Chapter 1 (adel A. Elbaset)

Chapter 1

INTRODUCTION AND PREVIOUS WORK

1-1 INTRODUCTION As energy demands around the world increase, the need for a renewable energy source that will not harm the environment is increased. Some projections indicate that the global energy demand will almost triple by 2050 [1]. Renewable energy sources currently supply somewhere between 15% and 20% of total world energy demand. Photovoltaic, PV, and wind energy system, WES, are the most promising as a future energy technology [2]. A 30% contribution to world energy supply from renewable energy sources by year 2020 as proposed in Ref. [1] would reduce the energy related to CO2 emission by 25 %. The main advantages of electricity generation from renewable sources are:1- Renewable energy sources, such as wind and solar do not emit smoke or create pollution when they are used. 2- The sunshine for all of us, is free of charge, and the wind blows for free.

Introduction and Previous Work

3- The overall cost of using solar and wind energy can be made them smart choices. 4- The renewable energy is environmental friendly compared to current level of CO2 emission associated with electricity generation. 5- Enhance diversity in energy supply markets and strengthen energy security make a major contribution to reduce global atmospheric emissions. 6- Create significant new employment chances in energy infrastructure manufacturing, and installation. 7- Contribute to the securing of long term, cost effective environmentally sustainable energy supplies. 8- Offer low operating cost. 9- High power quality [1]. Renewable energy are said to be one of the most prominent sources of electrical energy in years to come. The increasing concerns to environmental issues demand the search for more sustainable electrical sources. Renewable energy is possible solutions for environmental-friendly energy production. Sources of renewable energy can be summarized as follows: 1-1-1 Biomass Energy The term "biomass" refers to organic matter which can be converted to energy. Some of the most common biomass fuels are wood, agricultural residues, and crops grown specifically for energy. In addition, it is possible to convert municipal waste, manure or agricultural products into valuable fuels for transportation, industry, and even residential use. There are an uncountable number of woodstoves being used to produce heat for buildings or for cooking in the world, making biomass one of the most common forms of energy [3]. According to the World Bank, 50 to 60 percent of the energy in the developing countries of Asia, and 70 to 90 percent of the energy in the devel-

2

Chapter 1

oping countries of Africa comes from wood or biomass, and half the world cooks with wood. Wood waste is used to fuel United States utility power plants as large as 80 Megawatts. Energy generation using wood has grown from 200 Megawatts in 1980 to over 7,800 Megawatts today [3]. All of today’s capacity is based on mature, direct-combustion boiler/steam turbine technology. The average size of existing biopower plants is 20 MW (the largest approaches 75 MW) and the average biomass-to-electricity efficiency of the industry is 20%. These small plant sizes lead to higher capital cost per kilowatt of installed capacity and to high operating costs as fewer kilowatthours are produced per employee. These factors, combined with low efficiencies which increase sensitivity to fluctuations in feedstock price, have led to electricity costs in the 0.08-0.12 $/kWh range [3]. 1-1-2 Geothermal Energy We can also get energy directly from the heat in the earth. This is known as geothermal energy, from "geo" for earth and "thermal" for heat. Geothermal energy starts with hot, molten rock (called magma) miles below the earth's surface that heats a section of the earth's crust. The heat rising from the magma warms underground pools of water is known as geothermal reservoirs. Geothermal power plants operating around the world proof that the Earth’s thermal energy is readily converted to electricity in geologically active areas. The United States geothermal power plants such as the steam plant at The Geysers in California, have a total generating capacity of 2700 Megawatts, enough to provide electricity for 3.7 million people [4]. 1-1-3 Hydropower In this type, the electrical power generated from kinetic energy of water driven turbine. The first hydroelectric power plant was built in 1882 in Appleton, Wisconsin to provide 12.5 kilowatts to light two paper mills and a home.

3

Introduction and Previous Work

Today's hydropower plants generally range in size from several hundred kilowatts to several hundred megawatts, but a few mammoth plants have capacities up to 10,000 MW and supply electricity to millions of people. Worldwide, hydropower plants have a combined capacity of 675,000 MW and annually produce over 2.3 trillion kilowatt-hours of electricity, the energy equivalent of 3.6 billion barrels of oil [5]. The capital cost of this type of plants is from 1000 $/kW and the operating cost 0.01 - 0.03 $/kWh. Some of power plants which produce Hydroelectric Power are:1- Glen Canyon Power Plant. 2- Flaming Gorge Power Plant. 3- Hoover Power Plant. 4- Pacific Northwest Hydro Projects. 5- Three Gorges dam in China - Spectrum article [5]. 6- High Dam hydroelectric power in Egypt. 1-1-4 Ocean Energy Generating technologies for deriving electrical power from the ocean include wave energy, tidal energy, and ocean thermal energy conversion [6]. (1) Wave energy Kinetic energy exists in the moving waves of the ocean. That energy can be used to power a turbine. The moving wave spins a turbine which can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed. This is only one type of wave-energy system. Others actually use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator. Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house [7].

