The objective of this work is to design a damping controller for a thyristor controlled series capacitor (TCSC) to damp robustly inter-area oscillations in power systems with an immunity against sub-synchronous resonance (SSR) oscillations which may lead to torsional oscillations. The new control strategy has two main loops; an SSR mitigation loop and a bang-bang loop, the latter is designed with the aim of damping inter-area oscillations with a settling time 8-10 sec. The appropriate selection of the bang-bang series compensation component, ∆KC, is addressed by considering the Eigen analysis of the generators’ shafts and an impedance scan of the series compensated line for different compensation levels. The SSR mitigation loop is designed with the aim of providing a fine tune control signal to be added to the main value of the inserted series compensation (KC), to damp SSR oscillations and related torsional mode of oscillations. To address this issue, a new observer-based multiple model adaptive control algorithm is designed to control a multi-stage TCSC. The SSR modelling challenges associated with the load dynamics and with the insertion of the series compensation into the transmission system are overcome by a fine tuning control loop, which adjusts the resultant series compensation (KC). Considering the integration and coordination of oscillation damping and distance protection in the transmission system, a new adaptive technique must be designed to control the distance relay (DR) to prevent its mal operation (during the damping process). The new strategy is illustrated through an 11-bus 4-machine 2-area benchmark power system. The performance and advantages of the new algorithm are validated using time domain simulation via PSCAD software.

Neste trabalho são exploradas as potencialidades e efeitos de possíveis aplicações do UPFC (Unified Power Flow Controller) em redes elétricas. Este recente equipamento da família FACTS, apesar de mais complexo, apresenta rapidez e versatilidade de respostas que podem justificar sua aplicação em redes elétricas. São apresentados modelos matemáticos deste dispositivo, para regime permanente e transitório, utilizando transformações para coordenadas ortogonais. Com base nas respostas obtidas, durante as simulações das aplicações estudadas, pode-se constatar que a tensão série e seu posicionamento angular, introduzidos pelo UPFC, desempenham um importante papel no controle rápido e eficiente do fluxo de potência. Como contribuição deste trabalho, explorou-se a conexão do conversor shunt ao enrolamento terciário de autotransformadores, demonstrando a viabilidade do controle do fluxo de potência nestes equipamentos de transformação. O esquema proposto, instalado em transformadores em paralelo, eleva a disponibilidade de operação do UPFC, aumentando a flexibilidade operativa do sistema em implementações práticas. Através da formulação apresentada, o transformador de acoplamento shunt, convencionalmente utilizado pelo UPFC, apresenta dimensões reduzidas. Foi também examinada a possibilidade de limitação de correntes de curto-circuito, equilibrados ou não, com a ação dos controles do UPFC, particularmente, aprofundando a análise do seu desempenho mais eficiente diante de curtos monofásicos. Os resultados satisfatórios obtidos permitem considerar a viabilidade de limitação destas correntes como um subproduto interessante da atuação deste dispositivo FACTS. / In this thesis, the UPFC (Unified Power Flow Controller) various capabilities and effects for possible network applications, are studied. Although its structure is relatively more complex, when compared to the other FACTS controllers, its fast response and versatility can justify its application within the network. By utilising the orthogonal co-ordinates transform both the steady-state and transient mathematical models of the UPFC, are presented herein. Based on the results obtained and regarding the applications studied, it can be stated that the UPFC series voltage along with its phase angle play an important role for the fast and efficient control of the power flow. As a contribution of the present work, it has been proposed the connection of the shunt converter to the tertiary winding of autotransformers, demonstrating in this way the feasibility for controlling the power flow over such transforming assets. The proposed scheme, which regards two paralleled transformers, offers the UPFC a high operation availability increasing the system operative flexibility in actual implementations. By means of the proposed approach, the shunt coupling transformer, usually utilised in a classical UPFC configuration, presents a reduced size. Also, by utilising the UPFC control actions, it has been examined the possibility of short-circuit limitation over balanced and unbalanced circuits. Particularly, it has been analysed the UPFC most efficient performance towards line-to-ground faults. The satisfactory results obtained lead to consider the UPFC feasibility in limiting such currents; this, as an interesting by-product of this FACTS device action.

