Optimal UPFC deployment for voltage stability enhancement: Application of weighted voltage stability indices and hybrid optimization

This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

This paper presents a placement method of fuzzy logic based unified power flow controller (UPFC) in power system network by analyzing dynamic voltage stability. Voltage stability indices namely LQP and voltage collapse point indicators (VCPI) indices are used to determine the weakest line for UPFC by dynamic load variation. The controllers of the shunt and series converters of the UPFC are developed using fuzzy logic (FL) and proportional integral (PI) controllers respectively to enhance the dynamic voltage stability of the power system network.The simulation has been conducted in power system computer-aided design (PSCAD) environment where IEEE-5 and IEEE-14 bus system have been chosen as test bench systems. The results obtained through simulations have ensured the effectiveness of the proposed placement method since fuzzy based UPFC’s placement in the obtained locations resulted in significant improvment in voltage stability.

A new approach of unified power flow controller (UPFC) optimal placement in the power system network based on dynamic analysis of voltage stability is presented in this paper. Voltage stability indices (VSIs), called line stability index LQP, voltage collapse point indicators (VCPIs), and line stability factor Lmn have been employed to explore the most suitable location for UPFC. The locations of UPFC are identified by dynamically varying loads across all the PQ buses by different percentages to satisfy the real power system conditions. The simulations are conducted in a power system computer-aided design (PSCAD) environment where IEEE-39 bus system has been chosen as case study. The effectiveness of the proposed method has been ensured from the simulation results because UPFC's placement in the obtained locations resulted in an improved voltage stability condition. Furthermore, to verify the suitability of the explored locations, a comparative study has been conducted after placing UPFC in the present locations and other locations obtained using optimization techniques like particle swarm optimization (PSO), differential evolution (DE), genetic algorithm (GA), and bacteria foraging algorithm (BFA). In all the cases, UPFC's placement in the identified locations using the proposed approach has resulted in better voltage stability condition improvement compared to heuristics approaches.

Modern power systems are subjected to widespread line failures due to excess load demands, leading to voltage instability and voltage collapse. The objective of this paper is to study the application of Unified Power Flow Controller (UPFC) devices in improving voltage profile and controlling the power flowing through the transmission lines during excess load increments. Voltage Stability Analysis of the network is carried out by computing the eigen values of the power system reduced Jacobian matrix for each case of load increments before and after placing the UPFC device in the system. The line outage for which we get maximum number of critical eigen values is termed as the critical line outage. Voltage Stability Index is computed for each line corresponding to this critical outage. The line which has got the highest VSI for the critical outage is called as the critical line which indicates the optimal location of UPFC device. After placing the UPFC device on the critical line, the voltage magnitudes of the severely affected buses for this crtical load increments is compared with those magnitudes during the critical outage‥ The proposed approach is demonstrated on the IEEE 14 bus system in Matlab PSAT( Power system analysis Toolbox) software. The results obtained shows that UPFC devices improves the voltage profile of the buses and controls both active and reactive power flows across the transmission lines thus, preventing their outages during excess load demands and making the power system network voltage stable.

Voltage instability and voltage collapse have been considered as a major threat to present power system networks due to their stressed operation. It is very important to do the power system analysis with respect to voltage stability. Flexible AC Transmission System (FACTS) is an alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability. A FACTS device in a power system improves the voltage stability, reduces the power loss and also improves the load ability of the system. FACTS have made the power systems operation more flexible and secure. Amongst the several FACTS controllers, the Unified Power Flow Controller (UPFC) is most effective to improve the enhancement of voltage stability and reduces the power loss. This study investigates the application of Particle Swarm Optimization (PSO) to find sizing of Unified Power Flow Controller (UPFC) device to minimize the voltage stability index, total power loss, load voltage deviation, and cost of FACTS devices to improve voltage stability in the power system. A new model is proposed in this thesis to improve existing power-based model by using the Norton Equivalent Theorem. The proposed model can be integrated with the Equivalent Current Injection (ECI) power flow model easily. By ECI algorithm, it is much quickly and precisely to implement power flow calculations. Finally It is observed from the results that the voltage stability margin is improved, the voltage profile of the power system is increased and real power losses also reduced by optimally sizing UPFC device in the power system. Index Terms: Voltage stability, Unified Power Flow Controller (UPFC), Equivalent -Current Injection (ECI), Modified particle swarm optimization (MPSO)