4

Chapter 1

Wave energy has a more general application, with potential along the California coast. The western coastline has the highest wave potential in the United States; in California, the greatest potential is along the northern coast [7]. (2) Tidal Energy Another form of ocean energy is called tidal energy. The rise and fall of the sea level can power electric-generating equipment. The gearing of the equipment is tremendous to turn the very slow motion of the tide into enough displacement to produce energy. Tidal energy traditionally involves erecting a dam across the opening to a tidal basin. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, traditional hydropower technologies can be used to generate electricity from the elevated water in the basin. Some researchers are also trying to extract energy directly from tidal flow streams. Some power plants are already operating using this idea. The largest facility, the La'Rance station in France, generates 240 Megawatts of power [7]. (3) Ocean Thermal Energy The final ocean energy idea uses temperature differences in the ocean. Power plants can be built that use this difference in temperature to make energy. A difference of at least 3.333 Co is needed between the warmer surface water and the colder deep ocean water. Ocean thermal energy conversion is limited to tropical regions, such as Japan, Hawaii, and to a portion of the Atlantic coast [7]. 1-1-5 Fuel Cell Fuel cells are often described as being continuously operating batteries, but this is an incomplete idea. Like batteries, fuel cells produce power without combustion or rotating machinery. They produce electricity by utilizing an electrochemical reaction to combine hydrogen ions with oxygen atoms. Hy-

5

Introduction and Previous Work

drogen ions are obtained from hydrogen-containing fuels. Fuel cells, unlike batteries, use an external and continuous source of fuel and produce power continuously, as long as the fuel supply is maintained. Two electrodes, an anode, and a cathode form an individual cell. They are sandwiched around an electrolyte in the presence of a catalyst to accelerate and improve the electrochemical reaction. Figure 1-1 shows a fuel cell that uses fuel to create chemical reactions that produce either hydrogen- or oxygen- bearing ions at one of the cell’s two electrodes. These ions then pass through the electrolyte, such as phosphoric acid, and react with oxygen atoms. The result is an electric current flowing between both electrodes plus the generation of waste heat and water vapor. This current is proportional to the cross sectional area of the electrodes. The voltage is limited electrochemically to about 1.23 volts per electrode pair, or cell. These cells then can be "stacked" until the desired power level is reached [8].

H2

Electron Flow

Anode (-) Catalyst Electrolyte Catalyst Cathode(+)

H2O

O2 Fig. 1-1 A scheme of a Fuel Cell [8]. There are many types of fuel cells, differing only in their design, but they all function the same way. The type of electrolyte used classifies fuel cells. The most common classification of fuel cells are:1) Proton Exchange Membrane (polymer) Electrolyte Fuel Cell, PEFC. 6

Chapter 1

2) Alkaline Fuel Cell , AFC. 3) Phosphoric Acid Fuel Cell , PAFC. 4) Molten Carbonate Fuel Cell , MCFC. 5) Solid Oxide Fuel Cell , SOFC. 1-1-6 Photovoltaic PV power generation, which directly converts solar radiation into electricity, contains a lot of significant advantages such as inexhaustible and pollutionfree, silent and with no rotating parts, and size-independent electricity conversion efficiency. Positive environmental effect of photovoltaic is replacing electricity generated in more polluting way or providing electricity where none was available before. With increasing penetration of solar photovoltaic devices, various anti-pollution apparatuses can be operated by solar PV power; for example, water purification by electrochemical processing or stopping desert expansion by photovoltaic water pumping with tree implantation [9]. In 2004, the photovoltaic industry production broke the 1GW barrier, produced worldwide some 1,200 MWp of photovoltaic modules and has become a 5.8 bill. € business. In the past 5 years, the yearly growth rate was an average of more than 40%, which makes photovoltaics one of the fastest growing industries at present [2]. The principal factors affecting the design and performance of PV systems are solar irradiance, ambient air temperature, electrical load characteristics, system configuration, and characteristics of the three major subsystems, namely, the array, batteries/grid, and power conditioning [10], [11]. Two types of grid-connected photovoltaic systems are considered in the Grid-Connected Photovoltaic System. 1- Grid-Connected PV Systems without Battery Storage. Grid-connected or utility-interactive PV systems shown in Fig. 1-2 are designed to operate in parallel with and interconnected to the electric utility, UG. The primary component in grid-connected PV systems is the inverter, or 7

Introduction and Previous Work

power conditioning unit, PCU. The PCU converts the DC power produced by the PV array into AC power consistent with the voltage and power quality requirements of the utility grid, and automatically stops supplying power to the grid when the utility grid is not energized [12].

