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COMPARISON OF HONEY COMB AND BRIDGE LINK TYPE CONFIGURATION OF SOLAR PHOTOVOLTAIC ARRAY UNDER PARTIAL SHADING CONDITIONS Mohd.Faisal Jalil1 Assistant Professor Department of Electrical &Electronics Engineering KIET,Ghaziabad 1 Abstract--- The performance of the photovoltaic (PV) array depends upon the temperature, solar radiation, shading and array configuration. The PV array gets shadowed completely or partially by building, electric pole, tower, tree and clouds. Partial shading of the PV array affects the generating power compare to the PV array with uniform insolation. The losses due to partial shading of the PV array depend upon the shading pattern of the PV array. This paper presents a MATLAB based modeling and simulation of the PV arrays its analysis under partial shading condition for honey comb and bridge link array configuration. A versatile model using MATLAB/SIMULINK is developed which represents different array configuration under partial shading conditions, The maximum power point is effected by the type of connection of the PV array for the same shading pattern of the PV array. Keywordsβ Array, circuit, equivalent, model, modeling, photovoltaic, PV, simulation, MMP. Santosh Kumar Shakya2, Vishal Kumar3, Popindar Prajapati4 234 Department of Electrical &Electronics Engineering KIET,Ghaziabad simulators [1β3]. In order to study electronic converters for PV systems, one first needs to know how to model the PV device that is attached to the converter. PV devices present a non-linear V-I characteristic with several parameters that need to be accommodate from experimental data of practical devices. The mathematical model of the PV device may be useful in the study of the dynamic analysis of converters, in the study of Maximum power point (MPPT) algorithms, and mainly to simulate the PV system and its components using circuit simulators. II. LITERATURE REVIEW A maximum power point tracking algorithm is conclusively necessary to increase the efficiency of the solar panel as it has been found that only 30-40% of energy incident is converted into electrical energy. I. INTRODUCTION Among all the MPPT methods, Perturb & Observe and Incremental Conductance are most commonly used because of their simple implementation and lesser time to The first step to study about an appropriate control method in photovoltaic systems is to know how to model and simulate a PV system attached to the converter and power grid. Commonly, PV systems present non-linear PowerVoltage and Current-Voltage characteristics which tightly depend on the receiving irradiance levels and climate conditions. The mathematical model of the photovoltaic system is significantly valuable for studying the maximum power point algorithms, doing research about the dynamic performance of converters, and also for simulating photovoltaic components by using circuit track the maximum power point and also other profitable reasons. Under abruptly changing weather conditions (irradiation level) as MPP changes progressively, P&O takes it as a change in MPP due to perturbation rather than that of irradiation and sometimes ends up in calculating erroneous MPP[7]. However this problem is ousted in Incremental Conductance method as the algorithm takes two samples of voltage and current to compute MPP. However, instead of more efficiency the ramification of the algorithm is very high as compared to the former one and hence the cost of execution increases. So we have to extenuate with a trade-off between complexity and efficiency. It has been examined that the efficiency of the system also relies upon the converter. Generally, it is maximum for a buck analysis, then for buck-boost analysis and minimum for a boost analysis. When more than one solar modules are connected in parallel, another analog technique which is known as TEODI is also very efficient which operates on the principle of equalization of output operating points in correspondence to force displacement of input operating Fig1. Single-diode model of the theoretical photovoltaic cell and equivalent circuit of a practical photovoltaic device including a series and parallel resistance points of the identical operating system. It is very rudimentary to carry out and has high efficiency both under stationary and time varying climatic conditions [8]. . III. MODELING OF PHOTOVOLTAIC ARRAY Fig2. I-V characteristics of photovoltaic cell. The net cell current I is composed of the light generated current πΌππ£ and diode current πΌπ A. Ideal photovoltaic cell The fundamental equation from the theory of semiconductors [1] that mathematically describes the I -V characteristic of the ideal photovoltaic cell is: ππ πΌ = πΌππ£,ππππ β πΌπ,ππππ [ππ₯π { β 1}] (1) πππ where Ipv,cell -- the current developed by the incident light (it is directly proportional to the Sun irradiation), Id -- the Shockley diode equation, I0,cell [A] is the reverse saturation or leakage current of the diode [A], q -- the electron charge [1.60217646 · 10β19C], k -- the Boltzmann constant [1.3806503 · 10β23J/K], T [K] -- the temperature of the p-n junction, and a is the diode ideality constant. Fig3. Characteristic I -V curve of a practical photovoltaic device and the three remarkable points: short circuit (0, Isc), maximum power point (Vmp, Imp) and open-circuit (Voc, 0). B. Modeling the photovoltaic array The fundamental equation (1) of the rudimentary photovoltaic cell does not represent the I -V characteristic of a practical photovoltaic array. Practical arrays are constituted of several connected photovoltaic cells and the examination of the characteristics at the terminals of the photovoltaic array requires the incorporation of additional parameters to the basic equation [1]: πΌ = πΌππ£ β πΌ0 [ππ₯π ( π+π π πΌ ππ‘ π β 1)] β π+π π πΌ π π (2) Where Ipv and Io are the photovoltaic and saturation π ππ currents of the array and ππ‘ = π β4 is the thermal voltage of the array with Ns cells connected in series .Cells connected in parallel increase the current and cells connected in series give the voltages. If the array is constituted of Np parallel connections of cells the photovoltaic and saturation current may be expressed as πΌππ£ = πΌππ£,ππππ . ππ , πΌ0 = πΌ0,ππππ ππ . Eq. (2) characterizes the single-diode model presented in Fig.1. Some Researchers have distinguished more sophisticated models that present better accuracy and serve for different purposes [2]-[6]. For simplicity, this paper explains the single-diode model. The simplicity of the single-diode model with the method for adjusting the parameters and the improvements suggested in this paper gives better accuracy and give the characteristics similar to the better model which is two diode models in which two diodes are represented instead of one for better accuracy. Manufacturers of photovoltaic arrays, give only a few experimental data about electrical and thermal characteristics. All Manufacturers gives only following information which are the nominal open-circuit voltage Voc,n, the nominal short-circuit current Isc,n, the voltage at the maximum power point Vmp, the current at the maximum power point Imp, the open-circuit voltage/temperature coefficient Kv, the short-circuit current/temperature coefficient Ki , and the maximum experimental peak output power Pmax,e. This information is always given with reference to the nominal or standard test conditions (STC) of temperature and solar irradiation. Some manufacturers give additional information like I-V characteristics and some other information. The practical photovoltaic device presents an hybrid behaviour, which may be of current or voltage source depend on situation. The practical photovoltaic device has a series resistance Rs whose impact is stronger when the device operates in the voltage source region and a parallel resistance Rp with stronger impact in the current source region of operation [9]-[15]. The Rs resistance is the sum of several architectural resistances of the device. The Rp resistance exists mainly due to the leakage current of the pn junction. The I-V characteristic of the photovoltaic device rely upon the internal characteristics of the device (Rs, Rp) and on external impacts such as irradiation level, temperature and shading. The output of the PV array is directly rely upon the sun radiations.. Datasheets only tell the nominal short-circuit current (Isc,n, maximum current available at the terminals of the practical device). The assumption Isc β Ipv is commonly used in photovoltaic models because in practical devices the series resistance is low and the parallel resistance is high [8]-]12], [14]-[17], [18]. The output current of the photovoltaic cell rely upon linearly on the solar radiation and is also effected by the temperature according to the following equation: Ipv = (Ipv,n + K I βT) G (3) Gn Where Ipv,n [A] -- the light-generated current at the nominal condition (usually 25 β¦C and 1000W/m2 ), βT = T β Tn (being T and Tn the actual and nominal temperatures [K]), G [W/m2 ] -- the irradiation on the device surface, and Gn is the nominal irradiation. The diode saturation current Io and its dependence on the temperature may be expressed by (4): Tn 3 qEg I0 = I0,n exp ( ) [ T ak ]( 1 Tn 1 β ) T (4) where Eg -- the band gap energy of the semiconductor (Eg β 1.12 eV for the polycrystalline Si at 25 β¦C), and Io,n -- the nominal saturation current: Io,n = Isc,n Voc,n )β1 aVt,n exp( (5) Vt,n -- the thermal voltage of Ns series-connected cells at the nominal temperature