Efficient Single Phase Grid Tie Inverter of PV System - Report Example

Abstract The main aim of the report is to provide details of a designed single phase grid Tie inverter of PV system. Simulations have been done on efficiency, durability and sustainability using MATLAB/Simulink. Electrical efficiency variation has been done and changes in electricity were noted. The performance of grid Tie inverter affects the overall energy production the data that as been used to measure the performance was corrected under operating conditions but different times of the year. Key words; MPPT, grid tie inverter, cascaded H-bridges, pulse width modulator I Introduction The feasibility of using solar energy in respect to the future takes into account its cost-effectiveness and its ability to provide solutions to the energy infrastructures of many developing and third world nations. By developing efficient technologies in the future, solar energy such as PV systems can potentially reduce expenses on electricity. An increasing number of research, conducted on PV technologies and solar cells has demonstrated this cost reduction effects, granting that government subsidies and manufacturing sectors support solar energy projects extensively[1]. In countries where industrial sources of electricity are scarce and limited, solar energy becomes a major solution to have access to electricity used in providing light to many far-flung communities and in powering conventional electronic equipment. The potential of solar energy to be set into extensive global use has been projected several times by researchers[12]. In order to harvest maximum energy from the sun rays by grid tie photovoltaic system an inverter plays an important role as it’s involved in converting direct current to alternating current. The inverter also is involved in regulating photovoltaic system by utilizing maximum power point tracking (MPPT) algorithm [2]. The tie grid inverter is critical because its inefficiency will cause unnecessary problems. The inverter can shut down grid to total black out or have low performance this report is looking at the efficiency, sustainability and durability of grid tie inverter. Improvement in efficiency of tie inverter will reduce the number of modules that are necessary for a certain amount of energy output. This will read in reduction in the cost of the total PV system [14]. Efficiencies of an inverter usually value with changes in operating conditions. This means that, inverters efficiency cannot be the same worldwide. In the modern times before any inverter is designed and produced for public use, the designer will simulate and determine its liner and non-liner behaviour. One of the systems that is used for simulation is Matlab. Matlab is used to design discrete-time control and continuous subsystems [1]. In determining the efficiency of single phase grid tie inverter there is need to consider some factors such as the temperature of the solar system in the area, solar radiation incident and the duration as well as the age of the inverter[2]. II Concept and Data The data has been analyzed using Matlab and the graphs of the overall trades for the inverters have been presented in this report. Grid tie inverters are used in converting direct current generated by PV system into AC. Therefore they play a very important role in the power generation. The amount of energy produced will depend on the power generated. In such a case, the load drawing maximum power varies with frequency of the solar rays. The following shows the characteristics of inverters used to measure performance [7]. Researchers state that voltage increases to the point where there is no further increase and the output begins to diminish [16]. At this point a dome shaped area of the curve is formed which is the maximum point and in this case it is called maximum power point tracking. The inverter that is used always uses grids in synchronizing AC power as well as voltage. Such kind of inverter usually senses voltage which exceeds the maximum point and changes it by shutting down for a few minutes [13]. The inverter is able to operate both indoor and outdoor since they are made out of materials which can withstand varies climatic conditions. The inverters have the ability to cool themselves because of the heat sink within it. This means that they have heat fins which allow circulation of air within it. Let us consider two converters which would be used in this case that is, Froniuns 2500 and PV powered 2800 .according to the manufacturer’s data the expected efficiency is between 92% and 95%. The graphs below show the efficiency of the two inverters [16]. According to manufacturer data and results the incident of solar radiation increases the efficiency increases to 95% and ceases to increase further [16]. III Investigation and design The amount of solar energy that enters the earth are affected by various factors. One of this factor is the length of the day. Apparently, the longer the daytime, the greater amount of solar energy is absorbed. Equatorial regions’ daytime is longer and more constant, having 12 hours per day for the whole year compared to other areas. Atmospheric conditions and weather also affect the amount of solar energy entering the earth. About 30% of incoming solar energy through radiation is reflected back quickly into outerspace from the clouds, atmosphere and land surface which leaves 70% of it absorbed by the surface. Half of this percentage is absorbed and re-radiated by the earth’s surface outwards under certain conditions. Water