AC Loads

PV Array

Inverter PCU

Distribution Panel

UG

Fig. 1-2 PV Array Connected with UG without Battery Storage 2- Grid-Connected PV Systems with Battery Storage. This type of system shown in Fig. 1-3 is extremely popular for homeowners and small businesses where backup power is required for critical loads such as refrigeration, water pumps, lighting and other necessities. Under normal circumstances, the system operates in a grid-connected mode, supplementing the on-site loads or sending excess power back onto the grid while keeping the battery fully charged. In the event the grid becomes de-energized, control circuitry in the inverter opens the connection with the utility through a bus transfer mechanism, and operates the inverter from the battery to supply power to the dedicated critical load circuits only. In this configuration, critical loads are typically supplied from a dedicated load sub panel [12].

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Chapter 1

Critical AC Loads

PV Array

Inverter PCU

Charge Controller

Battery Storage

Non-Critical AC Loads

Distribution Panel

UG

Fig. 1-3 PV Array Connected with UG Accompanied with Battery Storage. 1-1-7 Wind Energy The electrical power generated by using the power in the wind to drive a wind turbine to produce mechanical power. This mechanical power can be converted into electrical power by using electrical generators. In 1995 alone, world capacity for wind generated electricity increased 35 percent over 1994 from about 3700 MW to 5000 MW. Nearly two-thirds of these new wind plants were installed in India and Germany. Wind power plants in California produced over 3.1 billion kWh of electricity during 1995, about 1.2 percent of the electricity used by California. Wind project today are being installed for less than five cents per kilowatt-hour, nearly a 100 percent decrease in cost from the early 1980s [13]. • WIND ENERGY CONVERSION SYSTEM Regarding to rotational speed, the two most important currently applied wind turbine generators, WTG concepts are:1. Fixed-speed Wind Turbines For the fixed-speed wind turbine the induction generator, IG is directly connected to the electrical grid. The rotor speed of the fixed-speed wind turbine is adjusted by a gear box, G. B. and the pole-pair number of the generator. The

9

Introduction and Previous Work

fixed-speed wind turbine system is often equipped with two induction generators, one for low wind speeds and one for high wind speeds [14], [15]. 2. Variable-speed Wind Turbines For a variable speed wind turbine, the generator is controlled by power electronic equipment. Up to 75% of all wind turbines built in 2001 and up to 80% of those that built in 2002 are variable speed wind turbines. They start at lower wind speeds, and increase the power with speed. Variable-speed systems also allow torque control of the generator and therefore the mechanical stresses in the drive train can be reduced. Resonances in the turbine and drive train can also be damped and the power output can be kept smoother. By lowering the mechanical stress the variable-speed system allows a lighter design of the wind turbine. It can increase the power production of the turbine by about 5 %, the noise is reduced and forces on the wind turbine generator system can be reduced [15], [16], [17]. Its major drawbacks are the high price and complexity of the converter equipment. • System Overview of Wind Farms Wind turbines can be connected individually to the grid or clustered in wind parks (wind farm type)[18]. The electrical components or wind turbines are designed for low voltages up to 1000 V for cost reasons. Therefore, transformers are necessary most of times. Only when individually connected, or when the small wind systems (0.1 to 100kilowatts) [19], they are connected to the low voltage grid. When their power is between 100 kW and 1MW, they supply to the medium-high voltage grid connection (10-66 kV). Large wind farms (e.g. 50 MW) are connected to the high voltage grid (110 - 132 kV). In some countries, a usual connection criterion requirement for wind farms is the ratio of the short circuit power of the connection point to the rated power of the wind farm. However, this is difficult to achieve when these farms are located in regions with low power transmission capacity [18]. 10

Chapter 1

• Concepts and Wind Turbine Configurations The interfacing of WES with UG requires high frequency and voltage stability to avoid WES get out of synchronization. There are number of ways to get a constant frequency constant voltage output from a wind electrical system. Each has its advantages and disadvantages and each should be considered in the design stage of a new wind turbine system. Some methods can be eliminated for economic reasons, but there may be several that would be competitive for a given application. The fact that one or two methods are most commonly used does not mean that the others are uncompetitive in all situations [14]. Most of the existing systems can be classified in the following way:I. Wind turbines with fixed rotational speed directly connected to the grid. A. Wind turbines with asynchronous generator B. Wind turbines with synchronous generator. II. Wind turbines with variable and partly variable rotational speed A. Synchronous or asynchronous generator with converter in the main power circuit. B. Asynchronous generator with variable slip control. There are three basic types of wind plant:1- WTG connected with UG. Wind turbines are most effective at supplying centralized electric power. Electricity from wind farms - large clusters of interconnected wind turbinesis fed into the local distribution grid and sold to local UG companies. Wind farms can generate electricity for as low as $ 0.03 to $ 0.07 per kilowatt-hour. Figure 1-4 shows the outputs of WTG converted into direct current by an AC generator and solid-state rectifier. The direct current is then converted to 50 Hz alternating current by an inverter. The frequency of the inverter operation is normally determined by the power line frequency, so when the power line 11

Introduction and Previous Work

is disconnected from the UG, the inverter does not operate. More expensive inverters capable of independent operation are also used in some applications [14]. UG

