Design and Simulation of Grid Connected PV System

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1 Design and Simulation of Grid Connected PV System Vipul C.Rajyaguru Asst. Prof. I.C. Department, Govt. Engg. College Rajkot, Gujarat, India Abstract: In this paper, a MATLAB based simulation of Grid connected PV system is presented. The main components of this simulation are PV solar panel, Boost converter; Maximum Power Point Tracking System (MPPT) and Grid Connected PV inverter with closed loop control system is designed and simulated. A simulation studies is carried out in different solar radiation level. Keywords: PV Solar Panel, Boost Converter, MPPT, PWM Inverter. INTRODUCTION The continuous use of fossil fuels has significantly affected the environment and caused of pollution and global warming. To fulfill the increasing demand of energy in daily life, renewable based energy resources widely used in the last several years. Among them, Photovoltaic (PV) Solar Energy is widely useful because it is pollution free, maintenance free and abounded in nature [1]. In PV Solar System, PV Solar cell converts the sunlight into the electricity by the photovoltaic effect. PV Solar Panels are used in many applications, such as, battery chargers, solar powered water pumping systems, grid connected PV systems, solar hybrid vehicles and satellites. Photovoltaic (PV) devices and storage battery sources produce low voltages, so a dc dc boost converter is generally required to adapt the voltage level for the grid-connected inverter. This dc dc converter, in addition to boosting, also regulates the inverter input voltage and sometimes isolates the low- and highvoltage circuits [2]. A Generalized Block Diagram of Grid connected PV System is shown in Figure 1. PV Solar cells are made from crystalline silicon which is connected series and parallel combination to form PV solar panels. And connection of PV solar Panels in series and parallel are form a PV solar array [3]. The PV solar array generates the DC Power which are varies with solar radiation level, In the morning and late evening periods, the solar radiation level is low, due to that the output power of PV solar panel is lower than rated level and during noon, the output power is maximum due to presence of higher solar radiation level. To harvests maximum power, Maximum Power Point Tracking (MPPT) System is used [4][5]. The output DC power is converted into the AC form, PWM based Inverter is used in practice. The design and Simulation of each component are presented in next section. 192 Vipul C.Rajyaguru Figure 1. Block Diagram of Grid Connected PV System

2 MATHEMATICAL MODELING OF PV SOLAR CELL A photovoltaic Panel consists of a number of photovoltaic cells connected in series and parallel configuration. It is important to understand the operation of a single photovoltaic cell, and then the operation of the module under different conditions is easier to understand. An ideal photovoltaic cell consists of a current source and a diode. An ideal model of a photovoltaic cell has an additional shunt resistance connected parallel to the diode and a series resistance is shown in the Figure 2. Figure 2. Equivalent circuit of PV Solar Cell. The basic equation from the theory of semiconductors [6] that mathematically describes the I V characteristic of the ideal PV cell is: I = I ph I d..... (1) I = I ph I o exp qv kt 1 (2) I = I ph I o exp qv +IRs nkt 1... (3) Where: Iph=photo generated current, Io=reverse saturation current, V= terminal voltage, q is the electron charge, k is Boltzmann constant ( J/K) and T is the junction temperature in Kelvin (K) and n is the diode ideality factor In order to model the solar panel accurately we can use two diode model but in this project our scope of study is limited to the single diode model. BOOST CONVERTER DC-to-DC power converter whose output voltage is greater than its input voltage is known as step-up converter or boost converter. Boost converter shown in Figure 3. To reduce the output voltage ripple a capacitor filter) is added at the output of converter. DC sources like batteries, solar panels, rectifiers or DC generators can be used to power the boost converter. DC to DC conversion is the process of changing one voltage to other voltage. A converter with an output DC voltage greater than source DC voltage is known as boost converter or step-up converter. Since power must be conserved, the output current is lower than the source current [7]. 193 Vipul C.Rajyaguru

