Renewable energy generation will play an important role in solving the climate change problem. With renewable electricity generation increasing, there will be some significant changes in electric power systems, notably through smaller generators embedded in the distribution network. Historically insignificant volumes of Embedded Generation (EG) mean that traditionally it has been treated by the transmission system operator as negative load, with its impact on the dynamic behaviour of power systems neglected. However, with the penetration level increasing, EG would start to influence the dynamics and stability of the transmission network. Hence the dynamic behaviour of distribution network cannot be neglected any more. In most cases, a detailed distribution network model is not always available or necessary for the study of transmission network dynamics and stability. Thus a dynamic equivalent model of the distribution network that keeps its essential dynamic behavior, is required. Most existing dynamic equivalencing methods are based on the assumption that the detailed information of the complete power system is known. Dynamic equivalencing methods based on coherency of the machines have been applied to transmission networks but cannot be applied to distribution networks due to their radial structure. Hence an alternative methodology has been developed in this project to derive the dynamic equivalent model of the distribution network using system identification, without the detailed information of the distribution network necessarily known. Case studies have been accomplished in PSS/E on a model of the Scottish transmission network with the distribution network in Dumfries and Galloway. Embedded generation with a certain penetration level in either conventional generation or DFIG wind generation has been added to the model of the distribution network. The dynamic equivalent models of the distribution network are compared with the original distribution network model using a series of indicators. A constant power model has also been involved in the comparison to illustrate the advantage of using the dynamic equivalent to represent the distribution network. The results suggest that a proper dynamic equivalent model derived using this methodology may have better agreement to the original power system dynamic response than constant power equivalent. A discussion on factors that influence the performance of the dynamic equivalent model, is given to indicate the proper way to use this methodology. The major advantage of the dynamic equivalencing methodology developed in this project is that it can potentially use the time series obtained from measurements to derive the dynamic equivalent models without knowing detailed information on the distribution network. The derived dynamic equivalent, in a simple spate-space form, can be implemented in commercial simulation tools, such as PSS/E.

abstract: Due to restructuring and open access to the transmission system, modern electric power systems are being operated closer to their operational limits. Additionally, the secure operational limits of modern power systems have become increasingly difficult to evaluate as the scale of the network and the number of transactions between utilities increase. To account for these challenges associated with the rapid expansion of electric power systems, dynamic equivalents have been widely applied for the purpose of reducing the computational effort of simulation-based transient security assessment. Dynamic equivalents are commonly developed using a coherency-based approach in which a retained area and an external area are first demarcated. Then the coherent generators in the external area are aggregated and replaced by equivalenced models, followed by network reduction and load aggregation. In this process, an improperly defined retained area can result in detrimental impacts on the effectiveness of the equivalents in preserving the dynamic characteristics of the original unreduced system. In this dissertation, a comprehensive approach has been proposed to determine an appropriate retained area boundary by including the critical generators in the external area that are tightly coupled with the initial retained area. Further-more, a systematic approach has also been investigated to efficiently predict the variation in generator slow coherency behavior when the system operating condition is subject to change. Based on this determination, the critical generators in the external area that are tightly coherent with the generators in the initial retained area are retained, resulting in a new retained area boundary. Finally, a novel hybrid dynamic equivalent, consisting of both a coherency-based equivalent and an artificial neural network (ANN)-based equivalent, has been proposed and analyzed. The ANN-based equivalent complements the coherency-based equivalent at all the retained area boundary buses, and it is designed to compensate for the discrepancy between the full system and the conventional coherency-based equivalent. The approaches developed have been validated on a large portion of the Western Electricity Coordinating Council (WECC) system and on a test case including a significant portion of the eastern interconnection. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Today’s power systems are based on a centralised system and distribution networks that are considered as passive terminations of transmission networks. The high penetration of Distributed Generation (DG) at the distribution network level has created many challenges for this structure. New tools and simulation approaches are required to address the subject and to quantify the dynamic characteristics of the system. A distribution network or part of it with DG, Active Distribution Network Cell (ADNC), can no longer be considered as passive. An equivalent dynamic model of ADNC is therefore extremely important, as it enables power system operators to quickly estimate the impact of disturbances on the power system’s dynamic behaviour. A dynamic equivalent model works by reducing both the complexity of the distribution network and the computation time required to run a full dynamic simulation. It offers a simple and low-order representation of the system without compromising distribution network dynamic characteristics and behaviour as seen by the external grid. This research aims to develop a dynamic equivalent model for ADNC. It focuses on the development of an equivalent model by exploiting system identification theory, i.e. the grey-box approach. The first part of the thesis gives a comprehensive overview and background of the dynamic equivalent techniques for power systems. The research was inspired by previous work on system identification theory. It further demonstrates the theoretical concept of system identification, system load modelling and the modelling of major types of DG. An equivalent model is developed, guided by the assumed structure of the system. The problem of equivalent model development is then formulated under a system identification framework, and the parameter estimation methodology is proposed. The validation results of the effectiveness and accuracy of the developed model are presented. This includes the estimation of the parameter model using a clustering algorithm to improve the computational performance and the analysis of transformer impedance effects on the ADNC responses. The evaluation of probability density function, eigenvalue analysis and parameter sensitivity analysis for the model parameters are also presented. Typical model parameters for different network topologies and configurations are identified. Finally, the developed equivalent model is used for a large power system application. The accuracy and robustness of the developed equivalent model are demonstrated under small and large disturbance studies for various types of fault and different fault locations.

