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This paper demonstrates the application of inverse filtering technique for power systems. In order to implement this method, the control objective should be based on a system variable that needs to be set on a specific value for each sampling time. A control input is calculated to generate the desired output of the system and the relationship between the two is used to design an auto-regressive model. The auto-regressive model is converted to a moving average model to calculate the control input based on the future values of the desired output. Therefore, required future values to construct the output are predicted to generate the appropriate control input for the next sampling time.

Using a simple test example, this paper demonstrates that a weakly damped eigen-oscillation of an electric power system can lead to a loss of stability in the presence of its resonance with forcing oscillation. Such resonant interactions can risk the power system security, as confirmed by recent events in the Western American and Nordic power systems. Conventional eigenvalue analysis cannot detect the observed instability due to its non-linear nature. We show that the critical condition for the appearance of this type of instability can be the value of the perturbation energy accumulated in the system over time. To quantify the risk of stability loss, we examine the model of forcing oscillations and the resonance response of power system in a linear approximation and compare it with the simulation results for the two-area Kundur test system.

La interconexión del Sistema Interconectado Central (SIC) con el sistema interconectado del Norte Grande (SING), ha sido uno de los temas más comentados del año 2013 en el sector eléctrico chileno. En este contexto, dos son los proyectos que se encuentran en discusión: un enlace de corriente alterna (HVAC) en 500 kV impulsado por GDF SUEZ, y otro en corriente continua (HVDC) en ±500 kV planeado por la Comisión Nacional de Energía (CNE). Los proyectos presentan diferencias importantes en la tecnología y existen pocos estudios sobre los problemas que puedan aparecer durante la operación por el tipo de interconexión. En el presente trabajo se estudian oscilaciones de baja frecuencia mediante un análisis modal para las dos alternativas de interconexión mencionadas. Para esto se crea un modelo del sistema SIC-SING proyectado al 2019 en el software DigSilent. El estudio incluye el análisis de dos escenarios: uno donde el SIC envía 1.000 MW al SING y otro donde el SING exporta 800 MW al SIC. Los resultados obtenidos del análisis modal muestran que la interconexión mediante un enlace HVAC, lleva al surgimiento de un valor propio inestable de frecuencia de oscilación cercana a los 0,5 Hz. El origen de este modo inestable se encuentra en la interconexión misma y está asociado a un grupo de máquinas térmicas del SING. Adicionalmente tanto para la conexión en AC como en DC, se observan modos de oscilación cercanos a 0,9 Hz débilmente amortiguados, firmemente relacionados con la evolución de ambos sistemas al 2019. The interconnection of the Central Interconnected System (SIC for its initials in Spanish) with the Northern Interconnected System (SING) have been one of the trending topics in the year 2013 in the Chilean electric industry. Two are the projects that are on target for the interconnection; a high voltage alternating current (HVAC) 500 kV connection, proposed by the French utility GDF SUEZ, and a high voltage direct current (HVDC) ±500 kV planned by the CNE, the Chilean electric regulator entity. Both projects have important differences in technology and there's not too much technical evidence of the problems that could arise in the operation, caused by the SIC-SING interconnection. Lowfrequency oscillations are studied in this work, using modal analysis for both interconnection projects. A SiC-SING model is developed using DigSilent software, considering 2019 as the year of a possible union of the networks. Two generation scenarios are studied; one where the central system (SIC) sends 1.000 MW to the northern system (SING), and another one where the SING sends 800 MW to the SIC. The modal analysis results show that interconnecting both systems with the HVAC gives arise to a 0.5 Hz unstable oscillation mode. This unstable mode has it origin on the interconnection and it's related to a group of steam machines on the SING system. Whether the SIC-SING system is connected with the HVAC or the HVDC, 0.9 Hz weakly damped modes are observed in both systems. These modes are related to the evolution of the systems at 2019

This paper presents the software implementation of a Phasor Measurement Unit (PMU) data-based mode estimation application in a decentralized mode estimation architecture. This work builds from previous efforts in the development of a mode estimator implemented using a centralized architecture, meaning a set of modes were estimated for the whole system in a single processing location. One drawback of mode estimators that use centralized mode architecture is that the observability and therefore estimation of important low-damped local electromechanical modes can be affected by the higher observability of other dominant modes of the systems (e.g inter-area modes). This work proposes, implements and tests a decentralized architecture in order to increase the observation capability to provide better estimates of local low damped oscillations. In this architecture, the data from a single PMU or a group of local PMUs could be processed by a processor to estimate the modal parameters observed at a specific part of the grid or observed by specific group of PMUs. The decentralized architecture and results of tests are presented in this paper together with comparison with a centralized architecture.

Inter-area oscillations are serious problems to large-scale power systems. A decentralized H ∞ generator excitation controller of a power system is proposed to damp the inter-area oscillations and to enhance power system stability. The design procedure for a linear composite system is presented in terms of positive semi-definite solutions to modified algebraic inequalities. The resulting controller guarantees closed-loop stability, robustness and an H ∞-norm bound on disturbance attenuation even under uncertainties such as high frequency noise. The control is decentralized in the sense that the control of each generator depends on local information only. The effectiveness of the H ∞ controller is demonstrated through digital simulation studies on a two-machine power system.

In this paper, the effect of fuzzy logic-based robust power system stabilizers on the improvement of the dynamics of a large-scale power system is investigated. The study is particularly focused on the Mexican Interconnected System and on adding damping to two critical inter-area system oscillation modes: the north-south mode and the western-peninsular mode. The fuzzy power system stabilizers (FPSSs) applied here are based on a significantly reduced rule base, small number of tuning parameters, and simple control algorithm and architecture, which makes their design and implementation easier and suitable for practical applications. Non-linear time-domain simulations for a set of test cases and results from Prony Analysis verify the robustness of the designed FPSSs, as compared to conventional PSSs. En el presente trabajo se investiga el efecto de estabilizadores de sistemas de potencia (PSSs) robustos, basados en lógica difusa, para mejorar la dinámica de sistemas de potencia complejos. En particular, el estudio se enfoca en mejorar el amortiguamiento de dos modos críticos de oscilación interárea del Sistema Interconectado Mexicano. Los PSSs difusos utilizados aquí se caracterizan por una base de reglas difusas reducida, pocos parámetros de sintonización y una arquitectura y algoritmo de control simples, lo cual facilita su diseño, implementación y aplicación práctica. Simulaciones en el dominio del tiempo con diversos escenarios de prueba y la aplicación del método de Prony comprueban la robustez de los PSSs difusos en comparación con PSSs convencionales.

The presence of inter-area oscillations has long affected stability constraints, and therefore, limited the power transfer capacity of interconnected power systems. Adequate damping of these inter-area oscillations is, thus, necessary to secure system operation and ensure system reliability while increasing power transfers. Power system stabilizers (PSS) are the most common devices used to enhance the damping of such oscillations. Many studies have demonstrated that PSSs using remote signals may perform better than using local signals. The advent of phasor measurement units (PMU) makes remote or wide-area signals become available, which enables various important applications. Of particular interest is wide-area damping control (WADC), which aims to utilize remote or wide-area measurements to damp the inter-area oscillations. However, two main challenges in WADC design are (1) feedback controller input signal selection (which PMU signal is best to use?), and (2) latency (which is inherent in the transmission of the measurements) considerations. In response to the first challenge, this thesis proposes a concept called dominant inter-area oscillation path, which serves to pinpoint a set of candidate signals that can be used as the feedback controller inputs by locating the interconnected corridors where the inter-area modal contents are the most observable. Derivation, identification, and use of the dominant inter-area oscillation paths are demonstrated throughout the thesis. Extensive analysis on the relationships between the proposed set of signals and system properties regarding stability and robustness is presented. To tackle the second challenge, the impacts of time delays on the system performance when using the dominant path signals are investigated. To date, several studies have proposed different control design methods using various oscillation dampers to design WADC. Nevertheless, neither a systematic method nor a concept that encompasses fundamental knowledge on power system dynamics has yet been offered. The objective of this thesis is, thus, to propose an analytical framework based on the dominant path concept which is built upon fundamental principles for feedback controller input signal selection in WADC. With this framework, a proper and systematic approach is developed. The proposed method allows to select appropriate signals and use them to effectively mitigate the inter-area oscillations that constrain power transfer capacity and affect system stability. QC 20150414

