Modeling and Simulation of a Synchronous Generator Driven by an

Engine at a Power Station

Ritesh Kumar Student Id No: s11048886

School of Engineering and Physics Faculty of Science and Technology

University of the South Pacific

November 2011.

Supervisor Mr. Mohammed Tazil

School of Engineering and Physics Faculty of Science and Technology

University of the South Pacific

A report submitted in fulfillment of the requirements for the degree of Bachelor of Engineering Technology.

Aim

To model and simulate a Synchronous Generator driven by an Engine at a Power Station

i

Objectives

• Model and simulate the Synchronous generator and test with manual controls.

• Behaviour of the Synchronous generator as the load varies.

• Model by connecting a prime mover (diesel engine) to the synchronous generator

and simulate with variable loads.

• Implement Basic Auto control System on the model and simulate for stable power

output

• Model and simulate synchronous generator connected to the grid driven by a

prime mover.

ii

Declaration of Originality I Ritesh Kumar hereby declare that the report being written in this project is to the best of

my knowledge and belief original, except as acknowledged in the text. The material has

not been submitted previously, either in whole or in part, for a degree at this or any other

institution.

________________________

Ritesh Kumar

(Student ID No. s11048886)

iii

Acknowledgments

I would like to take this opportunity to thank all those people who assisted and supported

me over the course of this project.

First and foremost, I would like to thank my project supervisor Mr. Mohammed Tazil for

his constant encouragement, guidance, enthusiasm and support throughout this project.

Without his vision and unlimited support such a project would not have been possible.

Secondly, I am very grateful to all the academic and technical staff members of the

School of Engineering and Physics for their encouragement and support during the phase

of this project.

All my friends, colleagues and relatives deserve earnest thanks for their support,

encouragement and understanding.

Finally, I thank the almighty lord for giving me strength and helped me built faith in

doing this project also I would like to thank the lord for giving me such wonderful

family members, without their support and understanding this project would not have

been possible.

iv

List of Figures

Figure: 1.1 Shows the picture of a wind turbine with its components 3

Figure: 1.2 Block diagram of the wind power generation system. 4

Figure: 1.3 Model of the wind turbine system in Simulink 4

Figure: 1.4 Shows the picture of steam turbine generator system 6

Figure: 1.5 Simulink model for control of a steam turbine generator. 7

Figure: 1.6 shows the picture of the hydro power plant station 8

Figure: 1.7 Simulink model for hydro electric generator 9

Figure: 1.8 Shows the diesel engine cycle with its intakes 10

Figure: 1.9 Block diagram of the diesel power generation system. 11

Figure: 1.10 Shows Simulink model of a generator set operating on a local

grid

12

Figure: 1.11 Shows the emergency diesel generator set 13

Figure: 2.1 shows cutaway view of a synchronous AC generator with a

solid cylindrical rotor capable of high speed rotation

16

Figure: 2.2 The full equivalent circuit for a three-phase synchronous

generator

17

Figure: 2.3 Shows Phasor diagram of a unity power factor load, (b)

voltage and current response of a resistive load

17

Figure: 2.4 shows Phasor diagram of a lagging power factor load, (b)

voltage and current response of a inductive load

18

Figure: 2.5 Shows Phasor diagram of a leading power factor load, (b)

voltage and current response of a capacitive load

18

Figure: 2.6 Synchronous Machines model in SimPowerSystem library 19

Figure: 2.7 shows the model of the synchronous machine that was used

for simulation

20

v

Figure 3.1

Block diagram structure of the diesel-engine generator

governor

21

Figure 3.2 Block diagram of a PID controller 23

Figure: 3.3 Block diagram of engine speed control system, Implemented

PID speed Controller

25

Figure: 3.4 diesel engine governor system 26

Figure: 3.5 Model of the diesel engine governor system in Simulink 27

Figure: 3.6 Excitation block 30

Figure: 3.7 Model of the speed governor and the excitation in Simulink 30

Figure: 4.1 Preliminary model 1 of the synchronous generator 31

Figure: 4.2 Shows the multimeter results for a 100W active power for

preliminary design 1

32

Figure: 4.3 Three-phase voltage outputs from the scope for preliminary

design 1

32

Figure: 4.4 Three-phase current outputs from the scope for preliminary

design 1

33

Figure: 4.5 Shows the machine outputs for preliminary design 1 33

Figure: 4.6 Preliminary model 2 for the synchronous generator 34

Figure: 4.7 Three-phase voltage outputs from the scope for preliminary

design 2

35

Figure: 4.8 Three-phase current outputs from the scope for preliminary

design 2

35

Figure: 4.9 The unity power factor form preliminary design 2 36

Figure: 4.10 The lagging power factor form preliminary design 2 36

Figure: 4.11 standalone model 37

Figure: 4.12 Unity power factor for a 1MW resistive load 38

Figure: 4.13 The synchronous machine outputs for 1MW Active Power

load

38

Figure: 4.14 lagging power factor for a 35KW active power and 20KW 39

vi

reactive power

Figure: 4.15 The synchronous machine outputs for 35KW Active Power

load and 20KW Reactive Power load

39

Figure: 4.16 Powergui block 40

Figure: 4.17 Load flow and Machine initialization block 41

Figure: 4.18 Steady state peak voltages and currents for a 800KW Active

Power Load

41

Figure: 4.19 Steady state rms voltages and currents for a 800KW Active

Power Load

42

Figure: 4.20 Steady state peak voltages and currents for a 500KW Active

Power Load and 800KW Reactive Power load

42

Figure: 4.21 Steady state rms voltages and currents for a 500KW Active

Power Load and 800KW Reactive Power load.

43

Figure: 4.22 Final model connected to the grid 44

Figure: 4.23 Unity power factor for a 1MW active power load 45

Figure: 4.24 Three-phase voltages for a 1MW active power load 45

Figure: 4.25 Three-phase currents for a 1MW active power load 46

Figure: 4.26 Synchronous machine outputs for a 1MW active power load 46

Figure: 4.27 Lagging power factor for a 200KW active power load and

800KW reactive power load

47

Figure: 4.28 Three-phase voltages for a 200KW active power load and

800KW reactive power load

48

Figure: 4.29 Three-phase currents for a 200KW active power load and

800KW reactive power load

48

Figure: 4.30 Synchronous machine outputs for a 200KW active power

load and 800KW reactive power load

49

Figure: 4.31 Leading power factor for a 100KW reactive power load 50

Figure: 4.32 Three-phase voltages for a 100KW reactive power load 50

Figure: 4.33 Three-phase currents for a 100KW reactive power load 51

Figure: 4.34 Synchronous machine outputs for a 100KW reactive power 51

vii

load

Figure: 4.35 Active and Reactive block Added to the Final model 52

Figure: 4.36 Active and Reactive Power Supplied to the grid after

simulating a 1MW active power load (resistive load)

53

Figure: 4.37 Active and Reactive Power Supplied to the grid after

simulating a 200KW active power load and a 800KW reactive

power load (inductive load).