As novas tecnologias FACTS aplicadas ao sistema de transmissão, com base em eletrônica de potência, podem também ser úteis à distribuição. Para tal é preciso conduzir um procedimento de consolidação da utilização e do desempenho destas, para sua aplicação sem riscos. Neste trabalho, dois aspectos serão contemplados. O primeiro se refere à aplicação do dispositivo FACTS atuando como um capacitor série. Em se tendo controle de módulo e da fase da tensão inserida em série com a linha pode-se fazê-la comportar-se como uma queda em uma reatância série capacitiva ou indutiva. O controle dessa reatância série (aumentando/diminuindo) permitirá a aplicação do conceito de compensação série em qualquer ponto do sistema de distribuição, provendo benefícios de um controle contínuo da tensão e também do controle do fluxo de carga no sistema independente da corrente. O segundo aspecto refere-se ao uso dos dispositivos na conexão de alimentadores controlando a potência ativa entre eles. Para esta operação outro dispositivo UPFC, com conceito similar ao descrito acima, entretanto atuando na fase da tensão entre 2 barras, comporta-se como um transformador defasador com variação contínua de ?taps?, podendo controlar a potência ativa entre os alimentadores. A aplicação destas tecnologias propiciarão vários benefícios para a expansão da distribuição tais como, flexibilização do uso da rede, interligação de alimentadores permitindo manobras de blocos de energia sem ?pisca?, ajuste contínuo do suporte de reativos durante a operação, controle dinâmico do fluxo de potência. O objetivo deste trabalho é estudar a aplicabilidade da tecnologia FACTS e estender este conceito para aplicação em sistemas de distribuição e conduzir simulações digitais em redes de distribuição (15kV) identificando o desempenho e os benefícios atingidos. O programa de simulação utilizado é o ATP (Alternative Transients Program). / The new FACTS technologies applied to the transmission system, based on power electronics, can also be useful to the distribution. For that, it is necessary to drive a procedure to consolidate the use and the performance for their application without risks. In this work two aspects will be approached. The first refers to the application of a FACTS device acting as series compensator. This device will be able to control the voltage in module and phase in order to act as a voltage drop in a serie reactance with capacitive or inductive features. The control of this series reactance (increasing/ decreasing) will allow the application of series compensation concept to any point of the distribution system, providing the benefits of continuous control of the voltage added to the load flow control in the system independent of the current. The second aspect refers to its use in the connection of two feeders controlling the active power between them. For this operation other device, UPFC, with similar concept as described previously, acts mainly in the phase of the injected voltage in the line, performing as a phase-shift with continuous taps variation and is able to control the active power flow between feeders. The application of this technology will provide several benefits for the distribution expansion, such as, a greater flexibility in the use of the network, connection of feeders without load flow interruption, continuous adjust of reactive power during the operation and dynamic control of power flow. The purpose of this work is to study the applicability of the FACTS technology, to extend this concept for the application in the distribution system by using digital simulations in distribution network up to 15kV identifying the performance and the reached benefits.