The objective of this study is to investigate the appropriateness of the term kami (神) as the translation of the term ‘God’ from the point-of-view of Dynamic Equivalent (DE) translation in Japan. The study argues that the translated term kami (神) in the Japanese Bible was adopted at first without sufficient investigation of its appropriateness but because of its penetrating character, it became the exclusive term to represent the monotheistic God. Discussion of the effect of the philosophy of Dynamic Equivalent translation in the history of Bible translation in Japan and the history of the changes of the Japanese notion of God is used to justify the validity of the above argument. As a procedure, two translation methods (DE and FE) seen in conventional Bible translations have been compared, supported by case studies where these methods are used. Next, to understand the mind of the Japanese who were the recipients of the new concept of God, the history of Japanese Shinto is discussed. Finally, the lives of two Japanese assistants of Japanese Bible translation, Anjirō and Otokichi, are studied. The study concludes that the adoption of kami (神) was appropriate from the point-of-view of DE translation, and the Japanese assistants also applied the DE translation method unconsciously. A reassessment of their selection of the terms for God is possible if they are seen as examples of the DE translation method.

The purpose of this research is to develop a method of making system equivalents for the Real Time Digital Simulator (RTDS), which should enhance its capability of simulating large power systems. The proposed equivalent combines a Frequency Dependent Network Equivalent (FDNE) for the high frequency electromagnetic transients and a Transient Stability Analysis (TSA) type simulation block for the electromechanical transients. The frequency dependent characteristic for FDNE is obtained by curve-fitting frequency domain admittance characteristics using the Vector Fitting method. An approach for approximating the frequency dependent characteristic of large power networks from readily available typical power-flow data is also introduced. A new scheme of incorporating TSA solution in RTDS is proposed. This report shows how the TSA algorithm can be adapted to a real time platform. The validity of this method is confirmed with examples, including the study of a multi in-feed HVDC system based network.

The purpose of this research is to develop a method of making system equivalents for the Real Time Digital Simulator (RTDS), which should enhance its capability of simulating large power systems. The proposed equivalent combines a Frequency Dependent Network Equivalent (FDNE) for the high frequency electromagnetic transients and a Transient Stability Analysis (TSA) type simulation block for the electromechanical transients. The frequency dependent characteristic for FDNE is obtained by curve-fitting frequency domain admittance characteristics using the Vector Fitting method. An approach for approximating the frequency dependent characteristic of large power networks from readily available typical power-flow data is also introduced. A new scheme of incorporating TSA solution in RTDS is proposed. This report shows how the TSA algorithm can be adapted to a real time platform. The validity of this method is confirmed with examples, including the study of a multi in-feed HVDC system based network.