vapor, clouds, ozone and particulate matters in the atmosphere retain the re-radiated solar energy. This explains why solar energy capturing systems have been designed in recent years to have sufficient energy output on the worst days. Thus, the development of solar energy as renewable energy resource for massive worldwide use in the future is highly feasible because knowledge on solar energy mechanisms, such as factors that will increase and decrease solar energy absorption, can provide baseline data for such development. The figure below shows the connection of the single phase grid tied inverter of the PV system. Figure 1: Block diagram showing Inverter The grid tied inverters will convert DC to AC depending on increase in solar radiation incident and temperature. Power flow in this inverter can take place from D.C side is possible by setting the firing angle between 90 and 180 , thus according to the direction of flow power, this converter can work In two modes of operation rectifier mode can take place (0) and inverter mode (90). Let the gate pulses be applied at a firing angle ‘’ to each thyristor when they are forward based. Inverter gate is connected to pulse circuit through pulse inverter which isolates power circuit from pulse circuit. If a pulse of long duration is applied core of pulse Efficient Single Phase Grid Tie Inverter of PV System gets saturated and no output is available after saturation. Hence even if input to Efficient Single Phase Grid Tie Inverter of PV System is of sufficient duration, on output side of inverter we get only one pulse of very small duration at the rising edge of the input pulse. If due to some reason Efficient Single Phase Grid Tie Inverter of PV System fails to turn on with this single pulse of short duration, it will not turn on till next pulse is applied. With this, output also is a pulse train and triggering becomes reliable. When integrated circuits are used in firing scheme, the power or current with ICs can deliver is generally small and is not sufficient to drive the gate, having medium or large power ratings [9]. The characteristics are shown in the figure 3 and 4 the drain current I increase linearly with the drain source voltage from zero. The slope of this rise is greater when the gate voltage V is high because with more value of V, the conducting channel becomes deeper and it’s resistance lower. However, the voltage drops along the channel due to drain current makes the channel thinner progressively as the drain end as the drain current increases. As a result the rise in I with rise in V becomes progressively lower until a point called the “pinch–off point” is reached and sustained condition is established. Any further increases in V will not change the drain current value at a fixed gate voltage V until breakdown occurs. This is called the pinch off region or saturation region. V Results The single phase grid tie inverter was implemented and simulation was done using Matlab considering various working to test durability, sustainability and efficiency. To measure the efficiency the temperature and solar radiation of the system are used as inputs of simulations to produce simulated output. The efficiency that was noted was over 90%. It was noted that when irradiance Levels were 25 or 50 Watts/m2, the efficiency was low. At 75 Watts/m2, there was maximum efficiency in voltage output. This means the efficiency of the single phase grid tie inverter of PV system is achieved when the radiation is high. When it comes low the efficiency reduces. The graph below shows efficiency and radiation incident Figure 2: From the graph above it can be noted that noted that increase in solar radiation and maintaining the temperature will increase the power output. This means an inverter should have ability to increase power if efficient designed. When the solar radiation incident is higher the output in terms of power and voltage increases is higher. From the graph it is clear the efficiency increases with the increase in solar radiation incident [4]. When it comes with the changes in temperature it was noted that if the temperature increases there is a decrease in voltage. Therefore, when designing single phase grid tie inverter of PV system one requires considering of solar radiation and temperature. Both affects power output and terminal voltage from the system[12]. This is shown in the graph below where the changes in temperature led in changes in the current, voltage and power Figure 3: From the above Looking at the peak efficiency of the inverters it was noted that they did not achieve 95% but between 85% to 90%. When 125W/m2was reached efficiency begun to decrease this is clearly shown in the figure 4 below. Figure 4: When the incident is below 200 power efficiency is seen to increase. This means that upon reaching the peak point efficiency begins to decrease due to increase in temperature within the inverter. Figure 5 : efficiency in the months of January and July The graph shows how efficient inverter in July when the solar radiation is oscillates between 200 to 800W/m2 and January when the solar radiation oscillates between 200 to 1100W/m2[15]. When an inverter is fed with DC, it changes terminal voltage and there are load-dependent losses. The change in terminal voltage depends on the magnitude and the power factor of the current, in other words, it depends on the solar radiation incident. The expression for regulation is = x 100% % voltage regulation = Where V2 = inverter terminal voltage and V`1 = input voltage Thus % voltage regulation = x 100% The efficiency of