Study of Inter Area Oscillations Using Phasor Measurement Units

Low-frequency oscillations in the power system have major repercussions on power system stability and the objective of maximum power transfer. Local and global control strategies have been developed to dampen and impede these oscillations. A modern local control strategy is supplying the automatic voltage regulation (AVR) of the generator with a power system stabilizer (PSS). Modern global control strategies include supplying the tie lines with flexible alternating current transmission systems devices (FACTS) and a power oscillation damper (POD). Including global signals in conjunction with local signals as an input on the generators PSS has been studied, but follows the same problems as PSSs tuned to enhance damping of the inter-area mode. Once satisfactory results are achieved on the inter-area mode, local modes of the machines involved in the inter-area mode tend to become less stable, or unstable. This type of interaction has caused most of the latest problems regarding damping of the inter-area mode with the use of the generators PSS. The following thesis investigates the impact on inter-area oscillations of including global measurements from phasor measurement units (PMU) in conjunction with local measurements as an input signal on a FACTS-device installed on the tie-line between two interconnected areas. A remote measurement feedback controller has been designed, tuned, and placed on the two-area; four-machine system, created for studying inter-area oscillations. Phasor measurements from optimally located measurement units were shown to improve the damping of the local and inter-area, low-frequency oscillations. The advantages of damping the before-mentioned oscillations were apparent through the ability to increase the power transfer capability in the tie-lines between the two areas following the implementation of the control method. The robustness of the suggested control method was analyzed through a small-signal stability test increasing tie-line power transfer, and a transient stability test using time-domain simulations of a severe fault, more specific a three-phase short circuit on the tie-lines

