ABSTRACT Quality of power has become an important issue in the power distribution system due to increase of power electronic loads. The basic issues in power quality are two fold, one is to maintain the utility voltage constant and second one is to supply the necessary reactive and harmonic power locally, so that it is not drawn from the supply. The major power quality problems are voltage sags and swells, harmonics, fluctuations, flickering etc. The voltage at the PCC, being the difference between the source voltage and the voltage across the source impedance, is distorted due to the loads. Other clients at the same PCC will receive distorted supply. It is therefore important to install compensating device at PCC to eliminate harmonic distortions, to mitigate voltage sags, swell conditions etc. Conventionally, power plants have been large, centralized units. A new trend is developing toward distributed energy generation, which means that energy conversion units are situated close to energy consumers, and smaller ones substitute large units. A distributed energy system is an efficient, reliable and environmental friendly alternative to the traditional energy system. Distributed Generation has started gaining importance in our country due to the shortage of power available in the near future. The main power quality problems with DG are sustained interruption, voltage regulation, Harmonics and voltage sags. The significance of voltage sags among power quality related phenomena seem to be increasing rapidly. Their impact as randomly timed and randomly shaped events makes them a special challenge for power distribution engineering. From an economic point of view, sags are definitely a problem worth studying and, in most cases, are also worth being solved. Economic losses due to sags are especially high for industrial customers. So to mitigate the sag and swell conditions, the systems are installed with DSTATCOM. Current power distribution systems are experiencing increased installation of distributed generators and application of custom power devices. The most common type of distributed generation employs ac-rotating machines (Induction Generators and
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Synchronous Generators). Although such technologies are well known, there is no consensus on what is the best choice under a wide technical perspective. In this thesis, the DSTATCOM is modeled and simulated with voltage regulation technique to mitigate the voltage sag and swell conditions in distribution systems. The simulation studies show that the DSTATCOM can effectively reduce the sag and swells. Also shown that The DSTATCOM installed with DG will effectively reduce the major power quality problems in the distribution system and also the results give the best Generator to be installed with DTSTACOM.
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CONTENTS Page Nos i
Abstract List of Figures v List of Tables
vii
Abbreviations
vii
Chapter 1 INTRODUCTION
1-3
1.1 Introduction
1
1.2 Objective
3
1.3 Outline of the Thesis
3
4-5
Chapter 2 LITERATURE SURVEY Chapter 3 POWER QUALITY ISSUES AND SOLUTIONS IN DISTRIBUTION SYSTEM
6-14
3.1 Introduction 6 3.2 Available Custom Power Devices
7
3.2.1 Dynamic Voltage Restorer 7 3.2.2 Unified Power Quality Conditioner 8 3.2.3 Solid State Transfer Switch 9 3.2.4 Solid State Breaker 10 3.3 Distributed Generation 3.3.1 Advantages of Distributed Generation
11 11
3.3.2 Power Quality problems with DG 12
iii
3.3.3 Interfacing to the Utility System 13 Chapter 4 DISTRIBUTION STATCOM
15-19
4.1 Introduction 15 4.2 Operating Principle of DSTATCOM 16 4.3 Principle of Voltage Regulation 17 Chapter 5 MODELING OF DSTATCOM
20-26
5.1 Introduction 20 5.2 Modeling of DSTATCOM in d-q frame 21 5.3 DSTATCOM Voltage Regulation Technique 24
Chapter 6 TEST SYSTEM AND SIMULATION RESULTS
27-46
6.1 Test System for Distribution System 27 6.1.1 Introduction 27 6.1.2 Test Details 28 6.1.3 Testing the DSTATCOM 28 6.1.4 Simulation Results 28
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6.1.5 Conclusion 33 6.2 Test System for Distributed Generation 34 6.2.1 Introduction 34 6.2.2 Test System 35 6.3 Simulation with DG 36 6.3.1 With fault at bus 4 and cleared by tripping line 2-4 36 6.3.2 With Fault in between buses 4-5 and cleared without line tripping 44 6.4 Case Study of Agasthyamuzhi sub-station 47 6.4.1 Introduction 47 6.4.2 Simulation Results 48 Chapter 7 CONCLUSIONS 50 7.1 Conclusion 50 7.2 Future work 50 References 51 Appendix
54-55
v
Appendix A
Data of Distribution System
Appendix B
Data of Distributed Generation
54 55 Appendix C
Case Study Data
56
LIST OF FIGURES Fig No
Title
Fig 3.1
Page No
Schematic representation of the DVR
7 Fig 3.2
Basic Block Diagram of UPQC
8 Fig 3.3
Basic Block diagram of SSTS 9
Fig 3.4
Block Diagram Of SSB
10 Fig 4.1
Block Diagram of the voltage source converter based DSTATCOM 16
Fig 4.2
A Simple Circuit for demonstrating the voltage regulation Principle 18
Fig 4.2 (a)
Phasor diagram for uncompensated
18 Fig 4.2 (b)
Phasor diagram for voltage regulation with compensation
19 Fig 5.1
Basic DSTATCOM connected to a load in a distribution System 20
Fig 5.2
Equivalent circuit of the above system with DSTATCOM
Fig 5.3
Phasor Diagram showing d-q and d1-q1 frame
21
23
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Fig 5.4
Block Diagram of DSTATCOM Control
25 Fig 6.1
Single Line Diagram of the system used.