53

Figure: 4.38 Active and Reactive Power Supplied to the grid after

simulating a 100KW reactive power load (capacitive load).

54

Figure: 4.39 Synchronous machine outputs 55

viii

List of Tables

Table 2.1 Synchronous machine Parameters 19 - 20

Table 3.1 The table below summarizes the PID terms and their

effect on a control system.

24

Table: 4.1 Results for different sizes Active Powers (Resistive

loads) used in for simulation

44

Table: 4.2 Results for different sizes Reactive Powers (Inductive

loads) used in for simulation.

47

Table: 4.3 Results for different sizes Reactive Powers (Capacitive

loads) used in for simulation.

49

ix

Table of Contents

Aim i

Objective ii

Declaration of Originality iii

Acknowledgements iv

List of Figures v

List of Tables ix

Table of contents x

Abstract xii

Chapter 1 Introduction and Literature Review

1.1 Introduction 1

1.2 Literature Review 2

1.2.1 Wind Power 2

1.2.2 Biomass Power 5

1.2.3 Hydroelectric Power 8

1.2.4 Diesel Power 10

1.2.5 Matlab/Simulink software 14

Chapter 2 Synchronous Machine (Generator)

2.1 Introduction 15

2.2 Behavior of synchronous machine with different types of

loads

17

2.3 Simulink Model of Synchronous Machine 18

2.4 Synchronous Machine Used in Simulation. 19

x

Chapter 3 Diesel Engine

3.1 Introduction 21

3.2 Speed Control of the Diesel Engine 22

3.3 PID Controller 23

3.4 Actuator Design 25

3.5 Voltage Regulator 27

Chapter 4 Simulation Results

4.1 Introduction 31

4.2 Modeling of the synchronous generator 31

4.2.1 Preliminary Model 1 31

4.2.2 Preliminary Model 2 34

4.3 Standalone model 37

4.4 Load Flow and machine initialization 40

4.5 Final Model connected to the Grid 43

4.6 Synchronous Machine Outputs 54

4.7 Loading effects on the synchronous generator 56

Discussion 57

Conclusion 58

Future Recommendations 60

References 61

xi

Abstract

This report presents the modeling and simulation of a synchronous generator driven by a

diesel engine at a power station. The modeling process involves reviewing of literature

and exploring what work has been already done in this area. The models were achieved

after studying various simulations of power systems. The simulation was done using the

Matlab/Simulink software package. Using software modeling of a diesel generator

system provides an in-depth understanding of the system operation before building the

actual system. Also the testing and experiments of the system operation under

disturbances is not possible on the actual system. Individual system components such as

the synchronous generator were simulated with constant values and the results were

analyzed. Stability aspects of the synchronous generator driven by diesel engine with

various types and sizes of load were also analyzed and discussed in detail. Finally,

recommendations were given for future work and conclusion made.

xii

Chapter 1

Introduction and Literature Review

1.1 Introduction

The increasing demand for energy, the continuous decrease in the current available

resources of fossil fuels and the growing concern regarding environmental pollution have

forced mankind to discover new production technologies for electrical energy using clean

renewable sources such as wind energy, solar energy and water energy.

The renewable sources of electric power technologies such as wind, solar and hydro are

clean, silent and reliable, with low maintenance costs and small environmental impact.

The sunlight, kinetic energy of flowing water and kinetic energy of the wind are free,

practically unlimited, however, electric power production systems using as primary

sources completely pose problems such as wind speed fluctuations during day, night,

summer and winter. Also not enough water in the damn to run the hydro turbines and

lack of sunlight for solar panels cannot produce enough power to meet the demand. As a

result, in autonomous regimes, to meet the demand of the power supply to the local grid

should be backed-up by other reliable sources of primary energy, such as diesel generator

sets. The combined sources of primary energy with diesel generator sets are known as

hybrid systems and are designed for decentralized production of electric power. By

combining renewable energy sources of wind, solar and diesel increases the reliability of

supply of electricity to the consumers.

The increased interest in using diesel generator sets as the main source in isolated areas

or as an emergency source has been very reliable and economical. Diesel generators

provide continuous electric power to the grid when the renewable sources of energy are

insufficient and unavailable. The diesel generator sets convert the chemical energy from

the fuel into mechanical energy by the means of internal combustion engines. The

1

synchronous generator is main part of the diesel generator set as it converts the

mechanical power produced from the diesel engine to electrical power. The analysis of

various complex aspects of diesel generator sets is done through software modeling and

simulation. The simulation of the diesel generator is done in different regimes and the

behavior of the machine is analyzed.

For this proposed project refers to the modeling and simulation of a synchronous

generator driven by a diesel engine at a power station. The system is connected to the

grid and the behavior of the system is analyzed in detail.

1.2 Literature Review

Engineers have developed numerous methods of controlling stable power output.

Software’s are mostly used to control the power system at power stations. The prime

mover always provides mechanical power to the synchronous machine to deliver

electrical power. However, the system has to precisely maintain constant voltage and

frequency at all times. These parameters widely simulated and controlled using numerous

power software’s.

A lot of research has been done in these areas to control for stable power outputs through

simulation. Different types of prime movers behave differently with the synchronous

machine and are accordingly modeled and simulated for a stable power output .The

following sections describe the types of modeling and simulation of various power

generation systems.

1.2.1 Wind Power

The increasing capacity of wind power penetration is one of today’s most challenging

aspects in power-system control [2]. The synchronous generator is driven by the wind

turbine which acts as the prime mover. The Kinetic energy of the wind is changes to the

mechanical energy which drive the electric generator to produce electricity.

