Implementation Of Unified Power Flow Controller (UPFC) For Improvement Of Voltage Stability In A Congested Electric Network

INTRODUCTION
1.1. BACKGROUND
The control of voltage and power flows is a major issue in power system operation. This is because, due to the topological differences between distribution and transmission systems, different strategies have evolved.
As the power systems are becoming more complex it requires careful design of the new devices for the operation of controlling the power flow in transmission system, which should be flexible enough to adapt to any momentary system conditions. The operation of an ac power transmission line, is generally constrained by limitations of one or more network parameters and operating variables By using FACTS technology such as STATCON (Static Condenser), Thyristor Controlled Series Capacitor (TCSC), Thyristor controlled Phase angle Regulator (TCPR), UPFC etc., the bus voltages, line impedances, and phase angles in the power system can be regulated rapidly and flexibly. FACTS do not indicate a particular controller but a host of controllers which the system planner can choose based on cost benefit analysis.

This project contains contributions for power flows control and voltage stability schemes for distribution and transmission systems. A particular interest is taken to the development of control schemes to avoid so-called voltage collapse, which can result in widespread outages. In order to achieve efficient and reliable operation of power system, the control of voltage and reactive power should satisfy the following objectives:
 Voltages at all terminals of all equipment in the system are within acceptable limits
 System stability is enhanced to maximize utilization of the transmission system
 The reactive power flow is minimized so as to reduce RI2 and XI2 losses.
This ensures that the transmission system operates mainly for active power. Since the power system supplies power to a vast number of loads and is feeding from many generating units, there is a problem of maintaining voltages within required limits. As load varies, the reactive power requirements of the transmission system vary. Since there is no cost free means of conveying reactive power over long distances, voltage control has to be effected by using special devices located through the system which possess difficulties in keeping sufficient levels of voltage in the power system network.
In recent decades, there has been significant progress in terms of equipment designed to improve the stability of voltage in power systems. This is mainly due to the development of power supply systems in the world, which requires seeking better ways of adjusting and controlling power flows and voltage levels.
The proper selection and coordination of equipment for controlling reactive power and voltage stability are among the major challenges of power system engineering. The UPFC is an advanced power system device capable of providing simultaneous control of voltage magnitude and active and reactive power flows in an adaptive fashion. Owing to its instantaneous speed of response and unrivalled functionality, it is well placed to solve most issues relating to power flow control in modern power systems. The UPFC can control voltage, line impedance and phase angles in the power system which will enhance the power transfer capability and also decrease generation cost (and improve the security and stability) of the power system. UPFC can be used for power flow control, loop flow control, load sharing among parallel corridors.
These challenges necessitated the evolution of certain to achieve control or compensation of reactive power. In order to cover the additional demand for reactive power and retain the ability to control voltage stability acceptable range, various sources of reactive power, particularly of the FACTS family has been employed.

1.2. Statement of Problem
The characteristics of a given power system evolve with time, as load grows and generation is added. If the transmission facilities are not upgraded sufficiently the power system becomes vulnerable to steady-state and transient stability problems, as stability margins become narrower, posing a limit on the ability of these lines to transmit power. In principle, limitations on power transfer can always be relieved by the addition of new transmission and generation facilities. Conversely, these are not easy to come by, coupled with the high cost of executing such projects. Alternatively, UPFC can enable the same objectives to be met with no major alterations to system layout. How UPFC can be used to attain a great degree of power flow and voltage profile controllability in power system network is the challenge of this project.

1.3. Aim and Objective
1.3.1 Aim
To implement unified power flow controller (UPFC) for improvement of voltage stability in a congested electric network

1.3.2 Objective

1. To develop mathematical models for transmission systems and UPFC, which can to be blended together, coded, and used extensively.
2. To illustrate the controllable features of UPFC in active and reactive power flows in a transmission line.
3. To maintain the nodal voltage magnitudes in a power system in the limit for system security

1.4. Project Outline
Chapter 1 introduces the work carried out in this project and lists its objectives and
limitations.
Chapter 2 focuses on the literature review.
Chapter 3 presents the methodology adopted in completing the project, the modeling equations and mathematical solutions backing up the work.
Chapter 4 presents the simulation work done in MATLAB and discuss the results.
Chapter 5 presents the conclusion, recommendations and future areas of research.