This paper examines the feasibility of coordinating variable-speed wind farms with other power system devices, such as flexible ac transmission systems and synchronous generators, to damp low-frequency oscillations. For this purpose, an observer-based state-feedback approach is used to build a power oscillation damping (POD) controller, implemented through coordinated actions of multiple control devices, and able to manage several measurement channels. The wide-area POD controller also presents a time-delay compensation stage to mitigate adverse effects of latency involved in wide-area communication systems. Several practical issues are discussed and analyzed, such as measurement and control selection, model order reduction, transmission time-delay compensation, impact of the POD control on wind farms, and robustness aspects. The control performance is evaluated and compared with other control schemes using eigenvalue analyses and nonlinear time-domain simulations over a wide range of operating conditions, for example severe system faults, N-1 outage contingencies, load/generation shedding and line tripping. Fil: Leon, Enrique Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Investigación en Ingeniería Eléctrica; Argentina. Universidad Nacional del Sur; Argentina Fil: Solsona, Jorge Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Investigación en Ingeniería Eléctrica; Argentina. Universidad Nacional del Sur; Argentina

Spectral analysis applied to synchrophasor data can provide valuable information about lightly damped low-frequency modes in power systems. This paper demonstrates application of two non-parametric spectral estimators focusing on mode frequency estimation. The first one is the well-known Welch spectral estimator whereas the application of Multitaper method is proposed here. In addition, the paper discusses mode estimator tuning procedures and the estimators' performances in the presence of 'forced' oscillations. The validity of the proposed application of the non-parametric estimators and tuning procedures is verified through both simulated data and PMU data originating from the high-voltage grid of the Nordic power system. Special attention is given to the analysis of the behaviour of different low frequency modes present in the Nordic grid, including that of forced oscillations. QC 20140113

A contribution to CIGRE WG B5-14 “Wide Area Protection and Control Technologies”Chapter: Assess the opportunities and benefits to be gained from real -time synchrophasors as applied to protection and control and synchronized sample measurements Chapter Task: SMU (PMU) supported applications for inter-area oscillationsQC 20130830

This article presents an implementation of a Nordic grid model in Power System Analysis Toolbox (PSAT) -a free and open-source software. A newly developed hydro turbine and hydro governor (HTG) model is implemented with this grid model and compared with the currently available PSAT turbine and governor models. Small-signal and transient stability analyses of the system using the two models are carried out and compared to demonstrate the difference and necessity of accurate hydro turbine and governor model utilization. The paper ends with a validation of the linearized Nordic grid model generated by PSAT including the newly implemented HTG models. This validation is done through nonlinear time-domain simulation by applying both large and small disturbances. QC 20120927

The traditional approach to damp inter-area oscillations is through the installation of Power System Stabilizers (PSSs) which provide damping control action through excitation control systems of the generating units. However, study of recent blackouts has shown that the control action provided by a PSS alone is not sufficient for damping oscillations in modern power systems which operate under stressed conditions. An integrated form of control using remote measurements to coordinate the different control elements present in the system is the need of the hour. One way of implementing such a coordinated control is through the development of a Linear Matrix Inequality (LMI)-based polytopic model of the system that guarantees pole placement for a variety of operating conditions. The size of the polytopic formulation is an issue for application of LMIs to large systems. The use of Selective Modal Analysis (SMA) alleviates this problem by reducing the size of the system. The previous attempts have used a model containing all the and modes, with SMA being used to eliminate all the other states. In practical applications the resulting system was still found to be too large to use in a polytopic model. This thesis presents an algorithm to reduce the size of the system to the relevant modes of oscillations. A 16 machine, 68 bus equivalent model of the New England-New York interconnected power system is used as the test case with DC lines and SVCs acting as the control. The algorithm is then applied to a 127-bus equivalent model of the WECC System. The use of ESDs as a form of control is also demonstrated. The results indicate that the proposed control successfully damps the relevant modes of oscillations without negatively damping the other modes. The control is then transferred to a more detailed 4000+ bus model of the WECC system to realize its performance on real-world systems. Master of Science

Dominant interaction paths are the passageways containing the highest modal content of particular oscillations in interconnected power systems. For the case of inter-area modes, pinpointing the dominant path that corresponds to each mode may allow for the extraction of signals that bear a significant modal content at a particular inter-area frequency. Strong modal content for these inter-area modes may also be spread onto secondary paths. These secondary paths bear similar properties as those shown by dominant paths. The aim of this study is thus to demonstrate the persistence of both dominant and secondary paths by employing “network modeshape” properties. The existence of the paths is verified by nonlinear time-domain simulations where modal content at each inter-area frequency is extracted. The proper selection of feedback signals from the dominating paths may increase the flexibility of WAPODs by providing a number of signal choices to be used as backup in the presence of contingencies. QC 20120927