Wind

Gearbox

AC G

Rectifier

Inverter

Fig. 1-4 WTG Connected to UG 2- Dispersed grid-connected systems Wind turbines are often used to produce electricity for homes, businesses and farms already connected to the UG. During low wind periods, electricity is purchased from the utility. When the wind turbines produce excess power, electricity is fed back into the UG. 3- Remote stand-alone systems For sites a half mile or further from the UG, small wind turbines provide a cost-effective source of energy. Remote applications include rural residences, water pumping and telecommunications. Batteries are often used to store excess electricity, and many systems use a diesel generator or solar panels as a back-up system to provide electricity during low wind periods [13]. 1-2 REVIEW OF RELATED RESEARCHES There are many researches on the design, interconnecting issues and simulation of the PV, WES and PV/WES Hybrid Electric Power System, HEPS with UG.

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Chapter 1

1-2-1 PV Design, Interconnection and Simulation T. Hiyama et. al. (1995) [20], [21] present a neural network application to the identification of the optimal operating point of PV modules and designed a PI-type controller for real-time maximum power tracking. Optimal operating voltages are identified through the proposed neural network by using the open-circuit voltages measured from monitoring cells and optimal operating currents are calculated from the measured short-circuit currents. The output of the neural network goes through the PI controller to the voltage control loop of the inverter to change the terminal voltage of the PV system to the identified optimal one. P. Mattavelli, et. al. (1997) [22]: In this reference a general-purpose fuzzy controller for DC/DC converters is investigated. The methodology is based on a qualitative description of the system to be controlled, fuzzy controllers are capable of good performances even for those systems where linear control techniques fail. The presented approach is general and can be applied to any DC/DC converter topologies. Kyoungsoo Ro (1997) [9]: In this reference a stand-alone PV system grid connected mode is studied. First, fuel cells for a backup of varying PV power is compared in detail with batteries. Next, maximizing performance of a gridconnected PV-fuel cell hybrid system by use of a two-loop controller is discussed. A neural network controller is designed for maximum power point tracking for PV system under varying conditions of insolation, temperature, and system load. T. Hiyama and K. Kitabayashi (1997) [23] present an application of neural network for estimation of maximum power generation from PV module. Joseph N. Wolete (1998) [24] develops an interactive menu-driven design tool called PVONE that may serve as a guide to engineers to decide whether a

13

Introduction and Previous Work

stand-alone PV system is feasible at a location. PVONE consists of three parts- insolation, system design and economic analysis. H. Hinz, P. Mutschler and M. Calais (1998) [25] present a control issue of a single phase three level inverter without transformer in a grid-connected PV system. A maximum power point tracker, MPPT in combination with a dcvoltage controller is developed to operate the system at the MPP for all environmental conditions. In the paper a sinusoidal line current is supplied by using a hysteresis controller which operates with an almost constant switching frequency. Kyoungsoo Ro., Saifur Rahman (1998) [26]: In this reference maximizing performance of a grid-connected PV-fuel cell hybrid system by use of a two loop controller is discussed. One loop is a neural network for MPPT and the other is a real/reactive power controller. El-Barbari S., Hofmann W. (2000) [27]: In this reference a three dimensional space vector modulation of a four leg inverter for stand-alone PV system presented to solve issues with unbalanced loads. A digital control strategy is based on a load current observer is introduced to control the whole system with a microcontroller. Björn Lindgren (2000) [28] described some important considerations when using PV in producing energy to the main grid. The function of PV cells is briefly described. Simulations of how shading affects the overall performance is presented. The paper showed a 48 % loss of energy when only 4.2 % of the area is shaded. Results of a designed 110 W low voltage inverter is presented showing a high energy-efficiency of 94 % and a low distortion on the grid with a total harmonic distortion for current (THDi) of 8.8 % for all frequencies.

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Chapter 1

D. Hansen et. al. (2000) [29] present a number of models for modeling and simulation of a stand-alone PV system with battery bank up verified against a system installed at Risφ national laboratory. The implementation is done using Matalb/simulink. Hang-Seok Choi, et. al. (2001) [30] present a new zero current switching inverter for grid-connected PV system. The proposed circuit provides zero current switching condition for all the switches, which reduces switching losses significantly. It is controlled to extract maximum power from the solar array and to provide sinusoidal current into the mains. G. Walker (2001) [31]: In this Reference an electrical model of PV module is presented based on the shockley diode equation. The model is used to evaluate the variation of maximum power point with temperature and insolation levels. A comparison of buck versus boost MPPT topologies is made, and compared with a direct connection to a constant voltage load. B. Estibals, et. al. (2002) [32] present an improvement of PV conversion chain efficiency. The authors in the first part presented an improved MPPT developed by LAASCNRS, which is the first step to increase electrical efficiency and decrease costs. In a second part they proposed a global design methodology dedicated to integrated power supplies. T. F. Wu, et. al. (2002) [33] present a design and implementation of a singlephase three-wire grid-connection PV power inverter with active power filter which is based on nonlinear programming and fast-zero-phase detection algorithm. The proposed inverter system can not only transmit PV power but can compensate harmonic currents, supply reactive power, and balance power at source side even when the line voltages are highly distorted. Soren Baekhoj, et. al. (2002) [34]: In this reference a full-bridge inverter for interfacing the UG is developed for a green power inverter application. It pre-

