Enhancement of Voltage Stability with Unified Power Flow Controller Considering Loadability Analysis

Voltage stability is an important issue in planning and operation of electric power system during both normal and under contingency conditions. This paper presents line voltage stability index (LVSI) for transmission lines voltage stability assessment and evaluation. The system stability under maximum loading and contingency conditions are analyzed using optimal power flow analysis. FACTS device is considered for a real-time control and a dynamic reactive power compensation of the system. Voltage source-based power injection model of unified power flow controller (UPFC) is used for the minimization of voltage deviation and losses on the network. Optimal location and sizing of UPFC is carried out using grey wolf optimization (GWO) technique in order to identify an optimal location where the FACTS device will be installed. UPFC device has proven to increase the line transmittable power, controls the voltage magnitude at the buses as well as enhancing the stability and security of the power system. The various conditions and scenarios used to test the efficacy of this model for system stability and security under contingency conditions are demonstrated on standard IEEE 14-bus test system

Optimization of FACTS devices : classification, recent trends, and future outlook

Since the inception of industrialization, power system has been an indispensable aspect of economy. With the progression of time, technology has impalpably commingled into our lifestyle. Alongside blooming technologies, energy demand is proliferating and power companies are begetting energy at their best to quench it. Growing reliance on power system has brought its quality into more advertence. Various electronic devices and topologies have been invented to enhance power quality and reliability; numerous others are still underway. During the course, power system has grown to an intricate network of sources, loads and control devices, leading to various issues such as transmission congestion and high losses. This paper discusses ways to ameliorate congestion and gives an overview of relationship between our present energy resources and ecological threats like global warming. Moreover, it points out various power system problems such as energy losses and transients. The necessity of FACTS devices has also been elaborated alongside their classification and comparison. Finally, numerous topologies and optimization methods proposed in the technical literature have been classified and analyzed to alleviate power system conundrums, and a glimpse into future energy trends is presented

GREY WOLF OPTIMIZER BASED OPTIMAL PLACEMENT OF MULTIPLE FACTS DEVICES IN THE TRANSMISSION SYSTEM UNDER DYNAMIC LOADING SYSTEM

The application of grey wolf optimization technique for multiple FACTS placement is presented in this paper for the reduction of total system losses and minimization of voltage deviation via optimal placement of Flexible AC Transmission System (FACTS) device. Grey wolf optimization (GWO) technique is inspired by social hierarchy and hunting behaviour of wolves and offers a right balance between exploration and exploitation during the search for global optimal. Series-shunt FACTS device; unified power flow controller (UPFC) is considered as a formidable device that can provides an alternative option for the flexible controllability and improvement of power transfer capability of a transmission lines. The analyses were conducted by increasing the number of UPFC in the network in order to evaluate the optimal number of FACTS devices that would give the least loss under maximum loading and contingency conditions. The efficacy of this proposed technique is demonstrated on 31-bus, 330 kV Nigeria National Grid (NNG) using MATLAB environment. The results show that optimal placement of FACTS device along with optimization technique provides a promising solution to the high power loss and voltage deviation bedevilling Nigeria National Grid

Study of Voltage Stability Using Intelligent Techniques

The continuous increase in the demand of active and reactive power in the power system network has limits as scope for network expansion many a times poses serious problems. The power system must be able to maintain acceptable voltage at all nodes in the system at a normal operating condition as well as post disturbance periods. Voltage instability is a serious issue in the system due to progressive and uncontrollable fall in voltage level. The research presented in this thesis is concerned with several facets of the voltage stability problem. The focus of this thesis is to improve the voltage stability of the system. The sensitivity analysis plays an important role as it monitors the nearness of the system towards the voltage collapse situation. The conventional offline data as well as the online data are processed to determine the weak areas are determined. As the system is having nonlinearities it is governed by differential and algebraic equations which are in turn solved by nonlinear techniques. In this work the system is analysed with steady state model. Once the system is represented in the form of differential equations and standard form is achieved advanced control techniques can be easily applied for its solution. The main focus of this thesis is aimed at placing FACTS device known as the Static compensator (STATCOM) at weak location of the system network to address the problem of voltage instability. With its unique capability to control reactive power flow in a transmission line as well as voltage at the bus where it is connected, this device significantly contribute to improve the power system. These features turn out to be even more prominent because STATCOM can allow loading of the transmission lines close to their thermal limits, forcing the power to flow through the desired paths. This opens up new avenues for the much needed flexibility in order to satisfy the demands. The voltage instability is improved with reactive power supports of optimal values at optimal locations. Also renewable energy sources offer better option than the conventional types and hence attempt has been made to include the wind energy for this study the wind generator is considered delivering constant output and is assumed as a substitute to the conventional power generators. Finally the system voltage stability is studied with design of a controller based on probabilistic neural network. The developed controller has provided much better performance under wide variations in the system loads and contingencies and shown a significant improvement in the static performance of the system. The proposed controller is tested under different scenarios of line outages and the load increase and found to be more effective than the existing ones. The research has revealed a veritable cornucopia of research opportunities, some of which are discussed in the thesis

