for electric power generation and electromagnetic radiation of solar energy directly converted into electrical energy by solar photovoltaic module. Solar Module consists of solar cell. Solar cell is basically a p-n junction fabricated in a thin wafer or layer of semiconductor. The photovoltaic modules are made up of silicon cells. The silicon solar cells gives output voltage of around 0.7V under open circuit condition. When large many such cells are connected in series we get a solar PV module. Generally there are 36 cells in a module which amounts for an open circuit voltage of approx 20V. The current ratings of the modules depends on the area of the individual cells. Higher the cell area, higher is the current output of the cell, to obtain higher power output, the solar PV modules are connected in series and parallel combinations forming solar PV arrays. When exposed to the sunlight, photons with energy higher than the band-gap energy of the semiconductor are absorbed and create some electron-hole pairs proportional to the incident irradiation. With the influence of the internal electric fields of the p-n junction, these carriers are pulled apart and creates a photo current which is proportional to solar isolation.
Fig. 1: Equivalent electrical circuit of a PV device www.ijeee-apm.com
PV system naturally exhibits a nonlinear V-I and P-V characteristics which vary with the insolation and cell temperature are shown as in Fig 2.a and Fig 2.b. Electrical characteristic of PV module (Standard radiance level of 1000 W/m2).
Figure2.a V-I characteristic of PVmodule.
Figure2.b P-V characteristic of PV module
A general mathematical description of V-I output characteristics for a PV cell has been studied for over past four decades. An equivalent circuit-based model is mainly used for the MPPT[2,3,10] technologies which consists of a photo current, a parallel resistor, a diode, expressing a leakage current and a series resistor denoting an internal resistance to the current flow, is shown in Fig 1. The V-I characteristic[8] equation of a solar cell is given as I = Ipv, cell – Id (1) Ipv, cell − Io, cell exp
−1
(2)
where Ipv, cell = Current generated by the Incident light Id = Schottky diode equation, Io, cell = Reverse Saturation or Leakage current of the diode, q = Electron charge, k = Boltzmann constant (1.3806503 × 10−23 J/K), T(K) = Temperature of the P–N junction, a = Diode ideality Constant.
ΔT = T − Tn I , n = Nominal current T = Actual Temperature, Tn = nominal temperatures [K], G = Actual irradiation (W/m2) Gn = Nominal irradiation (W/m2) Reverse saturation Current is calculated as (5) , ∆ I = (5) ∆ Minimum Value of Parallel Resistance, Rp V V ,n + V Rp, min = + (6) I , n + Imp I_mp I ,n = I .n (7)
Where Isc,n = Nominal Current (short circuit) Voc,n = Nominal Voltage (open circuit ) Vmp = Maximum Power Point Voltage Imp = Maximum Power Point Current Kv= Voltage Temperature Coefficient Ki=Current Temperature Coefficient Maximum value of Power is defined as V + R I Pmax, m = V I − exp −1 aV V +R I − aV = Pmax, e (8) Basically, Pmax, m − Pmax, e = 0 (9) Parallel Resistance (Rp) is defined as Rp=
{
(
)
_
(10) Where P max, e =Estimated power V = N ∗
, }
IV. SIMULATION AND ANALYSIS OF PV MODEL WITH ITS V-I AND P-V CHARACTERISTICS The output V-I and P-V characteristics after simulation are obtained as shown in Fig 3.
