A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015
*1(Sinhgad Institute of Technology, Lonavala. Electrical Engineering Department)
*2(Sinhgad Institute of Technology, Lonavala. Electrical Engineering Department) dhanashree.shinde108@gmail.com*1,avt.sit@sinhgad.edu*2
Abstract
The grid integration of renewable energies is more and more influencing the short circuit capacity
(SCC) of power systems through the world. The performance of renewable energy sources, e.g. w ind and solar energy, is d ifferent from that of classical synchronous generators during symmetrical or unsymmetrical short circuits. The r esponse of renewable energy generation units to short circuits is more or less convenient by the power electronics used in the converter system and the corresponding control algorithms. These differences have to be considered during planning grid extensions by the power system operator and designing protective or security functions for the network and its compon ents. In this paper describe the short circuit current contribution of a photovoltaic power plant. For photovoltaic system connected to a medium voltage power sy stem, three different short circuit faults scenarios (single-phase-toground, phase-to-phase and three-phase faults) and the corresponding short circuit current contribution of the power plant were calculated and the results illustrated and discussed. status quo. The fast control of the power electronics in wind and photovoltaic power conversion systems has the capability to control the current injection during balanced as well as unbalanced grid faults.
Large scale photovoltaic (PV) systems are one part of the efforts to increase the share of renewable energy sources in the energy hybrid. Different configurations are available to feed in power to the grid. In Germany the majority of existing photovoltaic systems are installed in households and are connected to the low voltage level with string or multi string inverters. By contrast large scale PV units are connected to the medium or even to the high voltage network using central inverters.
In this paper describe the behavior of a photovoltaic power plant equipped with central inverters during different types of short circuits. The next chapter explains the currently applicable performance in A R DIGITECH regarding the behavior during short circuits. In the next chapter the control of a three-phase photovoltaic central inverter system is derived in detail. Also the structure of the test power system is illustrated and explained and
Key Words
Photovoltaic (PV), Inverter, Control,
Short Circuit Current (SCC), Unbalanced Current
(UC).
Published
the fault scenarios are introduced. Hereby the different grid faults (single-line-to-ground fault, two-phase fault and three-phase fault) and the response of the PV power some concluding remarks. plant and grid are described, and this is followed by
The objective of the project is to analyze the fault current contribution in Grid connected Renewable
Nowadays, energy and environmental crises have energy sources. In this paper solar energy is taken as a become one of the main issues around the world. In renewable energy source response to energy requirements and environmental concerns, renewable technologies are considered the
future energy technologies. Renewable energy is harvested from nature. Also, it is clean and free. The short circuit current in power systems is still dominated by classical synchronous generators of conventional large scale coal or nuclear power plants. As a result of the ever increasing share of renewable energy sources the short circuit current in the future will differ from the
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A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015
Fig.1.Proposed system for analysis
The electrical behaviour of PV application basically depends on the control of the inverter system. Large scale PV power plants are equipped with a certain amount of central inverter systems. In this case study a test PV power plant with a nominal power of 3 MW equipped with 30 inverters and the corresponding PV array was simulated. Each inverter has a nominal power of 100 kW operating at the nominal voltage of 270 V and a nominal current of 214 A. For linking these medium voltage (MV) level of 20 kV a three winding transformer is used. The primary winding of the transformer is delta connected while the secondary and tertiary is star connected. The total nominal apparent power of each transformer is 1.25 MVA while the short circuit impedance between the primary to secondary and primary to tertiary windings are both 0.12 p.u. Core
Published simulation study but may influence the behaviour during faults). Five inverters are connected in parallel to one low voltage terminal of the step up transformer. This means that the nominal total current in the secondary and tertiary windings is roughly 1 kA.
The MV windings of the transformers are connected via a bus bar to the MV power system. The star point of the
MV power system is directly grounded which has to be taken into account during unbalanced earth fault scenarios. Fig.1 illustrates the schematic arrangement of the PV power plant.
Photo
means light and voltaic
means voltage producer or Voltas is one of the scientist related to
Electricity. So Photo Voltaic is nothing but Light
Electricity. PV cell convert light energy into electricity.
PV cell is basic building block of PV generating unit.
