The reliability and optimal data usage of BGAN satellite communications for remote outstations

Telecommunications are a crucial element of smart grid technologies. Utility communication systems need to combine cost effectiveness with the need for high reliability. Due to its wide geographic coverage, satellite communication can be an appropriate alternative for power system automation in order to reach remote substations. This paper presents the experimental testing of Broadband Global Area Networks (BGAN) M2M technology between the supervisory control and data acquisition (SCADA) system running a primary front end processor (FEP) and the reclosers. Hardware test results for a number of different scenarios are discussed, compared and validated. The challenges for keeping the polls reliability at highest levels are also discussed

Vulnerability analysis of satellite-based synchronized smart grids monitoring systems

The large-scale deployment of wide-area monitoring systems could play a strategic role in supporting the evolution of traditional power systems toward smarter and self-healing grids. The correct operation of these synchronized monitoring systems requires a common and accurate timing reference usually provided by a satellite-based global positioning system. Although these satellites signals provide timing accuracy that easily exceeds the needs of the power industry, they are extremely vulnerable to radio frequency interference. Consequently, a comprehensive analysis aimed at identifying their potential vulnerabilities is of paramount importance for correct and safe wide-area monitoring system operation. Armed with such a vision, this article presents and discusses the results of an experimental analysis aimed at characterizing the vulnerability of global positioning system based wide-area monitoring systems to external interferences. The article outlines the potential strategies that could be adopted to protect global positioning system receivers from external cyber-attacks and proposes decentralized defense strategies based on self-organizing sensor networks aimed at assuring correct time synchronization in the presence of external attacks

Towards an Enhanced Wide Area Control System for Damping Out Low Frequency Oscillations in Power Grid

This thesis presents enhanced methodologies in a wide area control system to damp out low frequency oscillations. The primary motivation behind this work is to design a wide area controller to avoid power system blackouts by damping out low frequency oscillations which are existing for longer time duration. The wide area controller can be designed in two ways: state feedback control and output feedback control. From the input point of view, the state feedback controller requires the information about all system states and are not possible to observe all system states in real-time. From the output point of view, the output signals of the controller can be given to the AVR/excitation system of all generators in both control techniques which will increase the cost of the communication network. Moreover, the time delay due to the communication network will affect the wide are controller performance. Therefore, to overcome these problems, in particular, this work addresses the design of a wide area controller with limited measurements to resolve the input side problems. The problems associated with the output side can be overcome by employing a reduced- scale wide area controller design. In addition, the time delay effects can be resolved by using bi-layer wide area control architecture with the incorporation of the practical supplementary controller. The important contributions of this work are as follows. 1. Designing a wide area controller to damp out inter-area oscillations by consid- ering limited measurements with unknown load composition. 2. Designing a reduced-scale architecture of the wide area control system by means of modal sensitivity analysis. 3. Designing a practical supplementary controller design for the bi-layer wide area control architecture through structurally constrained H2-norm optimization. The contribution of the first work is to design a wide area controller with limited measurements without knowing load composition. The primary objective of this work is to design a state feedback controller to damp out the inter-area oscillations in the power system network with limited wide area measurements. The conventional state feedback controller designed through LQR optimization requires all the state variables as input. However, the dynamics of a power system is governed by a large number of state variables. Therefore, it is, practically, not possible to place sensors everywhere for monitoring the complete system state in real-time. To address the particular issue, an optimized state feedback controller is proposed, which can be implemented with the limited number of state inputs. The structurally constrained H2-norm optimization technique is employed to perform the proposed state feedback controller design. The reference frame requirement for defining the rotor angles of generators under the scenario of limited state observability is also investigated. The performance of the wide area controller with limited state inputs is verified through a case study on the New England 39-bus system under different scenarios of state unobservability. Since the WAC design requires a full system description, appropriate load modeling may be critical in the WAC design. Therefore, a mathematical framework is developed to carry out WAC design in the presence of multiple types of load. Both static and dynamic loads are considered. In order to exempt the dynamic load states from the input of WAC, the structurally constrained H2-norm optimized WAC design is performed. By recognizing the practical difficulty of obtaining the precise information about actual load composition, this work further investigates the suitability of representing all the loads as constant power loads in the WAC design. Detailed case studies are performed on the IEEE 39-bus system. The contribution of the second work is to develop an efficient scheme for the proper selection of entities in the wide area control (WAC) loop so as to yield a cost-effective and simplified WAC architecture without compromising with its damping performance. The methodology proposed is based upon a concept of mode-path susceptibility matrix that is obtained by means of the modal sensitivity analysis. Inspecific, the significance of a feedback path to change mode shapes is determined by evaluating the sensitivities of different modes to the respective elements of the feedback gain matrix. This is unlike the traditional controllability and observability based approaches. A generalized utility ranking of potential source and sink points of the wide area damping controller is further carried out based upon the mode- path susceptibility matrix. Both the state feedback and the output feedback are taken into account in the methodology proposed for the scale reduction of a WAC architecture. Detailed case studies are performed to verify the effectiveness of the proposed reduced-scale WAC architecture through both off-line simulations and real- time experimentations. The contribution of the third work is to develop a suitable methodology for the practical realization of the bi-layer wide area control (WAC) architecture. The bi-layer WAC system retains the capability to overcome the communication related problems to a great extent through the deployment of a supplementary wide area damping controller (WADC) along with the conventional WADC. The supplementary WADC was envisaged as a controller that may not have any communication requirements to deliver control signals. It is, therefore, essential to design the supplementary WADC in a way so that the same can be practically implemented without the requirement of any communication network. The precise concern of the present work is to address the proper design of the aforementioned supplementary WADC. The design of the supplementary WADC is carried out through a structurally constrained H2-norm optimization calculation. The solution procedure of the particular H2-norm optimization problem is established. Detailed simulation studies are performed to evaluate the performance of the proposed supplementary WADC in the standalone mode. The usefulness of the bi-layer WAC architecture to improve the damping of inter-area oscillations under the proposed controller design is thoroughly validated through real-time experimentations