15

Introduction and Previous Work

sented also some aspects of controlling the green power inverter interface towards the UG. It presented also that the LCL filter was a good choice fro lowering the harmonics to the UG. R. Sharma (2002) [35] shows that removal of the ripple currents can be achieved without sacrificing the overall conversion efficiency of the inverter. The proposed method involves modifying the design of the main inductor used in the inverter outer current loop and adding a capacitor and a resistor to carry the ripple current. This research presented a new approach to the design of a switching frequency filter for a unipolar, current control, transformerless inverter for utility connected PV connections. Filtering of the switching frequency harmonic currents is realized without sacrificing the overall conversion efficiency of the inverter system. Hiroshi Matsukawa, et. al. (2003) [36] present a quite new proposal to measure the dynamic control ability of MPPT for PV inverters under the condition of fluctuating irradiance. Basic functions are given by a specially designed PV array I-V curve simulator composed of the active power load. Gregor P. Henze & Robert H. Dodier (2003) [37] investigated an adaptive optimal control of a grid-independent PV system consisting of a collector, storage, and a load. Leonard G. Leslie (2003) [38] focused on the design of a dual function system that would provide solar generation as well as harmonic and reactive compensation. The paper outlined the modeling and development of the control system for the active filter/PV generation system. Armstrong Matthew (2003) [39]: In this reference an alternative solution using current sensing and control techniques to eliminate DC without the need for a transformer has been proposed to improve the power quality output of grid connected PV inverters and lower equipment costs for these systems.

16

Chapter 1

Dousoky (2004) [40] presents a design of PV power system to be interconnected with UG. Dousoky discussed a design of the PCU for PV power system and also a modeling of the inverter with different types of switching techniques. 1-2-2 WES Design, Interconnection and Simulation A. Grauers (1994) [16]: In this reference an electrical system for variablespeed wind power plants is investigated. It consists of a synchronous generator, a diode rectifier and a thyristor inverter. It discusses the system design and control, to model the losses and to compare the average efficiency of this variable-speed system with the average efficiency of a constant-speed and a two-speed system. The model is verified for a 50 kVA generator. Wind generated electrical power have enormous growth [41], [42], [43], [44], [45], [46] in last ten years, lead by Denmark, Spain, Germany and Egypt. More than 70% of the total world-wide electricity-generating wind turbines (17500MW total) installed in Europe. The European wind manufacturing industry is booming with two-thirds of the world market share. Wind power is now seen as a clean, cost-effective alternative to other forms of conventional electricity production with clear benefits to the environment. In Egypt, the renewable energy strategy to supply 3% of the electricity production from renewable energy sources by the year 2010. The total installed wind generation capacity is expected to rise from 63 MW in 2002 to 1750 MW in the year 2010 [46]. Modeling of wind turbines of varying complexity have been presented in many researches. Some reported models seem to be overparameterized, which obstruct their implementation because the parameters for the detailed description are not generally available. Simplified aerodynamic modeling of wind turbines is presented in Reference [42]. The prediction of voltage fluctuations caused by variable-speed turbines and impact of

17

Introduction and Previous Work

wind turbines on power system stability are dealt with in the literature [41], [42], [43], [44]. Thiringer T. et. al. (2001) [47], [48] investigate power quality issues of wind turbine interconnected to utility. Muljadi E., Mckenna H. E. (2001) [49]: The power quality issues, the interaction of diesel generation and wind turbine are investigated. The purpose of this literature shows the impact of the wind power plant on the entire system. Also, it discussed how the startup of the wind turbine and the transient condition during load changes affect voltage and frequency in the system. Muljadi E. et. al. (2002) [50] investigate a power-system interaction resulting from power variations at wind farms using steady-state analysis. The paper presents also different types of capacitor compensations and use phasor diagrams to illustrate the characteristics of these compensations. Pedro Rosas (2003) [51]: presents the basics influences of wind power on the power system stability and power quality issues. The thesis introduces also an aggregate wind farm model that support power quality and stability analysis from large wind farm. Petru, T. (2003) [52]: Issues of the power quality impact of wind turbines on the electric grid and the response of the wind turbines to faults in the electric grid are investigated. Model structures suitable for grid fault response simulations of the fixed-speed and the variable-speed wind turbine systems is suggested. The fault response of variable-speed wind turbine systems is, to a high extent, influenced by the power electronic converters that are utilized in these systems. V. Akhmatov (2003) [53]: In this reference a wind turbine concept is treated with respect to modeling in dynamic simulation tools, maintaining of transient voltage stability issues and uninterrupted operation issues when the transmission power network is subjected to a three-phased short-circuit fault.