2

The wind blows on the blades of the turbine and makes them turn which turns the shaft

inside the nacelle (the box at the top of the turbine).The shaft goes into a gearbox which

increases the rotation speed enough for the generator, which uses magnetic fields to

convert the rotational energy into electrical energy. The power output goes to a

transformer, which converts the electricity coming out of the generator to the right

voltage for distribution system.

Figure: 1.1 shows the picture of a wind turbine with its components.

The instruments to measure the wind speed and direction are fitted on top of the nacelle.

When the wind changes direction motors turn the nacelle, and the blades along with it,

around to face the wind. The nacelle is also fitted with brakes, so that the turbine can be

switched off in very high winds, like during storms. This prevents the turbine being

damaged. All this information is recorded by computers and transmitted to a control

center, which means that people don't have to visit the turbine very often, just

occasionally for a mechanical check [4].

Various software’s methods are used by electrical engineers to study the load flow,

steady state voltage stability, dynamic and transient behavior of power systems through

computer models. This application is also applied to the wind turbine power generation

system. Today these tools must incorporate extensive modeling capabilities with

3

advanced solution algorithms for complex power-system studies, as in the case of wind

power applications [3].

Figure: 1.2 Block diagram of the wind power generation system.

The Figure below shows the modeling and simulation of the wind turbine power

generation in MATLAB/Simulink software. A 30kw 480V permanent magnet

synchronous generator (PMSM) is used to provide power to the grid.

Figure: 1.3 Model of the wind turbine system in Simulink

Advantages of wind Power

• Wind is free and in abundance.

• Installing the wind turbines for the first time is expensive while maintain is not

very expensive.

4

• It can be used to generate own power where the country grid cannot supply.

• Installing the wind turbine may take a very small piece of land while taking the

components up may be challenging.

• No pollution – clean power.

Disadvantages of wind Power

• A number of pollutants are given off into the surrounding in creation of the wind

turbines.

• Wind turbines are quite noisy.

• The wind speed is not constant hence there is no definite supply of electricity

always.

1.2.2 Biomass Power

Biomass energy is important for dual applications such as heat and power generation. It is

a clean renewable energy resource derived from the waste of human and natural

activities. It excludes organic material which has been transformed by geological process

into substances such ac coal and petroleum. The biomass energy is extracted from wood,

waste, alcohol fuels, crops, landfill gases.

Producing energy from biological mass (biomass) is a quite simple process. The bi-

product such as wood or crop remaining is burnt in furnaces. The created is used to boil

water and the energy from the steam is used to rotate turbines of the electric generators.

Sometimes it is also called steam turbine generators. Also when garbage is burned or

allowed to decompose it gives out methane gas which is also known as landfill gas. These

gases are collected and used to make energy for the power plants. This is also known as

gas turbine generators where the gas is used to turn the turbines.

5

Figure: 1.4 Shows the picture of steam turbine generator system

This system is widely used by many industries to produce in-house power and also by

countries to meet consumers’ power demand. However, the control of stable power with

different load and frequency is done through computer software’s. The Figureure below

shows a 600MVA 22kV synchronous generator driven by a steam turbine for stable

power output. The software used for simulation is Matlab/Simulink.

6

Figure: 1.5 Simulink model for control of a steam turbine generator.

Advantages of biomass energy

• Biomass does not add co2 to the atmosphere as it absorbs the carbon in growing as

it releases when consumed as fuel.

• Can be used with the same power plants that are used for fossil fuels.

• It’s cheap and also sensible to use waste products

• Reduces dependence on foreign oil and biomass energy has the potential to

greatly reduce greenhouse gas emissions.

Disadvantages of Biomass energy

• Sufficient quantity of waste may not be readily available

• Very little greenhouse gases are created while burning the fuel.

• Some materials are not always available.

7

1.2.3 Hydroelectric Power

Hydroelectric power plants produce about 24 percent of the world’s electricity which

supply more than one billion people with power. According to the National Renewable

energy Laboratory, the total output of the world’s hydropower plants is about 675,000

megawatts, which is equal to the energy of 3.6 billion barrels of oil.

Hydro power is the process of changing the kinetic energy of flowing water in a reservoir

into electrical power that we can use. The turbine acts as a prime mover for the

synchronous generator. The turbines are turned by the flowing water from the dam which

converts the kinetic energy of the water to mechanical energy. This mechanical energy is

used by the synchronous generator to produce electricity. Then the transformer in the

power house transforms the electricity into a usable form, and the electricity travels

through the power lines and goes for commercial and business use.

Figure: 1.6 shows the picture of the hydro power plant station

However, the control of steady state voltage, load flow and dynamic and transient

behavior of power systems is done through standard software simulated by electrical

engineers. The Figure below shows an example a hydroelectric turbine modeled in

Matlab/Simulink Software for control power output. A 200MVA 13.8kV synchronous

machine has been used for supplying stable power.

8

Figure: 1.7 Simulink model for hydro electric generator

Advantages of Hydro Power

• Pollution and waste free

• It’s a renewable energy source

• Very reliable and not expensive to maintain once the dam has been built

• Can increase and decrease the production depending on the demand of power

• Water can be stored and used in peak times.

Disadvantages of Hydro Power

• It takes a lot of time and expensive to build a dam.

• The dam will change the habitat and landscape, as much more land will be

submersed.

• The land below the dam is also affected as flow of water is reduced.

9

1.2.4 Diesel Power

In today’s world, where fuel prices are rapidly increasing as a result of rise in its demand

and minimal supply one needs to choose a cost effective fuel to meet their demand. The

diesel engine has proved to be extremely efficient and cost effective. The price of diesel

fuel is much higher than gasoline but diesel has a higher energy density than gasoline.

Diesel engines are widely used as a prime mover to provide mechanical power for the

synchronous generator to produce electricity.

A diesel generator consists of an internal combustion (IC) engine and a synchronous

generator coupled on the same shaft. The internal combustion engines convert chemical

energy from the fuel to mechanical energy. The pistons of the engine are connected to the

crankshaft, and the up-down motion of the pistons, known as the linear motion, creates

the rotary motion needed to turn the shaft of the synchronous generator. In a diesel air is

compressed first and then the fuel is injected because air heats up when it is compressed

and the fuel ignites.

Figure: 1.8 Shows the diesel engine cycle with its intakes

10

The diesel engine uses a four-stroke combustion cycle. The four strokes are:

• Intake stroke – the air moves in through the intake valve and moves the piston

down. Compression stroke -- The piston moves back up and compresses the air.