Detecção e controle de oscilações eletromecânicas usando sistemas de medição fasorial sincronizada

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia ElétricaNeste documento são apresentadas técnicas de processamento digital de sinais com a finalidade de analisar oscilaçoes e detectar modos eletromecânicos pouco amortecidos de sistemas elétricos de potência. Os sinais usados para a deteção de modos eletromecânicos são oriundos de sistemas teste implementados em programas de análise de estabilidade transitória e também de um Sistema de Medição Fasorial Sincronizada (SMFS), instalado na baixa tensão, que possibilita o monitoramento de todas as regiões do sistema elétrico brasileiro. Dentre as ferramentas utilizadas para análise de sinais, estao o método de Prony e sua extensão para análise de múltiplos sinais, o modelo ARMA, o método de identificação de subespaço de espaço de estados N4SID com e sem a utilização do fator de esquecimento 1. Foi proposta a utilização de um índice de dominância modal (IDM) em conjunto com o método de Prony e o N4SID. O uso conjunto do IDM com os referidos métodos possibilita que a ordenação modal seja feita automaticamente e para o N4SID também permite que a monitoração contínua de modos possa ser feita de forma automática. Também foram utilizadas as transformadas de Hilbert-Huang e a de Teager-Huang, esta última se baseia no operador de energia de Teager-Kaiser (TKEO). Uma extensão para o TKEO foi proposta, já que tal operador fornece apenas amplitudes e frequências instantâneas de sinais unimodais. A extensão proposta neste trabalho permite calcular o amortecimento instantâneo via o operador de energia de Teager- Kaiser. Foi provado, após manipulações, que a fórmula proposta para o cálculo do amortecimento instantâneo via TKEO é bastante similar à utilizada para estimar o amortecimento instantâneo quando se usa a transformada de Hilbert. Os algoritmos de análise de sinais foram validados em sistemas teste e utilizados em análises de ocorrências reais do Sistema Interligado Nacional (SIN), cujos dados foram fornecidos pelo SMFS. Monitorações contínuas foram feitas e os principais modos inter-área puderam ser rastreados perante a presença ou não de grandes distúrbios no SIN. Técnicas de controle multivariável foram utilizadas com a finalidade de projetar controladores centralizados para amortecer oscilações eletromecânicas. Foram considerados projetos de controladores via técnicas de controle ótimo (LQR) com e sem restrições estruturais e o uso de Inequaçoes Matriciais Lineares (LMIs) 2, ambos com realimentações de saída. Na utilização de LMIs, os controladores foram projetados considerando a modelagem do sistema elétrico de potência tanto na forma de equaçõoes de estado quanto na de sistemas descritores. O projeto de controladores a partir de técnicas de otimização não-convexa também foram exploradas. Com a metodologia utilizada é possível pré estabelecer a ordem dos controladores, que podem variar desde ganhos a polinômios com elevado grau. Durante a síntese de controladores, foi necessário considerar a modelagem de atrasos causados pelo tempo de transmissão de dados devido a utilização de sinais remotos do SMFS de diversas regiões geograficamente distantes. A proposta desta tese é identificar sistemas elétricos de potencia a partir de dados de SMFS e, partir dos sistemas identificados, projetar controladores robustos realimentados por sinais locais e remotos de SMFS. Esta meta dificilmente pode ser atingida, ao menos no estágio atual, devido às técnicas de identificação de sistemas não serem capazes de identificar sistemas com a exatidão necessária em certas circunstâncias e ao fato que o projeto