IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm A Publisher for Research Motivation........ Email: [email protected]Volume 3, Issue 5, May 2015 ISSN 2321-600X Volume 3, Issue 5, May 2015 Page 1 ABSTRACT In this paper we are modelling a solar based non-conventional energy generation system using MATLAB software. A 500-KW grid connected PV system in a radial 2-bus test system is modeled and simulated using Matlab/Simulink software to study the effects of this technology on the system under different levels of solar irradiation. PV module with a central three level inverter is developed in the thesis, which is more suitable for medium power applications. However, the output of solar arrays varies due to change of solar irradiation and weather conditions. Therefore, the maximum power point tracking algorithm is implemented in DC/DC converter (Boost converter) to enable PV arrays to operate at maximum power point. The widely used MPPT technique, incremental conductance algorithm is employed to control the boost converter. Then the central three level inverter is controlled by decoupled current (Id, Iq) control algorithm and interfaced with the utility grid via the distribution network. Besides, the current control of the inverter is independent of maximum power point control of the DC/DC converter. Finally, system performance and transient responses are analyzed. And system stability is evaluated when solar irradiation change or system fault happens. The system is simulated in MATLAB. Keywords: MPPT, voltage source converter, Boost converter, Inverter, utility grid. 1. INTRODUCTION The need for renewable energy sources is on the rise because of the acute energy crisis in the world today. At present, solar cell (PV) generation is assuming increased importance as a renewable energy sources application because of distinctive advantages such as simplicity of allocation, high dependability, absence of fuel cost, low maintenance and lack of noise and wear due to the absence of moving parts. Many research institutions have dedicated their time to harness the optimum power from it[1]. India plans to produce 20 Gigawatts Solar power by the year 2020, whereas we have only realized less than half a Gigawatt of our potential as of March 2010. Solar energy is a vital untapped resource in a tropical country like ours. The main hindrance for the penetration and reach of solar PV systems is their low efficiency and high capital cost. In case of PV plant, the optimum efficiency is affected mainly by three factors: the efficiency of the PV panel (in commercial PV panels it is between 8-15%[2]), the efficiency of the inverter (95-98%[3]) and the efficiency of the maximum power point tracking (MPPT) algorithm (which is over 98%[4]).Improving the efficiency of panels and inverter is not easy as it depends on the technology availability and expenses, however improving the MPPT algorithm is an inexpensive way. The VSC controller is also used to reduce the Total Harmonic Distortions (THD) and synchronize the inverter output current with the grid voltage, in order to obtain a unitary power factor. 2.THE PHOTOVOLTAIC CELL A simple solar cell consist of solid state p-n junction fabricated from a semiconductor material (usually silicon), when it is exposed to sunlight the photons are absorbed and hole-electron pairs may be formed as shown in figure 1. If these mobile charge carriers reach the vicinity of the junction, the electric field in the depletion region will push the holes into the p-side and push the electrons into the n-side. The p-side accumulates holes and the n-side accumulates electrons, which creates a voltage that can be used to deliver current to a load[5]. If electrical contacts are attached to the top and bottom of the cell, electrons will flow out of the n-side into the connecting wire, through the load and back to the p-side. Since wire cannot conduct holes, it is only the electrons that actually move around the circuit. When they reach the p-side, they recombine with holes completing the circuit. By convention, positive current flows in the direction opposite to electron flow. Modelling, Simulation and Control of Utility Grid Integrated Solar Photovoltaic System Using Matlab Kiran R Patil 1 , Shiddalingesh Akki 2 , Gaurav Nayak 3 , Ashok Muvva 4 ,Basavaraj Totad 5 1 Asst. Professor, BVB college of Engg. & Tech, Hubli 2 Student, BVB college of Engg. & Tech, Hubli
Transcript
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 1
ABSTRACT In this paper we are modelling a solar based non-conventional energy generation system using MATLAB software. A 500-KW grid connected PV system in a radial 2-bus test system is modeled and simulated using Matlab/Simulink software to study the effects of this technology on the system under different levels of solar irradiation. PV module with a central three level inverter is developed in the thesis, which is more suitable for medium power applications. However, the output of solar arrays varies due to change of solar irradiation and weather conditions. Therefore, the maximum power point tracking algorithm is implemented in DC/DC converter (Boost converter) to enable PV arrays to operate at maximum power point. The widely used MPPT technique, incremental conductance algorithm is employed to control the boost converter. Then the central three level inverter is controlled by decoupled current (Id, Iq) control algorithm and interfaced with the utility grid via the distribution network. Besides, the current control of the inverter is independent of maximum power point control of the DC/DC converter. Finally, system performance and transient responses are analyzed. And system stability is evaluated when solar irradiation change or system fault happens. The system is simulated in MATLAB. Keywords: MPPT, voltage source converter, Boost converter, Inverter, utility grid.
