thesis fina123

CHAPTER-IINTRODUCTION

1.1 GENERAL

In a remote area there used to be two general solutions for its electrification making a

connection to the closest grid or using diesel generation to get self-sufficiency. Both

methods are incredibly expensive and that is the origin for the hybrid systems, which

means the combination between that dispatch able diesel source and a renewable one.

Wind-diesel Hybrid Power Systems are designed to provide electrical generating

capacity to remote communities and facilities that are not linked to a power grid. The

introduction of wind-diesel hybrid systems reduces reliance on diesel fuel, which

creates pollution and is costly to transport.

Wind energy has received considerable public attention since the last decade, and

has been the fastest growing energy source. The global installed wind capacity is

expected to grow much more rapidly in the next decade as many policies around the

world have implemented or are in the process of implementing policies such as

Renewable Portfolio Standard (RPS) [5]. Acceptance of the RPS is a commitment to

produce a specified percentage of the total power generation from renewable sources

within a certain date. Most of this renewable energy will come from wind as other

renewable sources are not very suitable for bulk power generation. Wind energy is non-

depleting, site-dependent, non-polluting, and a potential source of the alternative energy

option.

The first wind turbine for electricity generation has already been developed at the

ending of the 19th century. During the winter of 1887-88, Brush built is today believed

to be the first automatically operating wind turbine for electricity generation. It has

been a giant in size but with a capacity of 12 kW. At the beginning of the 20th century,

the research institute began to pay attention of wind power technology, and the first

wind power journal has been published by Poul la Cour (1846-1908) [1]. During the

period of 1940-1950, two significant technical improvements have been made: first, the

3 blades structure of wind turbine; second, AC generator replaced DC generator. In the

1970s, the oil crisis rekindled the interests of wind power. The capacity of wind power

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units has increased to several hundred kW. From 1980, a wind turbine of MW has

begun to be implemented in power system. Moreover, another direction of wind

technology is to reduce the cost, which is one major difficulty, which wind power

researchers has faced. By the end of the 1990s, the wind power has re-emerged as one

of the most important sustainable energy resources. The wind power is expected to play

a comparatively significant role in the future national energy scene [1].

At the beginning of 2004, the total installed capacity of wind energy systems all over

the world reached 39 GW with an annual growth rate of about 30% [2]. It is predicted

that 12% of the total world electricity demands is expected to be supply from wind

energy by 2020 [3]. As for Canada, the total wind energy production now is 1451 MW

with an annual average growth rate of about 35% [4]. The main goal to be achieved, as

reported by the Canadian Wind Energy Association (Can-WEA), is to generate more

than 10GW electricity from wind energy by 2010 (10 X 10 Canada Wind Vision

Program) [4].

Diesel generators also known as Generation sets, provide reliable power when

properly maintained. The initial cost of a complete diesel power system is also

relatively low. They can be easily transported and are having low-technical problems

which aids in their reliability and ensures ease of operation. Consumption of fuel takes

place even at zero loads [5]. In some areas of the world where wind power is not

abundant other forms of renewable energy such as solar and hydro power can be used

and in some cases the diesel generator has been done away with all together. Hybrid

systems range in size from a few Kw to several Mw of power. The variable nature of

most renewable energy sources means that hybrid systems often have to have extensive

control systems so that demand can met and power quality assured. Hybrid systems can

guarantee the certainty of meeting load demands at all times at reasonable cost, for

certain latitudes and escapes of the total dependency of the resources of the

hydrocarbons and the economic viability of some other energetic alternatives.

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1.2 HYBRID SYSTEMS

The rapid depletion of fossil fuel resources on a worldwide basis has necessitated

an urgent search for alternative energy sources to cater to the present day demands.

Alternative energy resources such as solar, wind, ocean thermal and tidal have attracted

energy sectors to generate power on a large scale. However, solar and wind energy

systems are being considered as promising power generating sources due to availability

and the topological advantages in local power generation. It is prudent that neither

standalone wind energy system nor solar system can provide a continuous supply of

energy due to seasonal that combine solar and wind generating units with battery

backups are implemented to satisfy the load demand. A great deal of research and has

been carried out on hybrid energy systems with respect to performance, optimization,

integration with diesel /biomass systems and other related parameters of significance.

Power systems using multiple generation sources can be more accurately described

by the term ‘hybrid power systems’ [6]. Hybrid power systems range from small

systems designed for one or several homes to very large ones for remote island grids or

large communities. Alternative energy resources such as solar, wind, ocean thermal and

tidal have attracted energy sectors to generate power on a large scale. However, solar

and wind energy systems are being considered as promising power generating sources

due to availability and the topological advantages in local power generation. It is

prudent that neither standalone wind energy system nor solar system can provide a

continuous supply of energy due to seasonal that combine solar and wind generating

units with battery backups are implemented to satisfy the load demand [7].

Power systems utilizing renewable energy such as wind, solar and micro-hydro

require control methods to maintain stability due to the real time variation of input

energy and load, while maximizing the use of renewable resources. In such cases, the

WDPS(Wind Diesel Power System) serves an entire isolated load and is responsible for

maintaining frequency and voltage stability (dynamic performance). The main focus in

WDPS design is to secure both fuel saving of diesel generator unit and reliable power

supply to load. Using, diesel generator installed capacity is sized to meet the peak

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power demand, but is used in practice to supply power only when the wind power

output is insufficient to meet the load demand.

1.2.1 ADVANTAGES OF THE HYBRID SYSTEMS

Optimum utilization of renewable energy sources in a remote area

The certainty of meeting load demands at all times is greatly enhanced by the

hybrid systems

In some hybrids, batteries are used in addition to the diesel generator, the batteries

meet the daily load fluctuation, and the diesel generator takes care of the long term

fluctuations.

Designed for easy to operate, service and maintenance when required.

Most eco friendly and clean source of power.

The hybrid systems provide more consistent year round renewable energy

production. These systems are modular and can be expand easily.

Lying of the expensive grid line, transmission and distribution losses can be

eliminated.

Eliminates any associated expensive electricity bills.

1.2.2 TYPES OF THE HYBRID SYSTEMS

Solar and wind Hybrid system

Wind and Diesel Hybrid system

Solar and Diesel Hybrid system

Wind and Diesel and Fuel cell Hybrid system

Wind and micro-Hyde Hybrid system

Wind diesel and solar Hybrid system

1.2.3 DESIGN CONSIDERATIONS OF HYBRID ENERG SYSTEMS

The design of hybrid energy systems involves the following steps

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Selection of the energy resources to be used (this will depend on the of

potential

of different renewable energy resources in the area).

Choice of the system configuration

Load profile determination of the area to be served

(seasonal/monthly/yearly)

Sizing of the system components and switchgear, distribution networks etc.

Economic analysis of the project (payback, NPV etc)

Environmental/socio-economic evaluation for sustainability

Provision for expansion, land costs and environmental clearances

Testing of the system design through simulation exercises.

Modification of the system configuration on the basis of simulation

feedback

Once the main considerations have been finalized, the system is ready for the

implementation stage. The subsequent performance of the system will then be governed

by appropriate system management strategies, which can promote local employment,

conservation and high efficiency.

1.3 LITERATURE REVIEW

Many in recent past have carried out research in Hybrid systems. H.S.Ko, T.NJImur,

K.Y.Lee [8] described an intelligent controller based on a neural network for a wind-

diesel power system .The goal is to design an intelligent controller to maintain a good

power quality under varying wind and load conditions. R.Sebastian, J Quesada [7] has

proposed distributed control system (DCS) by analyzing the control requirements for

frequency control in different modes of operation and described the actuation of its

sensor and actuator nodes for isolated wind systems. J.K.Kaladellis [6] has focused on

presenting a detailed mathematical model describing the operational behavior of the

basic hybrid system components, along with the representative calculation results based

on the developed mathematical model. Accordingly, an integrated numerical algorithm

is build to estimate the energy autonomy configuration of the hybrid system.

5

R.Sebastian [9] has proposed a control technique for smooth transition from wind to

wind diesel mode and vice versa for high penetration autonomous wind diesel hybrid

system with battery storage. Das D, Aditya, SK, Kothari D.P [10] has focused on

dynamics of diesel and wind turbine generators on an isolated power system.

S.H.Karki, R.B.Chedid and R.Ramdan [11] Explained about production cost evaluation

for wind diesel system using probalistic techniques.Yeager KE, Willis JR [12] has

proposed a Modeling of diesel generators in a nuclear power plant and explained about

designing actuator and speed governor system for diesel generator set. S. Roy, 0. P.

Malik and G. S. Hope [13] has proposed an adaptive control technique for fuel flow

into diesel engine. P.A.Stott, M.A.Mueller.[14] has given a new topology for a fully

variable speed hybrid wind/diesel power system modeled in Matlab/ Slimulink. Use of

the variable speed diesel generators is shown to increase the fuel savings over a

constant speed generator in a hybrid system. The load matching capabilities of the

variable speed diesel generator to wind speed drops in the hybrid system are then

assessed. Finally integration of a variable speed wind turbine and new variable speed

diesel generator through the DC-link stage of an AC/DC/AC power converter has been

simulated to establish compatibility

Farid Katiraei, Chad Abbey [15] introduced an energy-flow model developed for

performance analysis and unit sizing of an autonomous wind-diesel Microgrid. The

model is employed to analyze the interaction of wind and diesel power plants in order

to identify alternative unit sizing approaches that improve wind-energy absorption rate

of the wind plant, and overall efficiency of the diesel plant. Ruben pena, Roberto

Cardenas [16] introduced a indirect vector scheme control structure for a variable

speed wind diesel energy system based on doubly fed induction generators to provide

an energy to an isolated load. This scheme uses a common DC bus enable super and

sub synchronous operations of both machines .Fadia M. A. Ghali, Shawki H. Arafah

introduced a hybrid systems combining wind energy conversion systems and diesel

generators are considered one of the alternatives to feed demands at lower energy cost and

acceptance reliability

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1.4 OUTLINE OF CHAPTERS

The work presented in this thesis is divided into six chapters which include the

literature review, system description, Voltage and frequency control with fixed speed

wind turbine and variable speed wind turbine for a wind diesel system ,smooth

transition from wind to wind diesel mode and its control circuit, Fault analysis on wind

diesel system and future work. The proposed work is organized in following chapters

Chapter I:

This chapter deals with the introduction to the hybrid power systems based on Wind diesel

system, types and advantages of hybrid system .This chapter also presents literature review

and various control schemes for voltage and frequency are reported in the literature on

wind diesel hybrid power systems.

Chapter II:

This chapter describes about the dynamic model equations of the wind turbine, different

types of wind turbine systems, modeling of diesel engine and its speed control

Chapter III:

This chapter deals with dynamic performance of wind diesel system (with fixed wind

speed turbine) in different modes of operation such as wind only mode, diesel only

mode and wind diesel mode. Performance of wind diesel system with a transmission

line between them and. fault analysis to ensure the system stability are also discussed.

Chapter IV:

This chapter deals with the operation of smooth transition model from wind to wind

diesel mode and the proposed control circuit

Chapter V:

This chapter deals with dynamic performance of wind diesel system (with Variable

wind speed turbine) in wind diesel mode. Performance of wind diesel system with a

transmission line between them and fault analysis to ensure the system stability are also

discussed is also discussed.

Chapter VI:

This chapter deals with the conclusions drawn on the basis of work carried out. More

over the scope of further work is also enlisted in brief.

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CHAPTER-II

WIND AND DIESEL ENERGY SYSTEM

2.1 GENERAL

Wind-diesel generating systems have been under development and trialed in a

number of locations during the latter part of the 20th century. A growing number of

viable sites have now been developed with increased reliability of the systems. This is

key to their success, as minimizing the cost of technical support in remote communities

is vital for the ongoing development and implementation of this technology.

2.2 WIND TURBINE

Wind turbine is a machine that converts the kinetic energy in wind into mechanical

energy. If the mechanical energy is used directly by machinery such as pumping or

grinding stones, the machine is called a windmill [18].Wind mills have been used for at

least 3000 years, mainly for grinding grain or pumping water, while in sailing ships the

wind has been an essential source of power for even longer. A wind turbine (WT)

consists of turbine blades, rotor, generator, nacelle (gearbox and generator drive), shaft,

drive or coupling device, converter and control system.

