THE UTILIZATION/IMPLEMENTATION OF A UNIFIED POWER FLOW CONTROLLER (UPFC) TO ENHANCE VOLTAGE STABILITY WITHIN A HEAVILY CONGESTED ELECTRICAL NETWORK

THE UTILIZATION/IMPLEMENTATION OF A UNIFIED POWER FLOW CONTROLLER (UPFC) TO ENHANCE VOLTAGE STABILITY WITHIN A HEAVILY CONGESTED ELECTRICAL NETWORK BY NNA MICHAEL CHIBUIKEM FUO/18/EEE/7613 DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING, FACULTY OF ENGINEERING, FEDERAL UNIVERSITY OTUOKE, NIGERIA A PROJECT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING, FACULTY OF ENGINEERING, FEDERAL UNIVERSITY OTUOKE IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF BACHELOR OF ENGINEERING (B.Eng.) DEGREE IN ELECTRICAL AND ELECTRONICS ENGINEERING AUGUST, 2024. DECLARATION I declare that this research work entitled ‘THE UTILIZATION/IMPLEMENTATION OF A UNIFIED POWER FLOW CONTROLLER (UPFC) TO ENHANCE VOLTAGE STABILITY WITHIN A HEAVILY CONGESTED ELECTRICAL NETWORK” was carried out by me in the Department of Electrical and Electronics Engineering. All sources of information used in this work have been properly acknowledged both in the text and in the list of references. This project has not been earlier submitted for the award of another degree in this or any other institution. NNA MICHAEL CHIBUIKEM _________________ _______________ (FUO/18/EEE/7613) SIGNATURE DATE CERTIFICATION This is to certify that this research work on ‘THE UTILIZATION/IMPLEMENTATION OF A UNIFIED POWER FLOW CONTROLLER (UPFC) TO ENHANCE VOLTAGE STABILITY WITHIN A HEAVILY CONGESTED ELECTRICAL NETWORK”, was independently carried out by NNA MICHAEL CHIBUIKEM with Matriculation Number, FUO/18/EEE/7613, meets the regulation governing the award of Bachelor of Engineering (B.Eng.) degree in Electrical and Electronics Engineering of Federal University Otuoke, Nigeria during the 2023/2024 academic session, it is approved due to its contribution to knowledge. ……………………… ……………………… PROF. DONATUS BASSEY DATE SUPERVISOR ………………………………… ……………………… ENGR. PROF. EMERITUS ADEKOLA SULAIMON DATE HEAD OF DEPARTMENT ……………………………… ………………………… ENGR. PROF. SCOTT BERNARD AKPILA DATE DEAN, FACULTY OF ENGINEERING …………………………… …………………………… ..……………………….. EXTERNAL EXAMINER SIGNATURE DATE DEDICATION This research work is dedicated to the ALMIGHTY GOD IN HEAVEN, for His infinite Mercy and Grace, and for giving me spiritual and moral support to complete this work AKNOWLEDEMENTS First of all, I am grateful to God for His protection, provision and guidance upon my life and His unconditional Love towards me which has brought about the successful completion of this program. With a grateful heart filled with appreciations, I acknowledge the contribution of my lovely mother, Mrs. Nna Christiana Omasirichi, my ever young and caring grandmother, Mother Nna Ada and entire family for their time, support and understanding and mostly their prayers for me all through my B.Eng. program. Special appreciation to the amiable Head of Department of the prestigious Electrical Electronics Engineering, Engr. Prof. Emeritus Adekola Sulaimon for your continuous care and support. To my supervisor, Prof. Donatus Bassey Emmanuel, thank you for the privilege to be under your care and guidiance. I must also express my gratitude to Engr. Adebayo Adeniyi, to whom stood as a father to me to ensure the success of this project, and also for ensuring that everything went well with the academic activities of the students in the department and for his readiness to assist and advice. Also, I express my appreciation to all the staff of Electrical and Electronic Engineering, Federal University Otuoke for their good works. I want to also appreciate the entire NUESA and SEEES for giving me the privilege to serve. Members of the National Union of Rivers State Students FUO Chapter, the entire family of Salvation Ministries Home of Success Otuoke Satellite and Campus Ministry thank you for a wonderful experience. I am also thankful to my entire course mates, you all are wonderful, and to my friends; Dappa Prince, Pascal, Tamunogbarachua George, Chidi Joy, Roy, Osomu Hope, Ekeh Jane, Queen Favour, Agbo John, Levi Nnamani and colleagues worthy of mention in no particular order, Finally, I would like to thank my humble self. for making the most of the chances given to me to study with and from such brilliant minds. ABSTRACT The daily increase in electricity useage puts strain on the electric networks of the power grids, causing congestion and unstable voltage which may lead to grid collapse. As a result, maintaining voltage stability throughout the network becomes extremely difficult. In order to prevent such, creating system redundancy is essential to guarantee voltage and system stability, but this has constraints on both an economic and environmental level. In order to ensure a dependable system, a more economical cost effective approach is presented that makes use of already- existing network components and incorporates less expensive schemes and rules. To improve overall system performance, including voltage profile across the network buses, transmission line flows, and losses, Flexible Alternating Current Transmission System (FACTS) such as the Unified Power Flow Controller (UPFC) must be used. One of the FACTS components that can offer phase angle shifting, line impedance control, and VAR correction is the Unified Power Flow Controller (UPFC). This research introduces the UPFC as an effective FACTS device to improve the overall performance of an electric system (grid) for effective functioning and voltage output. KEYWORDS FACTS Devices, Unified Power Flow Controller (UPFC), Voltage Stability, Power Flow Improvement. TABLE OF CONTENT Title Page……………………………………………………………… ….……………………I Declaration..…………………………..………………………… …………………………......II Certification…………………………………………………… ……………………………...III Dedication………….…………………………………………… …………………………....IV Acknowledgements.…………...………………………………… ………………………..…..V Abstract………….……………………………………………… ……………………….......VI Table of Content…..……………………………………………………… ……………..….VII List of Figures…………………………………………………………… ……………...……IX List of Tables…………………………………………………………… …………...…..……X CHAPTER ONE: INTRODUCTION 1.1 Background of the Study.…………………………………………………………..... 1 1.2 Statement of Problem…...………………………………………..…………… ……..2 1.3 Justification of the Study…………………………………………………………….. 3 1.4 Aim……………………………………………………...……… ……………………3 1.5 Objectives…………….…………………………………….…… …………………...3 1.6 Scope of Study…………….……………………………….……………… …………3 1.7 Limitations……………………………………...…...………..… …………………....3 1.8 Thesis Organization………………………...………………………….. ……….........4 CHAPTER TWO: LITERATURE REVIEW 2.1 Review of Related Works……...…………..……………………………..………… …….5 2.2 Voltage Stability…………...……….…………………………………… ……...………...8 2.3 Voltage Collapse…..……………………………………………………… ……..………..8 2.4 Flexible Alternating Current Transmission System (Facts)...………………….……….....9 2.5 Facts Compensating Devices ………………………………………………...…………..11 2.5.1 Static Synchronous Compensator (STATCOM)………………..……………....11 2.5.2 Thyristor-Switched Series Capacitor (TSSC)…………………………………..12 2.5.3 Static Synchronous Series Compensator (SSSC)……………………………….13 2.5.4 Thyristor-Controlled Series Capacitor (TCSC)…………………………………14 2.6 Unified Power Flow Controller (UPFC)…………………………………………………..15 CHAPTER THREE: METHODOLOGY 3.1 Location of UPFC……………………..…………………………….……… …………….21 3.2 Newton Raphson Load Flow Method …………..………………………………………...22 3.2.1 Formation of the Y- Bus………………………………………………………….23 3.2.2 Forming the Jacobian Matrix…………………………………………………....25 3.3 Incorporating the UPFC in Newton Raphson Load Flow……………….…………...…....26 CHAPTER FOUR: SIMULATION AND RESULTS ANALYSIS 4.1 Case 1………………………………………………….……………… …………………..29 4.2 Case 2……………..…………………………………………………… ………………….30 CHAPTER FIVE: CONCLUSION AND RECOMMENDATION 5.1 Conclusion………….…………………………………………… …….………………….34 5.2 Recommendations...……….………….………………………… …………………….…..35 APPENDIX A …………………..….…………………………………………… …………...36 REFERENCES…………..