1. INTRODUCTION The need for renewable energy sources is on the rise because of the acute energy crisis in the world today. At present, solar cell (PV) generation is assuming increased importance as a renewable energy sources application because of distinctive advantages such as simplicity of allocation, high dependability, absence of fuel cost, low maintenance and lack of noise and wear due to the absence of moving parts. Many research institutions have dedicated their time to harness the optimum power from it[1]. India plans to produce 20 Gigawatts Solar power by the year 2020, whereas we have only realized less than half a Gigawatt of our potential as of March 2010. Solar energy is a vital untapped resource in a tropical country like ours. The main hindrance for the penetration and reach of solar PV systems is their low efficiency and high capital cost. In case of PV plant, the optimum efficiency is affected mainly by three factors: the efficiency of the PV panel (in commercial PV panels it is between 8-15%[2]), the efficiency of the inverter (95-98%[3]) and the efficiency of the maximum power point tracking (MPPT) algorithm (which is over 98%[4]).Improving the efficiency of panels and inverter is not easy as it depends on the technology availability and expenses, however improving the MPPT algorithm is an inexpensive way. The VSC controller is also used to reduce the Total Harmonic Distortions (THD) and synchronize the inverter output current with the grid voltage, in order to obtain a unitary power factor.
2.THE PHOTOVOLTAIC CELL A simple solar cell consist of solid state p-n junction fabricated from a semiconductor material (usually silicon), when it is exposed to sunlight the photons are absorbed and hole-electron pairs may be formed as shown in figure 1. If these mobile charge carriers reach the vicinity of the junction, the electric field in the depletion region will push the holes into the p-side and push the electrons into the n-side. The p-side accumulates holes and the n-side accumulates electrons, which creates a voltage that can be used to deliver current to a load[5]. If electrical contacts are attached to the top and bottom of the cell, electrons will flow out of the n-side into the connecting wire, through the load and back to the p-side. Since wire cannot conduct holes, it is only the electrons that actually move around the circuit. When they reach the p-side, they recombine with holes completing the circuit. By convention, positive current flows in the direction opposite to electron flow.
Modelling, Simulation and Control of Utility Grid Integrated Solar Photovoltaic System Using
1Asst. Professor, BVB college of Engg. & Tech, Hubli
2Student, BVB college of Engg. & Tech, Hubli
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 2
Figure 1 Generic PV cell
3.THE PV CELL MODEL A simple equivalent circuit model for a photovoltaic cell consists of a real diode in parallel with an ideal current source as shown in Figure 2. The ideal current source delivers current in proportion to the solar flux to which it is exposed.
Figure 2 A simple ideal equivalent circuit for a PV cell
The practical model is obtained after considering the following parameters:
Temperature dependence of the diode reserved saturation current Is. Temperature dependence of the photo current Iph. Shunt resistance Rsh, in parallel with the diode, this corresponds to the leakage current to the ground. Series resistance Rs [6](internal losses due to the current flow) which gives a more accurate shape between the
maximum power point and the open circuit voltage.
Figure 3 Practical equivalent circuit of a PV cell
The load current is given by
(1)
Where,
The photo current is given by,
(2)
The diode current is given by,
(3)
The current flowing through the parallel resistance is given
by,
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 3
(4)
The saturation current is given by,
(5)
The reverse saturation current is given by,
(6)
Where k is the Boltzmann constant (1.38 x 10-23 JK-1), q is the electronic charge (1.602 x 10-19 C), T is the cell temperature (K),
n is the diode ideality factor, RS the series resistance (Ω) and RSh is the shunt resistance (Ω). GK is the solar irradiance ratio. Eg is the Band-gap energy of the cell, 1.12eV. NS is the number of cells connected in series. Np is the number of cells connected in parallel. TOP is cell operating temperature, Tref is the cell temperature at 250 c, IS is Diode reversed saturation current, Irs is Diode reversed saturation current at operating temperature.