In the Nordic power network, the existence of poorly damped low-frequency inter-area oscillations (LFIOs) has long affected stability constraints, and thereby, limited power transfer capacity. Adequate damping of inter-area modes is, thus, necessary to secure system operation and ensure system reliability while increasing power transfers. Power system stabilizers (PSS) is a prevalent means to enhance the damping of such modes. With the advent of phasor measurement units (PMUs), it is expected that wide-area damping control (WADC), that is, PSS control using wide-area measurements obtained from PMUs, would effectively improve damping performance in the Nordic grid, as well as other synchronous interconnected systems. Numerous research has investigated one ``branch'' of the problem, that is, PSS design using various control schemes. Before addressing the issue of controller design, it is important to focus on developing proper understanding of the ``root'' of the problem: system-wide oscillations, their nature, behavior and consequences. This understanding must provide new insight on the use of PMUs for feedback control of LFIOs. The aim of this thesis is, therefore, to lay important concepts necessary for the study of power system small signal stability analysis that considers the availability of synchrophasors as a solid foundation for further development and implementation of ideas and related applications. Particularly in this study, the focus is on the application addressed damping controller design and implementation. After a literature review on the important elements for wide-area damping control (WADC), the thesis continues with classical small signal stability analysis of an equivalent Nordic model; namely, the KTH-NORDIC32 which is used as a test system throughout the thesis. The system's inter-area oscillations are identified and a sensitivity analysis of the network variables directly measured by synchrophasors is evaluated. The concept of network modeshapes, which is used to relate the dynamical behavior of power systems to the features of inter-area modes, is elaborated. Furthermore, this network modeshape concept is used to determine dominant inter-area oscillation paths, the passageways containing the highest content of the inter-area oscillations. The dominant inter-area paths are illustrated with the test system. The degree of persistence of dominant paths in the study system is determined through contingency studies. The properties of the dominant paths are used to construct feedback signals as input to the PSS. Finally, to exemplify the use of the dominant inter-area path concept for damping control, the constructed feedback signals are implemented in a PSS modulating the AVR error signal of a generator on an equivalent two-area model, and compared with that of conventional speed signals.

This article discusses the degree of persistence of dominant inter-area oscillation paths: the passageways containing the highest content of inter-area oscillations in large-scale power networks. To this aim, a number of contingency studies are carried out: faults being imposed on the lines connecting to the dominant inter-area path. The path persistence is then examined using the relationship between sensitivities of network variables (i.e. voltages and current, magnitude and angle), and mode shapes describing the contribution of the oscillations among the generators variables (e.g. speed and angle). This relationship is termed network modeshape. The larger in magnitude and the lesser the variation the network modeshape is, the more observable and the more robust the signals measured from the dominant path becomes. The outcome is a proposed signal combination to be used as inputs to the damping controller for mitigation of inter-area oscillations in large-scale power systems. QC 20131007

In order to reduce the detrimental effects of inter-area oscillations on system stability, it is possible to use Linear Matrix Inequalities (LMIs) to design a multi-objective state feedback. The LMI optimization finds a control law that stabilizes several contingencies simultaneously using a polytopic model of the system. However, the number of cases to be considered is limited by computational complexity which increases the chances of infeasibility. In order to circumvent this problem, this paper presents a method for solving multiple polytopic problems having a common base case. The proposed algorithm determines the necessary polytopic control for a particular contingency and classifies the data as belonging to that polytopic domain. The technique has been tested on an 8-machine, 13 bus, system and has been found to give satisfactory results. Master of Science

Damping electromechanical oscillations in power systems using feedback signals from remote sensors is likely to be affected by occasional low bandwidth availability due to increasing use of shared communication in future. In this paper, a predictor corrector (PC) strategy is applied to deal with situations of low-feedback data rate (bandwidth), where conventional feedback (CF) would suffer. Knowledge of nominal system dynamics is used to approximate (predict) the actual system behavior during intervals when data from remote sensors are not available. Recent samples of the states from a reduced observer at the remote location are used to periodically reset (correct) the nominal dynamics. The closed-loop performance deteriorates as the actual operating condition drifts away from the nominal dynamics. Nonetheless, significantly better performance compared to CF is obtained under low-bandwidth situations. The analytical criterion for closed-loop stability of the overall system is validated through a simulation study. It is demonstrated that even for reasonably low data rates the closed-loop stability is usually ensured for a typical power system application confirming the effectiveness of this approach. The deterioration in performance is also quantified in terms of the difference between the nominal and off-nominal dynamics.