Este trabalho foi baseado na metodologia desenvolvida para modelagem computacional de equivalentes dinâmicos de sistemas elétricos de potência apresentada em BRITO, 2009 [5]. Sendo que nesse trabalho desenvolveu um método de modelagem de equivalentes dinâmicos de sistemas elétricos de potência com geradores, máquinas e seus controladores. O equivalente dinâmico consiste em uma substituição de uma parcela de um Sistema Elétrico de Potência, composta por linhas de transmissão, barras de carga e barras geradoras, de forma que estas serão sintetizadas e minimizadas de forma que o número de elementos seja diminuído, mas conservem o comportamento dinâmico elétrico da área original, sendo o mais próximo possível do encontrado no sistema elétrico de potência original. Foram realizados cálculos teóricos para obtenção dos equivalentes estáticos e dinâmicos do referido sistema de potência. Para isso utilizamos o programa ANAREDE para obtenção dos resultados dos fluxos de carga do sistema completo e do sistema reduzido. Estes resultados foram utilizados em um programa de análise de pequenas perturbações, denominado PACDYN, o qual verifica o comportamento dinâmico dos sistemas. Para possibilitar essa análise foi inclusa uma pequena perturbação de tensão no sistema, próxima à sua barra de referência angular. Os resultados encontrados pelo programa PACDYN foram exportados para um programa de análise matemática e simulações, denominado MATLAB, onde foram gerados os gráficos dos resultados obtidos e aplicada a técnica de mínimos quadrados, para ajuste dos resultados. Por meio da comparação dos fluxos de potência dos sistemas completo e equivalente, obteve-se a validação do trabalho, sendo utilizado o sistema New England, como sistema-teste. Neste trabalho aplicamos a metodologia desenvolvida em BRITO, (2009) [5] no sistema de potência-teste New England, complementando o trabalho original, em que a parte interna e externa do sistema, escolhida para construção do equivalente dinâmico eram interligadas por uma única barra de fronteira. Em nosso trabalho utilizamos uma área que nos demandou a utilização de quatro barras de fronteira, quatro linhas de transmissão e uma barra fictícia de acoplamento, onde foi conectado o gerador equivalente e cargas equivalentes. Comparando os resultados do sistema completo e reduzido obtivemos valores próximos o bastante para comprovar a robustez do sistema fictício e validar mais uma vez a metodologia. / This work was based on the methodology developed for computer modeling of dynamic of electric power systems equivalents presented in BRITO, 2009 [5]. And in this work we developed a method of modeling of dynamic equivalents of electric power systems with generators, machines and their controllers. The dynamic equivalent consists of a substitution of a portion of an Electric Power System, consisting of transmission lines, the load buses and generating bars, so that these will be synthesized and minimized so that the number of elements is decreased, but retain the electric dynamic behavior of the original area, with the closest to the found in the electrical system of original power. Theoretical calculations for obtaining the static and dynamic equivalents of said power system were performed. For that use the ANAREDE program to obtain the results of the full system load flows and reduced system. These results were used in a parsing program small disturbances, called PACDYN, which checks the dynamic behavior of the system. To enable this analysis has included a small voltage perturbation in the system, next to its angular reference bar. The results found by PACDYN program were exported to a mathematical analysis and simulation program called MATLAB, which graphs the results obtained and applied the technique of least squares were generated to adjust the results. By comparing the equivalent of complete systems and power flows obtained if the validation work, by using the New England system as test system. In this paper we apply the methodology developed in BRITO, (2009) [5] in the New England power test system, complementing the original work, in which the inside and outside of the system, chosen to build the dynamic equivalent were joined by a single border bar. In our work we use an area which required us to use four border bars, four transmission lines and a dummy coupling bar, which was connected to the equivalent generator and equivalent charges. Comparing the results of the full and reduced system obtained values close enough to demonstrate the robustness of the dummy system and to validate again the methodology.

This thesis introduces a new modeling approach that allows very large power systems to be modeled on a real time electro-magnetic transients (EMT) digital simulator with reduced hardware costs. The key step in achieving this is the development of an improved wide-band multi-port equivalent, which reduces a large power network into a small manageable equivalent model that preserves wideband behaviors. This approach has a foundation method that use a two part equivalent in which the high frequency behavior of the equivalenced network is represented by a terminating frequency dependent network equivalent (FDNE), with the low frequency behavior being modeled using a detailed Transient Stability Analysis (TSA) model that only models the electromechanical behavior. This approach allowed the modelling of medium size electric regions up to hundreds of buses in real time. This thesis extends the equivalent by implementing a reduced order of the detailed electromechanical TSA equivalent mentioned above. Coherency based reduction is used for the electromechanical model of the power network to be equivalenced, and is implemented as a Transient Stability Analysis (TSA) type electromechanical equivalent. A challenge in implementing the FDNE is to ensure that it is a passive network, as otherwise its inclusion could lead to unstable simulation. This thesis also introduces a practical procedure to enforce passivity in the FDNE. The validity of the proposed technique is demonstrated by comparing the approach with detailed electromagnetic simulations of the well-known 39 bus New England system and a modified 39 bus system with an HVDC infeed with coupling between the dc line and an adjacent ac line, in addition to a 108 bus ac system. The power of the method is demonstrated by the real-time simulation of a large system with 2300 busses and 139 generators. It has been shown that this approach has the potential to increase by at least one order of magnitude the size of the network that can be modeled and thus on a real time electro-magnetic transients (EMT) digital simulator with reduced hardware costs.