Neste trabalho são exploradas as potencialidades e efeitos de possíveis aplicações do UPFC (Unified Power Flow Controller) em redes elétricas. Este recente equipamento da família FACTS, apesar de mais complexo, apresenta rapidez e versatilidade de respostas que podem justificar sua aplicação em redes elétricas. São apresentados modelos matemáticos deste dispositivo, para regime permanente e transitório, utilizando transformações para coordenadas ortogonais. Com base nas respostas obtidas, durante as simulações das aplicações estudadas, pode-se constatar que a tensão série e seu posicionamento angular, introduzidos pelo UPFC, desempenham um importante papel no controle rápido e eficiente do fluxo de potência. Como contribuição deste trabalho, explorou-se a conexão do conversor shunt ao enrolamento terciário de autotransformadores, demonstrando a viabilidade do controle do fluxo de potência nestes equipamentos de transformação. O esquema proposto, instalado em transformadores em paralelo, eleva a disponibilidade de operação do UPFC, aumentando a flexibilidade operativa do sistema em implementações práticas. Através da formulação apresentada, o transformador de acoplamento shunt, convencionalmente utilizado pelo UPFC, apresenta dimensões reduzidas. Foi também examinada a possibilidade de limitação de correntes de curto-circuito, equilibrados ou não, com a ação dos controles do UPFC, particularmente, aprofundando a análise do seu desempenho mais eficiente diante de curtos monofásicos. Os resultados satisfatórios obtidos permitem considerar a viabilidade de limitação destas correntes como um subproduto interessante da atuação deste dispositivo FACTS. / In this thesis, the UPFC (Unified Power Flow Controller) various capabilities and effects for possible network applications, are studied. Although its structure is relatively more complex, when compared to the other FACTS controllers, its fast response and versatility can justify its application within the network. By utilising the orthogonal co-ordinates transform both the steady-state and transient mathematical models of the UPFC, are presented herein. Based on the results obtained and regarding the applications studied, it can be stated that the UPFC series voltage along with its phase angle play an important role for the fast and efficient control of the power flow. As a contribution of the present work, it has been proposed the connection of the shunt converter to the tertiary winding of autotransformers, demonstrating in this way the feasibility for controlling the power flow over such transforming assets. The proposed scheme, which regards two paralleled transformers, offers the UPFC a high operation availability increasing the system operative flexibility in actual implementations. By means of the proposed approach, the shunt coupling transformer, usually utilised in a classical UPFC configuration, presents a reduced size. Also, by utilising the UPFC control actions, it has been examined the possibility of short-circuit limitation over balanced and unbalanced circuits. Particularly, it has been analysed the UPFC most efficient performance towards line-to-ground faults. The satisfactory results obtained lead to consider the UPFC feasibility in limiting such currents; this, as an interesting by-product of this FACTS device action.

Nowadays power transmission networks are capable of delivering contracted power from any supplier to any consumer over a large geographic area under market control, and thus transmission lines are incorporated with FACTs series compensated devices to increase the power transfer capability with improvement to system integrity. Conventional fault location methods developed in the past many years are not suitable for FACTs transmission networks. The obvious reason is that FACTs devices in transmission networks introduce non-linearity in the system and hence linear fault detection methods are no longer valid. Therefore, it is still a matter of research to investigate developing new fault detection techniques to cater for modern transmission network configurations and solve implementation issues maintaining required accuracy. This PhD research work is based on developing an accurate and robust new fault location algorithm for series compensated high voltage transmission lines, considering many issues such as transmission line models, configurations with series compensation features. Building on the existing knowledge, a new algorithm has been developed for the estimation of fault location using the time domain approach. In this algorithm, instantaneous fault signals from the transmission line ends are measured and applied to the algorithm to calculate the distance to fault. The new algorithm was tested on two port transmission line model developed using EMTP/ATP software and measured fault data from the simulations are exported to the MATLAB space to run the algorithm. Broad range of faults has been simulated considering various fault cases to test the algorithm and statistical results obtained. It was observed that the accuracy of location of fault on series compensated transmission line using this algorithm is in the range from 99.7 % to 99.9% in 90% of fault cases. In addition, this algorithm was further improved considering many practical issues related to modern series compensated transmission lines (with TCSC var compensators) achieving similar accuracies in the estimation of fault location.