…………………………………… ……………………………..40 LIST OF FIGURES Figure2.1 Overview of the main FACTS Devices…………………………………..10 Figure2.2 A static synchronous compensator……………………………………….12 Figure2.3 (a) Circuit diagram of a TSSC, (b) Course of capacitor voltage for the basic element in a TSSC………………………………………………………..13 Figure2.4 (a) A two machine system with a series capacitor compensated line, (b) its associated phasor diagram………………………………………………………… ……………14 Figure2.5 Thyristor-Controlled Series Capacitor (TCSC)…………………………..15 Figure2.6 Schematic diagram of the UPFC…………………………………………17 Figure2.7 Concept of the UPFC in a two-machine power system…………………..18 Figure2.8 Implementation of UPFC…………………………………………………19 Figure3.1 One line diagram of the power system model…………………………….21 Figure3.2 A two bus system for illustrating Newton Raphson Power flows………...24 Figure3.3 Unified power flow controller equivalent circuit………………………....26 Figure 4.1 Voltages of the buses without the UPFC between buses 3 and 4………...29 Figure 4.2 Voltages of the buses with the UPFC between buses 3 and 4……………31 LIST OF TABLES Table 2.1 FACTS Applications and cost Comparison………………………………20 Table 4.1 Bus voltages without the UPFC…………………………………………..29 Table 4.2 Line Flows and Losses without UPFC……………………………………30 Table 4.3 Bus voltages with UPFC…………………………………………………..30 Table 4.4 Line Flows and Losses with UPFC ………………………………………..31 Table 4.5 voltages of the buses with and without the UPFC between buses 3 and 4………………………………………………………………… …………….32 Table 4.6 Bus Data: IEEE 5 Bus System…………………………………………….33 Table 4.7 Line Data for IEEE 5 Bus…………………………………………………33 i CHAPTER ONE INTRODUCTION 1.1 BACKGROUND OF THE STUDY For electric utilities as well as users, the high cost of electricity has taken on greater significance. Disturbances on the utility and customer sides cause transients, waveform distortions, and terminal voltage variations on the electric grid, which ultimately lead to a power quality issue. The term "maintaining the waveforms of voltages and currents as sinusoidal at rated frequency and magnitude" relates to power quality, or PQ. Due to the advent of equipment with power electronic devices, which are more susceptible to power quality issues, power systems sustaining power quality has recently become the most critical issue (Asha Kiranmai, 2010). The rising usage of non-linear loads, such as electronic control gears, variable speed drives, and power electronic equipment, is what most affects power quality. The safe, dependable, and effective functioning might be impacted by poor power quality. Voltage sag, voltage swell, voltage fluctuations, voltage unbalance, harmonics, etc. are some of the elements of power quality. Power electronic devices, such Flexible AC Transmission Systems (FACTS) and custom power devices, have opened up new avenues for power- quality improvement by introducing an expanding field of technology that gives the power system more flexible new control capabilities. To reduce electricity costs, the current power system is deregulated, meaning that generation, transmission, and distribution are handled by separate entities. With the increasing demand for electric power, it is crucial to make full use of existing generating units, push transmission lines to their thermal limits, and maintain system stability. Additionally, it is important to minimize losses in the transmission lines. Flexible AC Transmission System (FACTS) devices are vital for controlling power flow and boosting the capacity of existing lines. These devices use power electronics to improve controllability and increase power transfer capability. FACTS technology could enable smarter electric transmission systems in the future. FACTS controllers include devices such as the Static Synchronous Compensator (STATCOM), Thyristor Controlled Series Capacitor (TCSC), Static Series Synchronous Compensator (SSSC), and Static VAR Compensator (SVC). These controllers are capable of rapidly adjusting network conditions to enhance voltage stability and power quality. Voltage instability arises when the system cannot meet the reactive power demand, which can occur during faults, heavy loading, or voltage fluctuations. FACTS devices can correct reactive power imbalances by injecting or absorbing reactive power as needed to stabilize the system (Mohanty, Ahamad, and Khan, 2013). The Unified Power Flow Controller (UPFC) is the most versatile device among the Flexible AC Transmission Systems (FACTS). It integrates the functions of multiple devices, including the Static Synchronous Compensator (STATCOM), Thyristor Switched Capacitor (TSC), Thyristor-Controlled Reactor (TCR), and Phase Angle Regulator. Additionally, the UPFC offers enhanced flexibility by combining select functions of these devices (Mathad, Basanagouda, 2014). The primary purpose of the UPFC is to regulate real and reactive power flow by injecting voltage in series with the transmission line, allowing independent control of voltage magnitude and phase angle. This enables power flow control in designated routes and optimal loading of transmission lines, approaching their thermal limits. Furthermore, UPFCs are employed to enhance the transient and small signal stability of the power system. 1.2 STATEMENT OF PROBLEM A power system's characteristics change over time as a result of growing loads and the addition of additional generation capacities. In both steady-state and transient scenarios, the power system is susceptible to stability problems in the absence of appropriate modifications to the transmission infrastructure. Reduced stability margins restrict power transfer capabilities and reduce transmission efficiency. Historically, building new transmission and generation infrastructure was necessary to meet these restrictions. These initiatives can, however, be costly, time-consuming, and fraught with environmental and regulatory issues. Using Flexible AC Transmission Systems (FACTS) technology, like the Unified Power Flow Controller (UPFC), is an alternate approach that can improve system performance without requiring significant alterations to the current infrastructure. The UPFC plays a major role in enhancing power flow and voltage profile controllability within the power system network. It can minimize system instability, optimize power flows dynamically, and control voltage stability. By deploying UPFC devices strategically at network nodes, operators can make the most of existing transmission facilities without having to make major infrastructure modifications. They are able to efficiently modify and control voltage profiles and power flow patterns as a result. Creating and implementing control methods that make the most of the Unified Power Flow Controller's (UPFC) capabilities is the difficult part. In order to ensure overall system efficiency and dependability, as well as appropriate power flow and voltage stability, sophisticated modeling, simulation, and real-time control approaches are needed. UPFC technology provides a cost-effective and efficient way to improve power system performance by offering enhanced flexibility and control over power flow and voltage profiles. This project focuses on exploring effective ways to leverage UPFC technology to meet these objectives, addressing the evolving challenges and demands of contemporary power systems. 1.3 JUSTIFICATION OF THE STUDY This research initiative is justified by its potential to supply a clean, sustainable, and dependable energy source for educational and scientific endeavors. 1.4 AIM The aim of this research is to Utilize/Implement a unified power flow controller (UPFC) for improvement of voltage stability in a congested electric network 1.5 OBJECTIVE Its specific objectives are to 1. Develop mathematical models for transmission systems and UPFC, which can to be blended together, coded, and used extensively. 2. Illustrate the controllable features of UPFC in active and reactive power flows in a transmission line. 3. Maintain the nodal voltage magnitudes in a power system in the limit for system security 1.6 SCOPE OF STUDY The limits and scope of this study's investigation into the Unified Power Flow Controller (UPFC) implementation for enhancing voltage stability in a crowded electric network are specified. It describes the particular areas of emphasis, the approaches used, the constraints, and the project's anticipated results. 1.7 LIMITATIONS Scope of Network Model: This study uses a simplified model of a congested electric network, which may not capture all complexities of real-world systems. Simulation Constrains: Results are based on simulations and may differ in actual field implementations due to unforeseen factors. Focus on UPFC: The study is limited to the UPFC only and does not consider other FACTS devices or alternative technologies. 