PV cells come in various sizes ranging from
10mmX10mm to 100mm X100mm, the most common size being 100mmX100mm cells. A single PV cell generates about 1 to 2 watts of electricity; an amount that is quite insignificant compared to what is required by most electrical equipment. Photovoltaic (PV) sources are used today in many applications as they have the advantages of effective maintenance and pollution free. One of the important applications of the solar PV based power generation is to feed the generated power into grid. So it is the supplementary energy generation for hydro-electric energy generation.
Two or more PV Cells are built to produce a
PV Module to provide higher wattages as required.
Photovoltaic’s (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that demonstrate the photovoltaic effect. Photovoltaic power generation employs solar panels collected of a number of solar cells containing a photovoltaic material.
It consists of number of components, including the photovoltaic modules, mechanical and electrical connections and mountings and means of regulating and or modifying the electrical output using the Sun as the power source.
Photovoltaic Cell
PV cells are prepared of semiconductor materials, such as silicon. For solar cells a thin semiconductor wafer is especially treated to form an electric field, positive on one side and negative on the other side. When light energy fall on the solar cell, electrons got loose from the atoms in the semiconductor material. If good electrical conductors are attached to the positive and negative sides, making an electrical circuit and the electrons can be captured in the form of an electric current - that is, electricity. Then this electricity can be used to power a load. A PV cell can
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A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015 either be circular or square in constructional configuration. is very small. Rp is the equivalent shunt resistance which has a very high value.
Photovoltaic Module
Applying Kirchoff’s law to the node where Rs, Rp,
Due to the low voltage generated in a PV cell
(around 0.5V), several PV cells are connected in series
(for high voltage) and in parallel(for high current) to form a PV module for required output. Separate diodes might be needed to avoid reverse currents in case of diode and Iph meet, we get
Iph = ID + IRp + I (1)
We get the below equation for the photovoltaic current:
I =Iph-IRp-ID (2)
=
+ .
− 1] partial or entire shading, and at night. The p-n junctions of mono-crystalline silicon cells may have adequate
−
+ .
(3) reverse current characteristics these are not necessary.
Where, Iph is the Insolation current
Reverse currents dissipate power and also lead to
I is Cell current overheating of shaded cells. Solar cells develop into
I0 is the Reverse saturation current less efficient at higher temperatures and installers try to
V is the Cell voltage provide good ventilation behind solar panels.
Rs is the Series resistance
Photovoltaic Array
Rp is the Parallel resistance
VT is the Thermal voltage (V )
The power that one module can produce is not
K is the Boltzman constant sufficient to meet up the requirements of home or
T is the Temperature in Kelvin business. Mainly PV arrays use an inverter to convert q is the Charge of an electron. the DC power into alternating current that can power the motors, loads, lights and other required applications
Modeling of PV Array: etc. The modules in a PV array are usually first
The building block of PV arrays is the solar cell, connected in series to obtain the desired voltages; the in A R DIGITECH allow the system to produce more current. which is basically a p-n junction that directly converts light energy into electricity: it has a equivalent circuit as shown below in Figure 3
Characteristics of PV Cell
Published
Fig 2: Equivalent circuit of a PV cell
An ideal is modeled by a current source connected in parallel with a diode. However no solar cell is ideal and so shunt and series resistances are added to the model as shown in the PV cell diagram above. Rs is the intrinsic series resistance whose value
Fig 3 Equivalent circuit of a PV cell
The current source I ph
represents the cell photo current; Rj is used to represent the non-linear impedance of the p-n junction; R sh
and R s
are used to represent the intrinsic series and shunt resistance of the cell respectively. Generally the value of R sh
is very large and that of R s
is very small, hence they may be ignored to simplify the analysis. PV cells are connected in larger units called PV modules which are further
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A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015 interconnected in series-parallel configuration to form
PV arrays or PV generators.
Mathematical model of PV used to simplify our PV array is represented by the equation:
= − ( ∗ − 1 ] (4)
Where, I is the PV array output current; V is the PV array output voltage; ns is the number of cells in series and np is the number of cells in parallel; q is the charge of an electron; k is the Boltzmann’s constant; A is the p-n junction ideality factor; T is the cell temperature
(K); I rs
is the cell reverse saturation current. The factor
A in equation (4) determines the cell deviation from the ideal p n junction characteristics; it ranges between 1-5 but for our case A=2.46. The cell reverse saturation current I rs
changes with temperature according to the following equation:
=
1
−
1
(5)
Fig 4 Modelling of PV array
The aim of this project is to improve power quality and system efficiency, a double tuned resonant circuit is studied to attenuate the second and fourth order harmonics at the inverter dc side. Carrier based
PWM Technique is analyzed to generate switching pattern for the IGBT switch of CSI. Where, T r
is cell reference temperature, I rr
is cell reverse saturation temperature at T r
and EG is band gap of the semiconductor used in the cell.