Present-day power systems have highly complex and stressed operating conditions owing to insufficient reactive power to meet the required power demand. This leads to increased real power and reactive power losses, as well as voltage instability within a power system. To achieve the flexible operation of the power system, Flexible Alternating Current Transmission System (FACTS) devices have been employed. The optimal location of FACTS devices influences the system's performance and significantly affects line/bus reactive power flows. Consequently, the line or bus voltage profiles have been improved, leading to a reduction in power losses. Particle Swarm Optimization (PSO) heuristic methods and HFPSO Hybrid heuristic methods have been used to identify the weakest bus/branch for the suitable placement of UPFC devices, improving voltage stability. This paper discusses a more significant reduction in power losses in a MATLAB environment. Flexible Alternating Current Transmission System (FACTS) devices address reactive power challenges in power systems and enhance operational flexibility. Strategic placement using Particle Swarm Optimization (PSO) and HFPSO Hybrid methods identifies weak points, optimizing Unified Power Flow Controller (UPFC) placement for improved voltage stability. UPFC integration strategically reduces real and reactive power losses, improving power transmission efficiency. This enhances line and bus voltage profiles, addressing instability and significantly reducing overall power losses. The paper offers a detailed analysis of the power system, highlighting the synergy between FACTS devices, heuristic optimization, and power loss reduction. Simulations in MATLAB validate the proposed methodology, demonstrating a noteworthy improvement in power system performance.

Due huge increase in power demand, power system network will lead to have major problems such as voltage instability and voltage collapse in the power system. To overcome these problems, Flexible AC Transmission System (FACTS) devices have been implemented in power system. By placing these devices in suitable locations, the power system can be operated far away from the instability point. In this paper, the optimal location and the ratings of FACTS devices such as Thyristor Controlled Series Capacitor (TCSC), Static VAR Compensator (SVC) and Unified Power Flow Controller (UPFC) are determined using Genetic Algorithm (GA). A multi objective optimization problem is formulated with the consideration of minimizing voltage stability index, real power loss and generator cost. Evolutionary algorithm such as GA is a population based search method is used for solving multi objective optimization problem that is capable of searching for multiple solutions concurrently in a single run and provide an optimal solution. It is observed from the results that the voltages stability index, real power loss and generator cost are reduced by optimally locating the FACTS devices in the power system. IEEE 14 bus system is used to demonstrate the effectiveness of the proposed algorithm.

This paper studies the important power system phenomenon and voltage stability by using continuation power flow method. Voltage collapse scenario is presented which can be a serious result of voltage instability and also the parameters that affected by voltage collapse are discussed. In analyzing power system voltage stability, continuation power flow method is utilized which consists of successive load flows. In this paper steady-state modeling of Static VAR Compensator (SVC) and Unified Power Flow Controller (UPFC) and effect of compensator and variation of line reactance on the voltage stability have been studied and Comparison between performance of UPFC and SVC and installation shunt capacitor and variation of line reactance for improve voltage stability has been done.Case studies are carried on 11 bus network in two areas. Simulation is done with PSAT in MATLAB. Continuation Power Flow was implemented using Newton Raphson method. Simulation results show the proper performance of UPFC, SVC, installation shunt capacitor and variation of line reactance to improve voltage control and significantly increase the loadability margin of power systems. Full Text: PDF