MODELING AND CONTROL OF INTERLINE POWER FLOW CONTROLLER FOR POWER SYSTEM STABILITY ENHANCEMENT

Mitigation of power system oscillations is the problem of concern in the power industry as these oscillations, when exhibiting poor damping; affect the transmission line power transfer capability and power system stability. These oscillations greatly restrict power system operations and, in some cases, can also lead to widespread system disturbances. In this context, the Flexible AC Transmission System (FACTS) device, Interline Power Flow Controller (IPFC) employed to improve the transmission capability can be additionally utilized for damping control of power system oscillations. IPFC based damping controller design for power system stability requires proper and adequate mathematical representation of power system incorporating the FACTS device. This thesis reports the investigation on the development of steady state model, the dynamic nonlinear mathematical model of the power system installed with the IPFC for stability studies and the linearized extended Phillips Heffron model for the design of control techniques to enhance the damping of the lightly damped oscillations modes. In this context, the mathematical models of the single machine infinite bus (SMIB) power system and multi-machine power system incorporated with IPFC are established. The controllers for the IPFC are designed for enhancing the power system stability. The eigenvalue analysis and nonlinear simulation studies of the investigations conducted on the SMIB and Multi-machine power systems installed with IPFC demonstrate that the control designs are effective in damping the power system oscillations. The results presented in this thesis would provide useful information to electric power utilities engaged in scheduling and operating with the FACTS device, IPFC

Enhancement of deregulated and restructured power network performance with flexible alternating current transmission systems devices.