• Combustion stroke – When the piston reaches the top, fuel is injected and

ignited, forcing the piston to move down again.

• Exhaust stroke -- The piston moves back to the top, and pushes the exhaust out

from the exhaust valve which was created from combustion.

The diesel generator sets are usually designed to run at 3000 rpm or 1500 rpm at a

frequency of 50 Hz. The internal combustion engine is equipped with mechanical

regulators to keep the desired speed, coupled in the injection pump and adjusted to obtain

an output frequency of about 52 Hz without load and 50 Hz for rated load. . The speed

regulator and voltage regulator are two major components of a diesel generator set. The

performance of these components is vital for the operation and utilization of diesel

generator set, their purpose is to exactly maintain the desired voltage and frequency.

Figure: 1.9 Block diagram of the diesel power generation system.

The analysis of the complex aspects of a diesel generator set requires the development of

reliable numerical models that allow for simulation in different operation systems,

specifically in conditions as close as possible to the reality of the assembly internal

11

combustion engine and the synchronous generator. The synchronous generator

represents a key component of a diesel generator set. It converts the mechanical power

produced by the primary mover into electrical power [5]. The Figureure below shows a

diesel engine modeled with a synchronous generator for constant frequency and voltage

outputs.

Figure: 1.10 Shows Simulink model of a generator set operating on a local grid

Diesel generators can be used as prime source of power or as a backup power. During the

grid blackout one can use the generator set as back up to supply power. Also when there

is less power supplied by renewable sources such as hydro and wind, diesel generator set

can be used to generate power to the grid.

12

Figure: 1.11 shows the emergency diesel generator set

Advantages of diesel Power

• Modern diesel engines have overcome disadvantages of earlier models of higher

noise and maintenance costs.

• Fuel cost is low and is highly efficient and produces higher torque compared to

other fuels.

• There is no sparking as the fuel ignites. The absence of spark plugs lowers

maintenance costs.

• A diesel generator has a longer life compared with gas generators.

• Out of all the fuels diesel is least flammable and fuel is readily available.

Disadvantages of diesel Power

• The startup during cold conditions takes some time.

• The cost of buying a diesel generator is quite expensive though the maintenance

is cheap.

13

• The installation process and its period take a lot of time and consume higher cost

than installation of other generators.

• Light loads can cause a diesel generator to experience “wet stacking.” This causes

the engine to run rough and smoke.

1.2.5 Matlab/Simulink software

MATLAB is a general purpose mathematical convenient program which provides

editing, plotting, debugging, and graphics capabilities, as well as access to an extensive

and sophisticated library of dominant computational processes, and is becoming widely

used throughout the engineering community [5]. Simulink is a software package designed

to run within MATLAB. Simulink can be used for modeling, simulating, and analyzing

energetic system, whose performance is described with sets of differential equations. The

package has a graphical user interface (GUI) for building the dynamic system model from a

comprehensive library of built-in or user-defined, functional blocks.

The main advantages of using MATLAB- Simulink are:

• Fast development of the product

• Access to stylish reliable mathematical solution algorithms

• Assistance in output control, particularly with regards to graphics and results [5].

14

Chapter 2

Synchronous Machine (Generator)

2.1 Introduction

Synchronous generators are primary source of energy. Large- scale of power is generated

by three-phase synchronous generators, known as alternators, driven by steam turbines,

gas turbines, reciprocating engines and hydro turbines. The synchronous generator

converts mechanical energy produced by the engines and turbines to electrical power for

the grid. Synchronous generators can extremely generate large amount of power up to

1500MW. Synchronous machines always operate at synchronous speed because the rotor

speed always matches to the supply frequency.

The armature windings of the synchronous machine are placed on the stationary part called

stator. The armature windings are designed for generation of balanced three-phase voltages

and are arranged to develop the same number of magnetic poles as the field winding that is

on the rotor [6]. The field requires a two to three percent of the machine rating power for its

excitation. The rotor is mounted on a shaft driven by prime mover. A field winding carries a

DC current to produce a constant magnetic field. An AC voltage is induced in the three-

phase armature winding to produce electrical power. The electrical frequency of the three-

phase output depends upon the mechanical speed and the number of poles. The synchronous

speed is given by the formula:

����� =120��

Where:

����� = synchronous speed

F = system frequency

P = number of poles

There are two types’ synchronous generators, stationary field and revolving field. For the

stationary field generators, poles on the stator (field winding) are supplied with DC to

create a stationary magnetic field and the armature windings on the rotor consist of three-

15

phase windings whose terminals connect to three slip rings on the shaft. The brushes

connect the armature to the external three-phase load. These arrangements work for low

power machines less than 5KVA. Revolving field synchronous generators are commonly

known as alternators. These generators are used for large power generation. Revolving

synchronous generators has a stationary armature with three-phase winding on stator

while the three- phase is directly connected to the load. The rotating magnetic field is

created by DC field windings on rotor powered by slip-rings/brushes.

Figure: 2.1 shows cutaway view of a synchronous AC generator with a solid cylindrical

rotor capable of high speed rotation

The most suitable way to determine the performance characteristics of synchronous

generators is by means of equivalent circuits. These equivalent circuits can become very

useful when analyzing machine losses and performance. The following Figureure shows

the equivalent circuit of a three phase synchronous generator. Where, Xs is the

synchronous reactance, EA is the internal generated voltage, Va123 is the phase voltage, RA

is the series resistance, Vf is the field voltage, Radj adjustable resistor which controls the

flow of field current and RF ,LF are the coil inductance and resistance in series.

16

Figure: 2.2 The full equivalent circuit for a three-phase synchronous generator

2.2 Behavior of synchronous machine with different types of loads

Power Factor is defined as the fraction of the apparent power that is actually supplying

real power to a load. It is always between the numbers 0 to 1. The three types of power

factors are listed below.

� Unity power factor - In an AC circuit that is purely resistive current and voltage

are in-phase, the power factor is unity.

Figure: 2.3 (a) shows Phasor diagram of a unity power factor load, (b) voltage and

current response of a resistive load

17

� Lagging power factor - In an AC circuit that is inductive, current and voltage are

out of-phase, the impedance angle (j) is positive and current lags voltage by a

phase angle (Φ).

