Tesi sul tema "Electric power systems"

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 103-115).
The electric power grid is recognized as an essential modern infrastructure that poses numerous canonical design and operational problems. Perhaps most critically, the inherently large scale of the power grid and similar systems necessitates fast algorithms. A particular complication distinguishing problems in power systems from those arising in other large infrastructures is the mathematical description of alternating current power flow: it is nonconvex, and thus excludes power systems from many frameworks benefiting from theoretically and practically efficient algorithms. However, advances over the past twenty years in optimization have led to broader classes possessing such algorithms, as well as procedures for transferring nonconvex problem to these classes. In this thesis, we approximate difficult problems in power systems with tractable, conic programs. First, we formulate a new type of NP-hard graph cut arising from undirected multicommodity flow networks. An eigenvalue bound in the form of the Cheeger inequality is proven, which serves as a starting point for deriving semidefinite relaxations. We next apply a lift-and-project type relaxation to transmission system planning. The approach unifies and improves upon existing models based on the DC power flow approximation, and yields new mixed-integer linear, second-order cone, and semidefinite models for the AC case. The AC models are particularly applicable to scenarios in which the DC approximation is not justified, such as the all-electric ship. Lastly, we consider distribution system reconfiguration. By making physically motivated simplifications to the DistFlow equations, we obtain mixed-integer quadratic, quadratically constrained, and second-order cone formulations, which are accurate and efficient enough for near-optimal, real-time application. We test each model on standard benchmark problems, as well as a new benchmark abstracted from a notional shipboard power system. The models accurately approximate the original formulations, while demonstrating the scalability required for application to realistic systems. Collectively, the models provide tangible new tradeoffs between computational efficiency and accuracy for fundamental problems in power systems.
by Joshua Adam Taylor.
Ph.D.

Voltage fluctuations which cause lamp flicker tend to propagate from the point of origin to various parts of a power system exhibiting some level of attenuation depending on factors such as system impedances, composition of loads and frequency components of the fluctuating waveform. Maintaining the flicker levels at various busbars below the planning limits specified by the standards is crucial, and in this regard it is important to develop an insight into the manner in which the flicker propagates via systems operating at different voltage levels. This thesis presents flicker transfer analysis methodologies applicable for radial and interconnected power systems particularly considering the influence of induction motor loads on flicker attenuation.In the first phase of the work, development of the foundations towards flicker transfer analysis methodologies is carried out by investigating the stand-alone behaviour of induction motors that are subjected to regular supply voltage fluctuations. The electrical and mechanical response of induction motors to two types of sinusoidal fluctuations in the supply voltage where (a) a positive or negative sequence sinusoidal frequency component is superimposed on the mains voltage and (b) mains voltage amplitude is sinusoidally modulated are examined. State space representation of induction motors is used to develop a linearised induction motor model describing the response of the stator current and the rotor speed to small voltage variations in the supply voltage. The results from the model reveal that various sub-synchronous and/or super-synchronous frequency components that exist in the supply voltage as small voltage perturbations can influence the dynamic response of the machine in relation to flicker. In particular, oscillations in the electromagnetic torque and rotor speed arising as a result of the applied voltage perturbations are found to be the key influencing factors controlling the stator current perturbations. It has been noted that, the speed fluctuation caused by a superimposed positive sequence voltage perturbation tends to produce extra emf components in the rotor which in turn can reflect back to the stator. This concept of multiple armature reaction has been found to be significant in large motors especially when the superimposed frequencies are closer to the fundamental frequency.The second phase of the work covers the development of systematic methods for evaluation of flicker transfer in radial and interconnected power systems taking the dynamic behaviour of induction motors into account. In relation to radial systems, small signal models are developed which can be used to establish the flicker propagation from a higher voltage level (upstream) to a lower voltage level (downstream) where induction motor loads are connected. Although this method can be applied for regular or irregular voltage fluctuations, emphasis has been given to sinusoidal voltage fluctuations arising from conventional sinusoidal amplitude modulation of upstream voltage. Moreover, the method examines the propagation of sub-synchronous and super-synchronous frequency components that exist in the supply voltage as side bands and hence determines the overall attenuation in the voltage envelope. The contribution of induction motors of different sizes and other influential factors such as system impedance, loading level of the motor are examined. It has been noted that in general higher frequency components of the upstream fluctuating voltage envelope tend to attenuate better at the downstream. A method is also presented which allows aggregation of induction motors at the load busbars in relation to flicker transfer studies.In relation to interconnected systems, a frequency domain approach which can be used to investigate the flicker transfer is presented. This approach can be considered as an extension to the impedance matrix method as described in the literature and can overcome some of the limitations of the latter method. In the proposed approach, induction motor loads are modelled in a more realistic manner to replicate their dynamic behaviour, thus enabling the examination of the frequency dependent characteristics of flicker attenuation due to induction motors and the influence of tie lines in compensating flicker at remote load busbars consisting of passive loads.To verify some of the theoretical outcomes real time voltage waveforms captured from a large arc furnace site have been used, in addition to the experimental work using a scaled down laboratory set up of a radial power system.

