The growth of Distributed Energy Resources is accelerating, causing significant changes in utility distribution systems due to the bidirectionality of power flow. As a result, protection systems will require upgrades to operate with these new requirements. The current-only directional relay (CODR) is a novel proposal that detects the direction of fault currents without the need for new devices, but instead upgrades the software logic of existing devices, making it a cost-effective solution. This work provides a complete description of how to implement a hardware testbed to review the CODR method. Findings show that CODR performs successfully in a real environment, but its algorithm needs to be upgraded if used in distribution systems where lines have a non-negligible resistive component. / Master of Science / The use of renewable energy sources, such as solar panels and wind turbines, is growing rapidly. This is causing changes in the way electricity is distributed, as power can now flow in both directions. To keep up with these changes, the systems that protect the electricity grid need to be updated. One cost-effective solution is to use a new type of relay, called the current-only directional relay (CODR), which can detect the direction of fault currents without the need for new devices. This work describes how to test the CODR method using a hardware testbed. The results show that the CODR performs well in a real environment, but its algorithm needs to be updated for use in certain types of distribution systems.

The thesis is devoted to the development of new algorithms for estimation of system frequency, power system phasors and transmission line fault location in the context of power system protection and control. A z-transform signal model combined with a nonlinear post-filtering scheme to estimate the operating frequency in a power system is first developed in the thesis. The signal model parameters are identified by an optimisation method in which the error between the model output and the actual signal that represents a voltage or current in the power system is minimised. The form and the structure of the signal model do not require iterations in the optimisation process for parameter identification. The system operating frequency is directly evaluated from the model parameters. Effects of noise and any frequency components other than the operating or supply-frequency on the accuracy are countered very effectively by applying a median post-filtering on the time series representing the frequency estimates derived from the model. Extensive simulation studies and comparisons with previously-published frequency estimation techniques confirm the high performance of the method developed in the thesis in terms of accuracy and time delay. With respect to power system phasor estimation, a method is developed based on waveform interpolation in the discrete time-domain to counter the spectral leakage errors arising in forming, by discrete Fourier transform (DFT), the supply frequency phasors representing power system voltages and currents when there are system frequency deviations from the nominal value. The interpolation scheme allows DFT evaluation to be performed with a time window length which is exactly equal to the fundamental period of the voltage or current waveform. Comparative studies presented in the thesis confirm the improvements achieved by the method proposed over other previouslypublished techniques in terms of accuracy and computing time. With the availability of accurate operating frequency and phasor estimates, an optimal fault location method based on multi-conductor distributedparameter line model is developed. The method is a general one which is applicable to any transmission line configurations, including multi-terminal lines. The fault location method is based on the minimisation of an objective function in which the fault distance is a variable. The objective function is formed from combining the phase-variable distributed-parameter equations of individual line sections from the fault point to the line terminals. The multivariable minimisation leads to high accuracy and robustness of the fault location algorithm in which any voltage/current measurement errors, including sampling time synchronisation errors, are represented in the estimation procedure as variables in addition to the fault distance. Extensive simulation studies are performed to verify that the method developed is highly accurate and robust. The thesis is supported by two international publications of which the candidate is a joint author.

Power systems are protected by numerical relays that detect and isolate faults that may occur on power systems. The correct operation of the relay is very important to maintain the security of the power system. <p>Numerical relays that use voltage measurements from the power system provided by coupling capacitor voltage transformers (CCVT) have sometimes difficulty in correctly identifying a fault in the protected area. The fundamental frequency voltage phasor resulting from these CCVT measurements may result in a deviation from the true value and therefore may locate this phasor temporarily in the incorrect operating region. This phasor deviation is due to the CCVT behavior and the CCVT introduces spurious decaying and oscillating transient signal components on top of the original voltage received from the power system in response to sudden voltage changes produced during faults. Most of the existing methods for estimating the voltage phasor do not take advantage of the knowledge of the CCVT behavior that can be obtained from its design parameters.<p>A new least squares error method for phasor estimation is presented in this thesis, which improves the accuracy and speed of convergence of the phasors obtained, using the knowledge of the CCVT behavior. The characteristics of the transient signal components introduced by the CCVT, such as frequencies and time constants of decay, are included in the description of the curve to be fitted, which is required in a least squares fitting technique. Parameters such as window size and sampling rate for optimum results are discussed.<p>The method proposed is evaluated using typical power systems, with results that can be compared to the response if an ideal potential transformer (PT) were used instead of a CCVT. The limitations of this method are found in some specific power system scenarios, where the natural frequencies of the power system are close to that of the CCVT, but with longer time constants. The accuracy with which the CCVT parameters are known is also assessed, with results that show little impact compared to the improvements achievable.