1.8 THESIS ORGANIZATION This thesis is organized into the following chapters: Chapter 1: Introduction: Provides an overview of UPFC, introduces the research objectives, and outlines the structure of the thesis. Chapter 2: Literature Review: Reviews relevant literature on UPFC technology, applications, and previous research studies. Chapter 3: Methodology and Simulation Tools: Describes the methodology used for modeling UPFC, selection of simulation tools, and validation techniques. Chapter 4: Results and Analysis: Presents the results of UPFC simulation studies and provides detailed analysis of the findings. Chapter 5: Conclusion and Recommendations: Summarizes the key findings, discusses implications, and provides recommendations for future research and practical implementation. CHAPTER TWO LITERATURE REVIEW 2.1 REVIEW OF RELATED WORKS A Flexible Alternating Current Transmission System (FACTS) can improve control over power flow, secure loading, and reduce power system oscillations by using power electronic controllers. A variety of power electronic systems are included in FACTS, such as the Unified Power Flow Controller (UPFC), Thyristor-Controlled Series Capacitor (TCSC), Static Condenser (STATCON), and Static VAR Compensator (SVC). One flexible power electronic system that provides phase angle adjustment, line impedance management, and VAR correction is the Unified Power Flow Controller (UPFC). It consists of two fully regulated power electronic converters that, by varying the injected voltage's magnitude and phase angle, allow for quick adjustment of the actual and reactive power flow in the transmission line. Laszlo Gyugyi and Fellow (1994) developed a revolutionary solution to real-time power flow regulation and dynamic correction in transmission systems using solid-state synchronous voltage sources. Using ate turn-off (GTO) thyristors, a multi-pulse inverter creates the synchronous voltage source. It can negotiate real power exchange with the ac system by interacting with an appropriate energy storage device in addition to being able to generate the reactive power required for network compensation internally. They created a thorough description of phase angle control, series compensation, and shunt compensation for solid-state synchronous voltage sources used in power flow management. It also describes the unique unified power flow controller that is able to control concurrently or selective all three network parameters (voltage, impedance, transmission angle) determining power transmission. In (1995) Gyqyi, and et al. described the basic concepts of the proposed generalized P and Q controller and compares it to the more conventional, but related power flow controllers, such as the thyristor-Controlled Series Capacitor and Thyristor- Controlled Phase Angle Regulator. And they also present results of computer simulations showing the performance of the UPFC under different system conditions. In (1996) Round, and et al. studied the performance of a unified power flow controller (UPFC) with four different controllers and evaluated through simulation and implementation in an experimental laboratory model. The controllers which were investigated are the PI controller, PI controller with decoupling, cross-coupling controller and robust H∞ controller. It is found that the cross- coupling and Robust H∞ controllers have the best performance when the exact value of the power transmission parameters is unknown. In (1997) M. Noroozian, et al. deal with optimal power flow control in electric power systems by use of unified power flow controller (UPFC). And they developed and analyzed Models suitable for incorporation in power flow programs. And demonstrated the application of UPFC for optimal power flow control through numerical examples. It is shown that a UPFC has the capability of regulating the power flow and minimizing the power losses simultaneously. In (2000) Zhengyu Huang, et al. discuss four principal main control strategies and the computer tests results support the discussion conclusion and also, they concluded the constant power flow control is good for steady state control and the constant series compensation control is useful for first swing stability. The supplementary control is very efficient in damping the power oscillation. The suggested UPFC control can realize the desired control strategy flexibly and improve system dynamic performance significantly. In (2010) Muthukrishnan and Nirmal Kumar dialed with digital simulation and implementation of power system using UPFC to improve the power quality. They deduce that UPFC is also capable of improving transient stability in a power system. In (2010), Mathukrishanan and nirmalkumar dialed with digital simulation of 14 – bus power system using UPFC to improve the power quality, they conclude that the UPFS has the capability of improving the transient stability in a power system. In (2010) Murali, and et al. investigates the improvement of transient stability of a two-area power system using UPFC and simulations are carried out in Matlab/Simulink environment for the two-area power system model with UPFC to analyze the effects of UPFC on transient stability performance of the system. The performance of UPFC is compared with other FACTS devices such as Static Synchronous Series Compensator (SSSC), Thyristor Controlled Series Capacitor (TCSC), and Static Var Compensator (SVC) respectively. The simulation results demonstrate the effectiveness and robustness of the proposed UPFC on transient stability improvement of the system. In (2011) Arup Ratan Bhowmik and Champa Nandi investigated the performance of Unified Power Flow Controller (UPFC) in controlling the flow of power over the transmission line and they dialed with digital simulation of standard IEEE 14-bus power system using UPFC to improve the real and reactive power flow control through a transmission line by placing UPFC at the sending end using computer simulation. In (2012) Aarti Rai includes first the optimal location of FACTS devices, second voltage stability analysis and third control of reactive power of system. The model can be simulated in MATLAB. The performance of the whole system such as voltage stability, transient stability, frequency and power swings will be analyzed and compared without FACTS and with FACTS device. In (2013) Rama Sekhara Reddy and Vijaya Kumar used a Unified Power Flow Controller (UPFC) to control the power flow in the transmission systems by controlling the impedance, voltage magnitude and phase angle in wind energy generation. This controller offers advantages in terms of static and dynamic operation of the power system. In (2013) Kumar Gaurav and Nitin Saxena conducted an investigation on the enhancement in voltage stability margin as well as the improvement in the power transfer capability in a power system with the incorporation of UPFC. A simple transmission line system is modeled in Matlab/Simulink environment. The load flow results are first obtained for an uncompensated system, and the voltage and power profiles are studied. The results so obtained are compared with the result obtained after compensating the system using UPFC to show the voltage stability margin enhancement. In (2013) Vaibhav S Kale et, al. proposed the real, reactive power and voltage control through a transmission line by placing UPFC at the sending end using computer simulation. The control scheme has the fast-dynamic response and hence is adequate for improving transient behavior of power system after transient conditions [19]. In (2013) K.Ravichandrudu and et al. introduced the concept of Distributed FACTS (D-FACTS) as an alternative approach to realizing cost-effective power flow control. They concluded that the UPFC is capable of improving transient stability in a power system and it is the most complex power electronic system for controlling the power flow in an electrical power system. The circuit model is developed for UPFC using rectifier and inverter circuits. The control angle is varied to vary the real and reactive powers at the receiving end. K.Ravichandrudu also demonstrated the performance of the UPFC in achieving harmonic mitigation and stability of the wind energy grid connected system by using MATLAB/SIMULINK. In (2014) B.Gopinath et, al. proposed a method based on Model predictive control (MPC) and using Bacterial Forging Algorithm (BFA) for modeling Unified Power Flow Controller. Modeling of UPFC is designed with its unique capability to control simultaneously real and reactive power flows on a transmission line as well as to regulate voltage at the bus where it is connected. Therefore, this device creates a remarkable quality impact on power system stability. UPFC with additional PI controller is used along with the UPFC main controller for this purpose. The simulation is carried out in MATLAB/simulink. In (2015) Koganti et, al. studied Power quality and stability improvement of HVDC transmission System using UPFC for different uncertainty conditions, they concluded that UPFC improves the system performance. It can control the power flow in the transmission line, effectively. With the addition of UPFC, the magnitude of fault current reduces and oscillations of excitation voltage also reduce. The