18

Chapter 1

Koch F., Erlich I. and Shewarega F. (2003) [54] present simulation results calculated using a representative network containing wind power generations of up to 30%. Furthermore, modeling and simulation of different types of wind generators integrated into a multi-machine power system are discussed. Koch F., et. al. (2003) [55] describe the effect of large wind parks on the frequency of the interconnected system on which they are operating. Additionally, the effect of the landscape and atmospheric condition at the location of the wind unit on the output power is incorporated into the simulation. Nicholas W. Miller et. al. (2003) [56] develop a simple model appropriate for bulk power system dynamic studies. This model has focused on how the WTGs react to grid disturbances, e.g. faults, on the transmission system. The model provides calculation of the effect of wind speed fluctuation on the electrical output of the WTG. The model is not intended for use in short circuit studies. Poul Sorensen, et. al. (2003) [57]: Models for wind power installations excited by transient events are developed and verified. A number of cases have been investigated, including comparisons of simulations of a three-phase short circuit, validation with measurements of tripping of single wind turbine, islanding of a group of two wind turbines, and voltage steps caused by tripping of wind turbines. Kim Johnsen, and Bo Eliasson (2004) [58] present an aggregate wind farm model for use in real-time power system. The model is developed in MATLAB/Simulink to operate with the ARISTO (Advanced Real-time Interactive Simulator for Training and Operation). M. Malinowski and S. Bernet (2004) [59] propose a simple direct power control using space vector modulation for three phase PWM converter connecting wind turbine generator with grid. The active and reactive power are used as

19

Introduction and Previous Work

the pulse width modulated ,PWM control variables instead of the three-phase line currents ever used. J. Pierik, J. Morren and S. de Haan (2004) [60] give an overview of wind farm dynamic models and concentrates on their use. Dynamic wind farm model based on individual turbine model is developed in Simulink. The model includes constant speed stall and variable speed pitch turbines. The model presents a powerful tool for the investigation of wind farm dynamics and wind farm-grid interaction. Florin Iov et al. (2004) [61] develop simulation platform for modeling, design and optimization of wind turbines. Four simulation tools (Matlab, Saber, DIgSILENT and HAWC) have been investigated to simulate the dynamic behavior of the wind turbines and the wind turbine grid-connected mode. 1-2-3 Hybrid PV/WES Design, Interconnection and Simulation H. H. El-Tamaly (1993) [62]: In this reference a complete design for standalone PV system and stand-alone WES is designed to feed a certain load. Ziyad M. Salameh and Bogdan S. Borowy (1996) (1997) [63], [64]: In these references a methodology for calculation of the optimum size of a battery bank and PV array is developed. The methodology was based on average power generated from PV and WES. The least square method is used to determine the best fit of the PV array and WTG. Debra J. Lew et. al. (1997) [65]: In this reference a hybrid wind/photovoltaic systems, using batteries but not using engine generators, for households in Inner Mongolia is designed using the optimization program HOMER and the simulation model Hybrid2. Various designs are compared on the basis of unmet load and annualized cost of energy. R. Chedid and Saifur Rahman (1997) [66]: In this reference a computer program have been proposed for the design of integrated hybrid wind-solar power system for either autonomous or grid-linked applications. The pro20

Chapter 1

posed analysis employs linear programming techniques to minimize the average production cost of electricity while meeting the load requirements. Siky Kim, et. al. (1997) [67]: In this reference a design procedure for PV/WES HEPS is presented. The hybrid system is composed of DC/DC converter for a PV, AC/DC converter for WES, a four switch IGBT's inverter converting the combined DC power to AC power and a back-up power battery. R. Chedid and Saifur Rahman (1998) [68] introduce a decision support technique for the design of PV/WES HEPS. The proposed PV/WES HEPS is composed of four design variables: (WTG's), PV arrays, batteries and a gridlinked substation. The design of a PV/WES HEPS is based on political and social conditions and uses trade-off /risk method. H. H. El-Tamaly and F. M. El-Kady (2000) [69]: In this reference a design for PV system and WES to be interfaced with UG is investigated. Optimum design, cost and reliability issues for different penetration ratio are estimated. E. Koutroulis, et. al. (2001) [70]: In this reference a hybrid renewable energy system is described which consists of twelve PV panels and a WTG and can supply continuous electric power of 1.5 kW. An energy management system is developed for this purpose in order to maximize the electric power produced using a MPPT method and consists of Buck-type DC/DC converters controlled by a microcontroller. Thiakoulis Tr. and Kaldellis J. K. (2001) [71]: In this reference a prospect of creating a combined wind-solar power station is investigated, in order to minimize their dependence on the local thermal power stations, with an acceptable investment cost. A complete analysis is carried out taking into consideration the local energy demand, the number and characteristics of the existing diesel machines, the local wind and solar potential.