Doctoral degree. University of KwaZulu- Natal, Durban.The increase in power transactions, consequent open access created by deregulation and restructuring has resulted into network operation challenges including determination as well as enhancement of available transfer capability (ATC), and congestion management among others. In this study, repeated alternating current power flow (RACPF) approach was implemented for determination of ATC. ATCs for inter-area line outage and generator outage contingency conditions were obtained and analyzed. Analyses of most severe line outage contingencies resulting from evaluation of different performance index (PI) ranking methods were carried out for severe line outage contingency identification. A comprehensive review of FACTS controllers with their various background, topological structures, deployment techniques and cutting-edge applications was carried out for network performance enhancement. In addition, different placement methods were investigated for optimal performance evaluation of FACTS devices. Following this, comparative performance of static var compensator (SVC) and thyristor-controlled series compensator (TCSC) models for enhancement of ATC, bus voltage profile improvement and real power loss minimization was investigated. In addition, particle swarm optimization (PSO) and brain-storm optimization algorithms (BSOA) were engaged for optimum setting of FACTS devices through multi-objective problem formulation and allocation purposes. Thereafter, sensitivity-based technique involving incorporation of proposed FACTS device loss with the general loss equation for the determination of optimum location with same objectives was developed and TCSC location was established based on this sensitivity factors analyses, obtained from partial derivatives of the resultant loss equations with respect to control parameters. Subsequently, investigation and analyses of capability of an optimized VSC-HVDC transmission system in enhancing power network performance were conducted. Furthermore, this optimized VSC-HVDC transmission system was applied for mitigation of bus voltage and line thermal limit violation as a result of n-1-line outage contingency. All these investigations and analyses were implemented for bilateral, simultaneous and multilateral transactions as characterized by network liberalization and IEEE 5 and 30 bus networks were used for implementation in MATLAB environment. RACPF method found to be more accurate especially when compared with other methods with 11.574 MW above and 29.014 MW below recorded ATC values. Voltage and real power PI have also been proven to be distinctly dissimilar in severe contingency identification. In placement method comparison however, disparities in ATC enhancement ranges between 2% and 85% were achieved while real power loss minimization of up to 25% was obtained for different methods. Real power loss minimization of up to 0.06 MW and voltage improvement of bus 21 to 30 were achieved with SVC, while ATC enhancement of up to 14% were recorded for both devices. However, BSO behaved much like PSO throughout the achievements of other set objectives but performed better in ATC enhancement with 27.12 MW and 5.24 MW increase above enhanced ATC values achieved by the latter. The comparison of set objectives values relative to that obtained with PSO methods depict suitability and advantages of BSOA technique. Sensitivity based placement technique resulted into ATC enhancement of more than 60% well above the values obtained when TCSC was placed with thermal limit method. In addition, a substantial bus voltage improvement and active power loss reduction were recorded with this placement method. With incorporation of a VSC-HVDC based transmission system into ac network however, there was an improvement in power flow up to 15.66% corresponding to 46 MW for various transactions, transmission line power loss minimization up to 0.38 MW and bus voltage profile deviation minimization. Besides, automatic alleviation of violated thermal and voltage limits during contingency present VSC-HVDC system as a solution for network performance optimization especially during various transactions occasioned by unbundling power processes. Therefore, ATCs were properly enhanced, bus voltage profile improved, and system real power loss minimized. Likewise, HVDC system enhanced network performance and automatically alleviated violated thermal and voltage limits during contingency

Improvement of voltage and power flow control in the GCC power grid by using coordinated FACTS devices

This work presents HVDC/FACTS control device implementation framework in the Gulf cooperative council’s countries. It comprises of five layers of FACTS control devices (STATCOM, SSSC, UPFC, HVDC and centralized/De-centralized Control). This five-layer architecture is designed in order to configure and produce the desired results; based on these outcomes, GCC power system network control and operational problems can be identified and addressed within the control architecture on the GCC power grid. In the context of power FACTS-FRAME, this work is to identify and determine a number of power systems operational and control problems which are persistent on the GCC power grid e.g. poor voltage quality (SAG-Swell), poor load flow control, and limited power transfer capacity issues. The FACTS-FRAME is configured and synthesized by integrating multiple FACTS control devices (STATCOM, SSSC, UPFC) in parallel at different locations on the GCC power grid in order to meet stringent power system control and operational requirements with improved power transfer capacity, controllability and reliability. The mathematical models are derived to indentify and determine operational constraints on the GCC power grid by incorporating real-time and estimated data and the acquired desired results. Herein, FACTS-FRAME is designed to handle distributed computation for intensive power system calculation by integrating multiple FACTS devices on multiple networks within the GCC power network. Distributed power flow algorithms are also derived in order to understand and implement centralized and decentralized control topologies as appropriate. The simulation results indicate the feasibility of FACTS devices implementation and their potential benefits under current operating conditions on the GCC power grid.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Improvement of Voltage and Power Flow Control in the GCC Power Grid by using Coordinated FACTS Devices

This work presents HVDC/FACTS control device implementation framework in the Gulf cooperative council’s countries. It comprises of five layers of FACTS control devices (STATCOM, SSSC, UPFC, HVDC and centralized/De-centralized Control). This five-layer architecture is designed in order to configure and produce the desired results; based on these outcomes, GCC power system network control and operational problems can be identified and addressed within the control architecture on the GCC power grid. In the context of power FACTS-FRAME, this work is to identify and determine a number of power systems operational and control problems which are persistent on the GCC power grid e.g. poor voltage quality (SAG-Swell), poor load flow control, and limited power transfer capacity issues. The FACTS-FRAME is configured and synthesized by integrating multiple FACTS control devices (STATCOM, SSSC, UPFC) in parallel at different locations on the GCC power grid in order to meet stringent power system control and operational requirements with improved power transfer capacity, controllability and reliability. The mathematical models are derived to indentify and determine operational constraints on the GCC power grid by incorporating real-time and estimated data and the acquired desired results. Herein, FACTS-FRAME is designed to handle distributed computation for intensive power system calculation by integrating multiple FACTS devices on multiple networks within the GCC power network. Distributed power flow algorithms are also derived in order to understand and implement centralized and decentralized control topologies as appropriate. The simulation results indicate the feasibility of FACTS devices implementation and their potential benefits under current operating conditions on the GCC power grid.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Busqueda tabú multi-objetivo para la localización y dimensionamiento óptimos de generación distribuida y FACTS en redes eléctricas