total harmonic distortion (THD) is also reduced well below the IEC standards. It is more economical for the HVDC transmission system to transfer more power. In (2015) Shantha Soruban et, al. proposed an ANN based control scheme for a UPFC to be used as an active power filter. The objective is to guarantee power to the load at the required power quality. The ANN control unit monitors the voltage at the point of common coupling. UPFC enables improved power quality by maintaining power factor nearer to unity rapid response time, the ability to provide reactive power at low voltage and to provide voltage compensation can be obtained. For unbalanced voltage compensation, two unbalanced controllers using the phase voltage amplitude and negative sequence component are proposed. In (2015) G. Srinivas and T. Santosh Chaitanya studied and analyzed the operation and performance of D-STATCOM to compensate the harmonics coming from grid side inverter and different loads in that most of the unbalanced and +nonlinear loads inject harmonic currents to source side and effects the source. This can be overcome by using D-STATCOM by connecting as shunt at the distribution side by means of a tie reactance connected to compensate the load current. This chapter presents a sum of papers that used a UPFC to improving the active and reactive power flow of the power systems. 2.2 VOLTAGE STABILITY Many journals and other publications have looked into the idea of reactive power compensation and voltage stability. Additionally, several writers and researchers have presented several approaches to reactive power compensation, ranging from traditional to fast-acting thyristor-based compensating systems. The ability of a power system to sustain constant, acceptable voltages at each bus in the system both during regular operation and following a disturbance is known as voltage stability. When a disturbance, rise in load demand, or modification in system conditions results in a gradual and uncontrollable reduction in voltage, the system enters a state of voltage instability. The primary cause of instability is the power system's incapacity to supply reactive power at the required rate. Usually, the voltage drop that happens when reactive and active power pass through the transmission network's inductive reactance is the main cause of the issue. These occurrences might cause the generators to become out of sync, which would further destabilize the system. (P. Kundur, 2012). 2.3 VOLTAGE COLLAPSE Voltage collapse remains a significant challenge for power system networks. Voltage collapse can be either total blackout, or partial. A major factor contributing to voltage collapse is the inadequacy of reactive power resources in the system. As system loads increase, voltages across the network tend to drop, and reactive power losses rise due to high current, with these losses being proportional to the square of the current. To counteract this increased reactive power demand, voltage-regulating devices such as generators, static VAR compensators, and capacitors are employed, if available (Anderson and Fouad, 2008). Due to inherent physical constraints, reactive power devices cannot provide unlimited reactive power. As electrical loads increase over time, these devices or multiple sources may reach their maximum capacity. When a reactive power source hits its limit, it can no longer maintain voltage regulation. This leads to accelerated voltage decline, necessitating even more reactive power. This increased demand can push additional voltage- regulating devices to their limits, further speeding up the voltage drop. This situation can cause a significant portion of the system to experience voltage loss, culminating in a voltage collapse. 2.4 FLEXIBLE ALTERNATING CURRENT TRANSMISSION SYSTEM (FACTS) Power electronics is a proven technology that has transformed every facet of the electrical power network, impacting not only the distribution, utilization, and transmission of AC power but also the transmission of high voltage direct current (HVDC) (X. Jiang, 2010). In order to achieve electronic controllability, the Flexible AC Transmission Systems (FACTS) concept makes considerable use of power electronic devices on the high-voltage side of the network. Electric Power Research Institute (EPRI) introduced FACTS in the 1980s; it capitalizes on advances in high-voltage and high-current power electronics (Narain G, 2000). Both steady-state and transient performance are improved by this method, which also improves control over power flows in the high-voltage section of the network. The design and construction of power plant equipment, as well as the planning and management of transmission and distribution networks, are being affected by the shift to electronic controllability. Because they allow for quick control over energy flow pathways, these advances are predicted to completely transform energy transactions. FACTS has garnered substantial backing from electrical equipment makers, utilities, and research institutions worldwide, owing to its noteworthy economic and technological advantages (P. Therond, 1994).Globally, a variety of FACTS controllers have been put into practice, each with a specific purpose in mind to maximize power system efficiency and operation: load tap changers, phase-angle regulators, static VAR compensators, thyristor-controlled series compensators, interphase power controllers, static compensators, and unified power flow controllers (P. Zhang, 2012). FACTS devices introduce a wide operational range to increase the thermal limits of a power system and improve its stability. FACTS devices have been used for: • Active and reactive Power control • Voltage control stability and Sub synchronous resonance mitigation • Power oscillation damping • Transients and dynamics stability • Fault current limiting • Flicker mitigation • Power system security enhancement Fig 2.1 Overview of the main FACTS Devices 2.5 FACTS DEVICES Within limited bounds, conventional devices provided satisfactory results. But given the substantial changes taking place in the power sector and the rising demand for electricity, power system operators must look into more efficient ways to run the system. This entails controlling energy flow pathways quickly in order to make the most use of the transmission infrastructure that is already in place. By utilizing cutting-edge power electronic tools and techniques, also known as Flexible AC Transmission Systems (FACTS), this objective is accomplished. The following section examines how FACTS devices serve as promising solutions for reactive power compensation. 2.5.1 STATIC SYNCHRONOUS COMPENSATOR (STATCOM) One device in a family of devices known as flexible AC transmission system (FACTS) devices is the solid-state shunt device STATCOM, which produces or absorbs reactive power. According to A. Suul (2010), the STATCOM and SVC are comparable in terms of response time, controllability, and power electronics utilization. The STATCOM synthesizes the reactive power output utilizing self-commutated power electronics as opposed to traditional capacitors, inductors, and thyristors. As a result, output capability is often symmetric, offering an equal amount of capacity for absorption and production. Because the STATCOM is solid-state, its controls can be built to give highly fast and efficient voltage control, just like the SVC. Although synchronous condensers and generators can handle short-term overloads better than STATCOM capacity, SVCs and capacitors are more severely affected by voltage degradation. Due to their current limitation, STATCOMs' MVAR capability reacts to voltage linearly as opposed to SVCs and capacitors' voltage- squared connection. This feature makes STATCOMs much more effective in averting voltage collapse. Figure2.2 A static synchronous compensator 2.5.2 THYRISTOR-SWITCHED SERIES CAPACITOR (TSSC) A bypass valve switches a capacitor, which is the fundamental component of a TSSC. If the matching thyristor valve is closed, the capacitor is connected into the line; if not, it is bypassed. When the current crosses zero, a thyristor valve is closed. Therefore, only at the zero crossings of the line current can the thyristor valve insert the capacitor into the line. However, in order to reduce the first surge current in the valve and the associated circuit transient, the thyristor valve should only be activated for bypass when the capacitor voltage is zero. As a result, turning on the valve may take up to one complete cycle longer. Consequently, after the capacitor is placed in the line, the line current will charge it from zero to the maximum during the first half