Thesis (M.S. in Operations Research)--Naval Postgraduate School, March 2004.
Thesis advisor(s): Javier Salmeron, R. Kevin Wood. Includes bibliographical references (p. 69-70). Also available online.

Thesis: Ph. D., Massachusetts Institute of Technology, Engineering Systems Division, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 235-240).
Scarce pipeline capacity in regions that rely on natural gas technologies for electricity generation has created volatile prices and reliability concerns. Gas-fired generation firms uniquely operate as large consumers in the gas market and large producers in the electricity market. To explore the effects of this coupling, this dissertation investigates decisions for firms that own gas-fired power plants by proposing a mixed-integer linear programming model that explicitly represents multi-year pipeline capacity commit- ments and service agreements, annual forward capacity offers, annual maintenance schedules, and daily fuel purchases and electricity generation. This dissertation's primary contributions consist of a detailed representation of a gas-fired power-plant owner's planning problem; a hierarchical application of a state-based dimensionality reduction technique to solve the hourly unit commitment problem over different tem- poral scales; a technique to evaluate a firm's forward capacity market offer, including a probabilistic approach to evaluate the risk of forced outages; a case study of New England's gas-electricity system; and an exploration of the applicability of forward capacity markets to reliability problems for other basic goods.
by Tommy Leung.
Ph. D.

Decreasing gas prices and the pressing need for fast-responding electric power generators are currently transforming natural gas networks. The intermittent operation of gas-fired plants to balance wind generation introduces spatiotemporal fluctuations of increasing gas demand. At the heart of modeling, monitoring, and control of gas networks is a set of nonlinear equations relating nodal gas injections and pressures to flows over pipelines. Given gas demands at all points of the network, the gas flow task aims at finding the rest of the physical quantities. For a tree network, the problem enjoys a closed-form solution; yet solving the equations for practical meshed networks is non-trivial. This problem is posed here as a feasibility problem involving quadratic equalities and inequalities, and is further relaxed to a convex semidefinite program (SDP) minimization. Drawing parallels to the power flow problem, the relaxation is shown to be exact if the cost function is judiciously designed using a representative set of network states. Numerical tests on a Belgian gas network corroborate the superiority of the novel method in recovering the actual gas network state over a Newton-Raphson solver. This thesis also considers the coupled infrastructures of natural gas and electric power systems. The gas and electric networks are coupled through gas-fired generators, which serve as shoulder and peaking plants for the electric power system. The optimal dispatch of coupled natural gas and electric power systems is posed as a relaxed convex minimization problem, which is solved using the feasible point pursuit (FPP) algorithm. For a decentralized solution, the alternating direction method of multipliers (ADMM) is used in collaboration with the FPP. Numerical experiments conducted on a Belgian gas network connected to the IEEE 14 bus benchmark system corroborate significant enhancements on computational efficiency compared with the centralized FPP-based approach.
Master of Science

Thesis (M.S.)--University of Missouri--Rolla, 1989.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed October 7, 2008) Includes bibliographical references (p. 89).