Power systems are protected by numerical relays that detect and isolate faults that may occur on power systems. The correct operation of the relay is very important to maintain the security of the power system. <p>Numerical relays that use voltage measurements from the power system provided by coupling capacitor voltage transformers (CCVT) have sometimes difficulty in correctly identifying a fault in the protected area. The fundamental frequency voltage phasor resulting from these CCVT measurements may result in a deviation from the true value and therefore may locate this phasor temporarily in the incorrect operating region. This phasor deviation is due to the CCVT behavior and the CCVT introduces spurious decaying and oscillating transient signal components on top of the original voltage received from the power system in response to sudden voltage changes produced during faults. Most of the existing methods for estimating the voltage phasor do not take advantage of the knowledge of the CCVT behavior that can be obtained from its design parameters.<p>A new least squares error method for phasor estimation is presented in this thesis, which improves the accuracy and speed of convergence of the phasors obtained, using the knowledge of the CCVT behavior. The characteristics of the transient signal components introduced by the CCVT, such as frequencies and time constants of decay, are included in the description of the curve to be fitted, which is required in a least squares fitting technique. Parameters such as window size and sampling rate for optimum results are discussed.<p>The method proposed is evaluated using typical power systems, with results that can be compared to the response if an ideal potential transformer (PT) were used instead of a CCVT. The limitations of this method are found in some specific power system scenarios, where the natural frequencies of the power system are close to that of the CCVT, but with longer time constants. The accuracy with which the CCVT parameters are known is also assessed, with results that show little impact compared to the improvements achievable.

This dissertation studies the performance of synchrophasor measurement obtained using substation Intelligent Electronic Devices (IEDs) and proposes new algorithms and test methodology to improve and verify their performance when used in power system applications. To improve the dynamic performance when exposed to sinusoidal waveform distortions, such as modulation, frequency drift, abrupt change in magnitude, etc, an adaptive approach for accurately estimating phasors while eliminating the effect of various transient disturbances on voltages and currents is proposed. The algorithm pre-analyzes the waveform spanning the window of observation to identify and localize the discontinuities which affect the accuracy of phasor computation. A quadratic polynomial signal model is used to improve the accuracy of phasor estimates during power oscillations. Extensive experimental results demonstrate the advantages. This algorithm can also be used as reference algorithm for testing the performance of the devices extracting synchronized phasor measurements. A novel approach for estimating the phasor parameters, namely frequency, magnitude and angle in real time based on a newly constructed recursive wavelet transform is developed. This algorithm is capable of estimating the phasor parameters in a quarter cycle of an input signal. It features fast response and achieves high accuracy over a wide range of frequency deviations. The signal sampling rate and data window size can be selected to meet desirable application requirements, such as fast response, high accuracy and low computational burden. In addition, an approach for eliminating a decaying DC component, which has significant impact on estimating phasors, is proposed using recursive wavelet transform. This dissertation develops test methodology and tools for evaluating the conformance to standard-define performance for synchrophasor measurements. An interleaving technique applied on output phasors can equivalently increase the reporting rate and can precisely depict the transient behavior of a synchrophasor unit under the step input. A reference phasor estimator is developed and implemented. Various types of Phasor Measurement Units (PMUs) and PMU-enabled IEDs (Intelligent Electronic Devices) and time synchronization options have been tested against the standards using the proposed algorithm. Test results demonstrate the effectiveness and advantages.

