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PERFORMANCE ANALYSIS OF A 11 kV GRID CONNECTED PHOTOVOLTAIC SYSTEM
Ashutosh Dubey
1,Anurag Tiwari
21PG Scholar, Electrical & Electronics Engg. Dept., CIST, Bhopal
2Professor, Electrical & Electronics Engg. Dept., CIST, Bhopal
Abstract: This paper present the performance analysis of an 11kV grid connected photovoltaic system. World energy consumption is increasing day by day .Growing scarcity and rising prices of fossil fuels may lead to economic instability. Continuously increasing energy consumption will overload the distribution grids as well as the power stations, therefore having a negative impact on power availability, security and quality. The photovoltaic system is green and renewable source of energy; it can enhance the operation of distribution system by improving the voltage profile and by reducing the energy losses of distribution feeders. The simulation diagrams of 11kV grid connected photovoltaic system are carried out in MATLAB (R2013A) / Simulink environment to evaluate the performance of grid connected system.
Keyword: Photovoltaic system; distribution system; power quality; voltage source inverters
Introduction: In the current global energy scenario, importance of power generation from renewable energy sources is increasing day by day. In India sector wise consumption of Electrical Energy
(utilities) during 2011-2012 in percentage was 22 in Domestic, 17 in Agriculture , 45 in Industry, 9 in Commercial,2 in Traction and railways, 5 in others. By 2013 total installed capacity of electrical power in India is 2, 25,793.10 MW, in which state sector is contributing 89,092.12 MW, central sector 65,612.94 MW and private sector 71,088.04 MW. Fuel wise power generation capacity varies as Total Thermal power is 153,847.99 MW in which Coal is 132, 288, 39MW,Gas is 20,359.85MW and Oil is 1,199.75MW, Hydro(Renewable) is 39,623.40MW, Nuclear is 4,780.00MW and renewable energy sources is 27,541.71MW.[2]
Fig.1.Sector wise consumption of Electrical Energy (utilities) during 2011-2012
The major power generation is due to fossil fuels but the availability these fuels are limited and various environmental hazards associated with traditional power generation methods. Out of the various grids connected renewable energy systems, solar photo-voltaic energy systems are most popular. The solar radiation falling on earth surface is about 90 PW or 90x1012 Watt; hence a small area use on earth surface can fulfil our electricity requirements. Energy supplied by the sun in one hour is equal to the amount of energy required by the human in one year. Solar power is available during the whole day but the solar irradiance levels change because of the changes in the sun’s intensity and shadows caused by many reasons.[1]
In this paper IGBT based boost converter for solar photovoltaic system is used to get required output voltage constantly and converter’s firing pulses are generated by INC MPPT technique.
A lot of MPPT algorithms have been used developed by researchers and industry delegates all over the world. They are perturbation and observation methods, incremental conductance method, hill climbing method, fractional short circuit current method, open circuit voltage method, beta method and so on.
2 Proposed System Architecture:
Fig.2. Block diagram of proposed architecture
The output of solar panel goes in to MPPT controller which tracks the maximum power by using P&O algorithm with the help of PI controller. This gives firing pulse to turn on the IGBT (BOOST Converter) to get higher output voltage and supplied to R load.
Characteristics of Solar PV system:The building block of PV array is a solar cell, which converts light energy into electricity. The photo current Iph depends on the solar radiation and cell temperature as follows.
Iph = [Iscr+Ki(T-Tr)] S/100
Where Iscr is the cell short circuit current at reference temperature and radiation, Ki is the short circuit current temperature coefficient and S is the solar radiation in MW/cm2.
The PV &IV characteristic is shown below.
Fig4 PV Current versus Voltage Characteristic
Fig 5 Power Characteristic for Different Levels of Irradiation.
DC-DC Boost Converter:A boost converter is a dc to dc voltage converter with an output dc voltage greater than input dc voltage. It is also known as Step- up converter. This is an SMPS containing at least two
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semiconductor switches (a diode which act as freewheeling diode two ensure a path of the current during the off state of other switch and a transistor connecting in series of the source 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.
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.
An IGBT based boost converter is used to increase the voltage level of 10 KV dc of solar panel to 11 KV dc. Its firing pulses are generated by P & O MPPT technique.
Fig.6. Ideal Boost converter circuit
Result and Simulation: Simulate the various effect of grid connected PV system on 11kV distribution system.
A two bus test system is simulated the system which is feed through 11kV utility grid comprised of 250 kW load with a total power of 300 KVA and 0.8 power factor. The produced D.C. voltage by each was raised using DC to DC boost converter. MPPT is implemented in the boost converter to efficiently control photovoltaic energy conversion furthermore the boosted DC is converted using a three phase voltage source converter. The figure 7 shows the simulation diagram of 11 kV grid connected photovoltaic system.
Fig7. 11 kV grid connected photovoltaic system
PV cell has non-linear current-voltage characteristics. The power delivered by an array increases to a point, as the current draw rises MPP tracker (MPPT) devices are used between the PV array and load to track MPP and ensure that it works at this point. The Perturb and Observe (P&O) algorithm is the most commonly used in commercial MPPTs. In this method, a small perturbation in array current is introduced at a regular interval and the resultant power is measured. This is usually done by slightly varying the duty cycle of the switching converter (the load) driven by the PV array. Changing the duty cycle changes the load current as well, effecting a small perturbation. Two sensors, one for PV voltage the other for PV current, are commonly used to determine if the perturbation resulted in an increase or decrease of instantaneous power[8].the figure 8 and 9 shows the MPPT controller and P & O algorithm respectively.
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Fig 8. MPPT controller
Fig9 Flow chart of P&O algorithm
When the temperature and solar radiation keeps T=25℃，S=1000 W/m2. The simulation result is shown in Figure 10 shows the grid voltage and current. The magnitude of the voltage is 10 KV volts and the current is 25 Amp
Fig 10 Grid voltage and current
The figure 11 shows the output value of the photovoltaic cell output current and voltages
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Fig 11 PV output current and voltage
Fig 12 Pulse generation
Figure 13 shows the THD of the grid connect pv system and output THD is limited as per standard. The total output current THD is 3.1 %
Fig 13 total harmonic distortion
Conclusion: In this paper, grid-connected solar PV system has been studied. This model can work well under sudden value of environment temperature or solar radiation. The maximum power of the PV cell is tracked with an adjusted P&O MPPT algorithm based on Boost DC to DC converter. A DC to AC inverter has been used to connect the PV cell to the grid and regulate the output voltage of DC to DC converter. The whole photovoltaic grid-connected system is simulated in MATLAB/Simulink.
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