de controladores não pode ser feito em tempo hábil. Uma alternativa utilizada, que satisfaz parcialmente os objetivos, foi a aplicação de um controle tipo Gain Schedule (GS), onde controladores previamente projetados para diferentes condições operativas do sistema podem ser chaveados. Os chaveamentos ocorrem a partir da identificação de condições operativas do sistema, feitas por algoritmos de identificação de sistemasIn this research digital signal processing techniques are presented in order to detect and analyze electromechanical oscillation modes in power systems. The analyzed signals, used for detecting electromechanical modes, are acquired from transient stability programs and also from a low voltage synchronized phasor measurement system (SPMS), which enables monitoring all regions of the Brazilian electric power system. The tools used for signal analysis were the Prony method, its extension, the multi-signal Prony method, ARMA models and subspace algorithms like the N4SID, the last implemented with and without a forgetting factor. It was also proposed the use of a modal dominance index (MDI) together with Prony method and the N4SID. The use of MDI with the mentioned methods allows the automatic modal ranking. For the N4SID it is also possible to perform continuous modal monitoring. The Hilbert-Huang and the Teager-Huang, based on the on the Teager-Kaiser energy operator (TKEO), transforms were also used. An extension of the TKEO, which originally allows just the calculation of instantaneous amplitudes and frequencies for monocomponent signals was proposed. This extension allows the calculation of the instantaneous damping via TKEO. It was also demonstrated that the proposed formula for damping calculation via TKEO is very similar to the one used to estimate instantaneous damping via Hilbert transform. All the algorithms used to analyze signals were validated in test systems and after that used to analyze real data from the Brazilian Interconnected Power System (BIPS). The real data were acquired by the SPMS. The main BIPS interarea electromechanical modes were tracked constinuously under ambient data with or without ringdowns. Output feedback multivariable control techniques were used to design centralized controllers to damp electromechanical oscillations. Among the used control techniques are the Linear Quadratic Regulator (LQR) with or without structural restrictions and Linear Matrix Inequalities (LMIs). LMI techniques were used to design controllers for power systems in state-space and also in descriptor systems form. The design of controllers using nonsmooth optimization techniques were also explored. With these methodos it is possible to preset the controllers order, which may vary from static gains to dynamic controllers. The SPMS signal transmission time delay was considered during the control design to account the transmission data time. The thesis puspose is to identify critical electromechanical oscillations through SPMS analysis, then design robust controllers after the identification. This is currently a hard task since identification techniques are not able to identify systems with precision all the time, and also due to the computational burden involved in the control design that also implies in a time delay. An alternative way, used in this work, to circumvent those problems was the Gain Schedule control. In the Gain Schedule control, a set of controllers is designed for several critical situations. When one of these situations is detected, the controller corresponding to the detected operating point is switche

Enhancement of power system stability using wide area measurement system based damping controller