Figure: 2.4 (a) shows Phasor diagram of a lagging power factor load, (b) voltage and

current response of a inductive load

� Leading power factor – in an AC circuit that is capacitive, current and voltage

are out of phase, the impedance angle (J) is negative, and the current leads the

voltage phase angle (Φ) .

Figure: 2.5 (a) Shows Phasor diagram of a leading power factor load, (b) voltage and

current response of a capacitive load

2.3 Simulink Model of Synchronous Machine

The SimPowerSystem is part of the Simulink library that contains all the synchronous,

asynchronous and DC machines. The SimPowerSystem library contains six different

models of the three-phase synchronous machines with its parameters in PU standard and

in SI standard. The synchronous machines can be operated in both motor mode and in

18

generator mode. If the mechanical power for the machine is negative it operates in motor

mode and if the mechanical power supplied is positive the machine operates in generator

mode. The excitation is provided by the built in excitation block available

SimPowerSystem library.

Figure: 2.6 Synchronous Machines model in SimPowerSystem library

The upper row of the Figure 2.6 represents simplified models of the synchronous

generator with permanent magnets on the rotor and the down row represents generators in

PU/SI standards, these can used for modeling of power plants.

2.4 Synchronous Machine Used in Simulation.

The synchronous machine used in the simulation was a 3.125MVA, 2400V and 50Hz.

The machine parameters in PU standard are listed below.

Table 2.1 Synchronous machine Parameters

Direct Axis Synchronous Xd

1.56

Direct Axis Transient X'd

0.296

19

Direct Axis Subtransient X"d

0.177

Quadrature Axis Synchronous Xq 1.06

Quadrature Axis Subtransient X"q 0.177

D- axis time constants

Short-circuit

Q - axis time constants

Open -circuit

Leakage reactance Xl 0.052

Direct Axis Open Circuit Transient Td' 3.7

Direct Axis Short Circuit Transient Td" 0.05

Direct Axis Open Circuit Subtransient Tq" 0.05

Stator resistance Rs 0.0036

Inertia coefficient 1.07

Friction factor 0

Pole pairs 2

Rotor type Salient pole

Figure: 2.7 shows the model of the synchronous machine that was used for simulation

20

Chapter 3

Diesel Engine 3.1 Introduction

The speed of a diesel-engine generator set is controlled through a speed governor. The

control of a diesel engine can be considered as a speed-feedback system. The operator

gives a change in speed value by adjusting the governor set, the engine governor which is

also acts as sensor, will distinguish the change between the actual speed and the desired

speed, and control the fuel supply to maintain engine speed within the range. The

governor defined as an electromechanical device that automatically controls the speed of

the engine by linking the intake of the fuel. There several types of governors which exist

as mechanical-hydraulic, direct mechanical type, electro hydraulic, electronic, and

microprocessor based governors [7].

Figure 3.1 Block diagram structure of the diesel-engine generator governor

The appropriate operation of a diesel-engine generator is determined to a great extent by

two main components, the speed regulator and the voltage regulator. The performances

of these components are vital for the operation and utilization of diesel-engine generator.

21

The purpose of the speed regulator and voltage regulator is to maintain constant voltage

and frequency with any given type and size of load.

3.2 Speed Control of the Diesel Engine

The speed regulator of a diesel-engine generator is designed to maintain constant speed

of the diesel engine. The speed governor changes the amount of fuel used-up by the

motor at different amount of loads to maintain constant speed of the diesel-engine. For

instance, for a constant load the fuel is held steady since desired speed is equal to the

actual speed. If the desired speed and actual speed are different, the fuel setting is

adjusted by the driver to make actual speed equal to the desired speed. The fuel is held

steady until a speed or load changes. As the load increases the speed of the diesel engine

decreases, hence the actual speed gets lower than the desired speed. The fuel supply is

increased to increase the speed of the diesel engine, which returns the actual speed to the

desired speed. More fuel is consumed to pick up the load then to maintain the load. When

the load decreases, the speed of the engine increases and the actual speed get higher than

the desired speed, the fuel input is decreased which decreases the engine speed. The

actual speed returns to the desired speed of the diesel engine.

The speed governor of the diesel engine maintains constant voltage and frequency at the

generator terminals. The frequency is directly proportional to the generator speed. For a

constant frequency the speed governor needs to provide a good accuracy and a short

response time. When various electronic loads are connected or disconnected at the

generator terminals the speed governor starts regulating. There are plenty speed

governing systems, they start from a simple spring base up to complex hydraulic and

electronics ones able to regulate the fuel to maintain the speed of the diesel engine at a

constant value.

However, it is a difficult task to control the speed of power generation plants driven by a

diesel engine as a prime mover. This is due to the presence of a dead time and changes in

parameters, these results plant dynamics [8]. To control the speed many different

approaches has been used. The most widely used controller is a PID controller.

22

3.3 PID Controller

PID stands for Proportional, integral, and Derivative. It is a feedback controller, used to

correct the error between the input and the output. Error is known as the difference

between the actual speed and the desired speed. It is a basic filter device used to regulate

some output based upon the combined function of factors. PID is actually a differential

equation solved in the frequency domain. PID controller is a combination of three

different controllers that is proportional, integral and derivative controller [9].

Figure 3.2 Block diagram of a PID controller

P -Proportional, I - Integral, D - Derivative. These terms define three elementary

mathematical functions applied to the error signal. The controller does the PID

mathematical functions on the error and applies the sum to a process. Tuning a system

means adjusting three multipliers �, � and � adding in various amounts of these

functions to get the system to behave the way you want. The table 3.1 summarizes the

effect of PID on the control systems.

23

Table 3.1 the table below summarizes the PID terms and their effect on a control system.

The transfer function of the PID controller looks like the following:

� � �� � �� = ��

� � �� � ��

Where:

� = ����������������

� = ������������

� = ���!���!�����

The PID transfer function of the diesel-engine generator set is:

"# = $ � � �%�&'� � $ � � �%�&' � �%�'(' � %�) (%∗ +%)

Where:

%� = ���� �������#�

%∗ = �������#����� (%,-.) % = ��������� ���/��0�#/����1���������� % = ��������� ���/��0�#/����1����������

The transfer function of the controller after laplace transformation is:

24

"� = 21 � 345'

21 � 3�' �3�3�'�5

Where:

3�, 3�,34 � 7��1�������8�#��������

Figure: 3.3 Block diagram of engine speed control system, Implemented PID speed

Controller

3.4 Actuator Design

"(')

"9�

:���

'� � ;�:��' �:���

Where:

"(') � ���<���#�1����������=�������1������/������

"9(') � ���<����!����������1���/������

:�� � ���/����1�����#�����������>1��#0���/��#�1����

;� � ���/� �8����#�����#�������/��#�1����

Then the transfer function of the actuator is after Laplace transformation is:

25

"(')"�

= 1 �3?'