inverter is given by П= x 100% The inverter is loaded to its full load and the efficiency = output power/ input power and voltage regulation are known. The power wasted in this test is considerable, but the results are obtained under the actual operating conditions, and hence are actual results. It can be noted that if the efficiency is operated below 50% there will poor power output for use [10]. In the month of January when temperature is high the efficiency is high. From the graphs it can be noted that solar radiation increase beyond the optimal will lead to reduced voltage. When it comes to temperature the graph below when simulated to high temperature voltage reduces[11]. The power received from the source of excitation can be utilized only for production of the field flux by the inverter, and the power is if the inverter is old as its windings will work less. Thus, the single phase D.C source must feed an active component of current to the motor. If the conditions are such that the A.C side feeds only the active component, the power factor is unity. There is a particular field current which correspond to such condition[8]. The graph below shows oscillation Figure 6: Single Phase Inverter Simulation From the waveforms of the circuit shown in figure 9, Vo have both positive and negative parts. As a result the average output voltage gets reduced in case of inductive load as compared to resistive load for the same firing angle “”. When inverter is fixed at rad. the current ‘ io’ will start from zero and will gradually rise till the input voltage is positive. At Vs will appear with a node terminal of inverter as a result it will reverse biased. The inverter current however can not become zero suds deny at because of the stored magnetic energy in the load inductance. After the device is subjected to reverse voltage it will still continue to conduct till the current is flowing through it is greater than the holding value IH. At the same angle and is called the conduction angle. Waveforms in the figure 9, the duration depends upon the magnitude of inductance in the load. For higher value of ‘L’ move time is taken by the current to become zero and hence duration will be more. V Conclusion Simulation was done on an inverter for artificial single phase PV system using mat lab. Simulation considered solar radiation incidences of 25 W/m2, 50 W/m2, 75 W/m2, 100 W/m2 and 125 W/m2 and temperature changes of 25, 50 and 75. The model calculated the voltage from valuables considered and the result showed that increase in temperature lead to reduction of power produced. This was seen as the opposite of solar radiation where there was increase in power as solar radiation increased. The age of an inverter was also simulates to determine the duration of an inverter and it appeared that the inverter’s age was critical as changes in age plot negative effect in performance. VI ACKNOWLEDGEMENTS I would like to give my special thanks to my tutor and faculty advisor for his support and encouragement. Their patience and comments on my project paved way for this project. I will not forget to give special appreciation to my fellow students who supported me without any misgivings VII References [1] Qian, Hao. A High-efficiency Grid-tie Battery Energy Storage System. Blacksburg, Va.: U Libraries, Virginia Polytechnic Institute and State U, 2011. Print. [2] Henry, Duo. A High-efficiency Grid-tie Solar Energy Storage System. Blacksburg, Va.: U Libraries, Virginia Polytechnic Institute and State U, 2011. Print. [3] Park, Sung Yeul. A Wide Range and Precise Active and Reactive Power Flow Controller for Fuel Cell Power Conditioning Systems. Blacksburg, Va.: U Libraries, Virginia Polytechnic Institute and State U, 2009. Print. [4] Henry, Duo. A High-efficiency Grid-tie Solar Energy Storage System. Blacksburg, Va.: U Libraries, Virginia Polytechnic Institute and State U, 2011. Print. [5] Sun, Pengwei. Cascade Dual-buck Inverters for Renewable Energy and Distributed Generation. Blacksburg, Va.: U Libraries, Virginia Polytechnic Institute and State U, 2012. Print. [6] Bergmann, Carlos P., and Aisha Stumpf. Efficient Single Phase Grid Tie Inverter of PV System. Dordrecht: Springer, 2013. Print. [7] Bhat, Sujata V. Solar inverters. Boston: Kluwer Academic, 2012. Print. [8] Curtis, R. V., and T. F. Watson. Dental Biomaterials Imaging, Testing, and Modelling. Burlington: Elsevier Science, 2009. Print. [9] Vadgama, P. Surfaces and Interfaces for Biomaterials. Cambridge: Woodhead Pub., 2011. Print. [10] B. J. Pierquet and D. J. Perreault, "A Single-Phase Photovoltaic Inverter Topology With," in IEEE Transactions on Power Electronics,, Washington , USA, 2013. [11] S.M.Cherati,N.A.Azli,S.M.Ayob and A.Mortezaei, “Design of a current mode PI controller for a Single-phase PWM Inverter”, IEEE Applied Power Electronics Collloquim(IAPEC)”, 2011. [12] Y.G. Paithankar and S. R. Bhide. Fundamentals of power system protection. New Delphi: PHI Learning(2010). [13]D. Kumar, N.D. Ramya, R. Indira and R.Ashok. Design and Analysis of Single Phase Grid Connected Inverter. International Journal of Innovative Research in Computer and Communication Engineering(2015) [14]R. Katnal. A Cascaded Inverter for Single-Phase Grid Connected Photovoltaic System. Department Of Electrical Engineering National Institute Of Technology, Rourkela [15]P. Denholm and R. Margolis, “Evaluating the limits of solar photovoltaic (PV) in traditional electric power systems,” Energy Policy 35, no. 5(2007): 2855. [16] F. Vignola, F. Mavromatakis & J Krumsick Performance of PV Inverters Read More