In this paper, a new procedure to design Supplementary Damping Controllers (SDCs) for Flexible Alternating Current Transmission System (FACTS) devices is proposed. The control design problem is formulated as a search for a feasible controller subject to restrictions in the form of Linear Matrix Inequalities (LMIs). The main objective, from the application viewpoint, is the improvement of the damping ratios associated to inter-area oscillation modes. Unlike other types of formulations existing in the literature, this new formulation is capable of explicitly modeling the constraints on the controller bandwidth, which are crucial to avoid undesired amplification of high frequency noise signals coming into the controller input. To illustrate the efficiency of the proposed procedure, the design of an SDC for a Thyristor Controlled Series Capacitor (TCSC) placed in the New England/New York benchmark test system is carried out. The results show the designed controllers are able to provide adequate damping for the oscillations modes of interest for several different operating conditions. Este artigo propõe um novo procedimento para projeto de controladores suplementares de amortecimento (ou SDCs, do inglês Supplementary Damping Controllers) para dispositivos FACTS. O problema de projeto do controlador é formulado como uma busca por um controlador que satisfaça um conjunto de restrições na forma de desigualdades matriciais lineares (ou LMIs, do inglês Linear Matrix Inequalities). Sob o ponto de vista de aplicação, o objetivo principal de controle é aumentar as taxas de amortecimento das oscilações inter-área. Ao contrário de outras formulações propostas na literatura, esta nova formulação é capaz de modelar, explicitamente, as restrições da banda passante do controlador, evitando assim que ruídos em alta frequencia sejam amplificados a partir do sinal de entrada do controlador. Para ilustrar a eficiência do procedimento proposto foi realizado um projeto de controlador suplementar para dispositivos TCSC instalados no sistema New England/New York. Os resultados mostram que os controladores projetados são capazes de fornecer amortecimento adequado para os modos de oscilação de interesse em diversas condições de operação.

In this paper, the use of dynamic breaking as a cost-effective measure for damping inter-area oscillations is considered. Proposed control scheme assumes possibility of multiple insertions of dynamic breaking resistor triggered whenever the speed of equivalent one-machine infinite bus (OMIB) system exceeds predefined value or controlled based on commanded electrical power calculated from OMIB transformation. OMIB is formed based on the measurements provided by phasor measurement units (PMUs) and data collected from energy management system. Results obtained using simple four machine and 68-bus test system are included to illustrate capabilities of investigated control scheme.

In this paper, the use of dynamic braking as a cost-effective measure for damping inter-area oscillations is considered. Proposed control scheme assumes possibility of multiple insertions of dynamic braking resistor triggered whenever the speed of equivalent one-machine infinite bus (OMIB) system exceeds predefined value or controlled based on commanded electrical power calculated from OMIB transformation. OMIB is formed based on the measurements provided by phasor measurement units (PMUs) and data collected from energy management system. Results obtained using simple four machine and 68-bus test systems, are included to illustrate capabilities of investigated control scheme.

This paper deals with a new method based on neural networks for eigenvalue predictions of critical stability modes of power systems. Our special interest is focused on inter-area oscillations in the European interconnected power system. The existing methods for eigenvalue computations are time-consuming and require the entire system model that includes an extensive number of states.

Low frequency oscillations are detrimental to the goals of maximum power transfer and optimal power system security. A contemporary solution to this problem is the addition of power system stabilizers to the automatic voltage regulators on the generators in the power system. The damping provided by this additional stabilizer provides the means to reduce the inhibiting effects of the oscillations. This thesis is an investigation of the use of synchronized phasor measurements as input signals for power system stabilizers installed on the generators of a two-area, 4-machine test power system. A remote measurement feedback controller has been designed and placed in the test power system. Synchronized phasor measurements from optimally sited measurement units were shown to improve the damping of low-frequency inter-area oscillations present in the test system when the proposed controller was included in the generator feedback control loop. The benefit of the damping of these oscillations was evident through the ability to increase the tie-line power flowing in the test system once the proposed control scheme was implemented. Time-domain simulations were used to verify the robustness of the proposed control during severe events, such as a short- circuit or sudden large variations of load. Master of Science