A medição fasorial sincronizada é utilizada hoje como forma de aprimorar a operação de um Sistema Elétrico de Potência (SEP), empregando unidades de medição fasorial estrategicamente localizadas e instaladas. Estas realizam a aquisição do sinal elétrico e posteriormente a estimação dos fasores de tensão e corrente sincronizados no tempo, os quais indicam o comportamento do SEP em uma localidade específica. Este trabalho multidisciplinar propõe a análise e implementação de um método computacional evolutivo, o Algoritmo Genético Compacto Multiobjetivo (AGCM) aplicado ao problema de medição fasorial, amplamente utilizado por exemplo, no monitoramento de um SEP, comportando-se assim como uma unidade medidora de fasor, ou Phasor Measurement Unit (PMU). O AGCM aqui apresentado tem como principal característica a análise multiobjetiva do problema. Pelo fato de todo SEP ser trifásico, é proposto esta nova abordagem, onde é considerando para a estimação fasorial as três fases de forma conjunta, e não mais estimadas independentemente. Assim o AGCM proposto considera em seu mapeamento genético dos indivíduos, as características do sinais das três fases, diferentemente da abordagem mono-objetivo, onde cada fase do SEP é modelada sobre um indivíduo diferente. Posteriormente para garantir a eficácia do método evolutivo quando em operação em um cenário de tempo real, é proposto uma plataforma de aquisição de dados e processamento, inspirada em trabalhos anteriormente desenvolvidos, permitindo a integração de todos os módulos que formarão um PMU para análise fasorial em tempo real. Aqui um sistema de Global Positioning System (GPS) existente é proposto como forma de sincronismo entre os PMUs, sincronizando uma gama de equipamentos em um única referência de tempo, com a precisão necessária. Para auxiliar na integração dos módulos necessários, uma biblioteca de funções desenvolvida no LSEE será expandida permitindo a execução do método evolutivo diretamente em uma interface Field Programmable Gate Array (FPGA) a qual atuará como um coprocessador genético da plataforma de tempo real. Os resultados aqui apresentados foram obtidos seguindo especificações normativas, através de sinais gerados sinteticamente, e também utilizando o Alternative Transient Program (ATP), permitindo assim ensaios mais realísticos para a validação dos métodos evolutivos. / The synchronized phasor measurement is used today as a way to enhance the operation of an Electric Power System (EPS), using phasor measurement units strategically located and installed. They perform the acquisition of the electrical signal and then, the estimation of the voltage and current phasors, synchronized in time, which indicates the SEPs behavior in a specific location. This multidisciplinary work proposes the analysis and implementation of an evolutionary computing method, the Multibjective Compact Genetic Algorithm (MCGA) applied to the phasor estimation method used in EPS, known as an Phasor Measurement Units (PMUs). The MCGA presented here has as a main characteristic the multiobjective analysis of the problem. Because all EPSs have three phases, this new approach is proposed , which is considering the phasor estimation for the three phases together, instead of doing it for each phase independently.Thus the proposed MCGA includes in its genetic mapping of individuals, the characteristics of the signals of the three phases, unlike the monoobjective where each phase of the Electric Power System (EPS) is modeled using a different individual. In order to ensure the effectiveness of the evolutionary method when operating in a real time scenario, a platform for data acquisition and processing is proposed, inspired by previous work, allowing the integration of all the modules that composes a PMU for real-time phasor analysis. A Global Positioning System (GPS) is proposed as a way to synchronize different PMUs, integrating pieces of equipment in a single time reference, with the precision required. In order to assist in the integration of the required modules, a library of functions developed in the Laboratory of Electric Power Systems will be expanded allowing the execution of the evolutionary method directly on a Field Programmable Gate Array (FPGA) interface, which will act as a genetic co-processor of a real-time platform. The results presented here were obtained following normative specifications, through signals generated synthetically, and also using the Alternative Transient Program (ATP), allowing more realistic tests to validate the evolutionary methods.