This thesis introduces a new modeling approach that allows very large power systems to be modeled on a real time electro-magnetic transients (EMT) digital simulator with reduced hardware costs. The key step in achieving this is the development of an improved wide-band multi-port equivalent, which reduces a large power network into a small manageable equivalent model that preserves wideband behaviors. This approach has a foundation method that use a two part equivalent in which the high frequency behavior of the equivalenced network is represented by a terminating frequency dependent network equivalent (FDNE), with the low frequency behavior being modeled using a detailed Transient Stability Analysis (TSA) model that only models the electromechanical behavior. This approach allowed the modelling of medium size electric regions up to hundreds of buses in real time. This thesis extends the equivalent by implementing a reduced order of the detailed electromechanical TSA equivalent mentioned above. Coherency based reduction is used for the electromechanical model of the power network to be equivalenced, and is implemented as a Transient Stability Analysis (TSA) type electromechanical equivalent. A challenge in implementing the FDNE is to ensure that it is a passive network, as otherwise its inclusion could lead to unstable simulation. This thesis also introduces a practical procedure to enforce passivity in the FDNE. The validity of the proposed technique is demonstrated by comparing the approach with detailed electromagnetic simulations of the well-known 39 bus New England system and a modified 39 bus system with an HVDC infeed with coupling between the dc line and an adjacent ac line, in addition to a 108 bus ac system. The power of the method is demonstrated by the real-time simulation of a large system with 2300 busses and 139 generators. It has been shown that this approach has the potential to increase by at least one order of magnitude the size of the network that can be modeled and thus on a real time electro-magnetic transients (EMT) digital simulator with reduced hardware costs.

Wind power installations have seen a significant rise all over the world in the past decade. Further significant growth is expected in the future. The UK’s ambitions for offshore wind installations are reflected through Round 1, 2 and 3 projects. It is expected that Round 3 alone will add at least 25 GW of offshore wind generation into the system. Current research knowledge is mostly limited to smaller wind farms, the aim of this research is to improve offline and online modelling techniques for large offshore wind farms. A critical part of offline modelling is the design of the wind farm. Design of large wind farms particularly requires careful consideration as high capital costs are involved. This thesis develops a novel methodology which leads to a cost-effective and reliable design of an offshore wind farm. A new industrial-grade software tool is also developed during this research. The tool enables multiple offshore wind farm design options to be built and tested quickly with minimal effort using a Graphical User Interface (GUI). The GUI is designed to facilitate data input and presentation of the results. This thesis also develops an improved method to estimate a wind farm’s energy yield. Countries with large-scale penetration of wind farms often carry out wind energy curtailments. Prior knowledge of estimated energy curtailments from a wind farm can be advantageous to the wind farm owner. An original method to calculate potential wind energy curtailment is proposed. In order to perform wind energy curtailments a network operator needs to decide which turbines to shut down. This thesis develops a novel method to identify turbines inside a wind farm that should be prioritised for shut down and given priority when scheduling preventive maintenance of the wind farm. Once the wind farm has been built and connected to the network, it operates as part of a power system. Real-time online simulation techniques are gaining popularity among system operators. These techniques allow operators to carry out simulations using short-term forecasted wind conditions. A novel method is proposed to probabilistically estimate the power production of a wind farm in real-time, taking into account variation in wind speed and effects of turbulence inside the wind farm. Furthermore, a new probabilistic aggregation technique is proposed to establish a dynamic equivalent model of a wind farm. It determines the equivalent number and parameters of wind turbines that can be used to simulate the dynamic response of the wind farm throughout the year.