ABSTRACT Power Quality problem has become an important issue in the power distribution network due to increase in usage of power electronic based loads. The basic issues in power quality are twofold, one is to maintain the utility voltage constant and second one is to supply the necessary reactive and harmonic power locally. 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 consumers at the same PCC will receive distorted supply. Therefore it is important to install compensating device at PCC to eliminate harmonic distortions and to mitigate voltage sags, swell conditions etc. The shunt connected custom power device called distribution static compensator ( DSTATCOM ) injects current at the point of common coupling (PCC) so that harmonic filtering, power factor correction, and load balancing can be achieved. It gives fast response and robustness to the system conditions. The transient response of the distribution static compensator (DSTATCOM) is very important while compensating rapidly varying unbalanced and nonlinear loads. Any change in the load affects the dc-link voltage directly. The proper operation of DSTATCOM requires variation of the dc-link voltage within the prescribed limits. Conventionally, a proportional-integral (PI) controller is used to maintain the dc-link voltage to the reference value. However, the transient response of the conventional PI dc-link voltage controller is slow. In this Project a fast-acting dc-link voltage controller based on the energy of a dc-link capacitor is designed to ensure the fast transient response. A fuzzy controller with fast reference voltage generation to regulate Unbalance voltage in three-phase system improves Power Quality even further. One of the main advantages of Fuzzy control over conventional controller is the inaccuracies of the sensors on the system performance can be reduced by adding additional rules, this reduces the need for costly sensors and cost of the control system is reduced without a compromise in performance. The simulation results show a very good performance of the method and the control scheme under arbitrary fault conditions of the utility supply. i.LIST OF SYMBOLS

Shunt Injected Current

Total Load Current

Fundamental Active Current

Fundamental reactive Current

Harmonic Current Component

Direct component of Voltage

Quadtrature component of Voltage

Phase angle between source voltages and compensator currents Average A.C load power D.C load Power,, Compensator reference currents

,, Load Currents D.C Storage Capacitor

Capacitor D.C Voltage

Compensator actual Currents

Source Voltages Transpose Operator ii. Proportional Controller gain Integral Controller gain D.C Link Reference Voltage

Energy of D.C Link Capacitor

Ripple period of the dc-link capacitor voltage

Energy based Proportional Controller gain

Energy based Integral Controller gain

Interface Inductor Interface resistor Hysteresis band limit iii.LIST OF FIGURES

Figure 2.1Voltage sag caused by an SLG fault.RMS waveform for Voltage Sag event

11Figure 2.2 Instantaneous Voltage Swell caused by an SLG fault12Figure 2.3Additive Third Harmonics

14Figure 2.4Voltage Notching caused by a Three-phase Converter15Figure 3.1 A simplified one-line diagram of a power system

16Figure 3.2A dynamic voltage restorer (DVR)

17Figure 3.3Schematic diagram of UPQC

18Figure 3.4Shunt connected DSTATCOM

19Figure 3.5 Basic circuit of a DSTATCOM

21

Figure 3.6 Basic Building Blocks of the D-STATCOM

22

Figure 3.7 No-load mode ( )

23

Figure 3.8 Capacitive mode ()

24 Figure 3.9 Inductive mode ()

24

Figure 3.10 DSTATCOM vector diagrams

25

Figure 3.11 Block diagram of the proposed DSTATCOM controller26

Figure 3.12 Multi-level control schemes for the DSTATCOM compensator27Figure 4.1Three-Phase, Four-Wire Compensated System using H-bridge Voltage Source Inverter Topology based Distribution Static Compensator

29 iv.

Figure 4.2Schematic Diagram of Conventional D.C. Link Voltage Controller

32Figure 4.3Schematic Diagram of Fast-acting D.C Link Voltage Controller

33Figure 5.1Conventional D.C Link Voltage Controller

38Figure 5.2Switching Circuit

39Figure 5.3MATLAB/SIMULATION Circuit

39Figure 5.4 Source voltages and source currents 40Figure 5.5 Compensator Currents 41Figure 5.6Compensated Source Current in Phase a

41Figure 5.7D.C Link Voltage with Conventional Controller takes 0.04 sec

to settle down to reference value.

41Figure 5.8Total Harmonic Distortion of 19.40%

42Figure 5.9Fast Acting D.C Link Voltage Controller Scheme

42Figure 5.10Compensated Source Current in Phase a

43Figure 5.11D.C Link Voltage with fast acting Controller,

Transient response improved by t=0.02 sec. 43Figure 5.12 Power factor improvements. 44Figure 5.13 Total Harmonic Distortion reduced to 10.16%

44

Figure 6.1 Fuzzy Inference System

49Figure 6.2 Fuzzy Logic IF-Then Rules 51Figure 6.3 MAT Lab circuit of Fuzzy Logic Controller 52Figure 6.4 Control Scheme of Fuzzy Logic Controller

53 v.

Figure 6.5 Three phase Compensated source voltages and currents54Figure 6.6 Transient response of Fuzzy logic controller D.C Link Voltage ts=0.002sec

54Figure 6.7 Power factor improvement

54Figure 6.8 Total Harmonic Distortion reduction to 4.78% in phase a 54LIST OF TABLESTable 2.1Power disturbances

7Table 5.1 Simulation Parameters

37Table 6.1 Fuzzy Rule Base

52Table 6.2 Comparison between Fuzzy and PI Controllers

55LIST OF ABBREVIATIONSAPCM

Active Power Control ModeAPF

Active Power Filter

ASD

Adjustable Speed Drives

CP

Custom Power

DSTATCOMDistribution Static CompensatorDVR

Dynamic Voltage RestorerEIA

American Energy Information Administration

EMI

Electro Magnetic Interruption

FACTSFlexible AC Transmission Systems IEA

International Energy Agency

IGBT

Insulated-Gate Bipolar TransistorMSC

Mechanically-switched capacitorPCC

Point of Common CouplingPLL

Phase Locked Loop vi

PFCM

Power Factor Control Mode PI

Proportional Integral

PQ

Power Quality

PSS

Power system stabilizer

SCL

Static Current Limiter

SRF

Synchronous Rotating FrameSSBs

Solid-State Circuit Breakers

SSTS

Solid State Transfer Switch

SSSC

Static synchronous series compensatorSTRR

Stationary Reference Frame

SVC

Static VAR compensatorTCR

Thyristor-controlled reactorTHD

Total Harmonic Distortion

TSC

Thyristor-switched capacitorTCSC

Thyristor-controlled series capacitorTCSR

Thyristor-controlled series reactorTSR

Thyristor-switched reactorTSSC

Thyristor-switched series capacitorTSSR

Thyristor-switched series reactorUPQC

Unified power Quality ConditionerVSI

Voltage Source Inverter vii. _1353094197.unknown

_1353094233.unknown

_1353094260.unknown

_1353094123.unknown