cycle and discharge it from the maximum to the zero during the next half cycle, or until the capacitor can be bypassed once more (IEEE, 2004). This can be seen in Fig. 2.3 (b). In series with the line reactance, the TSSC can be thought of as a controllable reactance. The line's compensation degree can be determined by dividing the line reactance by the ratio of the TSSC reactance that was introduced. (a) (b) Figure2.3 (a) circuit diagram of a TSSC, (b) course of capacitor voltage for the basic element in a TSSC 2.5.3 STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC) To control the transmitted electric power, a static synchronous generator that is powered by an internal electric energy source can be used as a series compensator. Its output voltage can be adjusted independently of the line current and is in quadrature with it. This allows the generator to adjust the overall reactive voltage drop across the line. In order to improve the power system's dynamic behavior, the SSSC may incorporate energy- absorbing or transiently rated energy storage devices. These can be used to temporarily raise or lower the total active (resistive) voltage drops across the line. For a better understanding, the basic working principles of the SSSC can be stated in terms of the traditional series capacitive compensation. The two machine systems with a traditional series capacitor and a basic comprehension of its phasor diagram are depicted in Figure 2.4. The above phasor diagram demonstrates how, at a certain line current, the series capacitor's voltage pushes the series line reactance's opposite polarity voltage to increase by the capacitor voltage's magnitude. Thus, in order for the series capacitive compensation to function, the voltage across the physical line's line impedance must be increased. This raises the corresponding line current and transmitted power. Figure 2.4 displays the voltage drop across the capacitor (VC) and the voltage drop across the line (VL), along with the line current (I). The phasor diagram indicates the magnitude of the sending and receiving end voltages (VS and VR), the reactance of the line (XC) and the capacitor (XL), and the angle between the two end source voltages (δ). (a) (b) Figure2.4 (a) A two machine system with a series capacitor compensated line, (b) its associated phasor diagram Thus the power flow in the line is increased by controlling the reactance of the line using series compensation as shown in equation 2.1 (2. 1) 2.5.4 THYRISTOR-CONTROLLED SERIES CAPACITOR (TCSC) A series compensator is the fundamental component of a Thyristor Controlled Series Capacitor (TCSC). Multiple of these compensators can be linked in series to provide the required voltage rating and operating characteristics. This configuration is comparable to the TSSC's, and it may be turned on and off in the same way as the TSSC if the reactor's impedance (XL) is low enough compared to the capacitor's (XC). The fundamental principle of the TCSC scheme is to partially negate the TCR's effective compensating capacitance in order to provide a continuously changing capacitor. Equation 2.5 displays the equivalent impedance of the TCSC. At the fundamental frequency, the TCR may have a continuously variable reactive impedance that is controllable by a delay angle. The steady-state impedance of the TCSC is that of a parallel LC circuit, made up of a variable inductive impedance (XL) and a fixed capacitive impedance (XC) (Sindekar and Parate, 2012). (2. 2) The scheme of a Thyristor-Controlled Series Capacitor is given in Fig. 2.5. A parameter to describe the TCSC main circuit is λ which is the ratio of the resonant frequency (fr) and the network frequency (f) resulting in . (2. 3) (2. 4) (2. 5) For the LC circuit, the resonant frequency is given by . (2. 6) substituting equations 2.4 and 2.5 into 2.6, we have . (2. 7) Figure2.5Thyristor-Controlled Series Capacitor (TCSC) 2.6 UNIFIED POWER FLOW CONTROLLER (UPFC) Overview The Unified power flow controller (UPFC) concept was proposed by Gyugyi in 1991.in the late 1980s, the Electric Power research Institute (EPRI) formulated the Flexible AC transmission voltage and power flow and reduces dynamic disturbances. Power flow over a transmission system is limited by some followings: • System stability • Loop flows • Voltage limits • Thermal limits of either lines or terminal equipment • High short circuit level limits Such transmission on power transfer are primarily due to the lack of high–speed control of inter related electrical parameters including voltage, current, impedance, phase angle, reactive and active power. FACTS controllers enhance the value of AC transmission assets by controlling any one or more of these parameters. Makombe and Jenkins, experimentally proved that a UPFC can control the three control parameters either individually or in appropriate combinations at its series-connected output while maintaining reactive power support at its shunt connected input device is to enhance the useable transmission capacity of lines and control the power flow. The third generation of FACTS devices, known as the Unified Power Flow Controller (UPFC), is by far the most comprehensive. It can implement power flow regulation in a steady-state power system, reasonably control line active power and reactive power, and improve the power system's transmission capacity. In a transient power system state, it can realize fast-acting reactive power compensation, dynamically support the voltage at the access point, and improve system voltage stability. In addition, it can improve power angle stability and damping of the system. The UPFC makes use of solid-state devices, which offer functional flexibility that traditional thyristor-controlled systems typically cannot match. A common DC voltage link connects a static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC), which together form the UPFC. Controlling the fluxes of both active and reactive power in the transmission line is the primary benefit of the UPFC. The UPFC will not function if the source side has any disruptions or malfunctions. Only a balanced sine wave source can run the UPFC. Phase angle, voltage, and reactance in the line are the UPFC's controllable parameters. L. Gyugyi of Westinghouse first presented the UPFC concept in 1995. A secondary but crucial function that the UPFC enables is stability control, which reduces power system oscillations and increases the power system's transient stability. In a publication titled "Power Quality Enhancement of Standard IEEE 14 Bus System using Unified Power Flow Controller," S. S. Khonde, S. S. Dhamse, and A. G. Thosar state that the unified power flow controller (UPFC) combines the characteristics of three compensators—phase angle, voltage magnitude, and impedance—to create a more comprehensive compensation. through adjusting phase angle, voltage magnitude, and impedance. The power flow in the transmission networks is managed by the unified power flow controller (UPFC). Two voltage source converters—series and shunt converters— that are linked to one another via a common dc link make up the UPFC. While the series converter, also known as the Static Synchronous Series Compensator (SSSC), is used to add controlled voltage magnitude and phase angle in series with the line, the shunt converter, also known as the Static Synchronous Compensator (STATCOM), is used to provide reactive power to the ac system. In addition, it will provide the dc power required for both inverters. Power electronic converters and transformers are found in every branch. There was a common DC capacitor between these two voltage source converters. This DC capacitor typically has a limited ability to store energy. As a result, the active power produced by the series converter and the active power drawn by the shunt converter must match. Greater control over power flow is possible due to the independent selection of reactive power in the shunt or series converter. The gadget is connected to the system via the coupling transformer. Fig 2.6 Schematic diagram of the UPFC One major development in the field of Flexible AC Transmission Systems (FACTS) is the Unified Power Flow Controller (UPFC). Precise control over voltage and power flow in AC transmission lines is achieved through the use of sophisticated power electronic components. By dynamically modifying line impedance and voltage parameters, UPFC plays a crucial part in optimizing grid performance and enhancing transmission stability and efficiency. This capacity is essential for improving grid reliability, reducing traffic, and making it easier to integrate renewable energy sources. Due to its