Tn. The saturation current Io of the photovoltaic cells rely upon the saturation current density of the semiconductor (Jo, generally given in [A/cm2 ]). The current density Jo relies upon the characteristics of the photovoltaic cell, which depend on physical parameters such as the coefficient of diffusion of electrons in the semiconductor, the intrinsic carrier density, and others [2]-[5]. the nominal saturation current Io,n is indirectly retrieved from the data through , which is obtained by calculating (2) at the nominal open-circuit condition, with V = Voc,n,I = 0, and Ipv β Isc,n. The value of the diode constant a may be assumed usually 1 β€ a β€ 1.5 or given by manufacturer. This constant affects the curvature of the I-V characteristic and varying a can slightly raises the model accuracy. C.Model improvement:The photovoltaic model explained in the previous section can be improved if equation (5) is replaced by: πΌ0 = πΌπ π,π+πΎπΌ βπ ππ₯π( (6) πππ,π +πΎπ βπ )β1 πππ‘ This adjustment aims to match the open-circuit voltages of the model with the experimental data for a very large range of temperatures. Eq. (6) is obtained from (5) by including in the equation the current and voltage coefficients Kv and Ki. The validity of the model with this equation has been tested through computer simulation and through comparison with experimental data. The open-circuit voltages of the model are equated with the open-circuit voltages of the real array in the range Tn < T < Tmax. By equalling (4) and (6) and solving for Eg at T = Tmax one gets: πΈπ = βππ [ 3 πΌπ π,ππππ₯ π )( π ) ππππππππ₯ πΌ0π ππππ₯ ππ .π ππ₯π( ππ πππ₯ )β1 π(ππ βππππ₯ ) πππ πππππ₯ ( ] . The model established in the preceding sections may be further improved by taking advantage of the iterative solution of Rs and Rp. Each iteration updates Rs and Rp towards the best model solution, so equation (10) may be concluded in the model. π°ππ,π = πΉπ +πΉπ πΉπ π°ππ,π (10) Eq. (10) uses the resistances Rs and Rp to examine Ipv , Isc. πΉπ,πππ = π½ππ π°ππ,πβπ°ππ β π½ππ,πβπ½ππ π°ππ (11) Parameters of the adjusted model of the KC200GT solar array at 25 °C, 1.5AM, 1000 W/m2 :(7) Where Imp 7.61A Vmp 26.3 V Pmax,e 200.000143 W D. Model adjustment: Isc 8.21A There are two parameters which are yet remain unknown are Rs and Rp. To adjusting Rs and Rp based on the fact that there is an only pair {Rs,Rp} that warranties that Pmax,m = Pmax,e = VmpImp at the (Vmp, Imp) point of the I-V curve, and solving the resulting equation for Rs, as (8) and (9) show [6],[8]. Voc 32.9V Io,n 9.825*ππβπ A Ipv 8.214 A A 1.3 Rp 415.405Ὠ Rs 0.221Ὠ K1 0.0032 A/K Kv -0.1230 V/K πΌπ π,ππππ₯ = πΌπ π,π + πΎπΌ β π πππ πππ,ππππ₯ = πππ,π + πΎπ β π , π€ππ‘β β π = ππππ₯ β ππ . π·πππ,π = π½ππ {π°ππ β π°π [πππ ( π½ππ +πΉπ π°ππ πΉπ πΉπ = π½ππ ( π ππ» . π½ππ +πΉπ π°ππ } = π·πππ,π ππ΅π ) β π] β (8) π½ππ +π°ππ πΉπ π½ππ +π°ππ πΉπ π {π½ππ π°ππ βπ½ππ π°π πππ[ . ]+π½ππ π°π βπ·πππ,π } π΅π π ππ» ) (9) Eq. (9) means that for any value of Rs there will be a value of Rp that forms the mathematical I-V curve cross the experiment (Vmp,Imp) point. IV.MATLAB MODELING & SIMULATION E.Further model improvement: The I-V curves of the Solarex MSX60 solar panel simulated with the MATLAB/SIMULINK and PSIM circuits. with partial shading condition and without Bypass diode. In this paper we are showing only two type of connections which are Bridge Link, Honey Comb with two different types of shading one is row wise and second is column wise to show the comparison between the MPP for both the connections. Fig.6 BL connection under row wise shading Fig.4 Basic Simulink model of Photovoltaic array system Fig.7 HC connection under row wisel shading Fig.5 Graph between V and Ipv for basic model The above fig shows output only for one module. Below figs shows the two types of Photovoltaic array connection Fig.8 difference among the different connection under row wise shading Fig.10 I-V and P-V characteristics under shading with Bypass diode Fig.9 difference among the different connection under REFERENCES column wise shading V. CONCLUSION This paper shows the different types of connections of photovoltaic array with two different types of shading which are row-wise shading and column-wise shading. After analyzing the row-wise shading for all the four types of connection it is concluded that the MPP is more efficient in BL connection than HP connection. The descending order of the MPP for all the connection with row-wise shading is :HC > BL But while analyzing the column wise shading the order of the MPP found is different .The order is in that type of shading is:BL > HC From the above two statement it is concluded that the MPP is depend on the different types of shading and connections. 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