Figure 4 Simplified diagram of the grid-connected PV system
To provide proper interface between grid-connected PV systems and the utility grid (Figure 4), some conditions must be satisfied, such as phase sequence, frequency and voltage level matching. Providing these conditions strongly depends on the applied power electronics technology of PV inverters. The electric characteristics of a PV unit can generally be expressed in terms of the current-voltage or the power voltage relationships of the cell. The variations in these characteristics directly depend on the irradiance received by the cell and the cell temperature. Therefore, to analyze the dynamic performance of PV systems under different weather conditions, a proper model is required to convert the effect of irradiance and temperature on produced current and voltage of the PV arrays.
4.THE BOOST CONVERTER A boost converter is a dc to dc voltage converter with an output dc voltage greater than input dc voltage. Filters made of capacitor and inductor is used to reduce the ripple in voltage and current respectively, is used at the output stage of the converter[7]. The basic operating principle of the converter consists of the two distinct states. In on state, switch is closed, resulting in an increase in the inductor current. In off state, switch is open, resulting in decrease in the inductor current.
Figure 5 DC-DC Boost Converter
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
So, with variable Duty cycle we can extract constant voltage with maximum power with the help of maximum power point tracking(MPPT).
5.INCREMENTAL CONDUCTANCE MPPT TECHNIQUE The disadvantage of the perturb and observe method to track the peak power under fast varying atmospheric condition is overcome by IC method . The IC can determine that the MPPT has reached the MPP and stop perturbing the operating point. If this condition is not met, the direction in which the MPPT operating point must be perturbed can be calculated using the relationship between dl/dV and –I/V This relationship is derived from the fact that dP/dV is negative when the MPPT is to the right of the MPP and positive when it is to the left of the MPP. This algorithm has advantages over P&O in that it can determine when the MPPT has reached the MPP, where P&O oscillates around the MPP. Also, incremental conductance can track rapidly increasing and decreasing irradiance conditions with higher accuracy than P and O.
Figure 6 Graph Power versus Voltage for IC Algorithm
Fig-6 shows that the slope of the P-V array power curve is zero at The MPP, increasing on the left of the MPP and decreasing on the Right hand side of the MPP. The basic equations of this method are as follows[8].
(8)
(9)
(10) This method exploits the assumption of the ratio of change in output conductance is equal to the negative output Conductance Instantaneous conductance. We have,
P = V I
Applying the chain rule for the derivative of products yields to
∂P/∂V = [∂(VI)]/ ∂V
At MPP, as ∂P/∂V=0
The above equation could be written in terms of array voltage V and array current I as ∂I/∂V = - I/V
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 5
The MPPT regulates the PWM control signal of the DC-DC boost converter until the condition: (∂I/∂V) + (I/V) = 0 is satisfied. In this method the peak power of the module lies at above 98% of its incremental conductance. The Flow chart of incremental conductance MPPT is shown below [9].
Figure 7 IC MPPT algorithm
6.POWER CONTROLLER The controller sense the grid voltage and grid current and give the corresponding grid active and reactive power. And also the power controller sense the inverter output voltage and current and give the corresponding active, reactive power. After that through PI controller we get the direct axis reference current (Idref) which is the one input of another controller which is current controller. Here we also sense the load voltage and load current and determine the RMS value of the load. By using PI controller we can get quadrature axis reference current which is another input of current controller.
7.CURRENT CONTROLLER The current controller mainly used for getting triggering pulse as per the reference value. Here we take the inverter output current and using by MATLAB software converts the current into direct axis and quadrature axis current. This two currents and current given by power controller outputs compared and using PI controller we get the pulse.