This thesis presents results on the dynamics and coordinated control of voltage behavior in power systems. The first part of the thesis is on dynamic modeling, with emphasis on tap-changing transformers and load dynamics. For both, highly simplified models are used in voltage stability analysis, despite the complex nature of the devices involved, i.e. tap changing operation and aggregate load. The operating conditions, under which the stability results based on these simplified models are reliable need to be clarified. A study is carried out on the influence of diiferent discrete and continuous tap models on voltage stability properties, particularly when combined with load dynamics. It has been found that small disturbance analysis, especially if based on the common continuous tap model with fixed time constant, is often an unreliable indicator of system stability. Some important differences in system responses with continuous and discrete tap models are highlighted along with the conditions under which they occur. Limit cycles are shown to characterize the system responses with discrete tap models. The limit cycles originate from the deadband nonlinearity embedded in the discrete tap operation and tap-load interactions. Describing functions for the nonlinearity of the discrete tap operation are derived and used to predict the existence of limit cycles. Furthermore, the feasibility of avoiding the limit cycles through adjusting deadband size is investigated. It has been shown that whether or not increasing deadband can always eliminate the existing limit cycle depends on the associated load dynamics. Following this, attention is given to load dynamics modeling. The focus is on use of generic dynamic load models. A simulation study is given on system behavior with generic dynamic loads as compared with the detailed physically based load models which they ap— proximate. Several simple and a more complicated load structures are considered, which include lower voltage tap changers, induction motors, thermostatically controlled heating and static load. It has been shown, for simple load structures, generic dynamic load models, if the parameters are properly identified, provide fairly accurate prediction of system stability behavior in all cases except the one with high percentage of induction motors. On the other hand, for a load structure with diverse compositions, generic dynamic load models have practically useful accuracy for representing the load. This suggests that ap— plying generic dynamic load models will be practically useful in reducing the complexity of system modeling and give reliable stability analysis results. The second part of the thesis is devoted to coordinated voltage control. A general frame work for coordinating optimally a diverse set of control actions is established. The benefit of control coordination is illustrated through a case study on coordination of capacitor switching and tap locking. By careful coordination of these controls, voltage collapse can be arrested with less overall control effort and less impact on the voltage profile than by either acting along. An analytical framework for coordinated voltage control based on coordination of dissimilar control actions is then presented. A 4-stage optimal control scheme is proposed along with detailed formulations. In the first three stages, a security constrained steady—state approach is used to define the optimal control direction for providing stability and adequate security margin. An algorithm based on differential dynamic programming based is then used to optimally schedule controls with different response time and dynamics. Finally, the dynamic sensitivity-based method is employed to refine the obtained control sequence; in terms of finding the optimal switching times for the control actions identified in earlier stages. In the final study of the thesis, application is made of the stability analysis and coordinated control techniques to a substantial physical power system, namely the New South Wales power grid. The algorithm and techniques proposed in previous chapters is tested in a more practical situation.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Begovic, Miroslav; Committee Member: Divan, Deepak; Committee Member: Harley, Ron; Committee Member: Petit, Marc; Committee Member: Verriest, Erik. Part of the SMARTech Electronic Thesis and Dissertation Collection.