Wind turbines can be classified to 2 types .Fixed speed wind turbine and variable

speed wind turbine. Fixed speed can only operate at a fixed speed, and use induction

machine as generators. While operational speed of variable speed wind turbine can

variant with a constant frequency. Variable speed wind turbines use doubly fed

induction machine (DFIG) or permanent magnet synchronous machine (PMSM) as the

generator. Wind turbine model can be mainly divided into 3 parts: mechanical drive

and control, generator, converter and control system, among which the model of the

generator is most important

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2.2.1 WIND TURBINE MODEL IN SIMULINK

The Simulink model of the wind turbine is illustrated in the following figure2.1. The

three inputs are the generator speed (ωr_pu) in pu of the nominal speed of the

generator, the pitch angle in degrees and the wind speed in m/s. The tip speed ratio λ in

pu of λ_nom is obtained by the division of the rational speed in pu of the base rotational

speed and the wind speed in pu of the base wind speed. The output is the torque applied

to the generator shaft.

Tm (pu )

1

wind _speed ^3

u(1)^3

pu ->pu

-K-

pu ->pu

-K-

lambda _nom

-K-

cp(lambda ,beta )

lambda

betacp

Product

Product

-1

Avoid divisionby zero

Avoid divisionby zero

1/wind _base

-K-

1/cp_nom

-K-

Wind speed(m/s)

3

Pitch angle (deg )

2

Generator speed (pu )

1

Pwind_puPm_pu

lambda

cp_pu

lambda_pu

wind_speed_pu

Fig.2.1 Simulink Model of Wind turbine

The mechanical power Pm as a function of generator speed, for different wind speeds

and for blade pitch angle β = 0 degree, is illustrated below. This figure is obtained with

the default parameters (base wind speed = 12 m/s, maximum power at base wind speed

= 0.73 pu (kp = 0.73) and base rotational speed = 1.2 pu). The turbine power

characteristics for different values of turbine speed at a pitch angle 0o are illustrated in

Fig 2.2.

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0 0.2 0.4 0.6 0.8 1 1.2 1.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1 pu

Max. power at base wind speed (12 m/s) and beta = 0 deg

6 m/s7.2 m/s

8.4 m/s

9.6 m/s

10.8 m/s

12 m/s

13.2 m/s

14.4 m/s

Turbine speed (pu of nominal generator speed)

Turb

ine o

utp

ut

pow

er

(pu o

f nom

inal m

echanic

al pow

er)

Turbine Power Characteristics (Pitch angle beta = 0 deg)

Fig.2.2 Wind turbine characteristics for different wind speeds

2.2.2 WIND TURBINE GENERATING SYSTEMS

The wind turbine continuously extracts the kinetic energy of the wind by decelerating

the air mass and feeds to the generator as a mechanical power. Fraction of mechanical

energy is converted into electrical energy. The power coefficient is a function of both

tip speed ratio λ and blade pitch angle β. The tip speed ratio, which is defined as the

ratio of speed at the blade tip to the wind speed can be given as [10].

The output power of the turbine is given by the following equation.

The turbine performance coefficient can be determined from the following equation

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Fig.2.3 characteristics, for different values of the pitch angle ß.

The characteristics, for different values of the pitch angle ß, are illustrated in

Fig.2.3. The maximum value of ( = 0.48) is achieved for ß = 0 degree and for

= 8.1. This particular value of is defined as the nominal value ( ).

2.3 TYPES OF WIND TURBINES

Wind turbines can operate with either fixed speed (actually within a speed range about

1 %) or variable speed. For fixed-speed wind turbines, the generator (induction

generator) is directly connected to the grid. Since the speed is almost fixed to the grid

frequency, and most certainly not controllable, it is not possible to store the turbulence

of the wind in form of rotational energy. Therefore, for a fixed-speed system the

turbulence of the wind results in power variations, and thus affects the power quality of

the grid [19]. For a variable-speed wind turbine, the generator is controlled by power

electronic equipment, which makes it possible to control the rotor speed. In this way the

power fluctuations caused by wind variations can be more or less absorbed by changing

the rotor speed [20] and thus power variations originating from the wind conversion

and the drive train can be reduced. Hence, the power quality impact caused by the wind

turbine can be improved compared to a fixed-speed turbine [27].

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The rotational speed of a wind turbine is fairly low and must therefore be adjusted to

the electrical frequency. This can be done in two ways: with a gearbox or with the

number of pole pairs of the generator. The number of pole pairs sets the mechanical

speed of the generator with respect to the electrical frequency and the gearbox adjusts

the rotor speed of the turbine to the mechanical speed of the generator. In this section

the following wind turbine systems are presented.

Fixed-speed wind turbine with an induction generator.

Variable-speed wind turbine equipped with a cage-bar induction generator

or

Synchronous generator.

Variable-speed wind turbine equipped with multiple-pole synchronous

Generator.

Multiple-pole permanent-magnet synchronous generator.

Variable-speed wind turbine equipped with a doubly-fed induction

generator.

2.3.1 FIXED SPEED WIND TURBINE

For the fixed-speed wind turbine the induction generator is directly connected to the

electrical grid according to Fig. 3.4. The rotor speed of the fixed-speed wind turbine is

Fig.2.4 Fixed-speed wind turbine with an induction generator.

In principle determined by a gearbox and the pole-pair number of the generator. The

fixed-speed wind turbine system has often two fixed speeds. This is accomplished by

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using two generators with different ratings and pole pairs, or it can be a generator with

two windings having different ratings and pole pairs [21].

2.3.2 VARIABLE SPEED WIND TURBINE

The system presented in Fig. 3.5 consists of a wind turbine equipped with a

converter connected to the stator of the generator. The generator could either be a cage-

bar induction generator or a synchronous generator. The gearbox is designed so that

maximum rotor speed corresponds to rated speed of the generator [22, 28].

Fig.2.5 Variable-speed wind turbine with a synchronous/induction generator.

2.3.3 VARIABLE SPEED WIND TURBINE WITHDFIG

This proposed system (Fig. 2.6), consists of a wind turbine with doubly-fed induction

Generator. This means that the stator is directly connected to the grid while the rotor

winding is connected via slip rings to a converter. This system has recently become

Fig.2.6 Variable-speed wind turbine with a doubly-fed induction generator (DFIG).

popular as generators for variable-speed wind turbines [23]. This is mainly due to the

fact that the power electronic converter only has to handle a fraction (20–30%) of the

total power [23, 29 and 30]. Therefore, the losses in the power electronic converter can

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be reduced, compared to a system where the converter has to handle the total power. In

addition, the cost of the converter becomes lower due to their reduced rating.

2.4 DIESEL ENGINE

Diesel engines are a common part of our everyday lives and they widely used in

automobiles and other applications. Diesel prime-movers are attractive for applications

requiring fast responding backups at the time of peak load demands, or where local

demand for additional power necessitates augmentation of power source. Since the

response of the prime mover itself is fast, it is imperative that control techniques that

are fast converging, and involve low computational burden. The dead time of the diesel

engine is non-linear function of operating conditions, and also of the engine speed. This

significantly degrades the performance of the prime mover under disturbances.

Although certain PID schemes presently in use give acceptable performance [13].

2.4.1 SPEED CONTROL OF DIESEL ENGINE

Speed control of power generation plants driven by diesel prime-movers is difficult

because of the presence of a dead time and changes in parameters. This results in slow

plant dynamics. Self tuning PID controller based on indirect estimation of the dead time

is proposed resulting in fast response at the startup and quick recovery, when a

disturbance occurs. By using indirect estimation of the dead time and recursive least

squares parameter estimation, an explicit estimate of the plant parameters and dead time

is obtained.

Typical diesel engine model describes the fuel consumption rate as a function of

speed and mechanical power at the output of the engine. It is usually modeled by a

simple first order relating the fuel consumption (fuel rack position) to the engine

mechanical power [24]. The task of the governor is to adjust the fuel flow and then

regulate the input of the engine and the generator so as to provide the required power to

meet changing in the load.

The presence of dead-time between the actuator fuel injection and the production of

mechanical torque is very important characteristic of the diesel engine. There are also

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system parameter uncertainties which together with the varying dead time significantly

degrade the performance of the prime mover, especially in case of a load. A diesel

engine is a nonlinear system together with a nonlinear, time-varying dead time between

the injection and production of the mechanical torque. It is commonly controlled with a

PI controller to prevent steady-state error in speed.

2.4.2 METHODS OF SPEED CONTROL OF DIESEL ENGINES

1. An adaptive speed controller method

2. Combination of neural network and fuzzy logic approaches

3. An H∞ controller for diesel engine systems.

4. Comparison of a k-predictive adaptive controller.

2.4.3 MODELING OF DIESEL ENGINE

There are many methods for modeling diesel engine, with comparison of those a k-

predictive adaptive controller method is used most widely. The general structure of the

fuel actuator system is usually represented as a first order phase lag network, which is

characterized by gain K2 and time constant τ2. Fig .5(a) shows the actuator model and

the current driver constant K3 [13]. The output of the actuator is the fuel-flow ‘υ’.

Fig 2.7 The Actuator Model and the current driver constant

The fuel flow then converted to mechanical torque ‘q’ after time delay τ1 [13].The

engine torque constant K1 which can be represented by the model of the diesel engine

as shown in Fig. 5(b).

Fig 2.8 the Diesel Engine Model

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The governor can be defined as a mechanical or electromechanical device for

automatically controlling the speed of an engine by relating the intake of the fuel.

Several types of governors exist as mechanical-hydraulic, direct mechanical type,

electro hydraulic, electronic, and microprocessor based governors. The values K3 and

K2 can be considered to be constant for a particular engine setup. K3 is a factor that

determines the amount of the mechanical torque obtained per unit of fuel flow. K3

depends on the operating point of the prime mover. Self tuning PID controller based on

indirect estimation of the dead time is proposed for control system. Fig. 5(c) Shows the

block diagram of diesel engine model with permanent magnet generator.

2.4.4 DIESEL GENERATORS

Diesel generators also known as Gensets, provide reliable power when properly

maintained. The initial cost of a complete diesel power system is also relatively low.

They can be easily transported and are low-tech which aids in their reliability and

ensures ease of operation. So far they sound like the ideal solution for the given

application but where they fall down is in the environmental and running costs.

Standard diesel generators are fitted with synchronous generators and consequently

are controlled to run at a constant speed to guarantee constant electrical frequency. Due

to the poor efficiency at low load, most of the engines manufacturers recommend their

plants be operated no lower than 40% of rated capacity in order to prolong diesel

engine lifetime. To achieve this dump loads may need to be installed at extra cost to the

consumer. The fuel consumption rate per Kw of power is increase at lower loads and

fuel consumption at no load is still 15-30% of the full load value. At low loads the

speed of the generator will be reduced ensuring the engine is running optimally in terms

of fuel economy. Due to the above considerations the variable speed diesel generators

were recommended, the main push for the variable speed revolution is the inherent

problems of fixed speed minimum operating load and poor efficiency at low load.

Permanent magnet synchronous generator is used as variable speed diesel generator for

most of the applications.

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Recent advancements in power electronics and control strategies have made it

possible to regulate the voltage of the Permanent Magnet Synchronous Generator

(PMSG) in many different ways. This has resulted in renewed interest in PM

synchronous generators, particularly in the remote areas with diesel engines, small-

scale power generation with small hydro heads and wind power. Fig 2.9 shows the

schematic diagram of diesel engine with Permanent Magnet Generator where K in the

fig is equal to K1*K2*K3. Typical values of system parameters were given in

Appendix A.

Fig 2.9 Block diagram of Diesel engine model with Permanent Magnet Generator

CHAPTER-III

WIND DIESEL HYBRID SYSTEM

3.1 GENERAL

In the last several years, interest in medium to large scale (100kw to multi-MW)

wind-diesel hybrid power systems for rural electrification has grown enormously

among energy officials and utility planners in the developing countries. Only a small

fraction of researchers and engineers working in the wind power industry, which is

relatively small itself, are involved in hybrid systems for off-grid applications. There is

therefore relatively little information available on the technical issues involved in

implementing a wind-diesel power system.