'(1 �3@')(1 �3A')

Where:

3?, 3@,3A � B#�1������8�#��������

Figure: 3.4 diesel engine governor system

The above model was to model the diesel engine governor system for the simulation. The

constants values were taken from reference [10]. The engine inertia is combined with the

generator inertia.

The model below shows the model of the system in MATLAB/Simulink.

26

Figure: 3.5 Model of the diesel engine governor system in Simulink

3.5 Voltage Regulator

The excitation block is used for voltage regulation, it is also known as the automatic

voltage regulator (AVR). It controls the voltage at the generator terminals. The voltage

regulator keeps the voltage constant during load variations by limiting voltage peaks and

over voltages as fast as possible. The excitation current is the parameter that changes the

voltage amplitude at the generator terminals. The mathematical implementation of the

excitation system is shown below.

The model of phase-compounding excitation system is expressed d-q component.

C, =D(C� + EF)� � (CF � E�=)� Where:

C, = �/��1��1�!���������/��=#�������1��� C� = �/���8��1�����8����!���������/���������� + �=��

CF = �/���8��1�����8����!���������/����������> + �=�� = √2

H

I

27

The voltage difference model is:

∆C = C,-. � C.K L + CM. � C�MLN + C..

CM. = D(C�)� � $CF&�. 11 � �3,

Where:

C,-. = �������#�!���������/��1��8���#!���������1�����

C.K = �������!��1����/��=#��������0���8

C�MLN = P��1� ���Q���!������

L = �/�����#��!������=#����

3, = ��8�#����������/���R����������

C.. = �1��1�!���������/���� S�#<����

∆C = �/�!������ �������#����������/�#�8���/����!�����

The compensator model is:

C� =∆C 1 � �3�1 � �3N

Where:

C� = �1��1�!���������/�#�8��������

3. = ��8�#����������/�#�8�����������

3N = ��8�#����������/�#�8�����������

The amplifier model is:

CL =C� L1 � �3L

Where:

CL = �/��1��1���!���������/��8�������

28

L = �������/��8�������

3L = ��8�#����������/��8�������

The model of the proportional saturation loop is:

T.� = CL � C, 0 ≤ T. ≤ T.VLW�� T. = T.�

T.VLW = #�������, � = 0

�, XM., � ≥ 0

Where:

T.� = �/��1��1�!���������/�!���������1�����

T. = �/��1��1�!���������/����������������1����������

T.VLW = �/�8�=�818�1��1�!���������/����������������1����������

The mathematical model of the alternating current exciter is given by:

C. = 13- � - T.�

Where:

- = ��8�#����������/������������#1������=#����

The feedback stability loop is given as:

C.. = C. � .1 � �3..

Where:

. = �/���� S�#<����

3.. = ��8�#����������/���� S�#<����

The following model shows the excitation system for the diesel generator system

modeled in Simulink. The block parameters are automatically changed as soon as the

29

load varies for the system. The initial values are implemented by Simulink since the

excitation block is available in the SimPowerSystem library. The X�and XF values are

taken from the synchronous machine output and connected directly the excitation block.

Figure: 3.6 Excitation block

Figure: 3.7 Model of the speed governor and the excitation in Simulink

30

Chapter 4

Simulation Results 4.1 Introduction

The synchronous generator will behave differently with different types of loads. This

chapter will show behavior of the model with different types of loadings and the

procedure followed to model the final circuit.

4.2 Modeling of the synchronous generator

4.2.1 Preliminary Model 1

The first objective of my project was to model and simulate a synchronous generator and

observe the behavior of the machine with different types and sizes of loads. Figure 4.1

first model of the synchronous generator which was made to see the outputs of the

system.

Figure: 4.1 Preliminary model 1 of the synchronous generator

An 8.1KVA 400V 50Hz pu standard synchronous generator was simulated with a 100W

active power (resistive load) and the results are shown below.

31

Figure: 4.2 Shows the multimeter results for a 100W active power for preliminary design

1

Figure: 4.3 Three-phase voltage outputs from the scope for preliminary design 1

32

Figure: 4.4 Three-phase current outputs from the scope for preliminary design 1

Figure: 4.5 Shows the machine outputs for preliminary design 1

The expected results were to get a pure sine wave from the model which was achieved

however the amplitudes were not correct since the generator was 400V and the voltage

output were near 2000V.

33

4.2.2 Preliminary Model 2

Another circuit was modeled using a 2000KVA 400V 50Hz synchronous generator in SI

standard. This time some changes were made to the circuit to compensate for the outputs

which were not correct. A 10KW Active power was used in the simulation. A small

resistance was applied as the resistance of the wire since the synchronous generator

cannot be connected directly to the scope. The model and results are shown below.

Figure: 4.6 Preliminary model 2 for the synchronous generator

34

Figure: 4.7 Three-phase voltage outputs from the scope for preliminary design 2

Figure: 4.8 Three-phase current outputs from the scope for preliminary design 2

However, the results gave pure sine waves for the system but the outputs were still out of

range. The behavior of the machine with a resistive and inductive load was tested and the

results are shown below.

35

Figure: 4.9 The unity power factor form preliminary design 2

Figure: 4.10 The lagging power factor form preliminary design 2

The machine outputs are different with a resistive load and a inductive load. For a

resistive current and voltage and current are in phase whereas for and inductive load

36

current lags the voltage by a phase angle. These two components are shown in Figure 4.9

and 4.10 above.

4.3 Standalone model

After modeling the synchronous machine the standalone model was made by connecting

the diesel engine governor system and the excitation block. A 3.125 MVA 2400 volts

50Hz synchronous generator was used to model the standalone system. The synchronous

machine and diesel engine parameters were taken from reference [6].

Figure: 4.11 standalone model

The standalone system was tested with different types and sizes of loads of which the

results are shown below.

37

Figure: 4.12 Unity power factor for a 1MW resistive load

Figure: 4.13 The synchronous machine outputs for 1MW Active Power load

38

Figure: 4.14 lagging power factor for a 35KW active power and 20KW reactive power

Figure: 4.15 The synchronous machine outputs for 35KW Active Power load and 20KW

Reactive Power load.