De nos jours, la plupart des véhicules sont équipés de Directions Assistées Electriques (DAE). Ce type de systèmes d'aide à la conduite permet de réduire les efforts que le conducteur doit fournir pour tourner les roues. Ainsi, grâce à un moteur électrique, la DAE applique un couple additionnel en accord avec le comportement du conducteur et la dynamique du véhicule. Il est donc nécessaire de développer une commande en couple basée en particulier sur le signal provenant d'un capteur mesurant le couple agissant au niveau de la barre de torsion (correspondant à une image du couple conducteur). Ce composant est donc essentiel au fonctionnement de la DAE. Or, une défaillance de ce capteur entraine le plus souvent une coupure de l'assistance, pouvant mener à un risque d'accidents. Au regard de la sécurité fonctionnelle, un développement d'un mode de sécurité est recommandé, par de plus en plus de constructeurs automobiles. D'autre part, le marché des équipementiers automobiles reste un secteur très concurrentiel où une baisse des coûts de production est un challenge constamment recherché afin de gagner de nouvelles parts de marchés. Cet aspect de réduction du nombre de capteurs et d'analyse de la dynamique du véhicule s'inscrit donc dans le prolongement de la stratégie de sécurité. Cette thèse, menée au sein de JTEKT Europe, aborde ces divers enjeux. Après une présentation des différents systèmes de directions assistés électriques, des modèles sont présentés pour être utilisés lors de la conception de lois de commande et d'estimateurs. Ensuite deux méthodes d'estimation du couple conducteur sujet aux perturbations de la route et aux bruits de mesures sont proposées : la première est un observateur proportionnel intégral (PI) à synthèse mixte $H_infty/H_2$, et la seconde une approche par filtrage $H_infty$. Puis plusieurs stratégies de commande sont proposées suivant deux cas de figures distincts, soit en utilisant un observateur PI qui estime les états du système et le couple conducteur (LQR, commande LPV par retour d'état), soit en faisant abstraction d'estimateur de couple conducteur (commande $H_infty$ par retour de sortie dynamique). Ce dernier aspect présente l'avantage de nécessiter moins de mesures que le précédent. Ces approches ont été validées en simulation et mises en œuvre sur un véhicule prototype où des résultats prometteurs ont été obtenus
Nowadays, modern vehicles are equipped with more and more driving assistance systems, among them Electric Power Steering (EPS) helps the driver to turn the wheels. Indeed, EPS provides through an electric motor, an additional torque according to the driver's behaviour and the vehicle's dynamics to reduce the amount of effort required to the driver. Therefore, a torque control is developed based on the torque sensor signal which measures in practice the torsion bar torque (corresponding to an image of the driver torque). Consequently, this component is essential to the functioning of EPS systems.Indeed, a torque sensor failure usually leads to shut-off the assistance which may increase the risk of accident. Regarding functional safety, a back-up mode is recommended and required by more and more car manufacturers. On the other hand, a major challenge for automotive suppliers is to reduce cost production in order to meet growing markets demands and manage in the competitive sector. This issue considering a reduction of sensors' numbers and analysis of vehicle's dynamics is therefore an extension of applying the safety strategy. This thesis, carried out within JTEKT Europe, addresses these various issues.After introducing an overview of the different EPS systems, some models used for the design of controllers and estimators are presented. Then, two methods to estimate the driver torque subject to road disturbances and noise measurements are proposed: the first is a proportional integral observer (PI) with mixed synthesis $H_infty / H_2 $, whereas the second is an $ H_infty $ filtering approach. Then, several control strategies are proposed according to two different cases, either by using a PI observer which estimates the system states and the driver torque (LQR, LPV feedback control) or by not taking into account the driver torque estimation ($ H_infty $dynamic output feedback control). This latter approach has the advantage to require less measurements than the previous one. These approaches have been validated in simulation and implemented on a prototype vehicle where promising results have been obtained

Thesis (Ph. D.)--Washington State University, August 2010.
Title from PDF title page (viewed on July 23, 2010). "School of Electrical Engineering and Computer Science." Includes bibliographical references (p. 76-81).

Em muitos países, redes elétricas de grande porte são formadas pela interconexão de companhias de energia elétrica cada qual possuindo seu próprio centro de controle. Para supervisionar eficientemente tais sistemas de potência, técnicas de estimação hierarquizada de estado devem ser consideradas. Esta tese apresenta um novo algoritmo que utiliza conceitos hierárquicos para resolver o problema da estimação dinâmica de estado para sistemas de potência de grande porte em regime quase-permanente de operação. O processo de estimação é feito em dois níveis de cálculo de modo a se obter uma solução satisfatória do ponto de vista computacional para as etapas usuais da estimação dinâmica de estado: estimação dos parâmetros do modelo, previsão do estado e filtragem do estado. A nível local, algoritmos convencionais de estimação dinâmica de estado são executados simultanea e independentemente para todos os subsistemas. A coordenação dessas estimativas locais é obtida em um centro nacional de supervisão e controle, operacionalmente de hierarquia superior no sistema elétrico interligado. Resultados numéricos mostram o desempenho do algoritmo proposto em diferentes condições de operação: normal, mudança brusca do estado e presença de erros grosseiros.
In many countries, huge power networks are formed from the interconnection of electric power companies each one having its own supervisory control center. In order to supervise efficiently such power systems, hierarchical state estimation techniques have to be considered. This dissertation presents a new algorithm using hierarchical concepts to solve the dynamic state estimation problem for large-scale electric power systems operating under quasi-static conditions. A two-level calculation is performed to give a satisfactory solution from the computational point of view for the usual steps of the dynamic state estimation procedure: model parameter estimation, state prediction and state filtering. At the local level, conventional dynamic state estimation algorithms are carried out simultaneously and independently for all subsystems. The coordination of these local estimations is obtained at a national center for supervision and control, which is at the top of operational hierarchy in the interconnected electrical system. Numerical results show the performance of the proposed algorithm under different operational conditions: normal, sudden variation of states and occurrence of bad data.