Desde la apertura del mercado eléctrico a compañías privadas, las redes de transmisión y distribución de potencia se han visto afectadas en la calidad de onda, perfil y/o estabilidad de voltaje, armónicos, desbalances, entre otros. En un principio, la localización de generación distribuida a lo largo del sistema de potencia ayudó a los operadores a mantener la estabilidad, aunque el uso excesivo puede provocar saturación y por tanto, problemas a la hora de operar la red eléctrica. La combinación de las unidades de generación distribuida y FACTS ha demostrado en esta investigación que es capaz de reducir el costo total del sistema de potencia, mejorando la estabilidad de voltaje y los límites térmicos de las líneas. Aquí se presenta un modelo multi-objetivo basado en búsqueda tabú para la localización y dimensionamiento óptimos de generación distribuida y FACTS considerando la inversión mínima en dispositivos, incluyendo el coste de instalación, operación y mantenimiento, anualizando los costes mediante un factor de recuperación de capital a 25 años de vida útil. Las soluciones se han evaluado con un código abierto de flujo de cargas (PSAT, Power System Analysis Toolbox), el algoritmo heurístico se ha programado en lenguaje Matlab. La validación del modelo propuesto se lleva a cabo en una red de 300~nodos perteneciente a la IEEE, donde la generación distribuida es simulada como un generador diésel y los FACTS considerados son el HVDC, SSSC, STATCOM, SVC, TCSC y el UPFC. Los resultados son comparados con las soluciones de la frontera óptimo de Pareto para dos variables: costo de inversión y costo de generación de potencia. Los resultados obtenidos consideran tres metodologías: concatenación de atributos, indicadores predictivos y la combinación de ambos; tres estrategias de instalación: solo generación distribuida, solo FACTS y la combinación de los dispositivos. Los resultados demuestran que la adición de generación distribuida es la más económica, mientras que añadir solo FACTS no representa una mejora de la estabilidad en los nodos y, combinar los dispositivos reduce el costo total de la red eléctrica.<br /

MODELING AND CONTROL OF INTERLINE POWER FLOW CONTROLLER FOR POWER SYSTEM STABILITY ENHANCEMENT

Mitigation of power system oscillations is the problem of concern in the power industry as these oscillations, when exhibiting poor damping; affect the transmission line power transfer capability and power system stability. These oscillations greatly restrict power system operations and, in some cases, can also lead to widespread system disturbances. In this context, the Flexible AC Transmission System (FACTS) device, Interline Power Flow Controller (IPFC) employed to improve the transmission capability can be additionally utilized for damping control of power system oscillations. IPFC based damping controller design for power system stability requires proper and adequate mathematical representation of power system incorporating the FACTS device. This thesis reports the investigation on the development of steady state model, the dynamic nonlinear mathematical model of the power system installed with the IPFC for stability studies and the linearized extended Phillips Heffron model for the design of control techniques to enhance the damping of the lightly damped oscillations modes. In this context, the mathematical models of the single machine infinite bus (SMIB) power system and multi-machine power system incorporated with IPFC are established. The controllers for the IPFC are designed for enhancing the power system stability. The eigenvalue analysis and nonlinear simulation studies of the investigations conducted on the SMIB and Multi-machine power systems installed with IPFC demonstrate that the control designs are effective in damping the power system oscillations. The results presented in this thesis would provide useful information to electric power utilities engaged in scheduling and operating with the FACTS device, IPFC