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It is tempting to view the addition of wind turbines to a diesel mini-grid or isolated

system as a straight forward task, only slightly more complicated than a conventional

grid-connected installation, requiring only a few ancillary components at a relatively

modest cost. This is true for low penetration wind-diesel hybrid systems, for high

penetration systems much more sophisticated controllers and more extensive

components in addition to the wind turbines are required. This thesis focuses to some of

the control challenges faced by developers of wind-diesel systems, system stability and

long term performance. Since 1995, the National Wind Technology Center (NWTC) at

NREL has been researching wind-diesel hybrid power systems.

3.2 MAIN PRINCIPLE

The power output from wind turbines varies during the day according to the

variations in wind speed. In a large grid these variations and fluctuations in wind power

are absorbed by the strong grid, thus controlling frequency and voltage. In a small and

isolated grid the power balance between production and consumption has to be

continuously maintained in order to keep frequency of the small grid within predefined

limits. As the wind power does not supply constantly, the power balance between the

consumption, the fluctuating wind power and the diesel power must be maintained by

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Figs 3.1 BLOCK DIAGRAM

19

DIESEL

GOVERNOR

SYNCHRONOUS

MACHINE

WIND

TURBINE

INDUCTION

MACHINE

CAPACITOR

BANK

SYSTEM

LOAD

DUMP

LOAD

EXCITER

BLOCK

Regulating the output of diesel generator to maintain system integrity of diesel

generators, the following two strategies are possible [5]. Fig.3.1 shows the model of

hybrid system.

Running the diesel continuously with some minimum load requirement

Starting and stopping the diesel to make up instantaneous wind short falls.

System which allows shutting down the diesel generator during the high wind power

availability (high wind speeds) is called as high penetration wind diesel system.

3.2.1 FREQUENCY CONTROL

Control of the hybrid power system frequency is maintained by the fast control of the

power balance between the fluctuating wind power, the dump load bank (electrical

heating elements) and the consumer load. In periods where the diesel engine is in

operation the frequency is controlled by the diesel engine governor. In periods with 100%

wind power, the frequency is controlled by absorbing the surplus wind energy in a

dynamic variable dump load or load bank.

3.2.2 VOLTAGE CONTROL

Control of the wind-diesel hybrid system voltage is maintained by the Automatic

Voltage Regulator (AVR) of the synchronous generator - also supplying reactive power

for energizing the induction generators in the wind turbines. At increasing load or

decreasing wind power, thus the wind power is not able to supply the complete

consumption the diesel genset is automatically started supplementing the wind power.

3.3 DIFFERENT MODES OF OPERATION

High penetration wind diesel system has three modes of operation. Table.1 shows the

actuation of different components in different modes [4].

1. Diesel only mode

2. Wind only mode

3. Wind diesel mode

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Table 1: WDHS components actuation in different modes

3.3.1 WIND ONLY MODE

Power systems for wind only mode consists of wind turbine generators, synchronous

machine, dump load and the consumer load. In wind only mode (WO), wind turbine

generator supply the power demanded by the consumer load. As the wind turbine

generator is a fixed pitch constant speed type, there is no control mechanism to regulate

the power output of WTG. Therefore to regulate the frequency in wind only mode,

concept of dump load is employed in this model.The dump load consists of eight three-

phase resistors connected in series with GTO (Gate Turn-Off) type based switches. The

dump load uses an 8-bit binary command so that the load can be varied in the range of 0

to the maximum power in 256 steps [3].

During high wind penetrations, frequency is maintained at constant value by dumping

the extra power after meeting the load into dump load [26]. Wind only mode can work

only if the power produced by the wind turbine generator is greater than the consumer

load [10].

3.3.2 DIESEL ONLY MODE

Most diesel energy conversion systems use a synchronous generator to supply energy

to the load. The excitation of the generator is regulated in order to control the generator

terminal voltage. Due to the restriction of load constant frequency the speed of the diesel

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Function Diesel only

mode

Wind only

mode

Wind diesel

mode

Active

power

generation

Diesel

generators

Wind

turbine

generators

Both wind

and diesel

generators

Frequency

control

DG speed

regulator

Dump load DG speed

regulator

engine is regulated at a constant value However, diesel engine has high fuel consumption

at light load at constant speed and usually a minimum load of about 40% is recommended

by the manufacturers

In periods with sufficient wind power to supply the electrical system and necessary

water production or heating the diesel engine(s) are disconnected from the generator by

means of a magnetic clutch and shut down in order to save fuel. In these periods the

power system is solely supplied from the wind turbine(s) (100% wind power penetration)

and there is no idle fuel consumption of the diesel engine(s). The standby diesel engine

shall be preheated in order to facilitate a fast start up.

3.3.3 WIND DIESEL MODE

In continuous wind diesel mode, both wind and diesel generators operate to meet the

load. Diesel governor regulates the diesel output power to balance the total generation

from both wind and diesel to the system load. Therefore the system frequency is

regulated by diesel governor for different wind speeds and loads. Synchronous machine

in the diesel generation set is used to regulate the system voltage. There is no concept of

dump load when both wind and diesel are in operation. In this mode diesel has to run

continuously, even at high wind speeds. In order to reduce the fuel cost of diesel gen set,

intermittent wind diesel mode is used where the diesel governor is disengaged or engaged

with synchronous machine by means of clutch. The cost of fuel in continuous wind diesel

mode is much more than the intermittent wind diesel mode. During high wind

penetrations clutch is disengaged and during low wind penetrations clutch is engaged.

3.4. MATLAB MODEL FOR DIESEL GOVERNOR SYSTEM

ACTUATOR

Pmec (pu )

1

TF 2

0.0384 s+1

1

TF 1

0.25s+1

0.009 s+1

ProductPID Controller

PID

Integrator

1s

ENGINETd

w (pu )

2

wref (pu )

1

TorqueTorque

Fig 3.2 Simulink model of diesel governor system.22

.

23

3.4.1 MATLAB MODEL FOR WIND DIESEL SYSTEM

Consumer Load

Consumer Load

HIGH PENETRATION WIND DIESEL SYSTEM WITH NO STORAGE

w

1

powergui

Discrete,Ts = 5e-005 s.

Wind 1

WT

A

B

C

a

b

c

Vtref (pu )3

1

Vtref (pu )1

1 Synchronous Condenser 480 V 330 kVA

Pm

Vf _

m

A

B

C

Switch 1

Subsystem1

MEASUREMENTS

Subsystem

MEASUREMENTS SecondaryLoad(0-446 .25 kW)

Con

tro

l A B C

Scope 5

Scope 1

SL

A

B

C

a

b

cP(w_Wind ,w_Turb )

Main Load100 kW

A B C

Load A B C

a b c

Gain 13

-1

GOVERNOR& DIESEL ENGINE

wref (pu)

w (pu)

Pmec (pu)

Iabc _WT

Vabc_WT

Iabc _Load

Vabc_Load

Vabc_SL

Iabc _S

Vabc_Load

[Iabc _SL]

[Vabc_SL]

Vabc_S

EXCITATION

vref

vd

vq

vstab

Vf

DiscreteFrequency Regulator

VabcControl

DemuxD

A

B

C

a

b

c

-C-

Asynchronous Generator480 V 330 kVA

Tm

mA

B

C

1800 rpm

-K-

<Rotor speed wm (pu)>

<Rotor speed (wm)>

Fig 3.3 Simulink model of wind diesel system

3.5 RESULTS AND DISCUSSION

3.5.1 WIND ONLY MODE

Results of wind only mode with dump load action are shown in following figures from

Fig.3.4 (a) to Fig.3.4 (d). Simulation is performed for 20 sec. sudden change of wind

speed from 10m/s to 11m/s is taken into consideration for observing the performance of

dump load for frequency regulation. Fig3.4 (a) shows the simulated wind speed. Initially

wind turbine generator generating 200 Kw, which is 150Kw more than the system load

Therefore, dump load takes 150Kw power till 10sec, to maintain system frequency at

desired value. As the wind power increases (system load constant), power absorbed by

the dump load also increases from 150Kw to 215Kw.Fig.3.4 (b), Fig.3.4(c) shows the

wind generator and dump load powers respectively. Frequency of system in wind only

mode is shown in Fig .3.4(d).

5 10 15 209.5

10

10.5

11

11.5

Time (sec)

Win

d sp

eed

in m

/s

(a)

8 10 12 14 16 18 20

59.6

59.8

60

60.2

60.4

60.6

Time (sec)

Freq

uecn

y of

Sys

tem

in H

z

(c)

5 10 15 200

50

100

150

200

250

300

350

Time (sec)

Load

and

Win

d G

ener

aor P

ower

in K

w

Load

Wind

Wind speedfrom 10 to

11m/s

266 Kw

(b)

9 10 11 12 13 14 15 16 17 18 19 20140

160

180

200

220

240

260

Time (sec)

Dum

p lo

ad p

ower

in K

w

Wind speedfrom 10 to

11m/s

(d)

Fig.3.4(a) –Fig 3.4(d):-Simulation results of the proposed system for wind only mode :( a) wind speed in m/s.

(b) Active Powers generated wind and supplied load in Kw. (c) System Frequency in Hz (d) Dump load in Kw

3.5.2 DIESEL ONLY MODE

In Diesel only mode (DO) diesel generators supply the active and reactive power

demanded by consumer load [4]. Frequency regulation in this case is performed by the speed

regulators of diesel engine generators. Results of diesel only mode for sudden change in load

at t=10 sec is shown in following figures. Simulation is performed for 14sec. Initially system

load of 100 Kw is met by diesel generator. As the sudden change of load (extra 30 Kw) takes

place at t= 10 sec, Synchronous machine speed (frequency) falls down from desired value. By

sensing this decreasing speed by diesel governor increases its fuel input to meet the extra load.

Finally frequency settles to desired value.

Fig.3.5(a), Fig.3.5(b) and Fig.3.5(c) shows active power generated by diesel engine

generator, frequency of power system in Hz and system load respectively. Diesel

8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 1360

80

100

120

140

160

180

Time (Sec)

Acti

ve P

ower

of D

iesel

Gen

erato

r in

Kw

(a)

4 6 8 10 12 14 16 18 2059.5

59.6

59.7

59.8

59.9

60

60.1

60.2

60.3

Time (Sec)

Syste

m F

requ

ency

in H

z

(c)

8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 1370

80

90

100

110

120

130

140

150

160

Time (Sec)

Load

Acti

ve P

ower

in K

w

(b)

Fig.3.5(a) –Fig 3.5(c):-Simulation results of the proposed system for Diesel Only Mode :(a) Active Power generated

by diesel engine in Kw. (b) System Frequency in Hz. (c) System Load in Kw.

3.5.3 CONTINUOUS WIND DIESEL MODE

In this mode, Diesel is continuously operating with wind turbine generator to meet the

system load. Fuel cost for the operation of diesel engine in continuous mode is 20% more

than the start-stop diesel operation i.e. intermittent diesel operation [10]. Simulation of

continuous wind diesel system is carried for different wind speeds and different load

conditions for an interval of 50 sec. System load is kept constant at 100 Kw till 40 sec. Wind

speed is kept constant at 6m/s till 15 sec, changed to 7 m/s at t=15sec and to7.5 m/s at t=30

sec. Fig .3.6(a) shows the simulated wind speeds for an interval of 50 sec. Fig .3.6(b),

Fig.3.6(c), Fig.3.6(d), Fig.3.6(e) shows active power generated by diesel generators, wind

turbine generator, system load and frequency of power system in Hz respectively. Table.2

shows the power sharing by diesel and wind turbine generator at different wind speeds and

load conditions. .

When the wind speed changes from 6m/s to 7m/s (generated power increases), therefore

intake of fuel to diesel generator is reduced to reduce the power generation by it. Therefore at

different load and wind speeds intake of diesel fuel is adjusted to meet the load generation

constraint.