III. BASIC V-I CHARACTERISTIC OF A PRACTICAL PV DEVICE In case of Practical PV Device Series Resistance (Rs) and Parallel Resistance (Rp) of device are considered as shown below I=Ipv,cell−Io, cell exp
−1 −
(3)
V = N ∗ ( ) Is Thermal Voltage
Ns = cells connected in series. Generally, Series resistance, Rs, is assumed low and parallel resistance, Rp, is assumed high. Variation of Ipv with Temperature & Insolation[5,6] I = I ,n + K ∆ ∗ (4) PV Device depends linearly on the solar irradiation and the temperature as shown above Equation (4). Standard conditions are considered as follows Where Tn = 25 ◦C and Gn =1000 W/m2 www.ijeee-apm.com
Figure 3: Simulated model of PV module with its V-I and PV characteristics
Solar Module and Array Model Since a PV cell produces less than 2W at 0.5V approximately, the cells are connected in series-parallel combinations on a module to produce enough high power. The equivalent circuit for the solar module arranged in NP parallel and NS series which is denoted by following equations. The general equation for the current and voltage of the array becomes as follows. International Journal of Electrical & Electronics Engineering
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I = NP IPH − NP IS[exp(q(V / NS + IRS / NP ) / kTCA)−1]− (NPV / NS + IRS )/RSH In fact, the PV efficiency is sensitive to small change in RS but insensitive to variation in RSH . For a PV module or an array, the series resistance becomes apparently imperative and the shunt resistance approaches infinity which is taken to be open. In many commercial PV products, these cells are generally connected in series configuration to form a PV module in order to obtain enough voltage. PV modules are then arranged in series-parallel structure to achieve desired higher power output. It can be shown that NS = NP = 1 for a PV cell, NP =1 and Ns : series number of cells for a PV module, and Ns and Np : series-parallel number for a array of PV. The mathematical equation of this model can be described as I = NP IPH − NP IS[exp(q(V / NS + IRS / NP ) / kTCA)−1] The equivalent circuit is described on the following equation I = NP I PH − NP IS [exp(qV/NSkTC A)−1] Simulation Model of PV array With its V-I And P-V Characteristics The PV simulated model of PV array with 6 PV modules connected in series and its output V-I and P-V characteristics are shown in Fig 4
[2]
Gow, J. A. and Manning, C. D. 1999. Development of a Photovoltaic Array Model for Use in Power-Electronics Simulation Studies. IEEE Proceedings of Electric Power Applications. Vol. 146, No. 2, pp. 193–200. [3] Pandiarajan, N., Ramaprabha, R., and Muthu. R. 2012. Application of Circuit Model for Photovoltaic Energy Conversion System. Hindawi Publishing Corporation: International Journal of Photo Energy, ID410401, 14 p. [4] Jamri, M., S., and Wei, T., C. 2010. Modeling and Control of a Photovoltaic Energy System Using the State Space Averaging Technique. American journal of Applied Sciences. ISSN 1546-9239. pp. 682-691. [5] S. Rustemli, F. Dincer, Modeling of Photovoltaic Panel and Examining Effects of Temperature in Matlab/Simulink. [6] Kumar A., Kumar K., Kaushik N., Sharma S., Mishra S. Renewable energy in India: Current status and future Potentials // Renewable and Sustainable Energy Reviews. – Elsevier, 2010. – No. 14(8). – P. 2434–2442. [7] Gomez-Amo J. L., Tena F., Martı´nez-Lozano J. A., Utrillas M. P. Energy saving and solar energy use in the University of Valencia (Spain) // Renewable Energy. – Elsevier, 2004. – No. 29(5). – P. 675–685. [8] B.K. Nayak, A.Mohapatra, B.Misra; Non Linear I-V Curve Of PV Module: Impacts On MPPT And Parameters Estimation [9] Kinal Kachhiya; MATLAB/Simulink Model of Solar PV Module and MPPT Algorithm. [10] E.M. Natsheh, A. Albarbar. “photovoltaic model with MPP tracker for standalone / grid connected applications”(2010)
Figure 4: Simulated model of PV array with its V-I and PV characteristics
V. CONCLUSION In summary, this paper dealt with the modelling of solar energy conversion through photovoltaic effect. An analytical model presented is constructed under MatlabSimulink and simulated for two effects: varying irradiance and varying temperature. Finally, simulation results show that more irradiance greatly increase the generation of energy while big variation of temperature reduces the current and power produced. This results obtained in form of two fundamental graphs namely power characteristic (power over voltage) and current characteristic (current over voltage) are very similar to empirical results known for solar system and this, further confirms the effectiveness of the proposed model. REFERENCES [1]
Alsayid, B., and Jallad, J. 2011. Modeling and Simulation of Photovoltaic Cells Module Arrays. International Journal of Research and Reviews in Computer Science (IJRRCS). Vol. 2, No. 6, pp. 1327-1331.
International Journal of Electrical & Electronics Engineering
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