This paper presents a screening technique for greatly reducing the computation involved in determining the optimal location of a unified power flow controller (UPFC) in a power system. The first-order sensitivities of the generation cost with respect to UPFC control parameters are derived. This technique requires running only one optimal power flow (OPF) to obtain UPFC sensitivities for all possible transmission lines. To implement a sensitivity-based screening technique for guidance in optimally locating a single UPFC in a power system, we propose a new UPFC model, wrach consists of an ideal transformer with a complex turns ratio and a variable shunt admittance. In this model, the UPFC control variables do not depend explicitly on UPFC input and output currents and voltages. Accordingly, this model does not require adding extra buses for UPFC input and output terminals. IEEE five-, 14- and 30-bus systems were used to frustrate the technique. Index Terms-Flexible ac transmission systems (FACTS), FACTS location, first-order sensitivity, optimal power flow (OPF), screening technique, unified power flow controller (UPFC), UPFC ideal transformer model, UPFC placement, UPFC uncoupled model. This study focuses on the development of an Ideal Transformer Unified Power Flow Controller (UPFC) model and its integration with Optimal Power Flow (OPF) first-order sensitivities analysis for determining optimal UPFC locations in power systems. The abstract outlines the significance of UPFCs in enhancing power system stability and efficiency by controlling voltage and power flow. It highlights the objectives of the research, including the development of the UPFC model, analysis of OPF first-order sensitivities, and their combined application for screening optimal UPFC locations. The study aims to contribute to the improvement of power system operation and control through strategic UPFC placement. The abstract provides a concise overview of the study, summarizing the key aspects of the research. It outlines the development of an ideal transformer Unified Power Flow Controller (UPFC) model, the analysis of Optimal Power Flow (OPF) first-order sensitivities, and their application in determining optimal locations for UPFC installation in power systems

Flexible Alternating Current Transmission Systems (FACTS) devices have been proposed to be effective for controlling power flow and regulating bus voltage in electrical power systems, resulting in an increased transfer capability, low system losses and improved stability. Unified Power Flow Controller (UPFC) is one of the most promising FACTS devices for power flow control. In principle, the UPFC is capable of providing active and reactive power control, as well as adaptive voltage magnitude control. Provided no operating limits are violated, the UPFC regulates all three variables simultaneously or any combination of them. Moreover, since the UPFC parameters are computed after the load flow has converged, there is no way of knowing during the iterative process whether or not the UPFC parameters are within limits. This has provided the motivation for developing a new UPFC model suitable for incorporating into an existing Newton-Raphson load flow algorithm. It is also necessary to determine the optimal setting of the device so that the net saving is maximized. In this work a new mathematical model of UPFC is developed which can be easily incorporated in Newton-Raphson load flow algorithm. Optimal location of UPFC is determined based on Voltage Stability Index. Particle Swarm Optimization (PSO) technique is used to set the parameters UPFC. The objective function formulated consists of two terms: cost for energy loss and cost related to UPFC, which has to be maximized for net saving. The results obtained using PSO is compared with that of results obtained using genetic algorithm. The validity of the proposed work is tested on IEEE 5-Bus and IEEE 14-Bus systems using MATLAB.

Problem statement: Estimating the margin in the loadability of the power system is essential in the real time voltage stability assessment. Voltage stability is currently one of the most important research areas in the field of electrical power system. In power system operation unpredictable events is termed as contingency and may be caused by line outage in the system which could lead to entire system instability. Voltage stability analysis and contingency analysis are would be performed in a power system by evaluating the derived voltage stability index. Approach: Voltage Stability Index Lmn can be useful for estimating the distance from the current operating point to voltage collapse point. The index can either reveal the critical bus of a power system or the stability of each line connected between two buses in an interconnected network or evaluate the voltage stability margins of a system. Results: Flexible Alternating Current Transmission Systems (FACTS) devices have been proposed as an effective solution for controlling power flow and regulating bus voltage in electrical power systems, resulting in an increased transfer capability, low system losses and improved stability. However to what extent the performance of FACTS devices can be brought out highly depends upon the location and the parameters of these devices. Unified Power Flow Controller (UPFC) is the most promising FACTS device for power flow control. Conclusion/Recommendations: The performance of this index is presented and the effectiveness of the analyzed methods is demonstrated through simulation studies in IEEE 14 bus reliability test systems.