Electricity systems are very complex systems and are composed of numerous transmission lines, generators and loads. The generating stations are generally far away from load centres and that may cause transmission line congestion and overloading. Series capacitive compensation is the most economical way to increase transmission capacity and improve transient stability of transmission grids. However, one of the impeding factors for the widespread use of series capacitive compensation is the potential risk of Subsynchronous Resonance (SSR). Subsynchronous Resonance is a phenomenon in which electrical power is exchanged with the generator shaft system in an increasing manner which may result in damage to the turbine generator shaft system. Therefore, mitigating SSR continues to be a subject of research and development aiming at developing effective SSR countermeasures.<p>This research work presents new methods of alleviating the SSR problem using a Static Synchronous Series Compensator (SSSC) and a Static Synchronous Compensator (STATCOM). These methods are based on using the SSSC and STATCOM to inject unbalanced series quadrature voltages and unbalanced shunt reactive currents in transmission line just after clearing faults. When the subsynchronous oscillations drive unsymmetrical phase currents, the developed electromagnetic torque will be lower than the condition when the three-phase currents are symmetrical. The unsymmetrical currents result in a lower coupling strength between the mechanical and the electrical system at asynchronous oscillations. Therefore, the energy exchange between the electrical and the mechanical systems at subsynchronous oscillations will be suppressed, thus, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance condition. The validity of proposed methods are demonstrated by time simulation results using the electromagnetic transient program EMTP-RV.

Electricity systems are very complex systems and are composed of numerous transmission lines, generators and loads. The generating stations are generally far away from load centres and that may cause transmission line congestion and overloading. Series capacitive compensation is the most economical way to increase transmission capacity and improve transient stability of transmission grids. However, one of the impeding factors for the widespread use of series capacitive compensation is the potential risk of Subsynchronous Resonance (SSR). Subsynchronous Resonance is a phenomenon in which electrical power is exchanged with the generator shaft system in an increasing manner which may result in damage to the turbine generator shaft system. Therefore, mitigating SSR continues to be a subject of research and development aiming at developing effective SSR countermeasures.<p>This research work presents new methods of alleviating the SSR problem using a Static Synchronous Series Compensator (SSSC) and a Static Synchronous Compensator (STATCOM). These methods are based on using the SSSC and STATCOM to inject unbalanced series quadrature voltages and unbalanced shunt reactive currents in transmission line just after clearing faults. When the subsynchronous oscillations drive unsymmetrical phase currents, the developed electromagnetic torque will be lower than the condition when the three-phase currents are symmetrical. The unsymmetrical currents result in a lower coupling strength between the mechanical and the electrical system at asynchronous oscillations. Therefore, the energy exchange between the electrical and the mechanical systems at subsynchronous oscillations will be suppressed, thus, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance condition. The validity of proposed methods are demonstrated by time simulation results using the electromagnetic transient program EMTP-RV.

No description available.