39

4.4 Load Flow and machine initialization

The machine state has to be initialized for constant speed and voltage output. The

Powergui block available in the Simulink library allows in doing the load initialization.

As soon as a model is simulated a Powergui block is automatically created. By clicking

on the block various components of the model are shown.

Figure: 4.16 Powergui block

After adding a load the load has to be initialized for constant voltage and frequency. By

clicking on the load flow and machine initialization block and choosing update circuit

measurements, the circuit measurements are automatically changed. The field voltage and

mechanical power values are changed to maintain constant voltage and speed of the

diesel engine.

40

Figure: 4.17 Load flow and Machine initialization block

The steady state current and voltage block determines the peak voltage, peak current, rms

voltage and rms current for that load. It gives the values expected after the simulation of

the model.

Figure: 4.18 Steady state peak voltages and currents for a 800KW Active Power Load

41

Figure: 4.19 Steady state rms voltages and currents for a 800KW Active Power Load

Figure: 4.20 Steady state peak voltages and currents for a 500KW Active Power Load

and 800KW Reactive Power load.

42

Figure: 4.21 Steady state rms voltages and currents for a 500KW Active Power Load and

800KW Reactive Power load.

4.5 Final Model connected to the Grid

The final model was made by connecting all the components to the grid. A 200MVA grid

was used to connect the final model. The behavior of the grid connected synchronous

machine driven by a diesel engine was tested with different types and sizes of loads. the

Figure below shows the final model.

43

Figure: 4.22 Final model connected to the grid

Table: 4.1 Results for different sizes Active Powers (Resistive loads) used in for

simulation

Active Power (W)

Reactive Power (VAR)

RMS Voltage

RMS Current

Frequency (HZ)

Peak Voltage

Peak Current

50000 0 1386 13.03 50 1960.099997 18.42720272

100000 0 1386 24.06 50 1960.099997 34.02597831

150000 0 1386 36.09 50 1960.099997 51.03896747

200000 0 1386 48.12 50 1960.099997 68.05195662

250000 0 1386 60.15 50 1960.099997 85.06494578

500000 0 1386 120.3 50 1958.685784 170.1298916

800000 0 1385 192.4 50 1958.685784 272.0946894

1000000 0 1385 240.5 50 1961.514211 340.1183618

2000000 0 1387 481.18 50 1961.514211 680.4912819

3000000 0 1387 722.5 50 1961.514211 1021.769299

44

Figure: 4.23 Unity power factor for a 1MW active power load

Figure: 4.24 Three-phase voltages for a 1MW active power load

45

Figure: 4.25 Three-phase currents for a 1MW active power load

Figure: 4.26 Synchronous machine outputs for a 1MW active power load

46

Table: 4.2 Results for different sizes Reactive Powers (Inductive loads) used in for

simulation.

Active Power (W)

Reactive Power (VAR)

RMS Voltage

RMS Current

Frequency (HZ)

Peak Voltage Peak Current

20K 35K 1384 9.705 50 1957.27157 13.72494262

100K 80K 1386 30.82 50 1960.099997 43.58606199

100K 150K 1385 45.61 50 1958.685784 64.50228058

100K 200K 1386 53.79 50 1960.099997 76.07054752

50K 250K 1386 61.33 50 1960.099997 86.73371778

200K 500K 1386 129.5 50 1960.099997 183.1406563

500K 800K 1385 226.9 50 1958.685784 320.8850573

1M 2M 1385 528 50 1958.685784 746.7047609

1M 3M 1385 761 50 1958.685784 1076.216521

1M 50K 1385 240.8 50 1958.685784 340.5426258

Figure: 4.27 Lagging power factor for a 200KW active power load and 800KW reactive

power load

47

Figure: 4.28 Three-phase voltages for a 200KW active power load and 800KW reactive

power load

Figure: 4.29 Three-phase currents for a 200KW active power load and 800KW reactive

power load

48

Figure: 4.30 Synchronous machine outputs for a 200KW active power load and 800KW

reactive power load

Table: 4.3 Results for different sizes Reactive Powers (Capacitive loads) used in for

simulation.

Reactive Power (-VAR)

Active Power (W)

RMS Voltage

RMS Current

Frequency (HZ)

Peak Voltage

Peak Current

50000 0 1386 12.03 50 1960.099997 17.01298916

20000 0 1386 4.814 50 1960.099997 6.808024089

100000 0 1386 24.06 50 1960.099997 34.02597831

150000 0 1386 36.18 50 1960.099997 51.16624669

200000 0 1386 48.41 50 1960.099997 68.46207855

250000 0 1386 60.48 50 1960.099997 85.53163625

500000 0 1386 120.3 50 1960.099997 170.1298916

800000 0 1386 192.4 50 1960.099997 272.0946894

1000000 0 1386 240.6 50 1960.099997 340.2597831

2000000 0 1386 481.1 50 1960.099997 680.3781449

49

Figure: 4.31 Leading power factor for a 100KW reactive power load

Figure: 4.32 Three-phase voltages for a 100KW reactive power load

50

Figure: 4.33 Three-phase currents for a 100KW reactive power load

Figure: 4.34 Synchronous machine outputs for a 100KW reactive power load

51

After testing the final model with various types and size of load I was required to verify if

the system was supplying power to the grid or extracting power from the grid. This was

done by adding an active and reactive power block to the model from the Simulink

library. Since the reactive supplied to the grid was negative it was concluded that it was

supplying power to the grid.

Figure: 4.35 Active and Reactive block Added to the Final model

52

Figure: 4.36 Active and Reactive Power Supplied to the grid after simulating a 1MW

active power load (resistive load)

Figure: 4.37 Active and Reactive Power Supplied to the grid after simulating a 200KW

active power load and a 800KW reactive power load (inductive load).

53

Figure: 4.38 Active and Reactive Power Supplied to the grid after simulating a 100KW

reactive power load (capacitive load).

4.6 Synchronous Machine Outputs

The synchronous machine outputs shown below shows the mechanical power provided

by the diesel engine, the field voltage, rotor speed and the terminal voltage of the

synchronous machine.