5 10 15 20 25 30 35 405.5

6

6.5

7

7.5

8

Time (sec)

Win

d Sp

eed

in m

/s

(a)

5 10 15 20 25 30 35 40 45 5010

20

30

40

50

60

70

80

90

Time (Sec)Activ

e Pow

ers fr

om W

ind

and

Dies

el in

Kw

Diesel

Wind

(b)

5 10 15 20 25 30 35 40 45 5090

95

100

105

110

115

Time (Sec)

Syste

m L

oad

in K

w

(c)

5 10 15 20 25 30 35 40 45 500.999

0.9995

1

1.0005

1.001

1.0015

1.002

1.0025

1.003

Time (Sec)

Spee

d of

a Sy

nchr

onou

s Mac

hine

in p

u

(e)

5 10 15 20 25 30 35 40 45 5059.9

59.95

60

60.05

60.1

60.15

60.2

60.25

60.3

Time (Sec)

Syste

m F

reque

ncy

in H

z

(d)

Fig.3.6(a) –Fig 3.6(e):-Simulation results of the proposed system for wind diesel mode :( a) wind speed in m/s.

(b) System Load in Kw. (c) Active Powers generated by wind and diesel generators in Kw .(d) System

Frequency in Hz.(e) Speed of Synchronous Machine in pu

Table 2.Power sharing in Wind diesel mode

Wind speed Wind

power

(Kw)

Diesel

power

(Kw)

Total

power

generated

load

6m/s (0<t<15) 16 84 100 100

7m/s (15<t<30) 50 50 100 100

7.5m/s(30<t<40) 71 29 100 100

7.5m/s(40<t<50) 71 39 110 110

3.5.4 WIND DIESEL SYSTEM WITH TRANSMISSION LINE

In this Mode, Wind turbine generator and Diesel Generator are separated by a

Transmission line of 1 mh .Wind generator and diesel generator are meeting their loads at

corresponding buses to maintain the active power balance. If one generator alone is unable to

supply its load, the extra load is met by the other generator via transmission line. Simulation

of this circuit is performed for 55 sec. Wind Speed is kept constant at 10m/s and sudden

decrease in wind speed to 9m/s from 10m/s takes place at 10 sec as shown in the Fig 3.7(a).

Load at Wind Generator is kept constant at 200Kw till 25 sec, and load increases to

250Kw at 25 sec. Load at Diesel Generator is Kept constant at 50Kw till 40 sec and sudden

increase of 50 Kw takes place at 40sec.At 10 m/s Wind generator can supply its own load.

But as the wind speed decreases to 9 m/s wind generator only produce Kw. So, in order to

maintain active power balance at Wind Generator bus extra power comes from Diesel

Generator through transmission line. Initially Diesel generator generates Kw to supply its

own load and extra power to load at wind generator bus.

At 25 sec, as the load at wind generator bus increases keeping the wind speed constant,

In order to maintain the active power balance extra power of comes from Diesel generator

through transmission line. The extra load increment at diesel generator bus is supplied by

diesel generator to maintain power balance Fig 3.7(a), Fig 3.7(b), Fig 3.7(c), Fig 3.7(d), Fig

3.7(e), Fig 3.7(f), Fig 3.7(g) and Fig 3.7(h) shows the wind speed in m/s, Active power

generated by generators, Load at generator buses, System frequency in Hz, Power flow in

line, Voltage at diesel generator bus, Voltage at wind generator bus and Reactive Power

generated by both generators respectively.

10 15 20 25 30 35 40 45 50 557

8

9

10

11

12

13

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

10 15 20 25 30 35 40 45 50 5550

100

150

200

250

Time (Sec)

Acti

ve P

ower

s in

Kw

Wind Power

Diesel Power

10 15 20 25 30 35 40 45 50 550

50

100

150

200

250

300

Time (Sec)

Load

Acti

ve P

ower

in K

w

Load at Diesel Bus

Load at Wind Bus

(c)

10 15 20 25 30 35 40 45 50 550

20

40

60

80

100

120

140

Time (Sec)

Pow

er F

low

in L

ine i

n K

w

(e)

10 15 20 25 30 35 40 45 50 55450

460

470

480

490

500

510

Time (Sec)

Vol

tage a

t Dies

el G

ener

ator b

us in

pu

(g)

10 15 20 25 30 35 40 45 50 5559.6

59.7

59.8

59.9

60

60.1

60.2

60.3

60.4

Time (Sec)

Syste

m F

reque

ncy

in H

z

(d)

10 15 20 25 30 35 40 45 50 55450

460

470

480

490

500

510

Time (Sec)

Vol

tage a

t Win

d G

ener

ator b

us in

pu

(f)

10 15 20 25 30 35 40 45 50 55-120

-100

-80

-60

-40

-20

0

20

40

Time (Sec)

Reac

tive P

owers

in K

var

Diesel

Wind

(h)

Fig.3.7(a) –Fig 3.7(h):-Simulation results of the proposed system for wind diesel system with transmission line

:( a) wind speed in m/s. (b) Active Powers generated by wind and diesel generators in Kw .(c) System Loads at

Load buses (d) System Frequency in Hz.(e) Power flow in line. (f) Voltage at diesel generator bus in pu. (g)

Voltage at wind generator bus in pu. (h) Reactive Power generated by both generators in Kvar

Table 2.Power sharing in Wind diesel mode with transmission line

3.5.5 FAULT ANALYSIS ON WIND DIESEL SYSTEM WITH TRANSMISSION LINE:

To ensure the system stability, fault analysis is performed on wind diesel system with

transmission line. Wind and diesel generators are separated by a transmission line of 1 mh

and meeting corresponding loads at wind and diesel buses. Wind speed is kept constant at

9m/s throughout the simulation interval as shown in the Fig 3.8(a).Load at diesel generator

and wind gen buses are kept constant at 100Kw and 200Kw respectively as shown in the Fig

3.8(d) and Fig 3.8(e).As the wind generates less than 200Kw as shown in the Fig 3.8(b),

extra power is generated by diesel and supplies through transmission line. Diesel speed

regulator is used to control the frequency. Voltage at diesel gen bus is controlled by exciter

Wind

speed

Wind

power

(Kw)

Diesel

power

(Kw)

Power

Flow in line

In Kw

Load at

Diesel

gen bus

Load

At wind

gen bus

10m/s (0<t<10) 200 50 0 50 200

9m/s (10<t<25) 143 107 57 50 200

9m/s (25<t<40) 143 157 107 50 250

9m/s (40<t<55) 143 207 107 100 250

of a synchronous machine where as voltage at wind gen bus is controlled by keeping

synchronous condenser at wind generation bus.

Short circuit fault is simulated for 10 cycles to show the response of the system under

fault conditions. Fig 3.8(c), Fig 3.8(f), Fig 3.8(g), Fig 3.8(h) and Fig 3.8(i) shows the active

power generated by diesel, system frequency, Fault current from diesel generator, fault

current from wind generator and total fault current respectively. Voltage is retained to

required value after removing fault at both wind and diesel gen buses as shown in the Fig

3.8(j) and Fig 3.8(k).Speeds of machines such as DFIG and synchrouns machine are shown

in the Fig 3.8(m) and Fig 3.8(l) respectively. Power flow in the line throughout the

simulation interval is shown in the Fig 3.8(n).

0 5 10 15 20 25 308

8.5

9

9.5

10

Time (Sec)

Wind

Spe

ed in

m/s

(a)

10 12 14 16 18 20 22 24 26 28 30-300

-200

-100

0

100

200

300

400

Time (Sec)

Dies

el A

ctive

Pow

er in

Kw

(c)

10 12 14 16 18 20 22 24 26 28 300

50

100

150

200

250

300

Time (Sec)

Load

at D

iesel

Gen

bus

in K

w

(e)

10 12 14 16 18 20 22 24 26 28 30-100

0

100

200

300

400

500

600

Time (Sec)

Wind

Acti

ve P

ower

in Kw

(b)

10 12 14 16 18 20 22 24 26 28 300

20

40

60

80

100

120

140

160

180

Time (Sec)Load

Acti

ve P

ower

at Di

esel G

en bu

s in K

w

(d)

10 12 14 16 18 20 22 24 26 28 3058

58.5

59

59.5

60

60.5

61

61.5

Time (Sec)

Syste

m Fr

eque

ncy i

n Hz

(f)

10 12 14 16 18 20 22 24 26 28 30100

200

300

400

500

600

700

800

Time (Sec)

Faul

t Cur

rent

from

Dies

el G

en in

Am

ps

(g)

0 5 10 15 20 25 30-3000

-2000

-1000

0

1000

2000

3000

4000

5000

6000

Time (Sec)

Fault

Cur

rent f

rom

Wind

Gen

in A

mps

(h)

0 5 10 15 20 25 30-3000

-2000

-1000

0

1000

2000

3000

4000

5000

6000

Time (Sec)

Faul

t Cur

rent

from

Win

d G

en in

Am

ps

(i)

10 12 14 16 18 20 22 24 26 28 30300

350

400

450

500

550

600

650

Time (Sec)

Vol

tage a

t Dies

el G

en b

us in

pu

(j)

10 12 14 16 18 20 22 24 26 28 300

100

200

300

400

500

600

Time (Sec)

Vol

tage a

t Win

d ge

n bu

s in

pu

(k)

10 12 14 16 18 20 22 24 26 28 300.97

0.98

0.99

1

1.01

1.02

1.03

1.04

1.05

1.06

Time (Sec)

Spee

d of

IG in

pu

(l)

10 12 14 16 18 20 22 24 26 28 300.96

0.97

0.98

0.99

1

1.01

1.02

1.03

1.04

1.05

Time (Sec)

Spee

d of

Syn

chro

nous

Mac

hine

in p

u

(m)

10 12 14 16 18 20 22 24 26 28 30-400

-300

-200

-100

0

100

200

300

Time (Sec)

Pow

er F

low

in li

ne in

Kw

(n)

Fig.3.8(a) –Fig 3.8(n) :-Simulation results of the proposed system for wind diesel system with transmission line :

( a) wind speed in m/s. (b) Active Powers generated by wind generator in Kw.(c) Active Powers generated by wind

generator in Kw .(d) System Load at wind bus (e) System Load at wind bus (f) System Frequency in Hz.(g)Fault

current from diesel gen bus (h) Fault current from wind gen bus (i) Total fault current (j) Voltage at diesel gen bus

(k) Voltage at wind gen bus (l) Speed of DFIG (m) Speed of synchronous machine (n) Power flow in line.

CHAPTER-IV

SMOOTH TRANSISTION FROM WIND TO WIND DIESEL MODE

4.1 INTRODUCTION

A wind diesel hybrid system uses the wind turbine generators along with the diesel

generators to obtain contribution by the intermittent wind resource to the total power

produced. If the wind diesel hybrid system is capable of shutdown the diesel generators

during the high wind penetrations, then the system is called a high penetration wind diesel

system. Smooth transition from wind to wind diesel mode is required at low wind speeds

(load constant). Wind only mode can only work, if the power produced by the WTG is

greater than the consumed power by the load. Facility for Diesel engine to engage (in both

diesel only and wind diesel modes) or disengage (in wind only mode) from synchronous

machine by means of a clutch. In the Fig 4.1, a, b, c indicates fuel used for diesel only

mode, continuous wind diesel mode and intermittent wind diesel systems. From the Fig

4.1,it is clear that the fuel cost reduced for intermittent wind diesel system compared to

continuous wind diesel mode

Fig 4.1 Fuel used in diesel generator for different modes of operation

4.2 DESIGN AND OPERATION OF CONTROL MECHANISM

Smooth transition from wind mode to wind diesel mode is required at low wind speeds

[4]. There is a facility for Diesel engine to engage (in both diesel only and wind diesel

modes) or disengage (in wind only mode) from synchronous machine by means of a

clutch as shown in the Fig 4.2 .Wind only mode can only work, if the power produced by

the WTG is greater than the consumed power by the load.

WIND TURBINE

CLUTCH

Fig 4.2 Model of wind diesel system with Clutch

When the condition is not satisfied, the system frequency will fall, so the control system of

WDHS (wind diesel hybrid system) must order to start the DE (Diesel engine) and when

the speed difference between the DE and SM (synchronous machine) is small enough,

clutch is engaged to changing to the WD mode [11]. With clutch locked, the diesel engine

will supply the necessary active power first to rise and after to keep the system frequency

constant. The locked clutch mechanism with only two states is shown in the Fig.4.1.