As novas tecnologias FACTS aplicadas ao sistema de transmissão, com base em eletrônica de potência, podem também ser úteis à distribuição. Para tal é preciso conduzir um procedimento de consolidação da utilização e do desempenho destas, para sua aplicação sem riscos. Neste trabalho, dois aspectos serão contemplados. O primeiro se refere à aplicação do dispositivo FACTS atuando como um capacitor série. Em se tendo controle de módulo e da fase da tensão inserida em série com a linha pode-se fazê-la comportar-se como uma queda em uma reatância série capacitiva ou indutiva. O controle dessa reatância série (aumentando/diminuindo) permitirá a aplicação do conceito de compensação série em qualquer ponto do sistema de distribuição, provendo benefícios de um controle contínuo da tensão e também do controle do fluxo de carga no sistema independente da corrente. O segundo aspecto refere-se ao uso dos dispositivos na conexão de alimentadores controlando a potência ativa entre eles. Para esta operação outro dispositivo UPFC, com conceito similar ao descrito acima, entretanto atuando na fase da tensão entre 2 barras, comporta-se como um transformador defasador com variação contínua de ?taps?, podendo controlar a potência ativa entre os alimentadores. A aplicação destas tecnologias propiciarão vários benefícios para a expansão da distribuição tais como, flexibilização do uso da rede, interligação de alimentadores permitindo manobras de blocos de energia sem ?pisca?, ajuste contínuo do suporte de reativos durante a operação, controle dinâmico do fluxo de potência. O objetivo deste trabalho é estudar a aplicabilidade da tecnologia FACTS e estender este conceito para aplicação em sistemas de distribuição e conduzir simulações digitais em redes de distribuição (15kV) identificando o desempenho e os benefícios atingidos. O programa de simulação utilizado é o ATP (Alternative Transients Program). / The new FACTS technologies applied to the transmission system, based on power electronics, can also be useful to the distribution. For that, it is necessary to drive a procedure to consolidate the use and the performance for their application without risks. In this work two aspects will be approached. The first refers to the application of a FACTS device acting as series compensator. This device will be able to control the voltage in module and phase in order to act as a voltage drop in a serie reactance with capacitive or inductive features. The control of this series reactance (increasing/ decreasing) will allow the application of series compensation concept to any point of the distribution system, providing the benefits of continuous control of the voltage added to the load flow control in the system independent of the current. The second aspect refers to its use in the connection of two feeders controlling the active power between them. For this operation other device, UPFC, with similar concept as described previously, acts mainly in the phase of the injected voltage in the line, performing as a phase-shift with continuous taps variation and is able to control the active power flow between feeders. The application of this technology will provide several benefits for the distribution expansion, such as, a greater flexibility in the use of the network, connection of feeders without load flow interruption, continuous adjust of reactive power during the operation and dynamic control of power flow. The purpose of this work is to study the applicability of the FACTS technology, to extend this concept for the application in the distribution system by using digital simulations in distribution network up to 15kV identifying the performance and the reached benefits.

Subsynchronous oscillations (SSO) were an issue that occurred in the past with conventional generators and were studied extensively throughout the years. However, with the rise of inverter-based resources, a new form of SSO emerged under the name subsynchronous control interaction (SSCI). More specifically, a resonance case occurs between Type-3 wind turbines and series compensation that can damage equipment within the wind farm and disrupt power generation. This work explores the types of SSCI and the various analysis methods as well as mitigation of SSCI. The work expands on the concept of frequency scan to be able to use it in an on-line setting with its output data used to mitigate SSCI through the modification of wind turbine parameters. Multiple frequency scans are conducted using PSCAD/EMTDC software to build a lookup table and harmonic injection is used in a parallel configuration to obtain the impedance of the system. Once the impedance of the system is obtained then the value of the parameters is adjusted using the look-up table. Harmonic injection is optimized through phase shifts to ensure minimal disruption of the steady-state operating point and is conducted using Python programming language with PSCAD Automation Library. Simulation results demonstrate the effectiveness of this approach by ensuring oscillations do not grow exponentially in comparison to the regular operation of the wind farm. / Master of Science / Due to climate change concern and the depletion of fossil fuel resources, electrical power generation is shifting towards renewables such as solar and wind energy. Wind energy can be obtained using wind turbines that transform wind energy into electrical energy, these wind turbines come in four different types. Type-3 wind turbines are the most commonly used in the industry which use a special configuration of the classical induction generator. These wind turbines are typically installed in a distant location which makes it more difficult to transfer energy from its location to populated areas, hence, series capacitors can be used to increase the amount of transferred energy. However, these series capacitors can create a phenomenon called subsynchronous control interaction (SSCI) with Type-3 wind turbines. In this phenomenon, energy is exchanged back and forth between the series capacitors and the wind turbines causing the current to grow exponentially which leads to interruptions in service and damage to major equipments within the wind turbine. This work explores SSCI, the tools to study it, and the currently available mitigation methods. It also presents a method to identify the cases where SSCI can happen and mitigates it using adjustable parameters.