The rising power demand has forced power systems all over the world to operate very close to their stability limits. When power systems are overloaded, faulty, or in lack of reactive power, voltage collapses would ensue. The capacity of a power system to keep the voltage of every bus constant under disturbances is called voltage stability. This dynamic phenomenon hinges on the load features. It is commonly known that flexible AC transmission systems (FACTS) can improve voltage stability. This paper puts forward a load flow model with the unified power flow controller (UPFC), and relies on the model to investigate the voltage stability of a power system through continuation power flow (CPF) method. The validity of the model was verified through a simulation, using the power system analysis toolbox (PSAT) in MATLAB/Simulink environment.

In this paper we are discussing about a FACTS device named as UPFC (unified power flow controller). Its special features are to control active and reactive power course in a transmission line and to adjust the voltage at the bus at which it is situated. This device gives great quality flow on power system stability; these features even more considerable and perceptive that the unified power flow controller can be apply to the transmission line with in their limits and enhancing the power to flow through the preferred path. So this device gives unique control on the power flow and voltage stability. In this paper the working of UPFC is in the field of control flow of power in transmission-line. This research regarding the 6-bus power system to control the active and reactive power in the course of transmission line by keeping this controller at the sending end by simulation tools. When there is no FACTs device (UPFC) the active power, reactive power and voltage through the transmission line cannot be controlled. The circuit model for UPFC is developed using rectifier and inverter circuits. In this thesis, the power system simulation models are made on MATLAB version 7.13. By making the power system simulation model, we are getting result without and with using UPFC and after that these results are compared in form of real and reactive power in the transmission line. On the basis of simulation results and to analyze the performance of UPFC, we can conclude that UPFC is ideal controller for performing such parameters.

Voltage stability is an important issue in power system operation. Flexible AC transmission systems, so-called FACTS devices, help to improve voltage stability and minimize real power losses. The effectiveness of FACTS devices depend on their proper location and rating. This paper presents a method, based on line flow sensitivity factors such as bus voltage stability index and line voltage stability index, to find suitable locations of multi-type FACTS devices. Also this paper proposes an application of particle swarm optimization (PSO) and harmony search algorithm (HSA) in optimizing the rating of FACTS devices. The proposed approaches are evaluated with three different objective functions namely, minimization of real power loss, improvement of voltage profile and enhancement of voltage stability. The performance of proposed methods is analyzed on IEEE 14 bus system by implementing FACTS devices such as static var compensator (SVC), thyristor controlled series capacitor (TCSC) and unified power flow controller (UPFC).The analysis shows that there is a reduction in real power loss and improvement in voltage stability and voltage profile of the system after employing FACTS devices. It also shows that both real power loss and bus voltage stability index (BVSI) have been reduced more with FACTS ratings obtained from PSO than with that from HSA.

The voltage collapse problem can avoid by providing proper reactive power resources to maintain specified voltage profile in the network. The traditional approaches are not sufficient to mitigate reactive power imbalance in the modern power system. Hence one of the emerging technologies like integration of Flexible AC Transmission System (FACTS) devices has been adopted in this paper. A hybrid algorithm is proposed to improve voltage stability of power system and to optimize the FACTS controllers. This Hybrid algorithm intended by the combination of genetic algorithm (GA) and gravitational search algorithm (GSA). For the implementation of this technique, one of the FACTS devices namely Unified power flow controller (UPFC) is selected. The GA is applied to identify best locations of UPFC and later GSA is implemented to optimize UPFC ratings in a sequential manner. The proposed method is implemented on IEEE-30 bus system using MATLAB working platform. The results have shown the effectiveness of proposed algorithm for practical applications.