A medição fasorial sincronizada é utilizada hoje como forma de aprimorar a operação de um Sistema Elétrico de Potência (SEP), empregando unidades de medição fasorial estrategicamente localizadas e instaladas. Estas realizam a aquisição do sinal elétrico e posteriormente a estimação dos fasores de tensão e corrente sincronizados no tempo, os quais indicam o comportamento do SEP em uma localidade específica. Este trabalho multidisciplinar propõe a análise e implementação de um método computacional evolutivo, o Algoritmo Genético Compacto Multiobjetivo (AGCM) aplicado ao problema de medição fasorial, amplamente utilizado por exemplo, no monitoramento de um SEP, comportando-se assim como uma unidade medidora de fasor, ou Phasor Measurement Unit (PMU). O AGCM aqui apresentado tem como principal característica a análise multiobjetiva do problema. Pelo fato de todo SEP ser trifásico, é proposto esta nova abordagem, onde é considerando para a estimação fasorial as três fases de forma conjunta, e não mais estimadas independentemente. Assim o AGCM proposto considera em seu mapeamento genético dos indivíduos, as características do sinais das três fases, diferentemente da abordagem mono-objetivo, onde cada fase do SEP é modelada sobre um indivíduo diferente. Posteriormente para garantir a eficácia do método evolutivo quando em operação em um cenário de tempo real, é proposto uma plataforma de aquisição de dados e processamento, inspirada em trabalhos anteriormente desenvolvidos, permitindo a integração de todos os módulos que formarão um PMU para análise fasorial em tempo real. Aqui um sistema de Global Positioning System (GPS) existente é proposto como forma de sincronismo entre os PMUs, sincronizando uma gama de equipamentos em um única referência de tempo, com a precisão necessária. Para auxiliar na integração dos módulos necessários, uma biblioteca de funções desenvolvida no LSEE será expandida permitindo a execução do método evolutivo diretamente em uma interface Field Programmable Gate Array (FPGA) a qual atuará como um coprocessador genético da plataforma de tempo real. Os resultados aqui apresentados foram obtidos seguindo especificações normativas, através de sinais gerados sinteticamente, e também utilizando o Alternative Transient Program (ATP), permitindo assim ensaios mais realísticos para a validação dos métodos evolutivos. / The synchronized phasor measurement is used today as a way to enhance the operation of an Electric Power System (EPS), using phasor measurement units strategically located and installed. They perform the acquisition of the electrical signal and then, the estimation of the voltage and current phasors, synchronized in time, which indicates the SEPs behavior in a specific location. This multidisciplinary work proposes the analysis and implementation of an evolutionary computing method, the Multibjective Compact Genetic Algorithm (MCGA) applied to the phasor estimation method used in EPS, known as an Phasor Measurement Units (PMUs). The MCGA presented here has as a main characteristic the multiobjective analysis of the problem. Because all EPSs have three phases, this new approach is proposed , which is considering the phasor estimation for the three phases together, instead of doing it for each phase independently.Thus the proposed MCGA includes in its genetic mapping of individuals, the characteristics of the signals of the three phases, unlike the monoobjective where each phase of the Electric Power System (EPS) is modeled using a different individual. In order to ensure the effectiveness of the evolutionary method when operating in a real time scenario, a platform for data acquisition and processing is proposed, inspired by previous work, allowing the integration of all the modules that composes a PMU for real-time phasor analysis. A Global Positioning System (GPS) is proposed as a way to synchronize different PMUs, integrating pieces of equipment in a single time reference, with the precision required. In order to assist in the integration of the required modules, a library of functions developed in the Laboratory of Electric Power Systems will be expanded allowing the execution of the evolutionary method directly on a Field Programmable Gate Array (FPGA) interface, which will act as a genetic co-processor of a real-time platform. The results presented here were obtained following normative specifications, through signals generated synthetically, and also using the Alternative Transient Program (ATP), allowing more realistic tests to validate the evolutionary methods.

Series compensation of transmission lines is an effectiveand cheap method of improving the power transmission systemperformance. Series capacitors virtually reduces the length ofthe line making it easier to keep all parts of the power systemrunning in synchronism and to maintain a constant voltage levelthroughout the system. In Sweden this technology has been inuse since almost 50 years. The possibility to improve the performance of the ACtransmission system utilizing power electronic equipment hasbeen discussed a lot since about ten years. Some newsemiconductor based concepts have been developed beside thesince long established HVDC and SVC technologies. The ThyristorControlled Series Capacitor (TCSC) is one such concept. Byvarying the inserted reactance an immediate and well-definedimpact on the active power flow in the transmission line isobtained. Several potential applications, specifically poweroscillation damping, benefit from this capability. The conceptimplied the requirement to design a semiconductor valve, whichcan be inserted directly in the high-voltage power circuit.This certainly presented a technical challenge but thestraightforward approach appeared to be a cost-effectivealternative with small losses. It was also realized that the TCSC exhibits quite differentbehaviour with respect to subsynchronous frequency componentsin the line current as compared to the fixed series capacitorbank. This was a very interesting aspect as the risk ofsubsynchronous resonance (SSR), which just involves such linecurrent components, has hampered the use of series compensationin power systems using thermal generating plants. The thesis deals with the modelling and control aspects ofTCSC. A simplifying concept, the equivalent, instantaneousvoltage reversal, is introduced to represent the action of thethyristor controlled inductive branch, which is connected inparallel with the series capacitor bank in the TCSC. The idealvoltage reversal is used in the thesis in order to describe andexplain the TCSC dynamics, to investigate its apparentimpedance at various frequencies, as a platform forsynthesizing the boost control system and as the base elementin deriving a linear, small-signal dynamical model of thethree-phase TCSC. Quantitative Feedback Theory (QFT) then hasbeen applied to the TCSC model in order to tune its boostregulator taking into account the typical variation ofparameters that exists in a power system. The impact of theboost control system with respect to damping of SSR is finallybeing briefly looked at. <b>Keywords:</b>Thyristor Controlled Series Capacitor, TCSC,FACTS, reactive power compensation, boost control, phasorestimation, Quantitative Feedback Theory, subsynchronousresonance, SSR.