adaptability and efficiency, UPFC is now widely used in power systems, helping to facilitate the continuous development of electrical grids that are more intelligent and resilient. The UPFC was created for dynamic compensation and real-time control of AC transmission systems. It has the ability to regulate every aspect of the transmission line's power flow. As an alternative, it has the ability to separately regulate the line's reactive and active power flows. In theory, the UPFC is a synchronous voltage source that is connected in series with the line and has programmable magnitude and angle. Both active and reactive power are exchanged between the voltage source and the transmission system. However, the voltage source is only able to generate reactive power; a power source or sink must provide it with active power. A power supply is a type of end bus. Currently, a UPFC is made up of two voltage-source converters that are powered by a common DC link and arranged back to back (DC storage capacitor). In Figure 2.7, this implementation is displayed. Figure2.7 Concept of the UPFC in a two-machine power system Between the converters' AC terminals, active power can move freely in either way, and each converter has the ability to independently produce and absorb reactive energy. As the voltage source, Converter 2 injects the voltage, which is tunable in both amplitude and phase, in series with the line. The converter internally generates the reactive power that is transferred at the AC terminal. In contrast, the active power is transformed into DC power, which manifests as a positive or negative active power demand at the DC connection. Converter 1 transforms this DC power requirement into AC power, which is then connected to the transmission line bus through the supply transformer. Furthermore, converter 1 can supply independent shunt reactive compensation for the line and, if needed, exchange reactive power with the line. Figure2.8 Implementation of UPFC Table 2.1 FACTS Applications and cost Comparison Because it can manage all the parameters that affect the transmission line power flow, such as voltage, phase angle, and impedance, UPFC, one of the FACTS devices listed in Table 2.1, can cover all the specified applications (N. Hingorani & L. Gyugyi, 2000). CHAPTER THREE METHODOLOGY This chapter's task is to examine the modeling and simulation techniques utilized for the power system network as well as the UPFC models that regulate the system's bus voltages. It also provides a thorough mathematical representation of the simulations' used solutions. One-line diagram of the power system used as the model for this project work is shown in figure the figure below. Figure3.1: One line diagram of the power system model 3.1 LOCATION OF UPFC UPFC must be installed in the correct places for the system to have higher voltage stability. The weak busses in the system were identified by a load flow analysis, which helped select the ideal position. Although there are other approaches for studying load flow, the Newton Raphson method has shown to be the most effective because of its robust convergence properties. Therefore, it was applied in this project to ascertain the steady state voltages at each of the system's busses. 3.2 NEWTON RAPHSON LOAD FLOW METHOD This approach uses iteration to solve the following set of nonlinear algebraic equations. (3. 1) where F represents the set of ‘n’ nonlinear equations, and X is the vector of ‘n’ unknown state variables. The essence of the method consists of determining the vector of state variables X by performing a Taylor series expansion of F(X) about an initial estimate X (0): higher-order terms (3. 2) where J(X (0)) is a matrix of first-order partial derivatives of F(X) with respect to X, termed the Jacobian, evaluated at X=X (0 ). This expansion lends itself to a suitable formulation for calculating the vector of state variables X by assuming that X (1) is the value computed by the algorithm at iteration 1 and that this value is sufficiently close to the initial estimate X (0 ). Based on this premise, all high-order derivative terms in Equation (3.2) may be neglected. Hence + (3. 3) In compact form, and generalising the above expression for the case of iteration (i), (3. 4) where i = 1, 2 . . . . Furthermore, if it is assumed that X(i ) is sufficiently close to the solution X(*), then FX(i ) ≈ FX(*) = 0. Hence, equation (3.4) becomes (3. 5) and solving for X(i ), (3. 6) The iterative solution can be expressed as a function of the correction vector ΔX(i)= X(i) - X(i -1), (3. 7) and the initial estimates are updated using the following relation: (3. 8) The calculations are repeated as many times as required using the most up-to-date values of X in equation (3.7). This is done until the mismatches ΔX are within a prescribed small tolerance (i.e. 1e -12). The essential equations must be represented in the form of Equation (4.7), where X is the set of unknown nodal voltage magnitudes and phase angles, in order to apply the Newton Raphson approach to the power flow problem. The power flow Newton Raphson algorithm can be described by the following connection since the power mismatch equations ΔP and ΔQ are enlarged around a base point (θ(0), V(0)): (3. 9) The various matrices in the Jacobian may consists of up to (nb - 1) × (nb - 1) elements of the form: (3. 10) where nb is the number of buses with the slack bus entries removed, and k and m are the values of 1,..., and nb, respectively. Additionally, the rows and columns for PV buses that relate to reactive power and voltage magnitude are removed. Moreover, the matching k–m item in the Jacobian is null when buses k and m are not connected directly by a transmission element. Because real power networks have relatively modest levels of connectedness, power flow Jacobians are quite sparse. They have the trait of being symmetrical in structure but not in value. extra Note that the correction terms ΔVm are divided by Vm in order to offset the multiplication of the Jacobian terms (∂PK/∂Vm)Vm and (∂QK/∂Vm)Vm by Vm. The derivative terms provided below demonstrate how this trick produces helpful calculations that can be made simpler. Figure3. 2: A two bus system for illustrating Newton Raphson Power flows Consider the element connected between buses k and m in Figure 3.2, for which self and mutual Jacobian terms are given below: 3.2.1 FORMATION OF THE Y-BUS In order to develop suitable power flow equations, it is necessary to find relationships between injected bus currents and bus voltages. Based on Figure 3.2 the injected complex current at bus k, denoted by IK, may be expressed in terms of the complex bus voltages Ek and Em as follows: (3.1 1) Similarly for bus m, (3.1 2) The above equations can be written in matrix form as, (3.1 3) or (3.1 4) where the bus admittances and voltages can be expressed in more explicit form: (3.1 5) (3.1 6) where i = k, m; j = k, m The complex power injected at bus k consists of an active and a reactive component and may be expressed as a function of the nodal voltage and the injected current at the bus: (3.1 7) where IK is the complex conjugate of the current injected at bus k. The expressions for and can be determined by substituting equations 3.15 and 3.16 into equation 3.17, and separating into real and imaginary parts (3.1 8) (3.1 9) Equations 3.18 and 3.19 are the two important power flow equations and are used in deriving the Jacobian matrix. 3.2.2. FORMING THE JACOBIAN MATRIX For k ≠ m, (3.20) (3.21) (3.22) (3.23) For K = m, (3.24) (3.25) (3.26) 3.3 INCORPORATING THE UPFC IN NEWTON RAPHSON LOAD FLOW Figure3. 