Tc

2

pm

1

SwitchProduct 1

Gain K 3

1/(Hs+Hd)

Gain K 2

Hd

Gain K 1

HsCLUTCH

Constant

0

Ts1

3

Ws2

Ts

1

Fig.4.3 Control circuit for Locked clutch mechanism

IG

DIESEL

ENGINE

LOAD

SM

Where Td and Ts are the DE and SM torques and and are the SM and DE inertias

respectively. Switch block in Fig.7 (a) selects between 0 and under the control of

CLUTCH signal .Input mechanical power to the SM block ( * ) is calculated.

In the disengaged state, the DE and SM axis are independent and the transmitted torque

is zero. In the locked CLUTCH state (CLUTCH=1), both the SM and DE have the same

speed, the two axes behave like only one and transmitted torque in pu is given by [4]

(4)

Fig .4.2 shows the DE along with its actuator and speed regulator which outputs the

diesel speed and mechanical torque (pu) necessary to take the diesel speed to its

reference speed. Finally the DE torque equation is given by [4]

(5)

ACTUATOR

Td

1

TF 2

0.0384 s+1

1

TF 1

0.25s+1

0.009 s+1

Switch For Speed Reference

SLOW

0.25

RATED

1

PID Controller

PID

Integrator 1

1s

Integrator

1s

ENGINETd

1/2Hd

1/1.50.5 Sec Delay

Tc

2

DRUN

1

TorqueTorque

Wd

Fig .4.4 Speed control circuit for diesel engine generator

The DRUN binary input to the diesel block is the output of the Boolean switch as

shown in the Fig4.3. This frequency relay (relay2) watches the frequency in WO mode

and when the system frequency falls due to the lack of active power (may be due to

increase in load or decrease in speed), output of frequency relay becomes 1.Fig .4.3 shows

the control circuit for active power regulator..

data type

boolean

Switch1

S-RFlip -Flop

S

R

QRelay 2

Relay 1

LogicalOperator 3

NOT

LogicalOperator 2

AND

CLUTCH

Wd

Ws

DRUN

1

DOFF

0

Add 2 Abs

|u|

Fig .4.5 Active Power regulators for transition from wind to wind diesel modes

Active power regulator receives inputs as speeds of DE and SM and binary DRUN. It

outputs the CLUTCH signal. The RS flip flop sets its output to ‘1’when the relative speed

between the DE and SM is very less

4.3 Results and Discussion:

Initially Wind turbine generator supplying 93Kw (8m/s) to supply the load of 93 Kw.

DE reference speed set at 0.25 pu even though it is not supplying any load to simulate the

cranking process. Sudden change in the load takes place at t=7 sec. Frequency relay senses

the change in frequency at t=7.15 sec and changes the DRUN signal to ‘1’ as shown in the

Fig4.6(a).To regulate the active power balance diesel engine must be engaged to SM via

clutch. When the DE is started the cranking system is switched on until the DE reached

the firing speed where the internal combustion process starts. Once the firing speed is

reached DE cranking system is switched off and the DE speed controller is activated with

a speed reference of 1 pu. For this study cranking time and firing speed is taken as 0.5 sec

and 0.3 pu respectively. Therefore speed reference to DE changes to 1 pu at t=7.65 sec

(7.15+0.5) .Fig .7(b) shows the difference in speeds of DE and SM. When the speed

difference is zero, CLUTCH signal is changed to ‘1’ at t=9.5sec.Fig .4.6(c) shows the

change in CLUTCH signal. Fig4.6 (d), Fig.4.6 (e), Fig.4.6 (f) and Fig.4.6 (g) shows the

active power generated by diesel engine generator, wind turbine generator, speed and

system load respectively.

6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 8

0

0.2

0.4

0.6

0.8

1

1.2

Time(sec)

DR

UN

(D

iese

l Run

) Si

gnal

Load changeat 7 sec

Mains failureat t=7.15sec

DRUN=1

(a)

4 5 6 7 8 9 10 11 12

0

0.2

0.4

0.6

0.8

1

Time (sec)

CL

UT

CH

Sig

nal

Clutch locked at t=9.5 sec

Load changeat t= 7 sec

(b)

0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (sec)

Dif

fere

nce

in s

peed

s in

pu

(SM

and

DE

)

Clucth locks at t=9.5 sec

Chnage of speed reference at t=7.65

sec (7.15+0.5).

(c)

4.4 MATLAB MODEL OF COMPLETE CONTROL MECHANISM

ACTUATOR

0.5 Sec Delay

pm

1

conversion

boolean

TF 2

0.0384 s+1

1

TF 1

0.25s+1

0.009 s+1Switch 2

Switch1

Switch Saturation

SLOW

-C-

S-RFlip -Flop

S

R

QRelay 2

Relay 1

RATED

1

Product 1

PID Controller

PID

Logical

NOT

Logica

AND

Integrator 1

1s

Integrator

1s

Hs

1

Hd

-K-

Gain K 4

1/1.5

Wd

Ws

ENGINETd

DRUN1

0

DOFF

0

Constant

0

Add 2 Abs

|u|

1/(Hs+Hd)

1/1.8

DRUN

3

Ws2

Ts1

Wd

Torque

Td

Td

DRUN

CLUTCH

Fig 4.7 Matlab model of control circui

5 10 15 20-20

0

20

40

60

80

100

Time (sec)

Act

ive

Pow

er o

f Sy

nchr

onou

s M

achi

ne S

et in

Kw

Clutch lockedat t=9.5 sec

Extra load at t = 7 sec

(d)

5 7 9 11 13 15 17 19 2020

40

60

80

100

120

140

Time (sec)

Out

put W

ind

Pow

er in

KW

at 8

m/s

ec

Extra loadat t= 7 sec

Clucth lockedat t= 9.65 sec

(e)

0 2 4 6 8 10 12 14 16 18 20

0.2

0.4

0.6

0.8

1

1.2

Time (Sec)

Spee

d / F

requ

ency

in p

u

DE Speed

SM speed

DE Crankingfinished att=7.65sec

Clutch lockedat t=9.65 sec

SM speed

(f)

4 6 8 10 12 14 16 18 2020

40

60

80

100

120

140

160

180

Time (sec)

Loa

d in

Kw

Extra load of 45Kw at t=7 sec

(g)

Figs 4.6(a)-4.6(g): (a) Change of diesel run (DRUN) signal from wind to wind diesel mode. (b) Change of

clutch (CLUTCH) signal from wind to wind diesel mode. (c) Difference in speeds of diesel generator and

synchronous machine. (d) Active Power generated by diesel engine generator in Kw (e) Active Power

generated by wind turbine generator in Kw (f) Speeds of SM and DE in transition from wind to wind diesel

mode (g) System load in Kw

CHAPTER-V

WIND DIESEL HYBRID SYSTEM WITH VARIABLE SPEED WIND TURBINE

5.1 GENERAL

A wind energy system can be added to diesel engine system to provide some of the

load power and fixed or variable speed operation may be considered. Variable speed

operation has many advantages in terms of reduction of mechanical stress and smooth the

fluctuation of the power injected into the supply. Moreover variable speed operation can

increase the production of the energy and reduce noise. A power electronic interface is

needed to match the AC bus fixed frequency and voltage with the variable voltage and

frequency of the wind energy system.

Wind turbines using a doubly-fed induction generator (DFIG) consist of a wound

rotor induction generator and an AC/DC/AC IGBT-based PWM converter modeled by

voltage sources. The stator winding is connected directly to the 60 Hz grid while the rotor

is fed at variable frequency through the AC/DC/AC converter. The DFIG technology

allows extracting maximum energy from the wind for low wind speeds by optimizing the

turbine speed, while minimizing mechanical stresses on the turbine during gusts of wind.

The optimum turbine speed producing maximum mechanical energy for a given wind

speed is proportional to the wind speed.

5.2 CONTROL TECHNIQUE FOR DFIG

The wind turbine and the doubly-fed induction generator (WTDFIG) are shown in

the Fig 5.1. The AC/DC/AC converter is divided into two components: the rotor-side

converter (Crotor) and the grid-side converter (Cgrid). Crotor and Cgrid are Voltage-

Sourced Converters that use forced-commutated power electronic devices (IGBTs) to

synthesize an AC voltage from a DC voltage source. A capacitor connected on the DC

side acts as the DC voltage source. A coupling inductor L is used to connect Cgrid to the

grid. The three-phase rotor winding is connected to Crotor by slip rings and brushes and

the three-phase stator winding is directly connected to the grid. The power captured by the

wind turbine is converted into electrical power by the induction generator and it is

transmitted to the grid by the stator and the rotor windings. The control system generates

the pitch angle command and the voltage command signals Vr and Vgc for Crotor and

Cgrid respectively in order to control the power of the wind turbine, the DC bus voltage

and the reactive power or the voltage at the grid terminals.

The model is based on using the grid-side converter (VSC) for the wind turbine

terminal voltage regulation. This is carried out in parallel with its main function and that is

to regulate the DC bus voltage of the back-to back converter. Moreover, the maximum

power tracking job is carried out by the generator (rotor) side converter. The connection

diagram of the DFIG with a brief description for the converter’s control actions and the

required signals are shown in Fig.5.1 [25].

Fig.5.1 Connection diagram of the DFIG with control technique signals

5.2.1 ROTOR SIDE CONVERTER CONTROL LOOPS

The q-axis component control loop is dedicated to track the maximum output power

using the instant values of the incident wind speed and the generator rotational speed with

a maximum power tracking characteristic for the turbine as shown in the Fig 5.2. The

difference between the optimum power (Pref) and the summation of the actual generated

power and the power losses activates a PI (proportional integral) controller that generates

the q-axis reference current (I*q). This reference current value is then compared with the

actual q-axis rotor current to activate a PI controller which in turn generates the reference

q-axis voltage reference signal (V*q) for the rotor-side converter.

Fig 5.2 Turbine power characteristics for a different value of turbine speed

On the other hand, the d-axis component control loop is dedicated to generate the d-axis

voltage reference signal (V*d). The q-axis reference current (I*d) is generated by passing

the error through PI controller generated by comparing reference Voltage at stator (Vref)

and actual voltage at stator (Vact). This reference current value is then compared with the

actual q-axis rotor current to activate a PI controller which in turn generates the reference

d-axis voltage reference signal (V*d) for the rotor-side converter. Using such reference

current settings, the rotor converter supplies only the reactive power of the rotor. By

setting of stator reference reactive power to zero, one gets unity power factor condition at

stator of the generator terminals. The rotor-side converter control loops are illustrated in

Fig. 5.3.

Vq*

2

Vd*

1

Rate Limiter 1

Rate Limiter Rate Limiter

Limiter 1

PIPI

PIPI

Iqr

6

P_B1

5

Refernce Power fromOptimum Power Tracker

4

Idr

3

V_B1

2

V_ref

1Idr*

Iqr*

Fig.5.3 Control loops for rotor side converter

In this figure, the d-axis and q-axis reference voltages (V’d and V’q) are added with the

voltage drops in the rotor circuit parameters to get the actual reference signal at the

converter side.

5.2.2 STATOR SIDE CONVERTER CONTROL LOOPS

The difference between the actual value of voltage of the DC link (VDC,actual) and the

required reference value (VDC,ref) activates a PI (proportional integral) controller to

produce the required d-axis current component control signal (I*d). This is then compared

with the actual grid-side converter d-axis current and the generated error activates another

PI controller to generate the d-axis reference voltage signal (V*d) for the grid-side

converter.

A similar scenario is applied for generating the q-axis voltage reference signal (V* q)

which is dedicated to regulate the grid terminal voltage (VGrid, actual) by making the q-axis

reference current as zero (I*q,ref). This is then compared with the actual grid-side converter

q-axis current and the generated error activates another PI controller to generate the q-axis

reference voltage signal (V*q) for the grid-side converter. The corresponding block

diagrams for the grid-side converter control loops are presented in Fig. 4.5.The parameters

of the Figures 4.3, 4.4 and 4.5 and for Eq.4.1 are presented in List of symbols.