21

Introduction and Previous Work

Salah I. Atta (2002) [72]: In this reference a design of PV/Wind hybrid power system integrated with battery storage system to feed a certain load in a remote area is discussed. The study is applied on East-Oweinat site in Egypt. K. Mitchell, J. Rizk and M. Nagrial (2002) [73] discuss the potential system benefits of simple predictive control routines, using seasonal averaged load wind and solar data, in both stand-alone and grid connected modes. O. Omari1, et. al. (2003) [74]: The DC-coupled PV/WES HEPS and its relation to the new criterion are discussed. Control and management strategies that applied to a simulation model of an example of this type are presented. Yarú Najem and Méndez Hernández (2003) [75]: The simulation models of the PV/WES HEPS verified with measured data in a real system located near the department of Efficient Energy Conversion of the Kassel University are investigated. Two simulation groups are determined: The first simulation group corresponds to a hybrid system with a fixed PV in an hourly radiation basis for a year. The second simulation group corresponds to a hybrid system with a two-axis tracking system in an hourly radiation basis for a year. H. H. Rakha (2005) [76] produces a modular design with complete methodology to obtain the optimum configuration and performance for each stand alone hybrid system of PV/diesel/battery, wind /diesel/battery and wind/PV /diesel/battery to feed a certain load in a remote area. The study is applied on East-Oweinat site in Egypt. This reference produces also an optimal operation control for stand alone hybrid system consisting of wind/PV/diesel/battery.

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Chapter 1

1-3 OUTLINE OF THE THESIS The contents of this thesis are summarized as follows:Chapter 1 This chapter presents the role and important need of renewable energies for todays and future, especially PV and wind energies. It also presents a brief description and utilization of major resources of renewable energy such as photovoltaic, wind, hydropower, biomass, geothermal, ocean and fuel cell. Previous work on the design, modeling and simulation of PV, WES and PV/WES HEPS are displayed. Chapter 2 This chapter introduces a proposed computer program for optimal design of a PV system to be interconnected with UG. The proposed computer program has been designed to determine an optimum number of PV modules based on maximum power point, MPPs, by using neural network. Many PV module types have been introduced to the computer program to choose the best type of PV module. The computer program can completely be used to design the PV system interconnected with UG and determines the optimum operation hour by hour through the year. Then, it estimates the monthly surplus energy, monthly deficit energy and yearly purchase or selling energy to / or from UG. The decision from the computer program is based on minimum price of the generated kWh from the PV system and maximum power extracted from PV system. Maximum power output from PV system changes when solar radiation and temperature vary. Control is needed for the PV system to track the MPPs. This controller has been designed by neural network approach. The computer programs can be applied to any site of the world. The computer program has been applied to Zafarâna site, Egypt as a case study. 23

Introduction and Previous Work

Chapter 3 This chapter introduces an application of an artificial neural network on the operation control of the PV/UG to improve system efficiency and reliability. There are two modes of PV system operation. Stand-alone PV system with battery storage and grid connected PV system without battery storage. This chapter focus on the operation control of a hybrid system consists of PV system accompanied with or without battery storage interconnected with UG taking into account the variation of solar radiation and load demand during the day. Different feed forward neural network architectures are trained and tested with data containing a variety of operation patterns. A simulation is carried out over one year using the hourly data of the load demand, insolation and temperature. It introduces also a complete computer simulation program of PV system interconnected with UG. The proposed computer simulation uses hysteresis current control and instantaneous p-q (real- imaginary) power theory. A computer simulation program has been designed to simulate phase voltage of the inverter leg, phase-tophase voltage of the inverter leg, current in each IGBT's, AC output current of the inverter that injected to the load/grid, load current, grid current, power output of the inverter and finally power factor of the inverter. The computer simulation program is confirmed on a realistic circuit model implemented in the simulink environment of Matlab. The computer programs can be applied to any site of the world. In this thesis, the computer program has been applied to Zafarâna site, Egypt as a case study. Chapter 4 This chapter introduces a proposed computer program for optimal design of a WES to be interconnected with UG. A proposed computer program has been

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Chapter 1

designed to determine an optimum number of WTG based on MPPs by using neural network. Many WTG types have been introduced to the computer program to choose the best type of WTG. By using the proposed computer program the WES components can be completely designed to be interconnected with UG. This program has a subroutine which by using it the optimum operation of WES can be determined hour by hour through the year. Then, the monthly surplus energy, monthly deficit energy and yearly purchase or selling energy to or from UG can be estimated. The decision from the computer program is based on minimum price of the generated kWh from the WES. Control is needed for the WTG to track the MPPs. This controller has been designed by the neural network approach. The computer programs can be applied to any site of the world. The computer program has been applied to Zafarâna site, Egypt as a case study. Chapter 5 This chapter introduces an application of an artificial neural network on the operation control of the WES/UG. The generated power from WTG has been calculated by a computer program under known wind speed. The computer program which is proposed here and applied to carry out these calculations is based on the minimization of the energy purchase from UG. This chapter focuses on a hybrid system which consists of WES accompanied with or without battery storage interconnected with electric utility taking into account variation of wind speed and load demand during the day. Different feed forward neural networks are trained and tested with data containing a variety of operation patterns. A simulation is carried out over one year using the hourly data of the load demand, wind speed. This chapter introduces also a computer modeling, simulation, analysis of a variable speed WTG intercon-