Contribution to wide area control of power systems

L'objectif principal des réseaux électriques est de convertir l'énergie d'une forme naturelle à la forme électrique et aussi de la distribuer aux clients avec la meilleure qualité. L'énergie électrique est une des formes d'énergie les plus utilisées dans l'industrie, dans les résidences, aux bureaux et dans le transport. Présentement, la complexité des réseaux électriques augmente continuellement en raison de la croissance des interconnexions et de l'utilisation des nouvelles technologies. Également, la croissance de la demande d'énergie électrique a forcé l'utilisation des réseaux électriques à leur capacité maximale et donc près de la limite de stabilité. Dans ces conditions, si le système est soumis à une perturbation, la chute de la tension ou celle de la fréquence serait très probable. Par conséquent, les équipements de contrôle, qui constituent une structure avec plusieurs niveaux de contrôle, peuvent aider les réseaux électriques à surmonter les événements imprévus. Les récentes pannes dans les réseaux électriques démontrent le besoin urgent d'une structure de contrôles multi-niveaux basés sur une technologie avec très rapide réponse appelée en anglais Wide Area Measurement and Control system (WAMAC). Présentement, le Wide Area Measurement System (WAMS) qui utilise le Global Positioning System (GPS) et la technologie satellite, joue un rôle important dans différentes parties du système de contrôle des réseaux électriques pour emp^echer les pannes globales ou locales du système. Les informations transférées par cette technologie seraient employées dans un contrôleur global appelé Wide Area Controller en anglais pour améliorer la performance dynamique des réseaux électriques pendant et après les perturbations. Donc, pour implémenter un Wide-Area Controller dans cette thèse, nous présenterons un plan multi-étapes pour l'amélioration de la stabilité du système et l'amortissement des oscillations du réseau. La première étape de ce plan serait l'estimation d'état dynamique des réseaux électriques en utilisant des phaseurs qui sont accessibles de Phasor Measurement Unit (PMU). Les angles des machines synchrones estimés à la première étape, qui pourrait nous montrer l'état des oscillations du réseau, seront utilisés comme des signaux d'entrée pour le contrôleur. La deuxième étape de notre plan est de trouver les meilleurs eplacements des dispositifs FACTS sur le réseau électrique pour augmenter la puissance transmise dans le réseau, maximiser la chargeabilité et minimiser les pertes. Après le placement optimal des dispositifs FACTS, la troisième étape consiste à implémenter le Wide-Area Controller. Ce contrôleur reçoit les états estimés, qui sont disponibles à partir des résultats de la première étape, et d'autres informations de partout dans le réseau en utilisant des PMUs. Après la vérification des signaux reçus, le contrôleur commande des contrôleurs locaux, tels que les contrôleurs des dispositifs FACTS qui ont été placés de façon optimale à la deuxième étape. Le contrôleur implémenté modifie les signaux de référence des éléments locaux pour améliorer la performance dynamique du système et amortir les oscillations du réseau.The main goal of power system is to convert the energy from one of its natural forms to the electrical form and deliver it to the costumers with the best quality. So far, the complexity of power system is continually increasing because of the growth in interconnections and use of new technologies. Also, the growth of electrical energy demand has forced the power networks to work with the maximum possible capacity and in turn near the stability limits. In this condition, if the system is subjected to a disturbance, the voltage or frequency collapse events would be more probable. Therefore the control equipments, which constitute a multi level control structure, can help the power system to overcome the contingencies. Recent collapse events in the power system networks show the urgent need for such a multi level control structure based on a rapid response technology such as Wide Area Measurement and Control (WAMAC). Nowadays, the wide area measurement and monitoring, which uses the Global Positioning System (GPS) and satellite technology, plays an important role in different parts of power system control strategies to prevent from global or local collapses. The information transferred by this technology would be employed in a master central controller, called wide area controller, to improve the power system dynamic performance during and after disturbances. From this point of view, in this thesis we will present a multi-step plan for system stability improvement and network oscillations damping by implementing a FACTS-based wide-area power oscillation damper (WA-POD) controller. The frrst step of this plan would be the dynamic state estimation of power system using the phasor measurements signals accessible from Phasor Measurement Units (PMUs). The estimated rotor angles of the synchronous machines from the first step, which could show us the network oscillations condition, will be used as the input signals of the wide-area controller. The second step of this plan is to find the best locations of FACTS devices to increase the power transmitted by network, maximize the system loadability and minimize the transmission line losses. After optimal placement of FACTS controllers, the third step is to implement a wide-area damping controller which receives the estimated rotor angles, available from the results of step one, and other information from all over the network, and then modifies the set points of optimized local control utilities such as FACTS device controllers. The implemented wide area controller, which acts as a master controller, sends the reference signals and setpoints to the local FACTS controllers such as UPFC to improve the oscillations damping performance. This result in higher transfer limits across major transmission interfaces and less blackouts in terms of frequency, duration and consequences

A Review On SVC Control For Power System Stability With And Without Auxiliary Controller

Since the beginning of the last century, power system stability has been recognized as a vital problem in securing system operation. Power system instability has caused many major blackouts. This paper reviewed the previous technical works consisting of various methods of optimization in controlling power system stability. The techniques presented were compared to optimize the control variables for optimization of power system stability. Power system stability enhancement has been investigated widely in literature using different ways. This paper is focusing on SVC performance for enhancing power system stability either through SVC controlled itself or SVC controlled externally by other controllers. Static VAR compensators (SVCs) are used primarily in power system for voltage control as either an end in itself or a means of achieving other objectives, such as system stabilization. The analysis on performance of the previous work such as advantages and findings of a robust method approach in each technique was included in this paper

Robust Design of FACTS Wide-Area Damping Controller Considering Signal Delay for Stability Enhancement of Power System

制度:新 ; 報告番号:甲3426号 ; 学位の種類:博士(工学) ; 授与年月日:2011/9/15 ; 早大学位記番号:新575

Enhancement of Power System Dynamic Performance by Coordinated Design of PSS and FACTS Damping Controllers