Vd*

2

Vq*

1PI

PIPI

Rate Limiter 3

Rate Limiter 2

Iq

5

Id

4

Iq_ref

3

Vdc

2

Vdc_ref

1Idref

Fig.5.4 Control loops for grid side converter

5.2.3 PITCH ANGLE CONTROL LOOP

As the turbine rotational speed (ω) exceeds the reference value at which the output

power of the turbine is 1 pu, the pitch angle actuator is activated to adjust the turbine

mechanical power to 1 pu. The corresponding block diagram for the pitch angle control

loop is presented in Fig. 4.6. The maximum pitch angle is set to be 45° while the pitch

angle rate of change is limited to 1°/s..

Fig.5.5 Pitch angle control loop

5.3 MODEL OF WIND DIESEL SYSTEM WITH DFIG

Fig.5.6 Block diagram model of wind diesel system with DFIG

Wind

TurbineDFIG

Diesel

Engine

Load SM

5.3.1 MATLAB BASED MODEL OF WIND DIESEL SYSTEM WITH DFIG.

w

1

powergui

Phasors

Wind1

Wind turbineData acquisition

V1_B575

I1_B575

P_mean

Q_mean

Wind TurbineDoubly -Fed Induction Generator

(Phasor Type )1

Wind (m/s)

Trip

mA

B

C

mA

B

C

Wind (m/s)

Trip

WindBus

A

B

C

a

b

c

Vtref (pu )3

1

Vtref (pu )1

1

Trip

0

Three2

Vabc

IabcA B C

a b c

Three1

Vabc

IabcA

B C

a b c

A

B

C

A

B

CSynchronous Machine

480 V 260 kVA

Pm

Vf _

m

A

B

C

Subsystem1

Measurements

Subsystem

Measurements

Scope 5

Scope 4

Scope 3

Scope 20

Scope 2

Scope 1

MW5

4/120

MW4

1800

Load 1 A B C

a b c

Load25 kW2

A B CLoad25 kW1

A B C

Load25 kW

A B C

Load A B C

a b c

GOVERNOR& DIESEL ENGINE

wref (pu)

w (pu)

Pmec (pu)

Iabc _S1

Vabc_S1

Iabc _Load

Iabc _Load 1

Vabc_Load

Iabc _S

Vabc_S

Vabc_Load 1

ExcitationSystem1

vrefvdvqvstab

VfDiesel

Bus

A

B

C

a

b

c

Demux

3-Phase Breaker

A

B

C

a

b

c

<Rotor speed wm (pu)>

<Vdc (V)>

<wr (pu)>

<P (pu)>

<Q (pu)>

<Pitch_angle (deg)>

Fig 5.7 Wind diesel system with transmission line

5.4 RESULTS AND DISCUSSION

The wind diesel hybrid system i.e., wind turbine ,diesel generator and doubly fed

induction generator along with proposed control loops for grid-side converter and rotor-

side converter are modeled in MATLAB/Simulink. The ratings of the DFIG (doubly-fed

induction generator), wind turbine and the simulation parameters of the system are

represented in the Appendix. The performance of the system has been analyzed with and

without transmission line for different loads

5.4.1 PERORMANCE OF WIND DIESEL SYSTEM WITH ‘R’ LOAD.

In this model, Variable speed wind generator is equipped with diesel generator is used

to supply stand alone loads. DFIG improves the system stability and efficiency of isolated

system. In this simulated model 275 Kw of DFIG is equipped with 275 Kw of diesel

generator. Pitch angle control mechanism is used to regulate the output power beyond the

particular speed. Diesel unit balances the system power for changing wind speeds. DFIG

control mechanism and synchronous machine uses to control the voltage of the system.

Simulation is performed for 60 sec. Wind speed is kept constant at 20sec and sudden

increase of wind speed from 10 to 12m/s is taken place at 20 sec. Fig5.8 (a) shows the

simulated wind speed. When the wind speed increases the power output from diesel

generator decreases in order to maintain the active power balance as shown in the

Fig5.8(b).Fig5.8(c),Fig5.8(d) and Fig5.8(e) shows the System load, system frequency and

speed of DFIG in pu respectively. As the load increases at 40 sec keeping the wind speed

constant, the extra load of 50Kw is met by diesel generator. DC voltage across capacitor

maintained constant at 800V by using stator side converter loops of doubly fed induction

generator. System voltage is maintained constant at 1pu by operating the DFIG in constant

voltage regulation mode. Frequency is maintained constant by using diesel governor

which senses the change in speed and acts according to it. Speed of DFIG increases from

1pu to 1.2 pu as wind speed changes from 10m/s to 12 m/s

Fig5.8 (f), Fig5.8 (g), and Fig5.8 (h) shows the dc voltage at capacitor, Reactive power

supplied by diesel and wind generators respectively.

15 20 25 30 35 40 45 50 55 607

8

9

10

11

12

13

14

15

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

15 20 25 30 35 40 45 50 55 60

140

160

180

200

220

240

260

280

Time (Sec)

Load

Acti

ve P

ower

in K

w

(c)

15 20 25 30 35 40 45 50 55 60

0

50

100

150

200

250

300

Time (Sec)

Activ

e Pow

er in

Kw

DieselPower

Wind Power

(b)

15 20 25 30 35 40 45 50 55 6059

59.5

60

60.5

61

Time (Sec)

Syste

m F

requ

ency

in H

z

(d)

15 20 25 30 35 40 45 50 55 600.9

0.95

1

1.05

1.1

1.15

1.2

1.25

Time (Sec)

Spee

d of

DFI

G in

pu

(e)

15 20 25 30 35 40 45 50 55 60790

795

800

805

810

815

Time (Sec)

DC v

oltag

e at C

apac

itor i

n Vo

lts

(f)

15 20 25 30 35 40 45 50 55 60

0.8

0.85

0.9

0.95

1

Time (Sec)

Syste

m Vo

ltage

in pu

(g)

20 25 30 35 40 45 50 55 60

-40

-30

-20

-10

0

10

20

30

40

Time (Sec)

Reac

tive P

ower

from

Dies

el G

en in

Kva

r

(h)

Fig.5.8 (a) –Fig 5.8(h):-Simulation results of the proposed system for Variable wind system equipped with

diesel system:( a) wind speed in m/s. (b) Active Powers generated wind and diesel in Kw. (c) Load active

power in Kw.(d) System Frequency in Hz (e) Speed of DFIG in pu.(f) DC Voltage at Capacitor in Volts.(g)

System Voltage in pu.(h)Reactive Power supplied by diesel generator in Kvar.

5.4.2 PERFORRMANCE OF WIND DIESEL SYSTEM FOR ‘RL’ LOAD

For this RL load Simulation is performed for 100 sec. Wind speed is kept constant till

40sec and sudden increase of wind speed from 8 to 12m/s is taken place at 40 sec. Fig5.9

(a) shows the simulated wind speed. At 8 m/s wind turbine generator is producing

maximum power of 55Kw.So in order to meet total load of 200 Kw, diesel is

producing145Kw. When the wind speed increases the power output from diesel generator

decreases in order to maintain the active power balance as shown in the Fig 5.9(b).

Load Reactive power kept constant at 70Kvar till 70 sec as shown in the Fig5.9(d), and

sudden increase in reactive load is met by DFIG and diesel generator in order to make the

system voltage constant. DFIG is operated in voltage regulation mode in order to maintain

voltage constant at diesel bus. Load active power is kept constant at 200Kw and sudden

increase of 50Kw takes place at 70 sec as shown in the Fig 5.9(c). This extra load is met by

diesel generator. System Voltage at both the buses and system frequency maintained

constant at desired value as shown in the Fig 5.9(e) and Fig 5.9(f) respectively.

Fig 5.9(g), Fig 5.9(h), Fig 5.9(i) and Fig5.9 (j) shows the Speed of DFIG in pu, DC voltage

across capacitor, Reactive powers supplied by diesel and wind generators respectively.

30 40 50 60 70 80 90 1006

7

8

9

10

11

12

13

14

15

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

40 50 60 70 80 90 100140

160

180

200

220

240

260

Time (Sec)

Load

Acti

ve P

ower

in K

w

(c)

40 50 60 70 80 90 10059

59.5

60

60.5

61

Time (Sec)

Syste

m F

reque

ncy

in H

z

(e)

30 40 50 60 70 80 90 100

0

50

100

150

200

250

Time (Sec)

Activ

e Pow

ers in

KW Wind Power

Diesel Power

(b)

40 50 60 70 80 90 10050

60

70

80

90

100

Time (Sec)

Load

Rea

ctive

Pow

er in

Kvar

(d)

40 50 60 70 80 90 100

0.8

0.85

0.9

0.95

1

1.05

Time (Sec)

Syste

m Vo

ltage

in pu

(f)

40 50 60 70 80 90 1000.7

0.8

0.9

1

1.1

1.2

Time (Sec)

Spee

d of

DFI

G in

pu

(g)

40 50 60 70 80 90 100

20

40

60

80

100

120

140

160

Time (Sec)

Reac

tive P

ower

from

DFI

G in

Kva

r

(i)

40 50 60 70 80 90 100795

800

805

810

815

Time (Sec)

DC V

oltag

e at C

apac

itor i

n Vo

lts

(h)

40 50 60 70 80 90 100-80

-60

-40

-20

0

20

40

60

80

Time (Sec)

Reac

tive P

ower

from

Dies

el G

en in

Kva

r

(j)

Fig.5.9 (a) –Fig 5.9(j):-Simulation results of the proposed system for Variable wind system equipped with

diesel system (For RL load) : ( a) wind speed in m/s. (b) Active Powers generated wind and diesel in Kw.

(c) Load active power in Kw.(d) Load Reactive power in Kw (e).System Frequency in Hz (f) System

Voltage in pu (g) Speed of DFIG in pu. (h) DC Voltage at Capacitor in Volts. (i) Reactive Power supplied

by DFIG in Kvar. (j) Reactive Power supplied by diesel generator in Kvar

5.4.3 PERFORMANCE OF WIND DIESEL SYSTEM WITH TRANSMISSION

LINE FOR ‘R’ LOAD.

In this model of simulation, a transmission line of 1 mH is used to transfer power between

wind and diesel energy systems. Loads are being met at both wind generator and diesel

generator buses. If the wind power is unable to meet its own load at particular wind speed,

extra load is met by diesel generator by transferring the power via transmission line .If the

wind is generating more power, then the extra power transfers to load at diesel generator

bus. So, diesel generator reduces its generation to maintain frequency to scheduled value.

Voltage at both the buses are maintained constant by operating DFIG in voltage regulation

mode and also by using the reactive power generated by synchronous machine.

Simulation is performed for 100 sec to obtain the performance of wind diesel

system for different wind speeds. Wind speed is maintained constant at 12m/s till 20 sec,

sudden increase from 12 to 14m/s at 20 sec and sudden decrease from 14m/s to 10m/s at

50sec is taken place as shown in Fig5.10(a). Load at diesel generator bus is maintained

constant at 140Kw throughout the simulation interval as shown in the Fig 5.10(d), where as

load at wind generator bus maintained constant at 140Kw till 75sec and sudden increase of

40Kw in its load took place at 75sec as shown in the Fig 5.10(c)

During 0<t<20 sec wind is able to generate 197Kw as shown in the Fig5.10(b), the extra

power of 57Kw flows through transmission line to supply the load at diesel generator bus.

so, the diesel generates 83Kw as shown in the Fig5.10(b) to maintain active power balance.

When the wind speed increases to 14m/s, pitch control is comes into action to limit the

turbine speed as shown in the Fig 5.10(e). During 20<t<40,when the wind speed increases

to 14m/s, which is the maximum speed the turbine can withstand. Speed of DFIG is shown

in the Fig5.10 (g). Diesel generator output decreases further, so that the maximum power

for load at diesel generator is met by wind generator via transmission line.

Power flow in line for different wind speeds and loads is shown in the Fig

5.10(f).System frequency is maintained constant at 60Hz as shown in the Fig5.10 (h), by

maintaining active power balance between total generation and load. Speed of synchronous

machine which is maintained constant at different conditions is shown in the Fig 5.10(i).

Fig 5.10(j),Fig 5.10(k),Fig 5.10(l) ,Fig 5.10(m),Fig 5.10(n),Fig 5.10(o) and Fig 5.10(p)

shows the dc voltage across capacitor, voltage at diesel generator load bus, voltage at wind

generator load bus, Reactive power generated by diesel generator ,Reactive power at wind

generator bus and reactive power flown in line respectively.