27 Fig 6.2
The Single line diagram implemented in MATLAB.
29 Fig 6.3
Terminal Voltage of Bus2 in per unit.
Fig 6.4
Active (P) and Reactive (Q) Powers injected by the
29
DSTATCOM 30 Fig 6.5
Terminal voltage of Bus2 Va in pu with DSTATCOM
30 Fig 6.6
Current Ia in pu injected by DSTATCOM into the network.
31 Fig 6.7
Dc capacitor voltage
31 Fig 6.8
Three phase currents injected by DSTATCOM in to the network. 32
Fig 6.9
The Id (Active current), i.e injected by DSTATCOM before converting to 3 phase from 2 phase 32
Fig 6.10
The Iq (Reactive current) injected by DSTATCOM before converting to 3 phase 33
Fig 6.2.1
Test System with DG and DSTATCOM 35
Fig 6.3.1
The Induction Generator terminal voltage 36
Fig 6.3.2
The rotor speed of Induction Generator 37
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Fig 6.3.3
The reactive power injected by DSTATCOM in to the network 37
Fig 6.3.4
The terminal voltage response of Induction Generator
38 Fig 6.3.5
The rotor speed of Induction generator
39 Fig 6.3.6
Reactive Power Injected by DSTATCOM
39 Fig 6.3.7
The terminal Voltage of induction generator
40 Fig 6.3.8
The Terminal voltage response of Synchronous Generator
41 Fig 6.3.9
The rotor speed of Synchronous generator
41 Fig 6.3.10
The terminal voltage response of Synchronous Generator
42 Fig 6.3.11
The rotor speed of Synchronous generator
43 Fig 6.3.12
Terminal Voltage of Synchronous Generator
44 Fig 6.3.13
Phase A stator currents of Synchronous generator with and without DSTATCOM 45
Fig 6.3.14
Phase A stator current of Induction Generator with and without DSTATCOM 46
Fig 6.4.1
Structural layout of Agasthyamuzhy Sub-Station 47
Fig 6.4.2
The Terminal voltage of the Synchronous Generator 49
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Fig 6.4.3
The terminal Voltage of the Induction Generator
49
LIST OF TABLES Table No Table 6.1 26
Title
Page No
The test system details of single line diagram used
LIST OF ABBREVIATIONS FACTS
Flexible AC Transmission Systems
CPD’s
Custom Power Devices
DVR
Dynamic Voltage Restorer
UPQC
Unified Power Quality Conditioner
SSTS
Solid State Transfer switch
SSB
Solid State Breaker
DSTATCOM
Distribution STATCOM
STATCOM
Static Synchronous Compensator
VSC
Voltage Source Converter
VSI
Voltage Source Inverter
THD
Total Harmonic Distortion
IGBT
Insulated Gate Bipolar Transistor
GTO
Gate Turn Off Thyristor
PLL
Phase locked Loop
ix
PCC
Point of Common Coupling
PQ
Power Quality
PI
Proportional and Integrator
PWM
Pulse Width Modulation
DG
Distributed Generation
x