In a large and dense power network, the transmission lines, the generators and the loads are considered to be continuous functions of space. The continuum technique provides a macro-scale analytical tool to gain an insight into the mechanisms by which the disturbances initiated by faults and other random events propagate in the continuum. This dissertation presents one-dimensional and two-dimensional discrete models to illustrate the propagation of electromechanical waves in a continuum system. The more realistic simulations of the non-uniform distribution of generators and boundary conditions are also studied. Numerical simulations, based on the swing equation, demonstrate electromechanical wave propagation with some interesting properties. The coefficients of reflection, reflection-free termination, and velocity of propagation are investigated from the numerical results. Discussions related to the effects of electromechanical wave propagation on protection systems are given. In addition, the simulation results are compared with field data collected by phasor measurement units, and show that the continuum technique provides a valuable tool in reproducing electromechanical transients on modern power systems. Discussions of new protection and control functions are included. A clear understanding of these and related phenomena will lead to innovative and effective countermeasures against unwanted trips by the protection systems, which can lead to system blackouts.
Ph. D.

Nowadays, in the large ships the electric propulsion solution is a viable alternative to the mechanical one. In fact, at present the latter is limited only to ships with peculiar requirements, such as the need of a high cruise speed or use of specific fuels. The use of electric propulsion, paired with progressive electrification of onboard loads, led to the birth of the All Electric Ship (AES) concept. An AES is a ship where all onboard loads (propulsion included) are electrically powered by a single power system, called Integrated Power System (IPS). The IPS is a key system in an AES, thus requiring both accurate design and management. Indeed, in AES electricity powers almost everything, highlighting the issue of guaranteeing both the proper Power Quality and Continuity of Service. The design of such a complex system has been conventionally done considering all the single components separately, to simplify the process. However, such practice leads to poor performance, integration issues, and oversizing. Moreover, the separate design procedure affects heavily system's reliability, due to the difficulty in assessing the effect on the ship of a fault in a single subsystem. For these reasons, a new design process is needed, able to consider the effect of all components and subsystems on the system, thus improving the ship design's most important drivers: efficiency, effectiveness, reliability, and cost saving. Therefore, the aim of the research has been to obtain a new design methodology, applicable to the AES’ IPS, which is able to consider the systems as a whole, with all its internal interdependencies. The results of such research are depicted in this thesis work, as a sub-process to be integrated into IPS’s design process. In this thesis, a wide review of the state of the art is done, to allow understanding the context, why such innovative process is needed, and which innovative techniques can be used as an aid in design. Each point is discussed focusing on the aim of this thesis, thus presenting topics, bibliography, and personal evaluations tailored to direct the reader to comprehend the impact of the proposed design process. In particular, after a first chapter dedicated to the introduction of All Electric Ships, in which are described how such ships have evolved, and what are the most impacting applications, a reasoned discussion on the conventional ship-design process is given in the second chapter. In addition to that, an in-depth analysis of the IPS design is done, to explain the context in which the proposed innovative design process has to be integrated. Several examples of issues coming from the conventional design process are given, to motivate the proposal of a new design process. Not only the above mentioned design issues, but also the upcoming introduction of innovative distribution systems onboard ships and the recent emergence of new requirements, whose impact on IPS is significant, are motivations calling for a new design process. Due to that, an excursus of both these two topics is given in the third chapter, referring to recent literature and research activities. Chapter four is dedicated to the description of the tools that will be used to build the innovative design process. The first part is dedicated to dependability theory, which is able to give a systematic and coherent approach to the determination of faults effects on complex systems. Through dependability theory and its techniques, it is possible: to assess the effect of single components faults on the overall system; to assess all the possible causes of a given system failure; to evaluate mathematical figures related to the system in order to compare different design solutions; and to define where the designer must intervene to improve the system. The second part of the fourth chapter is dedicated to power system’s software simulators and hardware in the loop testing. In particular, the use of such systems as an aid in designing power systems is discussed, to allow comprehending why such tools have been integrated in the innovative design process developed. The fifth chapter is dedicated to the developed design process. Discussion is presented on how such process work, how it should be integrated in ship design process, and which is the impact it have on the design. In particular, the developed procedure implies both the application of dependability theory techniques (in particular Failure Tree Analysis), and the simulation of the dynamic behavior of the power system through a mathematical model of the system tailored on electromechanical transients. Finally, to demonstrate the applicability of the proposed procedure, in chapter six a case of study has been analyzed: the IPS of a Dynamic Positioned Offshore Oil & Gas drillship. This has been done due to the stringent requirements these ships have, whose impact on power system’s design is significant. The analysis of the IPS done through the Fault Tree Analysis technique is presented (though using a simplified detail level), followed by the calculation of several dependability indexes. Such results, together with applicable rules and regulations, have been used to define the input data for simulations, carried out using a mathematical model of the IPS built on purpose. Simulations outcomes have been used in turn to evaluate the dynamic processes bringing the system from relevant faults to failure, in order to improve the system’s response to the fault events.
