introduction wind pv renewable energy source

Chapter 1

INTRODUCTION AND PREVIOUS WORK

1-1 INTRODUCTION

As energy demands around the world increase, the need for a renewable en-

ergy source that will not harm the environment is increased. Some projections

indicate that the global energy demand will almost triple by 2050 [1]. Renew-

able 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 pro-

posed 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

2

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 electri-

cal 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 en-

ergy. Some of the most common biomass fuels are wood, agricultural resi-

dues, 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 uncount-

able 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 en-

ergy [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-

Chapter 1

3

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 to-

day’s capacity is based on mature, direct-combustion boiler/steam turbine

technology. The average size of existing biopower plants is 20 MW (the larg-

est 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 kilowatt-

hours are produced per employee. These factors, combined with low efficien-

cies 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 Apple-

ton, Wisconsin to provide 12.5 kilowatts to light two paper mills and a home.


4

Today's hydropower plants generally range in size from several hundred

kilowatts to several hundred megawatts, but a few mammoth plants have ca-

pacities 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].

Chapter 1

5

Wave energy has a more general application, with potential along the Califor-

nia 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 equip-

ment is tremendous to turn the very slow motion of the tide into enough dis-

placement 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-


6

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 oxy-

gen- 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 gen-

eration 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

Anode (-)CatalystElectrolyte

CatalystCathode(+)

O2

H2O

Electron Flow

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.

Chapter 1

7

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 pollution-

free, silent and with no rotating parts, and size-independent electricity conver-

sion 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 stop-

ping 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 be-

come 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 condi-

tioning [10], [11]. Two types of grid-connected photovoltaic systems are con-

sidered 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 de-

signed to operate in parallel with and interconnected to the electric utility,

UG. The primary component in grid-connected PV systems is the inverter, or


8

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 re-

quirements of the utility grid, and automatically stops supplying power to the

grid when the utility grid is not energized [12].

PVArray

InverterPCU

DistributionPanel

AC Loads

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 cir-

cumstances, 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 cir-

cuitry in the inverter opens the connection with the utility through a bus trans-

fer 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].

Chapter 1

9

PVArray

ChargeController

BatteryStorage

DistributionPanel

InverterPCU

UG

Non-CriticalAC Loads

Critical ACLoads

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 con-

verted 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 con-

nected 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


10

fixed-speed wind turbine system is often equipped with two induction genera-

tors, 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 elec-

tronic 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 sys-

tems 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 low-

ering 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 sys-

tem 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, trans-

formers 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 lo-

cated in regions with low power transmission capacity [18].

Chapter 1

11

• Concepts and Wind Turbine Configurations

The interfacing of WES with UG requires high frequency and voltage stabil-

ity 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 elimi-

nated for economic reasons, but there may be several that would be competi-

tive for a given application. The fact that one or two methods are most com-

monly 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 turbines-

is 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


12

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 Gear-box

ACG 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 ex-

cess 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 simula-

tion of the PV, WES and PV/WES Hybrid Electric Power System, HEPS with

UG.

Chapter 1

13

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 identi-

fied 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 grid-

connected PV-fuel cell hybrid system by use of a two-loop controller is dis-

cussed. 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


14

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 dc-

voltage controller is developed to operate the system at the MPP for all envi-

ronmental conditions. In the paper a sinusoidal line current is supplied by us-

ing 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 pre-

sented 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 frequen-

cies.

Chapter 1

15

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 us-

ing Matalb/simulink.

Hang-Seok Choi, et. al. (2001) [30] present a new zero current switching in-

verter for grid-connected PV system. The proposed circuit provides zero cur-

rent 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 evalu-

ate 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 effi-

ciency 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 single-

phase three-wire grid-connection PV power inverter with active power filter

which is based on nonlinear programming and fast-zero-phase detection algo-

rithm. 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-


16

sented also some aspects of controlling the green power inverter interface to-

wards the UG. It presented also that the LCL filter was a good choice fro low-

ering 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 fre-

quency harmonic currents is realized without sacrificing the overall conver-

sion efficiency of the inverter system.