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Introduction and Previous Work

nected with UG. The proposed computer simulation program uses the instantaneous reactive power theory, IRPT. A computer simulation program has been designed to simulate phase voltage, line voltage of the inverter leg and current in each IGBT's. It also simulates AC output current from the inverter that injected to the load/grid, load current, grid current, power output from the inverter, power delivered to or from grid and finally power factor of the inverter and grid. The computer simulation program is confirmed on a realistic circuit model which implemented in the Simulink environment of Matlab and works as if on line. The computer programs can be applied to any site of the world. The computer program has been applied to Zafarâna site, Egypt as a case study. Chapter 6 This chapter introduces a proposed computer program for optimal design of a PV system, WES and PV/WES HEPS to be interconnected with UG. The computer program has been designed to determine the optimum number of PV modules and optimum number of WTG's based on MPPs and using neural networks. Many WTG and PV module types have been introduced to the computer program to choose the best type and the penetration ratio for WTG and PV modules. The computer program can completely be used to design the hybrid system interconnected with UG and determines the optimum operation hour by hour through the year. Then, it estimates the monthly surplus energy, monthly deficit energy and yearly purchase or selling energy to or from UG. The decision from the computer program is based on minimum price of the generated kWh from the system. This chapter presents also an application of an artificial neural network, ANN on the operation control and interconnection of the PV/WES with UG. Different FFNN architectures have been trained and tested with data containing a 26

Chapter 1

variety of operation patterns. This chapter introduces also a computer modeling, simulation, analysis of a HEPS interconnected with UG. A computer simulation program has been designed to simulate all quantities of HEPS such as phase voltage of the inverter leg and current in each IGBT's for PV and WTG. It also simulates AC output current of the inverter that injected to the load/grid, load current, grid current, power output from PV and WTG, power delivered to or from grid and finally power factor of the inverter for PV, WTG and grid. The computer simulation program is confirmed by using a realistic circuit model which implemented in the Simulink environment of Matlab and works as if on line. Chapter 7 This chapter presents a complete study, from reliability point of view, to determine the impact of interconnecting PV/WES HEPS into UG. Four different configurations of PV/WES/UG have been investigated and a comparative study between these four different configurations has been carried out. The overall system is divided into three subsystems, containing the UG, PV and WES. The generation capacity outage table has been built for each configuration of these subsystems. These capacity outage tables of UG, PV/UG, WES/UG and PV/WES/UG are calculated and updated to incorporate their fluctuating energy production. This chapter also presents a fuzzy logic technique to calculate and assess the reliability index for each HEPS configuration under study. Chapter 8 This chapter presents the conclusions and suggestions for future work.

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Introduction and Previous Work

1-4 THESIS OBJECTIVES As discussed in this chapter, PV and WES are the most promising as a future energy technology and can be clean sources of electric energy in the world. Due to the unexpected power variation of these sources the interface of these sources with UG is a challenging aspect and focus of the thesis. This thesis presents a proposed package of computer programs based on Matlab software. This package presents a complete design and control strategy of interconnecting PV system, WES and PV/WES HEPS accompanied with or without battery storage, BS with UG. It can be applied for design any hybrid electric power system consists of PV, WES or PV/WES to feed a load in any site in the world as stand-alone or interconnected with UG. This thesis introduces, also, a new technique based on NN to achieve the optimal operation of interconnecting PV, WES and PV/WES accompanied with or without BS with UG. This proposed technique can solve some of interconnection issues of PV, WES or PV/WES HEPS. This thesis also presents a new computer program based on Matlab/Simulink has been proposed for modeling and simulation of any PV system, WES and PV/WES HEPS interconnected with UG. The proposed computer program uses hysteresis current control and instantaneous p-q (real- imaginary) power theory, which are commonly used in the filed of active power filter control. The computer program has been designed to simulate all quantities of PV/UG, WES/UG and PV/WES HEPS interconnected with UG such as phase voltage of the inverter leg and current in each IGBT's for PV and WTG. It also simulates AC output current of the inverter that injected to the load/grid, load current, grid current, power output from PV and WTG, power delivered to or from grid and finally power factor of the inverter for PV, WTG and grid. The computer simulation program is confirmed on a realistic circuit model which implemented in the Simulink environment of Matlab and works as if on line.

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Chapter 1

By using this computer program the interconnection issues between PV, WES and PV/WES with UG can be treated and solved. Also, a new approach based on fuzzy logic proposed to evaluate the reliability index (LOLP). This approach can be used for generating LOLP curves and also can be used in sizing PV/UG system, WES/UG system and PV/WES HEPS interconnected with UG.

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