Oggigiorno, nelle grandi navi la propulsione elettrica è una valida alternativa a quella meccanica. Infatti, attualmente quest'ultima è limitata solo alle navi con requisiti particolari, quali la necessità di una elevata velocità di crociera o l’uso di combustibili specifici. L'uso della propulsione elettrica, in coppia con la progressiva elettrificazione dei carichi di bordo, ha portato alla nascita del concetto di All Electric Ship (AES). Una AES è una nave in cui tutti i carichi di bordo (propulsione inclusa) sono alimentati da un unico sistema elettrico, chiamato Sistema Elettrico Integrato (Integrated Power System - IPS). L'IPS è un sistema chiave in una AES, per cui richiede una progettazione ed una gestione accurata. In effetti, in una AES tale sistema alimenta quasi tutto, mettendo in evidenza il problema di garantire sia la corretta Power Quality, sia la continuità del servizio. La progettazione di un sistema così complesso viene convenzionalmente fatta considerando i singoli componenti separatamente, per semplificare il processo. Tuttavia tale pratica può portare a prestazioni ridotte, problemi di integrazione e sovradimensionamento. Come se non bastasse, la procedura di progettazione separata influisce pesantemente sull'affidabilità del sistema, a causa della difficoltà nel valutare l'effetto sulla nave di un guasto in un singolo sottosistema. Per questi motivi è necessario un nuovo processo di progettazione in grado di considerare l'effetto di tutti i componenti e sottosistemi del sistema, consentendo così di migliorare i più importanti driver applicati nella progettazione di una nave: efficienza, efficacia, affidabilità e riduzione dei costi. Date queste premesse, l'obiettivo della ricerca era di ottenere una nuova metodologia di progettazione applicabile al sistema elettrico integrato delle AES, in grado di considerare il sistema nel suo insieme, comprese tutte le sue interdipendenze interne. Il risultato di tale ricerca è descritto in questo lavoro di tesi, e consiste in un sub-processo che dovrà essere integrato nel processo di progettazione convenzionale del sistema elettrico integrato. In questa tesi viene effettuata un'ampia rassegna dello stato dell'arte, per consentire la comprensione del contesto, del perché tale processo innovativo è necessario e quali tecniche innovative possono essere utilizzate come un aiuto nella progettazione. Ogni punto è discusso concentrandosi sullo scopo di questa tesi, presentando così argomenti, bibliografia, e valutazioni personali volte ad indirizzare il lettore a comprendere l'impatto del processo di progettazione proposto. In particolare, dopo un primo capitolo dedicato all’introduzione delle AES in cui sono descritte come tali navi si sono evolute e quali sono le applicazioni più impattanti, si effettua una discussione ragionata sul processo di progettazione convenzionale delle navi, contenuta nel secondo capitolo. In aggiunta a questo viene effettuata un'analisi approfondita del processi di progettazione dell’IPS, per spiegare il contesto in cui il processo di progettazione innovativo deve essere integrato. Alcuni esempi di problemi derivanti dal processo di progettazione tradizionale sono dati, per motivare la proposta di un processo nuovo. In aggiunta ai problemi dovuti alla progettazione, altre motivazioni portano alla necessità di un rinnovato processo di progettazione, quali l'imminente introduzione di sistemi di distribuzione innovativi a bordo nave e la recente comparsa di nuovi requisiti il cui impatto sull’IPS è significativo. Per questo, un excursus su questi due temi è fatto nel terzo capitolo, con riferimento alle più recenti fonti letterarie e ricerche. Il quarto capitolo è dedicato alla descrizione degli strumenti che verranno utilizzati per costruire l'innovativo processo di progettazione. La prima parte del capitolo è dedicata alla teoria della fidatezza (dependability), in grado di dare un approccio sistematico e coerente alla determinazione degli effetti guasti sui sistemi complessi. Attraverso la teoria della fidatezza e le sue tecniche è possibile: determinare l'effetto sul sistema dei guasti ai singoli componenti; valutare tutte le possibili cause di un dato evento di avaria; valutare alcuni indici matematici relativi al sistema, al fine di confrontare diverse soluzioni progettuali; definire dove e come il progettista deve intervenire per migliorare il sistema. La seconda parte del quarto capitolo è dedicata ai software per la simulazione del comportamento dell’IPS ed ai test hardware-in-the-loop. In particolare viene discusso l'uso di tali sistemi come aiuto nella progettazione di sistemi di potenza, per permettere di comprendere perché tali strumenti sono stati integrati nel processo di progettazione sviluppato. Il quinto capitolo è dedicato al processo di progettazione sviluppato nel corso della ricerca. Viene discusso come tale processo funziona, come dovrebbe essere integrato nel processo di progettazione convenzionale, e qual è l'impatto che esso ha sulla progettazione. In particolare, la procedura sviluppata implica sia l'applicazione delle tecniche proprie della teoria della fidatezza (in particolare la Failure Tree Analysis), sia la simulazione del comportamento dinamico dell’IPS attraverso un modello matematico del sistema tarato sui transitori elettromeccanici. Infine, per dimostrare l'applicabilità della procedura proposta, nel sesto capitolo viene analizzato un caso di studio: l'IPS di una nave da perforazione offshore oil & gas dotata di posizionamento dinamico. Questo caso di studio è stato scelto a causa dei requisiti molto stringenti di questa classe di navi, il cui impatto sul progetto dell’IPS è significativo. Viene presentata l'analisi dell’IPS tramite la tecnica di Fault Tree Analysis (anche se con un livello di dettaglio semplificato), seguita dal calcolo di diversi indici di affidabilità. Tali risultati, unitamente a norme e regolamenti vigenti, sono stati utilizzati per definire i dati di input per le simulazioni, effettuate utilizzando un modello matematico dell’IPS costruito appositamente. I risultati delle simulazioni hanno consentito di valutare come il sistema dinamicamente si porta all’avaria a partire dai guasti rilevanti, e pertanto di proporre soluzioni migliorative.