3 Figure 3. Schematic Diagram of Boost Converter. Design Parameters of Boost Converter: The parameters involved in the design of boost converters are shown below: Vo = L = C = Vs 1 K K 1 K R 2f K 2fR (4). (5). (6) Where V0 = output voltage, Vs = input voltage, K= duty cycle = Ton/T, f = switching frequency (Hz). MAXIMUM POWER POINT TRACKING SYSTEM (MPPT) Maximum Power Point Tracking, frequently referred to as MPPT, operates Solar PV modules in a manner that allows the modules to produce all the power they are capable of generating. MPPT is not a mechanical tracking system but it works on a particular tracking algorithm and it based on a control system. The voltage at which PV module can produce maximum power is called maximum power point Maximum power varies with solar radiation, ambient temperature and solar cell temperature. In MPPT model Vpv voltage and Ipv current taken by PV panel. These voltage and current connect a filter block, after filtering voltage will change Vn and Vb, after filtering current will change In and Ib. The power Pn=Vn*In and Pb=Vb*Ib will obtained, difference of this power is ΔP =Pn-Pb and difference between Vn-Vb is ΔV. This signal is compare to threshold switch. In this signal obtained duty cycle of the converter. This duty cycle is compare to 10KHz frequency carrier wave and obtained PWM based duty cycle [8]. P =V*I.(7) Differencing the eq. 7 gives: dp/dv =dvi. (8) In condition of zero slope of PV curve where: dp/dv = 0.(9) We have di/dv= -I/V..(10) When, di/dv< -I/V the voltage must be reduced in order to achieve MPP operation. When di/dv> -I/Vthe voltage must be raised in order to achieve the maximum power point of the PV generation. In the case of grid-connected PV system, different inverter topologies and controllers are usually used for interfacing the PV modules and the utility grid. The IGBT based three phase full bridge inverter topology is the most widely used configuration in three phase systems [9]. 194 Vipul C.Rajyaguru

4 SIMULATION AND RESULTS This section represents the MATLAB based simulation of Grid connected PV system. A parameters used for this simulation is shown in the Table 1. Parameters of solar array at STC I mp 5.58A V mp 54.7V P max W I sc 5.96A V oc 64.2V I pv R sh 6A 270Ω R se 0.37Ω PV Array Nss= 5, Npp = 66 Solar Radiation (G) 1000 W/m 2 Temperature (T) 298K Parameters of Boost Converter Input Voltage (V in ) 250V Output Voltage (V out ) 500V Duty Cycle (D) 0.5 L in 13mH C in 100µF Parameters of PV Inverter DC Link Voltage Switching Frequency Filter Inductance DC Link Capacitor 500V 10kHz 25mH 29mF 195 Vipul C.Rajyaguru MVA Rating Transformation Ratio Grid Voltage Grid Frequency PV Interfacing Transformer Table 1. Simulation Parameters 100 kva 260/25kV 25kV 50 Hz The Grid connected PV system of the rating of 100kW is connected with 25kV Grid is simulated in MATLAB shown in Figure 4.

5 Figure 4. Simulation of Grid Connected PV System. The I-V and P-V characteristics of Simulated PV panel in different solar radiation level are depicted in Figure 5 and Figure 6, respectively. From this characteristic it can be notice that the Output of PV solar farm is varies with the different solar radiation level. Figure 5. I-V Characteristic of Simulated PV Panel in Different Solar radiation. Figure 6. P-V Characteristic of Simulated PV Panel in Different Solar radiation. 196 Vipul C.Rajyaguru

6 Figure 7. Output Power of PV Solar Farm. Figure 8. Grid Voltage Waveform. 197 Vipul C.Rajyaguru Figure 8. Output Current of PV Solar Farm.

7 CONCLUSION: In this Paper, The Grid connected PV Solar Farm is simulated in MATLAB Environment. The design of the system is carried out for feeding 100KW power to the grid The Inverter is controlled in order to feed active power to the grid. The output of PV Solar arrays is depends on the Level of Solar radiation. In higher solar radiation level, the output of PV Array is Maximum. REFERENCES: [1] Renewables 2015 global status report, by REN21, the Renewable Energy Policy Network for the 21st Century. [2] Rong-Jong Wai, and Wen-Hung Wang (2008) "Grid-Connected Photovoltaic Generation System" IEEE Transactions on Circuits and Systems, Vol. 55, No. 3, pp [3] A. Yazdani and R. Iravani, Voltage-Sourced Converters in Power Systems- Modeling, Control and Applications, IEEE Press, John Wiley & Sons Inc. Publications [4] Niraj Solanki, Jatinkumar Patel. Photovoltaic Solar Farms Operating in VAR Mode: A Review. Journal of Power Electronics and Power Systems. 2016; 6(1): [5] Robins Anto, Josna Jose, Performance Analysis Of A 100kW Solar Photovoltaic Power Plant, International Conference on Magnetics, Machines & Drives (AICERA-2014 icmmd), July [6] M. G. Villalva, J. R. Gazoli, and E. R. Filho, "Comprehensive approach to modeling and simulation of photovoltaic arrays," IEEE Trans. Power Electron., vol. 24, no. 5, pp , May [7] Muhammad H. Rashid, power electronics handbook, devices, circuits, and applications. Academic Press is an imprint of Elsevier, [8] H. Desai and H. Patel, "Maximum power point algorithm in PV generation: An overview", Proc. 7th Int. Conf. Power Electron. Drive Syst., Nov. 2007, pp [9] A. D. Rajapakse and D. Muthumuni, "Simulation Tools for Photovoltaic System Grid Integration Studies," IEEE Electric Power & Energy Conference (EPEC), pp Vipul C.Rajyaguru

Single Stage Grid Interactive Photovoltaic System

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