54

Figure: 4.39 Synchronous machine outputs

The mechanical power stabilizes near 0.285 pu however, it takes almost 1 second to the

system to stabilize. As soon as the mechanical power gets stable the whole system gets

stable. Initially the field voltage goes up to 5 pu to keep the terminal voltage at 1 pu. As

soon as the rotor speed comes to 1 pu the field voltage also comes near 1 pu. This is

evident from the formula:

TZ = [%

Where:

= #��������������������/�#�����1#�������/�8�#/���

[ = ��1=���/�8�#/���

% = ���� ���/������

TZ = ���������������� !������

55

To maintain the internal generated voltage (Vt) the flux (Vf) has to go up as the machine

starts. Once the machine is operating at its normal speed with the appropriate mechanical

power provided the field voltage comes back to 1 pu.

4.7 Loading effects on the synchronous generator

The synchronous generator behaves differently with a resistive load, inductive and a

capacitive load. With a resistive load the synchronous generator give a unity power factor

means the current and voltage are in phase. An inductive load gives a lagging effect

where the current lags the voltage by a phase angle. This is called the lagging effect.

Since a pure inductive load does not exist with every simulation a resistive load is added

with the inductive load. For a capacitive load leading power factor is shown where the

current leads the voltage by a phase angle. These components are clearly shown in the

results.

56

Discussion

Although I managed to meet my objectives of the project and do various tests on the

model there were some difficulties I faced due to lack of resources and time.

One of the common problems was to get a suitable data sheet for the synchronous

generator. The data sheet available by the manufacturers did not have all the parameters

needed for simulation. Also Matlab\Simulink does not have a standard size generator in

their Power library. So to overcome this problem I used a generator size which had been

used in a journal paper available online. The diesel engine parameters were also taken

from a journal paper.

The second problem was that the Matlab\Simulink some time did not give correct outputs

as expected. For instance, a while modeling the synchronous generator alone the

frequency supplied was 50Hz and the output was just coming out to be 0.5Hz. However

after the inclusion of the diesel engine the problem was solved and the output was 50Hz

every time. This is shown in the results in chapter 4.

Finally, various tests were done on the model and the outputs are shown in chapter 4.

These results coincide with the theory in chapter 2 and 3.

57

Conclusion

This project has been a very good practice of the studies done in the BETECH program.

It has also allowed a good experience in this field of work. The graphs achieved after the

simulation have a lot of resemblance to the theoretical aspects learnt over the years. The

synchronous machine behaves differently with different types and sizes of loads

however; it still delivers constant voltage and frequency to the grid. The outputs directly

coincide with the theory no matter what type and size of load is added to the system.

In this course I have been able to learn how to model and simulate synchronous generator

driven by a prime mover to generate electricity. This course has enabled me to broaden

my knowledge about Power generation system and has been a great means of experience

gaining. I have been able to enhance my skills and knowledge in the many ways.

I have gained a lot of experience in modeling a diesel generator set and simulating it for

stable power output. I have also learnt how to calculate values for the excitation system

of the synchronous generator and also how to control the diesel engine speed using an

automatic voltage regulator. I have also learnt how to control the speed through PID

when the load on the shaft changes to provide enough mechanical power to maintain

constant voltage and frequency of the diesel generator.

Moreover, it was a great experience of modeling and simulation with Matlab\Simulink

software. Though I had a very low knowledge of using Simulink this project has made

me understand the use Simulink in depth. I have used this software in some of my

previous units but not in detail. This project had made me understand the modeling and

simulation procedure in detail.

Finally, this course had been a very interesting experience and a chance to learn a lot

about Power generation system. The EE300 course has taught me how to manage time,

58

work under pressure and being committed to the project. It has enabled me to learn a

whole lot about diesel generator sets used in for generating electricity.

59

Future Recommendations

I would like to recommend the students who will be doing this project in future to:

• Calculate synchronous machine parameters and then model it using power system

software.

• Calculate the diesel engine parameters to connect to the synchronous generator

• Try and model synchronous generators operating in parallel connected to the grid

• Try using any other power system software to model and simulate diesel

generator set.

60

References

[1] Tylor and Francis Group, Chapter 3, Prime Movers, Synchronous Generators,

2006 LLC

[2] Sebastian Achilles and Markus Poller “Direct Drive Synchronous Machine

Models for Stability Assessment of Wind Farms” journal pp 1-9

[3] Ashwani Kumar, K. S. Sandhu, S. P. Jain, and P. Sharath Kumar “ Modeling

and Control of Micro-Turbine Based Distributed Generation System “

International journal of circuits, systems and signal processing .pp 65 – 72

[4] http://www.bwea.com/energy/how.html

[5] Tiberiu Tudorache, and Cristian Roman “ The numerical Modeling of Transient

Regimes of Diesel Generator sets” Acta Polytechnical Hungarica, Vol 7 , No. 2,

2010.

[6] Yeager, K.E., and J.R.Willis, "Modeling of Emergency Diesel Generators in an

800 Megawatt Nuclear Power Plant," IEEE Transactions on Energy

Conversion, Vol. 8, No. 3, September, 1993

[7] Matlab help file, Emergency diesel generator set. , Matlab 2007b

[8] Mohammad Tazil, Chapter 3, Synchronous generators, EE221, Department of

Engineering, University of the South Pacific

[9] Department of Engineering University of the South Pacific, EE300 Project, Designing, Development and Testing of a PIC Micro-controller based

Differential Drive Line Tracing Vehicle-2 with PID, 2010 61

[10] Mohd Dzarif Bin and Mohd Bakhari, “Speed Control Of Diesel Engine System

Through PID” TJ223.M39 2007

[11] Zheng-Ming Ge and Ching-I “Lee,Non-linear dynamics and control of chaos

for a rotational machine with a hexagonal centrifugal governor with a spring”,

Journal of Sound and Vibration 262 (2003) 845–864

[12] ] Dale Querrey, Peter Reichmeider, and Damir Novose, “Using MATLAB

Simulink for Transient Analysis in Synchronous Machines.” Auburn University,

Auburn, AL 36849 USA.

[13] Lan Gao and Hehe Fu, “The Control and Modeling of Diesel Generator Set in Electric

Propulsion Ship” international journal of Information Technology and Computer

Science, 2011, 2, 31-37, March 2011.

[14] Jun Ho Kenneth Mun , “ Implementation of Controls to a Synchronous Machine

(Simulation using MATLAB)” School of Information Technology and Electrical

Engineering, University of Queensland, 2003.

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