The aerospace industry is currently looking at options for fulfilling the technological development targets set for the next aircraft generations. Conventional engines and aircraft architectures are now at a maturity level which makes the realisation of these targets extremely problematic. Radical solutions seem to be necessary and Electric Distributed Propulsion is the most promising concept for future aviation. Several studies showed that the viability of this novel concept depends on the implementation of a superconducting power network. The particularities of a superconducting power network are described in this study where novel components and new design conditions of these networks are highlighted. Simulink models to estimate the weight of fully superconducting machines have been developed in this research work producing a relatively conservative prediction model compared to the NASA figures which are the only reference available in the literature. A conceptual aircraft design architecture implementing a superconducting secondary electrical power system is also proposed. Depending on the size of the aircraft, and hence the electric load demand, the proposed superconducting architecture proved to be up to three times lighter than the current more electric configurations. The selection of such a configuration will also align with the general tendency towards a superconducting network for the proposed electric distributed propulsion concept. In addition, the hybrid nature of these configurations has also been explored and the potential enhanced role of energy storage mechanisms has been further investigated leading to almost weight neutral but far more flexible aircraft solutions. For the forecast timeframe battery technology seems the only viable choice in terms of energy storage options. The anticipated weight of the Lithium sulphur technology is the most promising for the proposed architectures and for the timeframe under investigation. The whole study is based on products and technologies which are expected to be available on the 2035 timeframe. However, future radical changes in energy storage technologies may be possible but the approach used in this study can be readily adapted to meet such changes.