20 30 40 50 60 70 80 90 1007

8

9

10

11

12

13

14

15

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

20 30 40 50 60 70 80 90 100130

140

150

160

170

180

190

Time (Sec)Loa

d A

ctiv

e P

ower

at

Win

d b

us in

Kw

(c)

20 30 40 50 60 70 80 90 1000

0.5

1

1.5

2

2.5

3

Time(Sec)

Pitc

h A

ngle

in

Deg

ress

(e)

20 30 40 50 60 70 80 90 1000.95

1

1.05

1.1

1.15

1.2

1.25

Time (Sec)

Spee

d of

DFI

G i

n p

u

(g)

20 30 40 50 60 70 80 90 1000

50

100

150

200

250

300

Time (Sec)

Act

ive

Pow

ers

in K

w

Diesel Power

Wind Power

(b)

20 30 40 50 60 70 80 90 100100

120

140

160

180

200

Time (Sec)Loa

d A

ctiv

e P

ower

at

Die

sel B

us in

Kw

(d)

20 30 40 50 60 70 80 90 100-150

-100

-50

0

50

100

Time (Sec)

Pow

er F

low

in L

ine

in K

w

(f)

20 30 40 50 60 70 80 90 10059

59.5

60

60.5

61

Time (Sec)

Syste

m F

requ

ency

in

Hz

(h)

20 30 40 50 60 70 80 90 1000.95

1

1.05

Time (Sec)

Spee

d of

Syn

chro

nous

Mac

hine

in p

u

(i)

20 30 40 50 60 70 80 90 1000.8

0.85

0.9

0.95

1

1.05

1.1

1.15

Time (Sec)

Vol

tage

at

Die

sel

Gen

Loa

d bu

s in

pu

(k)

20 30 40 50 60 70 80 90 10010

20

30

40

50

60

70

80

90

100

Time (Sec)

Rea

ctiv

e Po

wer

from

Die

sel G

en in

Kva

r

(m)

20 30 40 50 60 70 80 90 100-60

-40

-20

0

20

40

60

Time (Sec)

Reac

tive P

ower

flow

in L

ine i

n K

var

(o)

20 30 40 50 60 70 80 90 100770

780

790

800

810

820

830

Time (Sec)

DC

Vol

tage

at

Cap

cito

r in

Vol

ts

(j)

20 30 40 50 60 70 80 90 100

0.85

0.9

0.95

1

1.05

1.1

1.15

Time (Sec)V

olta

ge a

t W

ind

Gen

erat

or B

us in

pu

(l)

20 30 40 50 60 70 80 90 100-50

0

50

Time (Sec)

Rea

ctiv

e Po

wer

from

DFI

G in

Kva

r

(n)

Fig.5.10 (a) –Fig 5.10(0):-Simulation results of the proposed system for Varaible wind system equipped

with diesel system (For R load) : ( a) wind speed in m/s. (b) Active Powers generated wind and diesel in

Kw. (c) Load active power in Kw at wind bus d) Load active power in Kw at diesel. e) Pitch angle in

degrees .f)Power flow in line in Kw. g)speed of DFIG in pu. (h).System Frequency in Hz (i) Speed of

synchronous machine in pu.(j) DC voltage at capacitor in volts (k) Voltage at diesel gen bus in pu (l)

Voltage at wind gen bus in pu (m) Reactive Power supplied by diesel in Kvar .(n) Reactive Power supplied

by DFIG in Kvar (o) Reactive power flow in line in Kvar.

5.4.4 PERFORMANCE OF WIND DIESEL SYSTEM FOR ‘RL’ LOAD WITH

TRANSMISSION LINE

In this model of simulation, a transmission line of 1 mH is used to transfer power

between wind and diesel energy systems. Reactive Loads are being met at both wind

generator and diesel generator buses. If the wind power is unable to meet its own load at

particular wind speed, extra load is met by diesel generator by transferring the power via

transmission line .If the wind is generating more power, then the extra power transfers to

load at diesel generator bus. So, diesel generator reduces its generation to maintain

frequency to scheduled value. Voltage at both the buses are maintained constant by

operating DFIG in voltage regulation mode and also by using the reactive power

generated by synchronous machine.

Simulation is performed for 100 sec to obtain the performance of wind diesel

system for different wind speeds. Wind speed is maintained constant at 12m/s till 20 sec,

sudden increase from 12 to 14m/s at 20 sec and sudden decrease from 14m/s to 10m/s at

50sec is taken place as shown in Fig5.11(a). Load at diesel generator bus is maintained

constant at 140Kw throughout the simulation interval as shown in the Fig 5.11(c), where

as load at wind generator bus maintained constant at 140Kw till 75sec and sudden

increase of 40Kw in its load took place at 75sec as shown in the Fig 5.10(c).During

0<t<20 sec wind is able to generate 197Kw as shown in the Fig5.10(b), the extra power

of 57Kw flows through transmission line to supply the load at diesel generator bus. So,

the diesel generates 83Kw as shown in the Fig5.11 (b) to maintain active power balance.

When the wind speed increases to 14m/s, pitch control is comes into action to limit the

turbine speed as shown in the Fig 5.10(e). During 20<t<40,when the wind speed

increases to 14m/s, which is the maximum speed the turbine can withstand. Speed of

DFIG is shown in the Fig5.10 (g). Diesel generator output decreases further, so that the

maximum power for load at diesel generator is met by wind generator via transmission

line.

Power flow in line for different wind speeds and loads is shown in the Fig

5.10(f).System frequency is maintained constant at 60Hz as shown in the Fig5.10 (h), by

maintaining active power balance between total generation and load. Speed of

synchronous machine which is maintained constant at different conditions is shown in the

Fig 5.10(i).Fig5.10(j),Fig 5.10(k),Fig 5.10(l) ,Fig 5.10(m),Fig 5.10(n),Fig 5.10(o) ,Fig

5.10(p) and Fig 5.10(q) shows the dc voltage across capacitor, voltage at diesel generator

load bus, voltage at wind generator load bus, Reactive power generated by wind

generator, load reactive power at diesel generator bus, reactive power flow in line,

Reactive power at diesel generator bus and reactive load at wind gen bus respectively.

20 30 40 50 60 70 80 90 1008

9

10

11

12

13

14

15

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

20 30 40 50 60 70 80 90 100100

110

120

130

140

150

160

Time (Sec)

Load

at D

iese

l gen

bus

in K

w

(c)

20 30 40 50 60 70 80 90 100

0

50

100

150

200

250

300

Time (Sec)

Activ

e Pow

ers in

Kw

Wind

Diesel

(b)

20 30 40 50 60 70 80 90 100130

140

150

160

170

180

190

Time (Sec)

Load

at W

ind

gen

bus i

n K

w

(d)

20 30 40 50 60 70 80 90 1000

0.5

1

1.5

2

2.5

3

Time (Sec)

Pitch

Ang

le in

Deg

rees

(e)

20 30 40 50 60 70 80 90 1000.95

1

1.05

1.1

1.15

1.2

1.25

Time (Sec)

Spee

d of

DFI

G in

pu

(g)

20 30 40 50 60 70 80 90 1000.95

1

1.05

Time (Sec)

Spee

d of

Syn

chrn

ous M

achi

ne in

pu

(i)

20 30 40 50 60 70 80 90 100-150

-100

-50

0

50

100

Time (Sec)

Powe

r Flow

in L

ine in

Kw

(f)

20 30 40 50 60 70 80 90 10059

59.5

60

60.5

61

Time (Sec)

Syste

m F

requ

ency

in H

z

(h)

20 30 40 50 60 70 80 90 100770

780

790

800

810

820

830

Time (Sec)

DC V

oltag

e at

Cap

acito

r in

Volts

(j)

20 30 40 50 60 70 80 90 1000.8

0.85

0.9

0.95

1

1.05

1.1

1.15

Time (Sec)

Volta

ge at

Dies

el Ge

n Bu

s in

pu

(k)

20 30 40 50 60 70 80 90 1000

20

40

60

80

100

Time (Sec)

Reac

tive P

ower

From

Win

d Ge

n in

Kva

r

(m)

20 30 40 50 60 70 80 90 100-40

-30

-20

-10

0

10

20

30

40

Time (Sec)

React

ive Po

wer F

low in

Line

in K

var

(o)

20 30 40 50 60 70 80 90 1000.8

0.85

0.9

0.95

1

1.05

1.1

1.15

Time (Sec)

Volta

ge at

Win

d Ge

n Bu

s in

pu

(l)

20 30 40 50 60 70 80 90 10010

20

30

40

50

60

70

80

Time(Sec)

Load

Rea

ctive

Pow

er at

Dies

el Ge

n bu

s

(n)

20 30 40 50 60 70 80 90 1000

20

40

60

80

100

Time (Sec)

Reac

tive P

ower

supp

lied

by d

iesel

gen

(p)

20 30 40 50 60 70 80 90 10035

40

45

50

55

60

65

Time (Sec)

Load

Rea

ctive

Pow

er at

Win

d Ge

n Bu

s

(q)

Fig.5.11 (a) –Fig 5.11(q):-Simulation results of the proposed system for Variable wind system equipped

with diesel system (For R load) : ( a) wind speed in m/s. (b) Active Powers generated wind and diesel in

Kw. (c) Load active power in Kw at diesel bus d) Load active power in Kw at wind. e) Pitch angle in

degrees .f) Power flow in line in Kw. g) Speed of DFIG in pu. (h).System Frequency in Hz (i) Speed of

synchronous machine in pu.(j) DC voltage at capacitor in volts (k) Voltage at diesel gen bus in pu (l)

Voltage at wind gen bus in pu (m) Reactive Power by wind in Kvar .(n)Load reactive power at diesel gen

bus (o) Reactive power flow in line in Kvar.(p) Reactive power supplied by diesel gen in Kvar.(q)

Reactive load at wind gen bus in Kvar

5.4.5 FAULT ANALYSIS ON WIND DIESEL SYSTEM FOR ‘R’ LOAD WITH

TRANSMISSION LINE

To ensure the system stability, fault analysis is performed on wind diesel system with

transmission line. Wind and diesel generators are separated by a transmission line of 1

mh and meeting corresponding loads at wind and diesel buses. Wind speed is kept

constant at 11m/s throughout the simulation interval as shown in the Fig 5.12(a).Load at

diesel generator and wind gen buses are kept constant at 140Kw and 140Kw respectively

as shown in the Fig 5.12(d) and Fig 5.12(e).As the wind generates less than 200Kw as

shown in the Fig 5.12(b), extra power is generated by diesel and supplies through

transmission line. Diesel speed regulator is used to control the frequency. Voltage at

diesel gen bus is controlled by exciter of a synchronous machine where as voltage at

wind gen bus is controlled by keeping synchronous condenser at wind generation bus.

Short circuit fault is simulated for 10 cycles to show the response of the system under

fault conditions. Fig 5.12(c), Fig 5.12(f), Fig 5.12(g), Fig 5.12(h) and Fig 5.12(i) shows

the active power generated by diesel, system frequency, Fault current from diesel

generator, fault current from wind generator and total fault current respectively. Voltage

is retained to required value after removing fault at both wind and diesel gen buses as

shown in the Fig 5.12(l) and Fig 5.12(n).Speeds of machines such as DFIG and

synchrouns machine are shown in the Fig 5.12(j) and Fig 5.12(m) respectively. Speed of

DFIG remains at 1.1 pu before and after the fault where as speed of synchronous machine

at 1 pu. Power flow in the line throughout the simulation interval is shown in the Fig

5.12(o).DC voltage across capacitor is shown in the Fig5.12 (k).