Contemporary power networks are gradually expanding incorporating new sources of electrical energy and power electronic based devices. The major stability issue in large interconnected power systems is the lightly damped interarea oscillations. In the light of growth of their incidents there are increased concerns about the effectiveness of current control devices and control systems in maintaining power system stability. This thesis presents a Wide Area Measurement System (WAMS) based control scheme to enhance power system stability. The control scheme has a hierarchical (two-level) structure comprising a Supplementary Wide-Area Controller (SWAC) built on top of existing Power System Stabilisers (PSSs). The SWAC's focus is on stabilising the critical interarea oscillations in the system while leaving local modes to be controlled entirely by local PSSs. Both control systems in the two levels work together to maintain system stability. The scheme relies on synchronised measurements supplied by Phasor Measurement Units (PMUs) through the WAMS and the only cost requirement is for the communication infrastructure which is already available, or it will be in the near future. A novel linear quadratic Gaussian (LQG) control design approach which targets the interarea modes directly is introduced in this thesis. Its features are demonstrated through a comparison with the conventional method commonly used in power system damping applications. The modal LQG approach offers simplicity and flexibility when targeting multiple interarea modes without affecting local modes and local controllers, thus making it highly suitable to hierarchical WAMS based control schemes. Applicability of the approach to large power systems is demonstrated using different scenarios of model order reduction. The design approach incorporates time delays experienced in the transmission of the SWAC's input/output signals. Issues regarding values of time delays and required level of detail in modelling time delays are thoroughly discussed. Three methods for selection of input/output signals for WAMS based damping controllers are presented and reviewed. The first method uses modal observability/controllability factors. The second method is based on the Sequential Orthogonalisation (SO) algorithm, a tool for the optimal placement of measurement devices. Its application is extended and generalised in this thesis to handle the problem of input/output signal selection. The third method combines clustering techniques and modal factor analysis. The clustering method uses advanced Principal Component Analysis (PCA) where its draw backs and limitations, in the context of power system dynamics' applications, are overcome. The methods for signal selection are compared using both small signal and transient stability analysis to determine the best optimal set of signals. Enhancement of power system stability is demonstrated by applying the proposed WAMS based control scheme on the New England test system. The multi-input multi-output (MIMO) WAMS based damping controller uses a reduced set of input/output signals and is designed using the modal LQG approach. Effectiveness of the control scheme is comprehensively assessed using both small signal and transient stability analysis for different case studies including small and large disturbances, changes in network topology and operating condition, variations in time delays, and failure of communication links.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Enhancement of power system stability using wide area measurement system based damping controller

Contemporary power networks are gradually expanding incorporating new sources of electrical energy and power electronic based devices. The major stability issue in large interconnected power systems is the lightly damped interarea oscillations. In the light of growth of their incidents there are increased concerns about the effectiveness of current control devices and control systems in maintaining power system stability. This thesis presents a Wide Area Measurement System (WAMS) based control scheme to enhance power system stability. The control scheme has a hierarchical (two-level) structure comprising a Supplementary Wide-Area Controller (SWAC) built on top of existing Power System Stabilisers (PSSs). The SWAC's focus is on stabilising the critical interarea oscillations in the system while leaving local modes to be controlled entirely by local PSSs. Both control systems in the two levels work together to maintain system stability. The scheme relies on synchronised measurements supplied by Phasor Measurement Units (PMUs) through the WAMS and the only cost requirement is for the communication infrastructure which is already available, or it will be in the near future. A novel linear quadratic Gaussian (LQG) control design approach which targets the interarea modes directly is introduced in this thesis. Its features are demonstrated through a comparison with the conventional method commonly used in power system damping applications. The modal LQG approach offers simplicity and flexibility when targeting multiple interarea modes without affecting local modes and local controllers, thus making it highly suitable to hierarchical WAMS based control schemes. Applicability of the approach to large power systems is demonstrated using different scenarios of model order reduction. The design approach incorporates time delays experienced in the transmission of the SWAC's input/output signals. Issues regarding values of time delays and required level of detail in modelling time delays are thoroughly discussed. Three methods for selection of input/output signals for WAMS based damping controllers are presented and reviewed. The first method uses modal observability/controllability factors. The second method is based on the Sequential Orthogonalisation (SO) algorithm, a tool for the optimal placement of measurement devices. Its application is extended and generalised in this thesis to handle the problem of input/output signal selection. The third method combines clustering techniques and modal factor analysis. The clustering method uses advanced Principal Component Analysis (PCA) where its draw backs and limitations, in the context of power system dynamics' applications, are overcome. The methods for signal selection are compared using both small signal and transient stability analysis to determine the best optimal set of signals. Enhancement of power system stability is demonstrated by applying the proposed WAMS based control scheme on the New England test system. The multi-input multi-output (MIMO) WAMS based damping controller uses a reduced set of input/output signals and is designed using the modal LQG approach. Effectiveness of the control scheme is comprehensively assessed using both small signal and transient stability analysis for different case studies including small and large disturbances, changes in network topology and operating condition, variations in time delays, and failure of communication links.EThOS - Electronic Theses Online ServiceGBUnited Kingdo