Hiroshi Matsukawa, et. al. (2003) [36] present a quite new proposal to meas-

ure 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 op-

timal control of a grid-independent PV system consisting of a collector, stor-

age, 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 compen-

sation. The paper outlined the modeling and development of the control sys-

tem for the active filter/PV generation system.

Armstrong Matthew (2003) [39]: In this reference an alternative solution us-

ing 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.

Chapter 1

17

Dousoky (2004) [40] presents a design of PV power system to be intercon-

nected with UG. Dousoky discussed a design of the PCU for PV power sys-

tem and also a modeling of the inverter with different types of switching tech-

niques.

1-2-2 WES Design, Interconnection and Simulation

A. Grauers (1994) [16]: In this reference an electrical system for variable-

speed wind power plants is investigated. It consists of a synchronous genera-

tor, 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 in-

dustry 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 re-

newable energy strategy to supply 3% of the electricity production from re-

newable 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 pre-

sented in many researches. Some reported models seem to be over-

parameterized, which obstruct their implementation because the parameters

for the detailed description are not generally available. Simplified aerody-

namic modeling of wind turbines is presented in Reference [42]. The predic-

tion of voltage fluctuations caused by variable-speed turbines and impact of


18

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 inter-

action 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 condi-

tion 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 dia-

grams 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 simula-

tions of the fixed-speed and the variable-speed wind turbine systems is sug-

gested. 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 transmis-

sion power network is subjected to a three-phased short-circuit fault.

Chapter 1

19

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 fre-

quency of the interconnected system on which they are operating. Addition-

ally, 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 elec-

trical 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 ex-

cited 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 trip-

ping 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 MAT-

LAB/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 con-

trol using space vector modulation for three phase PWM converter connecting

wind turbine generator with grid. The active and reactive power are used as


20

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 in-

cludes constant speed stall and variable speed pitch turbines. The model pre-

sents 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 be-

havior 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 stand-

alone 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 de-

termine 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 In-

ner Mongolia is designed using the optimization program HOMER and the

simulation model Hybrid2. Various designs are compared on the basis of un-

met load and annualized cost of energy.

R. Chedid and Saifur Rahman (1997) [66]: In this reference a computer pro-

gram have been proposed for the design of integrated hybrid wind-solar

power system for either autonomous or grid-linked applications. The pro-

Chapter 1

21

posed analysis employs linear programming techniques to minimize the aver-

age 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 con-

verter 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 bat-

tery.

R. Chedid and Saifur Rahman (1998) [68] introduce a decision support tech-

nique 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 grid-

linked 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 de-

sign, 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 pro-

duced 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 ac-

ceptable investment cost. A complete analysis is carried out taking into con-

sideration the local energy demand, the number and characteristics of the ex-

isting diesel machines, the local wind and solar potential.


22

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 re-

mote 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 rela-

tion 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 methodol-

ogy 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.

Chapter 1

23

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 inter-

connected with UG and determines the optimum operation hour by hour

through the year. Then, it estimates the monthly surplus energy, monthly defi-

cit 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. Maxi-

mum power output from PV system changes when solar radiation and tem-

perature 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.


24

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 instan-

taneous p-q (real- imaginary) power theory. A computer simulation program

has been designed to simulate phase voltage of the inverter leg, phase-to-

phase 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


WES to be interconnected with UG. A proposed computer program has been

Chapter 1

25

designed to determine an optimum number of WTG based on MPPs by using

neural network. Many WTG types have been introduced to the computer pro-

gram to choose the best type of WTG. By using the proposed computer pro-

gram 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 va-

riety 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-


26

nected with UG. The proposed computer simulation program uses the instan-

taneous 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 pro-

grams 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


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 defi-

cit 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. Differ-

ent FFNN architectures have been trained and tested with data containing a

Chapter 1

27

variety of operation patterns. This chapter introduces also a computer model-

ing, 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 in-

jected 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 us-

ing 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 de-

termine the impact of interconnecting PV/WES HEPS into UG. Four differ-

ent 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 configura-

tion 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 tech-

nique 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.


28

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 Mat-

lab 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 intro-

duces, 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 simu-

lates AC output current of the inverter that injected to the load/grid, load cur-

rent, 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.

Chapter 1

29

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.

introduction wind pv renewable energy source

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