Due to environmental and economical constraints, it is difficult to build new power lines and to reinforce the existing ones. The continued growth in demand for electric power must therefore to a great extent be met by increased loading of available lines. A consequence of this is reduction of power system damping, leading to a risk of poorly damped power oscillations between generators. To suppress these oscillations and maintain power system dynamic performance, one of the conventional, economical and effective solutions is to install a power system stabilizer (PSS). However, in some cases PSS may not provide sufficient damping for the inter-area oscillations in a multi-machine power system. In this context, other possible solutions are needed to be exposed. With the evolution of power electronics, flexible AC transmission systems (FACTS) controllers turn out to be possible solution to alleviate such critical situations by controlling the power flow over the AC transmission line and improving power oscillations damping. However, coordination of conventional PSS with FACTS controllers in aiding of power system oscillations damping is still an open problem. Therefore, it is essential to study the coordinated design of PSS with FACTS controllers in a multi-machine power system. This thesis gives an overview of the modelling and operation of power system with conventional PSS. It gives the introduction to emerging FACTS controllers with emphasis on the TCSC, SVC and STATCOM controllers. The basic modelling and operating principles of the controllers are explained in this thesis, along with the power oscillations damping (POD) stabilizers. The coordination design of PSS and FACTS damping controllers over a wide range of operating conditions is formulated as an optimization problem. The objective function of this optimization problem is framed using system eigen values and it is solved using AAPSO and IWO algorithms. The optimal control parameters of coordinated controllers are obtained at the end of these optimization algorithms. A comprehensive approach to the hybrid coordinated design of PSS with series and shunt FACTS damping controllers is proposed to enhance the overall system dynamic performance. The robustness and effectiveness of proposed hybrid coordinated designs are demonstrated through the eigen value analysis and time-domain simulations. The proposed hybrid designs provide robust dynamic performance under wide range in load condition and providing significant improvement in damping power system oscillations under severe disturbance. The developed hybrid coordinated designs are tested in different multimachine power systems using AAPSO and IWO algorithms. The IWO based hybrid designs and AAPSO based hybrid designs are more effective than other control designs. In addition to this, the proposed designs are implemented and validated in real-time using Opal-RT hardware simulator. The real-time simulations of different test power systems with different proposed designs are carried out for a severe fault disturbance. Finally, the proposed controller simulation results are validated with real-time results

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

IMPACT OF GENERIC AND MULTIBAND POWER SYSTEM STABLIZER (PSS) ON ELECTRIC POWER SYSTEM STABILITY

Sustained power system oscillation has become a serious problem for power system operation and control nowadays. Oscillations cause safety problems in electric power equipment and limit the transmission capacity of long-distance power transmission. Oscillations can reach an amount that can compromise the stable operation of the synchronous generator and the power system in general. One way to suppress oscillations is to use a stabilizer of the power system as an integral part of the excitation systems of generators. The task of the power oscillation stabilizer is to produce a torque damping component of the electromagnetic torque through the excitation systems. This paper reveals the impacts of Generic and Multiband power system stabilizers (PSS) to enhance the damping of low frequency oscillations in a two machine power system. The impact of the Multiband PSS was seen to be better that of Generic PSS on the two machine power system in Matlab Simulink. KEY WORD: Power, Stability, Simulation, Oscillations, Faults. DOI: 10.7176/CEIS/12-2-04 Publication date: April 30th 202

Adaptive Rat Swarm Optimization for Optimum Tuning of SVC and PSS in a Power System

This paper presents a new approach for the coordinated design of a power system stabilizer- (PSS-) and static VAR compensator- (SVC-) based stabilizer. For this purpose, the design problem is considered as an optimization problem, while the decision variables are the controllers' parameters. This paper proposes an effective optimization algorithm based on a rat swarm optimizer, namely, adaptive rat swarm optimization (ARSO), for solving complex optimization problems as well as coordinated design of controllers. In the proposed ARSO, instead of a random initial population, the algorithm starts the search process with fitter solutions using the concept of the opposite number. In addition, in each iteration of the optimization, the new algorithm replaces the worst solution with its opposite or a random part of the best solution to avoid getting trapped in local optima and increase the global search ability of the algorithm. The performance of the new ARSO is investigated using a set of benchmark test functions, and the results are compared with those of the standard RSO and some other methods from the literature. In addition, a case study from the literature is considered to evaluate the efficiency of the proposed ARSO for coordinated design of controllers in a power system. PSSs and additional SVC controllers are being considered to demonstrate the feasibility of the new technique. The numerical investigations show that the new approach may provide better optimal damping and outperform previous methods