The energy gap of the semiconductor is depends on temperature and this dependence is given by: in A R DIGITECH
= (0) −
+
(6)
The photo current depends on the solar radiation and cell temperature as follows:
= + ( − )] (7)
Where I scr
100
Published temperature and radiation, K i
is the short circuit current temperature coefficient, and S is solar radiation in mW/cm2. The PV power can be given by equation (8) as follows:
= = ∗ – 1 (8)
Fig 5: Basic inverter modelling
The current fed bridge inverter with a parallel resonant load is taken for analysis. In above circuit the inductance L dc is so large that input current remains constant and a square-wave current is impressed on the resonant-load circuit. The load voltage is nearly sinusoidal. The IGBT switch are turned off by the reactive power supplied by the load itself, provided the inverter operating frequency is equal to the resonance frequency of the load. In this circuit no separate turn-off arrangement is required.
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A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015
Solar Insolation (irradiation)
Solar temperature
1000w/
25
°
Table1: Description and parameter of solar cell
Fig 7: I-V curve of designed PV system
in A R DIGITECH
Published
Solar Cell
ITEM VALUE
Open circuit voltage of one cell
(Voc)
Short circuit current of one cell
(
)
0.5(V)
3.75(A)
PV system open circuit voltage
(Voc)
PV system Short circuit current
( )
Rated output power (Pout)
80(V)
15 (A)
800 watt
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A R DIGITECH
International Journal Of Engineering, Education And Technology (ARDIJEET) www.ardigitech.in
ISSN 2320-883X,VOLUME 3 ISSUE 2 ,01/04/2015 effects of a possible controlled negative sequence current injection of generation units on the power system is the subject of current investigation and the results will appear in future publications.
[1] Hongrae Kim, Babak Parkhideh, Tim D. Bongers, and Heng Gao
“Reconfigurable Solar Converter: A Single-Stage Power Conversion
PV-Battery System,”
IEEE Trans. Power Electron., vol. 28, no. 8,
Aug . 2013.
[4] Kuo-Ching Tseng, Chi-Chih Huang, and Wei-Yuan Shih, “A High
Step-Up Converter With a Voltage Multiplier Module for a
Photovoltaic System,”
IEEE Trans. Power Electron., vol. 28, no.6, pp. 3047-3051, June 2013.
[5] Tomáš Sko č il, Manuel Pérez Donsión, “Mathematical Modeling and Simulation of Photovoltaic Array,”
IEE Proc., Electr. Power
Appl., vol.151, no. 4, pp. 467–476, 2004.
Fig 8: Simulation results for various faults
This paper has presented simulation results of the short circuit current contribution of a PV power plant to the MV power system under different fault contions. Due to the fast response of inverter control systems the performance of large scale PV applications is controllable even during the
Published injection of PV and other renewable energy generation units differ from the response of synchronous generators considering the peak currents as well as the steady state fault current.
These days the positive sequence voltage support due to the injection of positive sequence reactive current has the control priority. Also nowadays the negative sequence current and the positive sequence active current is generally concealed to zero by the inverter control. Regarding the control algorithms of the protection components in the power system the different behavior of PV and other renewable energy applications may requires new protection concepts. The
[6] Yu Zou, Malik E. Elbuluk, and Yilmaz Sozer, “Simulation
Comparisons and Implementation of Induction Generator Wind
Power Systems,”
IEEE Trans. On industry A pplications, vol. 49, no.
3, pp. 1119–1128,May/June 2013
D. Mahinda Vilathgamuwa, “Modeling and Analysis of a Novel
Variable-Speed Cage Induction Generator,”
IEEE Trans. On
Industrial Electron., vol. 59, no. 2, pp. 1020-1028, Feb. 2012.
[8] Ahmed G. Abo-Khalil, “Synchronization of DFIG output voltage to utility grid in wind power system,”
in SciVerse ScienceDirect
Renewable Energy, 2012, pp. 193–198.
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