3:Unified power flow controller equivalent circuit The UPFC voltage sources are: (3.27) (3.28) where and are the controllable magnitude ( ) and phase angle ( 2) of the voltage source representing the shunt converter. The magnitude and phase angle of the voltage source representing the series converter are controlled between limits ( and ( 2), respectively. The phase angle of the series-injected voltage determines the mode of power flow control. If is in phase with the nodal voltage angle, the UPFC regulates the terminal voltage. If is in quadature with respect to , it controls active power flow, acting as a phase shifter. If is in quadrature with the line current angle then it controls active power flow, acting as a variable series compensator. At any other value of , the UPFC operates as a combination of voltage regulator, variable series compensator, and phase shifter. The magnitude of the series-injected voltage determines the amount of power flow to be controlled. Based on the equivalent circuit shown in figure 3.3 and equations (3.27) and (3.28), the active and reactive power equations at bus k are: (3.29) (3.30) at bus m: (3.31) (3.32) Series converter: (3.33) (3.34) Shunt converter: (3.35) (3.36) Assuming loss-less converter valves, the active power supplied to the shunt converter, , equals the active power demanded by the series converter, ; that is, Furthermore, if the coupling transformers are assumed to contain no resistance then the active power at bus k matches the active power at bus m. Accordingly, The UPFC power equations, in linearized form, are combined with those of the AC network. For the case when the UPFC controls the following parameters: (1) voltage magnitude at the shunt converter terminal (bus k), (2) active power flow from bus m to bus k, and (3) reactive power injected at bus m, and taking bus m to be a PQ bus, the linearized system of equations is as follows: (3.37) The MATLAB script implementing the above Newton-Raphson load flow and the incorporation of the UPLC equations is given in appendix A CHAPTER FOUR SIMULATION AND RESULTS ANALYSIS This chapter presents the results obtained from the simulations and analyzed in line with the stated objective of the project. 4.1 CASE 1: Newton-Raphson load flow carried out without the UPFC, considered as the normal condition. This is result is depicted in tables 4.1 and 4.2. Table 4. 1:BUS VOLTAGES WITHOUT THE UPFC bus voltage in pu voltage angle in degree 1.0600 0.0000 1.0000 -2.0612 0.9872 -4.6367 0.9841 -4.9570 0.9717 -5.7649 Figure 4. 1:voltages of the buses without the UPFC between buses 3 and 4 Table 4. 2. LINE FLOWS AND LOSSES WITHOUT UPFC 4.2 CASE 2: Newton-Raphson load flow carried out with the UPFC incorporated between buses 3 and 4 to control nodal voltage and increase active power flows. This is result is depicted in tables 4.3 and 4.4 Table 4. 3. BUS VOLTAGES WITH UPFC bus voltage in pu voltage angle in degree 1.0600 0.0000 1.0000 -1.7693 1.0000 -6.0161 0.9917 -3.1906 0.9745 -4.9741 Figure 4. 2: voltages of the buses with the UPFC between buses 3 and 4 Table 4. 4. LINE FLOWS AND LOSSES WITH UPFC The power flows in the UPFC-upgraded network are different from the original situation, as was to be expected. The two most obvious differences are that bus 3 is receiving an additional 20% and 53% more active power from generator buses 1 and 2, respectively. The increase is a result of the UPFC series converter's high active power requirements. The robustness of the UPFC shunt bus will determine the maximum amount of active power transferred between the UPFC and the AC system, 3. The generator at bus 1 reduces its reactive power generation by roughly 5.6% because the UPFC generates its own reactive power, and the generator linked at bus 2 increases its reactive power absorption by roughly 22.6%. Additionally, bus 3's nodal voltage magnitude is maintained at 1 p.u. by the UPFC shunt converter. It's important to remember that the UPFC keeps the active and reactive powers at 40MW and 2MVAR, respectively, when they leave the UPFC and head towards bus 3. Table 4.5: voltages of the buses with and without the UPFC between buses 3 and 4 Bus No Bus Code Voltage Magnitude Angle Load (MW) Load (MVAR) Gen (MW) Gen (MVAR) Qmin Qmax 1 1 1.06 0 0.0 0.0 0.0 0.0 -500 500 2 2 1 0 20.0 10.0 40.0 0.0 -300 300 3 3 1 0 46.0 16.0 0.0 0.0 0 0 4 3 1 0 40.0 6.0 0.0 0.0 0 0 5 3 1 0 60.0 10.0 0.0 0.0 0 0 Table 4.6 Bus Data: IEEE 5 Bus System From Bus To Bus R X B 1 2 0.02 0.06 0.06 1 3 0.08 0.24 0.05 2 3 0.06 0.18 0.04 2 4 0.06 0.18 0.04 2 5 0.04 0.12 0.03 3 4 0.01 0.03 0.02 3 5 0.08 0.24 0.05 Table 4.7 Line Data for IEEE 5 Bus CHAPTER FIVE CONCLUSION AND RECOMMENDATIONS 5.1 CONCLUSION Both real powers expressed in watts, and reactive power, expressed in volt-amperes reactive, or var, are produced and consumed by components of AC systems. Useful task (like driving motors and lighting lamps) is completed by real power. The voltages that need to be regulated for system reliability are supported by reactive power. Controlling reactive power generation, absorption, and flow throughout the network improves the voltage profile. System losses are avoided by minimizing reactive power flows. A power flow solution is a network solution under steady state circumstances that is subject to specific limitations that govern how the system functions. Given a set of power injections at every bus and defined voltages, the power flow solution provides the nodal voltages, phase angle, and power flows. Reactive power generation, absorption, and network-wide flow are all managed to provide voltage regulation. Reactive power sources and sinks include rotating synchronous condensers, shunt capacitors, shunt reactors, UPFCs, and other FACTS devices. The UPFCs are adaptable devices that use power electronic switching components to regulate nearly every parameter that may be controlled in a power system. This project concentrated on reactive power compensation and the use of UPFCs to boost active power flows in transmission lines. The power-flow problem has been solved using the Newton-Raphson load flow method. A modified UPLC power flow model was used to investigate the impact of UPFC on the power system. The modified load flow program was utilized to access the impact of UPFC on the system, and UPLC was positioned between buses 3 and 4. In MATLAB, the simulation was carried out. Plots were used to depict the findings of a load flow analysis conducted on a five- bus system, which revealed that the voltage profile of the system had improved. Additionally, it was clear that the UPFC was positioned at a bus where the voltage magnitude was kept at one p.u. Based on the data, it can be said that the UPFC has the greatest influence on voltage compensation and that power flows to the bus closest to it, with its impact decreasing with increasing distance from the bus. 5.2 RECOMMENDATIONS One research project's completion creates opportunities for work in numerous other adjacent fields. Future work in the following areas has been identified in the course of this research: • A bigger interconnected power system, such as the IEEE 14 & IEEE 30 bus or the IEEE 118 bus, or even larger, can be used for the load flow research. • In addition to the UPFC, IPFC, STATCOM, and other FACTS controllers can be included, and the impact on the system can be examined. Fuzzy logic and genetic algorithms can be used to determine the ideal position of the UPFC. • A comparison of the FACTS devices' economics to alternative approaches can be done. APPENDIX A % THE PROGRAM WITHOUT UPFC PowerFlowsData; %Function to read network data [YR,YI] = YBus(tlsend,tlrec,tlresis,tlreac,tlsuscep,... tlcond,shbus,shresis,shreac,ntl,nbb,nsh); %Function to calculate the Ybus % GENERAL SETTINGS D = zeros(1,nmax); flag = 0; it = 1; % CALCULATE NET POWERS [PNET,QNET] = NetPowers(nbb,ngn,nld,genbus,loadbus,PGEN,QGEN,... PLOAD,QLOAD); while ( it < itmax && flag==0 ) % CALCULATED POWERS [PCAL,QCAL] = CalculatedPowers(nbb,VM,VA,YR,YI); % CHECK FOR POSSIBLE GENERATOR’S REACTIVE POWERS LIMITS VIOLATIONS [QNET,bustype] = GeneratorsLimits(ngn,genbus,bustype,QGEN,QMAX,... QMIN,QCAL,QNET, QLOAD, it, VM, nld, loadbus); % POWER MISMATCHES [DPQ,DP,DQ,flag] = PowerMismatches(nmax,nbb,tol,bustype,flag,PNET,... QNET,PCAL,QCAL); % JACOBIAN FORMATION [JAC] = NewtonRaphsonJacobian(nmax,nbb,bustype,PCAL,QCAL,VM, VA,... YR,YI); % SOLVE FOR THE STATE VARIABLES VECTOR D = JAC\DPQ'; % UPDATE STATE VARIABLES [VA,VM] = StateVariablesUpdates(nbb,D,VA,VM); it = it + 1; end [PQsend,PQrec,PQloss,PQbus] = PQflows(nbb,ngn,ntl,nld,... genbus,loadbus,tlsend,tlrec,tlresis,tlreac,tlcond,tlsuscep,PLOAD ,... QLOAD,VM,VA); Psend=real(PQsend*100)'; Prec=real(PQrec*100)'; Ploss=real(PQloss*100)'; Qsend=imag(PQsend*100)'; Qrec=imag(PQrec*100)'; Qloss=imag(PQloss*100)'; PQbus=(PQbus*100)'; % End function Newton-Raphson % Results VA=VA*180/pi; %Nodal voltage phase angles (deg) disp(['bus voltage in pu ','voltage angle in degree']) SM = [VM;VA]; % - - - Main UPFC Program PowerFlowsData; %Function to read network data UPFCdata; %Function to read the UPFC data [YR,YI] = YBus(tlsend,tlrec,tlresis,tlreac,tlsuscep,... tlcond,shbus,shresis,shreac,ntl,nbb,nsh); %Function to calculate the Ybus % GENERAL SETTING D = zeros(1,nmax); flag = 0; it = 1; % CALCULATE NET POWERS [PNET,QNET] = NetPowers(nbb,ngn,nld,genbus,loadbus,PGEN,QGEN,... PLOAD,QLOAD); while ( it < itmax && flag==0 ) % CALCULATED POWERS [PCAL,QCAL] = CalculatedPowers(nbb,VM,VA,YR,YI); % CHECK FOR POSSIBLE GENERATOR’S REACTIVE POWERS LIMITS VIOLATIONS [QNET,bustype] = GeneratorsLimits(ngn,genbus,bustype,QGEN,QMAX,... QMIN,QCAL,QNET, QLOAD, it, VM, nld, loadbus); % UPFC CALCULATED POWER [PspQsend,PspQrec,PQcr,PQvr,PCAL,QCAL] = UPFCCalpower... (nbb,VA, VM,NUPFC,UPFCsend,UPFCrec,Xcr,Xvr,Vcr,Tcr,Vvr,Tvr,PCA L,... QCAL); % POWER MISMATCHES [DPQ,DP,DQ,flag] = PowerMismatches(nmax,nbb,tol,bustype,flag,PNET,... QNET,PCAL,QCAL); % UPFC POWER MISMATCHES [DPQ,flag] = UPFCPowerMismatches(flag,tol,nbb,DPQ,VM,VA,NUPFC,Flo w,... Psp,PSta,Qsp,QSta,PspQsend,PspQrec,PQcr,PQvr); if flag == 1 break end % JACOBIAN FORMATION [JAC] = NewtonRaphsonJacobian(nmax,nbb,bustype,PCAL,QCAL,... VM,VA,YR,YI); % MODIFICATION OF THE JACOBIAN FOR UPFC [JAC] = UPFCJacobian(nbb,JAC,VM,VA,NUPFC,UPFCsend,... UPFCrec,Xcr,Xvr,Flow,PSta,QSta,Vcr,Tcr,Vvr,Tvr,VvrSta); % SOLVE JOCOBIAN D = JAC\DPQ'; % UPDATE THE STATE VARIABLES VALUES [VA,VM] = StateVariablesUpdates(nbb,D,VA,VM); % UPDATE THE TCSC VARIABLES [VM,Vcr,Tcr,Vvr,Tvr] = UPFCUpdating(nbb,VM,D,NUPFC,UPFCsend,PSta,... QSta,Vcr,Tcr,Vvr,Tvr,VvrTar,VvrSta); %CHECK VOLTAGE LIMITS IN THE CONVERTERS [Vcr,Vvr] = UPFCLimits(NUPFC,Vcr,VcrLo,VcrHi,Vvr,VvrLo,VvrHi); it = it + 1; end %Function to calculate the power flows in the UPFC controller [UPFC_PQsend,UPFC_PQrec,PQcr,PQvr] = PQUPFCpower(nbb,... VA,VM, NUPFC,UPFCsend,UPFCrec,Xcr,Xvr,Vcr,Tcr,Vvr,Tvr); [PQsend,PQrec,PQloss,PQbus] = PQflows(nbb,ngn,ntl,nld,genbus,... loadbus,tlsend,tlrec,tlresis,tlreac,tlcond,tlsuscep,PLOAD,QLOA D,... VM,VA); Psend=real(PQsend*100)'; Prec=real(PQrec*100)'; Ploss=real(PQloss*100)'; Qsend=imag(PQsend*100)'; Qrec=imag(PQrec*100)'; Qloss=imag(PQloss*100)'; PQbus=(PQbus*100)'; % End of UPFC main program %Print results it; %Number of iterations VA=VA*180/pi; %Nodal voltage phase angles (deg) disp(['bus voltage in pu ','voltage angle in degree']) SM = [VM;VA]; fprintf('%15.4f %23.4f\n',SM) REFERENCES S. Asha Kiranmai, M. Manjula and V.R.S. Sarma, “Mitigation of Various Power Quality Problems Using Unified Series Shunt Compensator in PSCAD/EMTDC,” 16th National Power Systems Conference, 15th-17th Dec. 2010. D. Mohanty, A, Ahamad, and M. A Khan, “Modeling, Simulation and Performance Analysis of FACTS Controller in Transmission line,” International Journal of Emerging Technology and Advanced Engineering, Vol. 3, No. 5, pp. 429-435, May. 2013. V. Mathad, F. R. Basanagouda, and S. H. Jangamshetti, “Voltage Control and Power System Stability Enhancement using UPFC,” International Conference on Renewable Energies and Power Quality (ICREPQ’14) , Apr. 2014, Vol.1, No.12, pp. 871-875. S. S. Khonde, S. S. Dhamse, and A. G Thosar, “Power Quality Enhancement of Standard IEEE 14 Bus System using Unified Power Flow Controller,” International Journal of Engineering Science and Innovative Technology (IJESIT), Vol. 3, No. 5, pp. 323-334, Sept. 2014. L. Gyugyi & Fellow, “DYNAMIC COMPENSATION OF AC TRANSMISSION LINES BY SOLID-STATE SYNCHRONOUS VOLTAGE SOURCES,” IEEE Transactions on Power Delivery, Vol. 9, No. 2, pp. 904- 911, Apr. 1994. L. Gyqyi, T. R. Rietman, A. Edris, C. D. Schauda, s. L . Willirms, and , D.R. Torgerson, “THE UNIFIED POWFBFLOW CONTROLLER: A NEW APPROACH TO POWER TRANSMISSION CONTROL,” IEEE Transactions on Power Delivery, Vol. 10, No. 2, pp. 1085- 1097, Apr. 1995. Q. Yu, S. D. Round, L. E. Norum, and T. M. Undeland, “Dynamic Control of a Unified Power Flow Controller,” IEEE, pp. 508-514, 1996. M. Noroozian, L, Angquist, M. Ghandhari and G. Anderson, “USE OF UPFC FOR OPTIMAL POWER FLOW CONTROL,” IEEE Transactions on Power Delivery, Vol. 12, No. 4, pp.1629-1634, Oct. 1997. Z. Huang, Y. Ni, C. M. Shen, F. W. Felix, S. Chen and B. Zhang, “ Application of Unified Power Flow Controller in Interconnected Power Systems—Modeling, Interface, Control Strategy, and Case Study,” IEEE Transactions on Power systems, Vol. 15, No. 2, pp. 817- 824, May. 2000. S. Muthukrishnan and A. Kumar, “Comparison of Simulation and Experimental Results of UPFC used for Power Quality Improvement,” International Journal of Computer and Electrical Engineering, Vol. 2, No. 3, pp. 555-559, June. 2010. S. Muthukrishnan and A. Kumar, “Enhancement of power Quality in 14 Bus System Using UPFC,” Research journal of Applied Sciences, Engineering and technology,” ISSN. 2040-7467, pp. 356-361, July. 2010. D. Murali, M. Rajaram and N. Reka, “Comparison of FACTS Devices for Power System Stability Enhancement,” International Journal of Computer Applications, Vol.8, No.4, pp.30-35, Oct. 2010. A. R. Bhowmik and C. Nandi, “Implementation of Unified Power Flow Controller (UPFC) for Power Quality Improvement in IEEE 14-Bus System,” Arup Ratan Bhowmik et al, Int. J. Comp. Tech. Appl., Vol. 2 (6),1889- 1896, 2011. A. Rai, “Enhancement of Voltage Stability & reactive Power Control of Distribution System Using Facts Devices,” International Journal of Scientific Research Engineering & Technology, Vol.1, No. 9, pp. 001-005, Dec. 2012. M R. S. Reddy and M. V. Kumar, “Power Quality Improvement in DFIG based Wind Energy Conversion System using UPFC,” IOSR Journal of Engineering (IOSRJEN) Vol. 3, No. 1, pp. 46-54, Jan. 2013. K. Gaurav and N. Saxena, “Power Quality improvement using UPFC,” International Journal of Electrical, Electronics and Computer Engineering , Vol.2, No.2, pp. 30- 33, 2013. S. Vaibhav Kale, R. P.Prashant and R. Khatri, “Unified Power Flow Controller for Power Quality Improvement,” International Journal of Emerging Science and Engineering (IJESE), Vol.1, No. 10, pp. 1-4, Aug. 2013. K. Ravichandrudu, P. S. Pramod Kumar, and, V.E. Sowjanya, “MITIGATION OF HARMONICS AND POWER QUALITY IMPROVEMENT FOR GRID CONNECTED SYSTEM USING UPFC,” International Journal of Application or Innovation in Engineering & Management (IJAIEM), Vol. 2, No. 10, pp. 141-156 Oct. 2013. B. Gopinath, N. Vinothini, and S. kumar, “Modeling of UPFC Using Model Predictive Control and Bacterial Foraging Algorithm,” International Journal of Innovative Research in Computer and Communication Engineering, Vol. 2, No. 1, pp. 2724-2731, Jan. 2014. K. S. Lakshmi, G. Sravanthi, L. Ramadevi, and K. H. Chowdary, “Power quality and stability improvement of HVDC transmission System using UPFC for Different uncertainty conditions,” International Journal of Scientific & Engineering Research, Vol. 6, No. 2, pp. 795-801, Feb. 2015. M. S. Soruban, J D. Sathyaraj, and J. J. Gnana Chandran, “Power Quality Enhancement Using UPFC as an Active Power Filter for Renewable Power Generation,” International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering Vol. 4, No. 3, pp. 1712-1718, March. 2015. G. Srinivas and T. Santosh Chaitanya, “Enhancement of Power Quality Using FACTS Devices (D-STATCOM),” International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, Vol. 4, No. 4, pp. 1956-1965, Apr. 2015 P. Kundur Power System stability and control McGraw- Hill, New York (2012) Anderson, P. M., & Fouad, A. A. (2008). Power System Control and Stability. Wiley-IEEE Press. X. Jiang, J. H. Chow, A.-A. Edris, B. Fardanesh, and E. Uzunovic, “Transfer path stability enhancement by voltage- sourced converter-based FACTS controllers,” IEEE Transactions on Power Delivery, vol. 25, pp. 1019-1025, Apr. 2010. L. G. c. E.-H. Narain G. Hingorani, consulting editor., Understanding FACTS : concepts and technology of flexible AC transmission systems New York : IEEE Press 2000 P. Therond, P. Cholley, D. Daniel, E. Joncquel, L. Lafon, and C. Poumarede, "FACTS research and development program at EDF," in Flexible AC Transmission Systems (FACTS) - The Key to Increased Utilisation of Power Systems, IEE Colloquium on (Digest No.1994/005), 1994, pp. 6/1-615. X.-P. Zhang, C. Rehtanz, and B. Pal, "FACTS-Devices and Applications," in Flexible AC Transmission Systems: Modelling and Control, ed: Springer, 2012, pp. 1-30 J. A. Suul, M. Molinas, and T. Undeland, "STATCOM-Based Indirect Torque Control of Induction Machines During Voltage Recovery After Grid Faults," Power Electronics, IEEE Transactions on, vol. 25, pp. 1240-1250, 2010. Thyristor-Controlled Series Capacitors for Power System Compensation," IEEE Transactions on Power Delivery, 2004. Sindekar, A & Parate, J. (2012). Reactive Power Control and Transmission loss reduction with realization of SVC and TCSC. (Electronic version). International Journal of Engineering Science and Technology. 4 (7), 3592 – 3600 Singh, B. etal. (2010). Incorporation of FACTS Controllers in Newton Raphson Load Flow for Power Flow Operation, Control and Planning: A Comprehensive Survey. (Electronic version). International Journal on Computer Science and Engineering. 2 (6), 2117- 2124 Youtube Video: Design and Analysis of UPFC to Improve Power Capacity: Technical University. Youtube Video: Lecture on Analysis pf Unified Power Controller: Technical University. Enrique, A etal. (2004). FACTS Modelling and Simulation in Power Networks. India: Thomson Press Ltd, New Delhi. 1