Design of a Wide Area Controller Using Eigenstructure Assignment in Power Systems

Small signal stability has become a major concern for power system operators around the world. This has resulted from constantly evolving changes in the power system ranging from increased number of interconnections to ever increasing demand of power. In highly stressed operating conditions, even a small disturbance such as a load change can make the system unstable resulting in small signal instability. The main reason for small signal instability in power systems is an inter-area mode/s becoming unstable. Inter-area modes involve a group of generators oscillating against each other. Traditionally, power system stabilizers installed on the synchrous machines were used to damp the inter-area modes. However, they may not be very suitable to perform the job since they use local I/O signals which do not have a good controllability/observability of the inter-area modes. Recent advancements in phasor measurement technology has resulted in fast acquisition of time-synchronized measurements throughout the system. Thus, instead of using local controllers, an idea of a wide area controller (WAC) was proposed by the power systems community that would use global signals. This dissertation demonstrates the design of a WAC using eigenstructure assignment technique. This technique provides the freedom to assign a few eigenvalues and corresponding left or right eigenvectors for Multi-Input-Multi-Output (MIMO) systems. This technique forms a good match for designing a WAC since a WAC usually uses multiple I/O signals and a power system only has a few inter-area modes that might lead to instability. The last chapter of this dissertation addresses an important aspect of controller design, i.e., robustness of the controller to uncertainties in operating point and time delay of feedback signals. The operating point of a power system is highly variable in nature and thus the designed WAC should be able to damp the inter-area modes under these variations. Also, a transmission delay is associated due to routing of remote signals. This time delay is known to deteriorate the performance of the controller. A single controller will be shown to achieve robustness against both these uncertainties

Oscillation Analysis and its Mitigation Using Inverter-Based Resources in Large-Scale Power Grids

In today\u27s interconnected power grids, forced oscillations and poorly damped low-frequency oscillations are major concerns that can damage equipment, limit power transfer capability, and deteriorate power system stability. The first part of the dissertation focuses on the impact of a wide-area power oscillation damping (POD) controller via voltage source converter-based high voltage direct current (VSC-HVDC) in enhancing the power system stability and improving the damping of low-frequency oscillation. The POD controller\u27s performance was investigated under a three-phase temporary line fault. The Great Britain (G.B.) power grid model validated the POD controller performance via active power modulation of VSC-HVDC through TSAT-RTDS hybrid simulation. The developed POD controller is also implemented on a general-purpose hardware platform CompactRIO and tested on a hardware-in-the-loop (HIL) test setup with actual PMU devices and a communication network impairment simulator. A variety of real-world operating conditions is considered in the HIL tests, including measurement error/noise, occasional/consecutive data package losses, constant/random time delays, and multiple backups PMUs. The second part of the dissertation proposes a two‐dimensional scanning forced oscillation grid vulnerability analysis method to identify areas/zones and oscillation frequency in the system critical to forced oscillation. These critical areas/zones can be considered effective actuator locations to deploy forced oscillation damping controllers. Additionally, a POD controller through inverter-based resources (IBRs) is proposed to reduce the forced oscillation impact on the entire grid. The proposed method is tested when the external perturbation is active power and compared with the reactive power perturbation result. The proposed method is validated through a case study on the 2000-bus synthetic Texas power system model. The simulation results demonstrate that the critical areas/zones of forced oscillation are related to the areas that highly participate in the natural oscillation. Furthermore, forced oscillation through active power disturbance can have a more severe impact than reactive power disturbance, especially at resonance. The proposed forced oscillation controller can mitigate the impact of the forced oscillation on the entire system when the actuator is close to the forced oscillation source. In addition, active power modulation of IBR can provide better damping performance than reactive power modulation