8.MATLAB / SIMULINK SIMULATIONS
Figure 8 grid connected PV farm
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 6
Figure 9 Output current from PV panel
Figure 10 Photocurrent, Iph
Figure 11 Shunt current, Ish
Figure 12 Diode current, Id
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 7
Figure 13 Reverse saturation current, Is
Figure 14 Reverse saturation current at Top, Irs
Figure 15 IC MPPT method
Figure 16 VSC Controller
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 8
9.RESULTS
Figure 17 Grid power
Figure 18 Grid voltage
Figure 19 Grid current
Figure 19 Error value produced in IC MPPT
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 9
10.CONCLUSION A MATLAB/SIMULINK model for the 500 KW, 2 radial grid connected PV farm was developed and presented in this paper. This model is based on the fundamental circuit equations of a solar PV cell taking into account the effects of physical and environmental parameters such as the solar radiation and cell temperature. We can use VSC controller to synchronize PV system with grid. As a result of the study, one can from this model as a photovoltaic generator in the framework of the Sim-Power-System MATLAB/SIMULINK toolbox in the field of solar PV power conversion systems. In addition, such a model would provide a tool to predict the behaviour of grid connected PV farm under climate and physical parameters changes.
11.ACKNOWLEDGMENT On the submission of the paper report of “MODELLING, SIMULATION AND CONTROL OF UTILITY GRID INTEGRATED SOLAR PHOTOVOLTAIC SYSTEM USING MATLAB” We would like to extend our gratitude and sincere thanks to our mentor Professor H.N.Siddrameshwar and supervisor Asst. Professor Kiran.R.Patil, for their constant motivation and support during the course of our paper. We truly appreciate and value their esteemed guidance and encouragement from the beginning to the end of this paper.
References [1] Sustainable Energy for All http://www.sustainableenergyforall.org [2] “Trends in photovoltaic applications. Survey report of selected IEA countries between 1992 and 2009”,
International Energy Agency, Report IEA-PVPS Task 1 T1-19:2010, 2010. [3] “Sunny Family 2010/2011 - the Future of Solar Technology”,SMA product catalogue,2010. [4] L. Piegari, R. Rizzo, "Adaptive perturb and observe algorithm for photovoltaic maximum power point tracking,"
Renewable Power Generation, IET, vol. 4, no. 4, pp. 317-328, July 2010. [5] Gilbert M. Masters, “Renewable and Efficient Electric Power Systems”. [6] Francisco M. González-Longat - 2do congreso iberoamericano de estudiantes de ingeniería eléctrica, electrónica y
computación, “Model of Photovoltaic Module in Matlab” (II CIBELEC 2005). [7] Daniel.W.Hart, “Power electronics”. [8] Azadeh Safari and Saad Mekhilef, Member, IEEE ,‟ Simulation and Hardware Implementation of Incremental
Conductance MPPT With DirectControl Method Using Cuk Converter”. [9] M.Lokanadham,PG Student, K.Vijaya Bhaskar,Asst. Professor,” Incremental Conductance Based Maximum Power
Point Tracking (MPPT) for Photovoltaic System” M.Lokanadham, K.Vijaya Bhaskar / International Journal of Engineering Research and Applications (IJERA) ISSN:2248-96.
AUTHORS Kiran R Patil received the B.E. degree in Electrical and Electronics Engineering from The National Institute of Engineering, Mysore and M.Tech. degree in Energy Systems & Management from Sri Jayachamarajendra College of Engineering, Mysore, Karnataka. He is currently perceiving Ph.D in BVBCET affiliated to VTU, Belgaum. His areas of interest are Distributed Generations, Non-conventional energy systems and Energy Auditing.. He is currently working as Asst. professor
in BVB College of Engineering & Technology, Hubli, Karnataka.
Shiddalingesh Akki is perceiving B.E. degree in Electrical and Electronics Engineering in BVB College of Engineering & Technology, Hubli, Karnataka and his areas of interests are Non-conventional energy systems and power Electronics. Gaurav Nayak is perceiving B.E. degree in Electrical and Electronics Engineering in BVB College of Engineering & Technology, Hubli, Karnataka.
Ashok Muvva is perceiving B.E. degree in Electrical and Electronics Engineering in BVB College of Engineering & Technology, Hubli, Karnataka.
IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm
A Publisher for Research Motivation........ Email: [email protected] Volume 3, Issue 5, May 2015 ISSN 2321-600X
Volume 3, Issue 5, May 2015 Page 10
Basavaraj Totad is perceiving B.E. degree in Electrical and Electronics Engineering in BVB College of Engineering & Technology, Hubli, Karnataka.