<p>Series compensation of transmission lines is an effectiveand cheap method of improving the power transmission systemperformance. Series capacitors virtually reduces the length ofthe line making it easier to keep all parts of the power systemrunning in synchronism and to maintain a constant voltage levelthroughout the system. In Sweden this technology has been inuse since almost 50 years.</p><p>The possibility to improve the performance of the ACtransmission system utilizing power electronic equipment hasbeen discussed a lot since about ten years. Some newsemiconductor based concepts have been developed beside thesince long established HVDC and SVC technologies. The ThyristorControlled Series Capacitor (TCSC) is one such concept. Byvarying the inserted reactance an immediate and well-definedimpact on the active power flow in the transmission line isobtained. Several potential applications, specifically poweroscillation damping, benefit from this capability. The conceptimplied the requirement to design a semiconductor valve, whichcan be inserted directly in the high-voltage power circuit.This certainly presented a technical challenge but thestraightforward approach appeared to be a cost-effectivealternative with small losses.</p><p>It was also realized that the TCSC exhibits quite differentbehaviour with respect to subsynchronous frequency componentsin the line current as compared to the fixed series capacitorbank. This was a very interesting aspect as the risk ofsubsynchronous resonance (SSR), which just involves such linecurrent components, has hampered the use of series compensationin power systems using thermal generating plants.</p><p>The thesis deals with the modelling and control aspects ofTCSC. A simplifying concept, the equivalent, instantaneousvoltage reversal, is introduced to represent the action of thethyristor controlled inductive branch, which is connected inparallel with the series capacitor bank in the TCSC. The idealvoltage reversal is used in the thesis in order to describe andexplain the TCSC dynamics, to investigate its apparentimpedance at various frequencies, as a platform forsynthesizing the boost control system and as the base elementin deriving a linear, small-signal dynamical model of thethree-phase TCSC. Quantitative Feedback Theory (QFT) then hasbeen applied to the TCSC model in order to tune its boostregulator taking into account the typical variation ofparameters that exists in a power system. The impact of theboost control system with respect to damping of SSR is finallybeing briefly looked at.</p><p><b>Keywords:</b>Thyristor Controlled Series Capacitor, TCSC,FACTS, reactive power compensation, boost control, phasorestimation, Quantitative Feedback Theory, subsynchronousresonance, SSR.</p>

System stability plays an important role in electric power systems. With the development of electric power system, the scale of the electric grid is now becoming larger and larger, and many renewable energy resources are integrated in the grid. However, at the same time, the stability and safety issues of electric power system are becoming more complicated. Frequency and phasors are two critical parameters of the system stability. Obtaining these two parameters have been great challenges for decades. Researchers have provided various kinds of algorithms for frequency tracking and phasor estimation. Among them, Least Squares (LS) algorithm is one of the most commonly used algorithm. This thesis studies the LS algorithm and the Total Least Squares (TLS) algorithm working on frequency tracking and phasor estimation. In order to test the performance of the two algorithms, some simulations have been made in the Matlab. The Total Vector Error (TVE) is a commonly used performance criteria, and the TVE results of the two algorithms are compared. The TLS algorithm performs better than LS algorithm when the frequencies of all harmonic components are given.