10 12 14 16 18 20 22 24 26 28 3010

10.5

11

11.5

12

Time (Sec)

Win

d Sp

eed

in m

/s

(a)

10 15 20 25 30 35 40-100

0

100

200

300

400

500

600

700

Time (Sec)

Dies

el A

ctive

Pow

er in

Kw

(c)

10 12 14 16 18 20 22 24 26 28 30-100

0

100

200

300

400

500

600

700

800

Time (Sec)

Win

d Tu

rbin

e Acti

ve P

ower

in K

w

(b)

10 12 14 16 18 20 22 24 26 28 300

100

200

300

400

500

600

700

800

Time (Sec)Load

Acti

ve P

ower

at Di

esel g

en bu

s in K

w

(d)

10 12 14 16 18 20 22 24 26 28 30-100

0

100

200

300

400

500

Time (Sec)Load

Acti

ve P

ower

at W

ind

Gen

bus

in K

w

(e)

10 12 14 16 18 20 22 24 26 28 300

200

400

600

800

1000

1200

1400

Time (Sec)

Faul

t cur

rent

from

dies

el ge

n in

Am

ps

(g)

10 12 14 16 18 20 22 24 26 28 30-1000

-500

0

500

1000

1500

2000

2500

Time (Sec)

Faul

t Cur

rent i

n Am

ps

(i)

10 12 14 16 18 20 22 24 26 28 3058

58.5

59

59.5

60

60.5

61

61.5

Time (Sec)

Syste

m F

requ

ency

in H

z

(f)

10 12 14 16 18 20 22 24 26 28 30

200

400

600

800

1000

1200

1400

Time (Sec)

Faul

t Cur

rent f

rom

Win

d Ge

n in

Am

ps

(h)

10 12 14 16 18 20 22 24 26 28 300.96

0.97

0.98

0.99

1

1.01

1.02

1.03

1.04

1.05

Time (Sec)

Spee

d of a

Syn

chro

nous

Mac

hine i

n pu

(j)

10 12 14 16 18 20 22 24 26 28 30500

1000

1500

2000

2500

3000

3500

Time (Sec)

DC V

oltag

e acro

ss Ca

pacit

or in

Vol

ts

(k)

15 20 25 30 35 401.085

1.09

1.095

1.1

1.105

1.11

1.115

1.12

Time (Sec)

DFI

G S

peed

in p

u

(m)

15 20 25 30 35 40-200

-150

-100

-50

0

50

100

150

200

250

Time (Sec)

Powe

r Flo

w in

line

in K

w

(o)

10 15 20 25 30 35 400

0.5

1

1.5

2

2.5

Time (Sec)

Volta

ge at

Win

d ge

n bu

s in

pu

(l)

10 15 20 25 30 350

0.5

1

1.5

2

2.5

Time (Sec)

Vol

tage a

t Dies

el ge

n bu

s in

pu

(n)

Fig.5.12(a) –Fig 5.12(o) :-Simulation results of the proposed system for wind diesel system with

transmission line :( a) wind speed in m/s. (b) Active Powers generated by wind generator in Kw.(c) Active

Powers generated by wind generator in Kw .(d) System Load at diesel bus (e) System Load at wind bus (f)

System Frequency in Hz.(g)Fault current from diesel gen bus (h) Fault current from wind gen bus (i) Total

fault current (j) Speed of synchronous machine (k) DC Voltage at capacitor (l)Voltage at wind gen bus (m)

Speed of DFIG (n) Voltage at wind gen bus (o) Power flow in line.

CHAPTER VI

CONCLUSIONS AND FUTURE WORK

6.1 GENERAL

The main objective of the work has been to Voltage and Frequency control of wind

diesel hybrid power system with fixed and variable wind turbines. The simulation of

wind diesel hybrid system has been done under different wind speeds and loads. The

following are the main conclusions of the investigations carried out in this thesis work.

6.2 CONCLUSIONS

The Hybrid system consists of wind turbine generators, diesel generators, dump load,

synchronous machine, Induction generator and the consumer load was simulated.

Frequency is regulated in all the modes of operation such as wind only mode, diesel only

mode and continuous wind diesel mode to assure the power quality. In order to reduce

the diesel fuel cost in continuous wind diesel mode, smooth control circuit was designed

for transition from wind to wind diesel mode during load wind penetrations and high

system loads. Locking clutch mechanism is used for engaging and disengaging the

diesel engine from synchronous machine in this transition.

Quality of power supplied to the autonomous system is improved by controlling the

frequency to a desired value. Power fluctuation has reduced much by using variable

speed wind turbine generator compared to fixed speed wind turbine. Compared with the

conventional diesel-wind system, the response of the system equipped with DFIG during

wind fluctuation and load changes is more stable, and the ability for reactive power

output of DFIG is improved the reactive power control in system operation observably.

Analysis also shows that in this kind of system, the diesel generator terminal voltage and

the upper limits for reactive power output of DFIG are important operative parameters

affecting the operation performance.

6.3 FUTURE WORK

This technique can be practically implemented and a thorough study can be made on its

performance for different wind speeds and loads. In the present work, voltage and frequency

control is done for isolated systems .It can be further extended to grid mode of operation.

Photovoltaic cell, Fuel cell and Micro turbine can also be integrated into wind diesel system.

The performance of isolated diesel-wind power systems can be improved effectively by

enhancing the wind generators. Moreover, the laboratory prototypes of these systems may

be developed to validate the design, model and control techniques.

REFERNCES

1. Anne-Marie Borbely and Jan F. Kreider, Distributed Generation: the power paradigm

For the new millennium, vol. I. United States of America: CRC, 2001, p.400.

2. T. Ackermann, Wind Power in Power Systems, England: John Wiley and Sons, Ltd,

pp. 53-78, 2005.

3. Wind Force 12, Report by the European Wind Energy Association (EWEA), October

2002.

4. Canadian Wind Energy Association (CanWEA), http://www.canwea.ca

5. Documentation on Wind diesel system with no storage.www.nrel.gov.in

6. J.K. Kaldellis, ―An Integrated model for performance simulation of hybrid wind-

diesel Systems, Renewable Energy, vol (32) (2007) pp.1544-1564

7. R.Sebastian, J.Quesada, “Distributed control system for frequency control in a

isolated Wind system,” renewable energy, vol (31) (2006) pp. 285-305.

8. H.S.ko, T.Niimura, K y.Lee, “An intelligent controller for a remote wind-diesel power

system-Design and Dynamic performance analysis,” IEEE Transcation on power

engineering , vol. (4), july ( 2003), pp:2147-2152

9. R.Sebastian, “Smooth transition from wind only to wind diesel mode in an

autonomous Wind diesel system with a battery based energy system” renewable energy,

vol (33) (2007) pp. 454-466.

10. Das D, Aditya SK, Kothari DP. “Dynamics of diesel and wind turbine generators on an

Isolated power system”. International Journal of Electrical Power & Energy Systems

1999; 21(3):183–9.

11. S.H.Karki, R.B.Chedid, and R.Ramdan “Probabilistic production costing of Diesel-

Wind energy conversions systems”, IEEE Transaction on energy conversion, Vol. (15),

(3), sep (2000), pp. 284-289.

12. Yeager KE, Willis JR. Modeling of emergency diesel generators in an 800 Megawatt

Nuclear power plant. IEEE Trans Energy Conversion1994;8(3).

13. S. Roy, 0. P. Malik and G. S. Hope, “Adaptive Control Of Speed And Equivalence

Ratio Dynamics Of A Diesel Driven Power-Plant” ,IEEE Transactions on Energy

Conversion, Vol. 8, No. 1, March 1993

14. P.A.Stott, M.A. Mucller, ―Modelling fully variable speed hybrid wind-diesel

systems‖, Universities Power Engineering Conference,vol(1) sep(2006) pp.212-217.

15. Katiraei Farid, Abbey Chad, “Diesel plant sizing and performance Analysis of a

remote wind-diesel microgrid ,” Power Engineering Society General Meeting, IEEE

(June) (2006), pp.1-8.

16. Ruben pena, Roberto Cardenas,” Control strategy for a doubly fed induction

generators for a wind diesel energy system,” Power Engineering Society General

Meeting, IEEE (June) (2002), pp.1-8.

17. Fadia M. A. Ghali Shawki H. Arafah, “Dynamic Analysis of Hybrid WindDiesel

SystemWith Three-Level Inverter”, ISIE 2001, Pusan, KOREA, pp.740-745, 2001.

18. Wind/diesel/desalination with high wind penetration. Internal report Danvest

energy. /www.danvest.com.

19. M. P. Papadopoulos, S. A. Papathanassiou, N. G. Boulaxis, and S. T. Tentzerakis,

“Voltage quality change by grid-connected wind turbines,” in European Wind Energy

Conference, Nice, France, 1999, pp. 783–785.

20. T. Petru and T. Thiringer, “Active flicker reduction from a sea-based 2.5 MW wind

park connected to a weak grid,” in Proc. Nordic Workshop on Power and Industrial

Electronics, Aalborg, Denmark, June, 13–16, 2002.

21. T. Thiringer and J. Linders, “Control by variable rotor speed of a fixed-pitch wind

turbine operating in a wide speed range,” IEEE Trans. on Energy Conversion, vol. 8,

no. 3, pp. 520–526, Sept. 1993.

22. D. Panda, E.L. Benedict, G. Venkataramanan, and T.A. Lipo, "A novel control

strategy for the rotor side control of a doubly-fed induction machine," in Proc. 2001

IEEE Thirty-Sixth IAS Annual Meeting Industry Applications Conf., Vol. 3, pp. 1695 -

1702.

23. R. Pena, J.C. Clare, and G.M. Asher, "Doubly fed induction generator using back-

tobackPWM converters and its application to variable-speed wind-energy generation,"

IEE Proc-Electr. Power Appl.., vol. 143, No. 3 pp. 231-241, May 1996.

24. G.S. Stavrakakis, G.N.Kariniotakisr, A general simulation algorithm for the accurate

assesment of isolated diesel-wind turbines system interaction ,IEEE transactions on

Energy Conversion, vol(10) sep(1995) pp.577-583.

25. T.H.M. EL-Fouly, E.F. EL-Saadany and M.M.A. Salama, “Voltage Regulation of Wind

Farms Equipped with Variable-Speed Doubly-Fed Induction Generators Wind

Turbines”, in Proc. of IEEE Power Engineering Society General Meeting, 24-28

June2007, pp. 1-8.

26. Matlab SimPower Software (Ver 7.3, 2006) [Online].Available:

www.mathworks.com/products/simpower/.

27. Woei-Luen Chen and Yuan-Yih Hsu, “Controller Design for an Induction GeneratorDriven

by a Variable-Speed Wind Turbine”, IEEE Trans. on Energy Conversion, vol.21, No. 3,

pp.625-635, September 2006

28. L. Zhang, C. Watthanasarn, and W. Shepherd, "Application of a matrix converter for the

power control of a variable-speed wind-turbine driving a doubly-fed induction generator,"

in Proc. 1997 23rd International Conference on Industrial Electronics, Control and

Instrumentation, IECON 97, vol. 2, pp. 906-911.

29. Roy Billinton, and Wijarn Wangdee, “Reliability-Based Transmission Reinforcement

Planning Associated With Large-Scale Wind Farms”, IEEE Trans. on Power Systems,

Vol. 22, No. 1, pp.34-41, February 2007.

30. Rogério G. de Almeida and J. A. Peças Lopes, “Participation of Doubly Fed Induction

Wind Generators in System Frequency Regulation”, IEEE Trans. on Power Systems,vol.

22, No. 3, pp.944-950, August 2007

APPENDIX

SIMULATION PARAMETERS

INDUCTION GENERATOR PARAMETERS:

275 KVA, 480V, 4 pole, 60 Hz three-phase induction generator.

Stator resistance (Rs) = 0.016 pu.

Rotor resistance (R’r) = 0.015 pu.

Stator leakage inductance (Lls) = 0.06 pu.

Rotor leakage inductance (L’lr) = 0.06 pu.

Magnetizing inductance (Lm) = 2.9 pu.

Inertia constant (H) = 2 s.

Number of pair poles (P) = 2.

Number of units = 1.

TURBINE PARAMETERS:

Base wind speed = 12 m/s.

CP(λ, β) coefficients: c1 = 0.5176, c2 = 116, c3 = 0.4, c4 = 5, c5 = 21, and c6 = 0.0068.

CP, max = 0.48.

λnom = 8.1.

K = 0.73.

ω base = 1.2.

SYNCHRONOUS GENERATOR PARAMETERS:

275KVA, 480V, 4 pole, 60 Hz three-phase synchronous generator.

Stator resistance (Rs) = 0.016 pu.

Inertia constant (H) = 2 s.

Number of pair poles (P) = 2.

Number of units = 1.