CIVINS
Large increases in the complexity of shipboard electric loads as well as development of electric drive, integrated electric drive and pulsed power systems make manifest the present and future importance of naval electric power systems. The most crucial attribute of these systems is their ability to fulfill their function in the presence of "large-signal" perturbations. Fundamental differences between shipboard and commercial electric power systems make all but the most general nonlinear, "large-signal" stability analyses inappropriate for the design and assessment of naval electric power systems. The tightly coupled and compact nature of shipboard systems are best accommodated by composite system stability analyses. Composite system methods, based upon Lyapunov's direct method, require that each component's stability be represented by a Lyapunov function. A new Lyapunov function which is based upon coenergy is developed for 3-phase synchronous machines. This use of coenergy is generalizable to all electromechanical energy conversion devices. The coenergy-based Lyapunov function is implemented as a "stability organ" which generates waveforms at information teirninals of a "device object" in the object oriented simulation environment of WAVESIM. Single generator simulation results are used to acquire a measure of the "over sufficiency" of the coenergy-based Lyapunov function. Some means of combining the components' Lyapunov functions is necessary with composite system stability criterions. To provide the largest stability region in a Lyapunov function convective derivative space, thereby reducing "over sufficiency", a "timevariant weighted-sum" composite system criterion is developed. This criterion is implemented as a "stability demon" "device object" within the WAVESIM environment. The "stability demon" is tested through RLC circuit simulations and a two-generator simulation. The output of the "stability demon" is suitable for use within an overall system stabilising controller.

Increasing penetration of non-dispatchable renewable energy resources and greater peak power demand present growing challenges to Bulk Power System (BPS) reliability and resilience. This research investigates the use of an Internet of Things (IoT) framework for large scale Distributed Energy Resource (DER) aggregation and control to reduce energy imbalance caused by stochastic renewable generation. The aggregator developed for this research is Distributed Energy Resource Aggregation System (DERAS). DERAS comprises two AllJoyn applications written in C++. The first application is the Energy Management System (EMS), which aggregates, emulates, and controls connected DERs. The second application is the Distributed Management System (DMS), which is the interface between AllJoyn and the physical DER. The EMS runs on a cloud-based server with an allocated 8 GB of memory and an 8 thread, 2 GHz processor. Raspberry Pis host the simulated Battery Energy Storage System (BESS) or electric water heater (EWH) DMSs. Five Raspberry Pis were used to simulate 250 DMSs. The EMS used PJM's regulation control signals, RegA and RegD, to determine DERAS performance metrics. PJM is a regional transmission organization (RTO). Their regulation control signals direct power resources to negate load and generation imbalances within the BPS. DERAS's performance was measured by the EMS server resource usage, network data transfer, and signal delay. The regulation capability of aggregated DER was measured using PJM's resource performance assessment criteria. We found the use of an IoT framework for DER aggregation and control to be inadequate in the current network implementation. However, the emulated modes and aggregation response to the regulated control signal demonstrates an excellent opportunity for DER to benefit the BPS.

With rapid depletion of fossil fuels and increasing environmental concerns, the trend to capture renewable energy, especially through wind energy resources, is increasing. The doubly fed induction generator (DFIG) is the most widely used generator for wind energy conversion because of its various advantages over other types of generators. In a DFIG, the rotor is fed through back to back converters via slip rings. The converters enable the generation control. This control property can be used to support reliable operation of a grid network system. Interarea oscillation has been a major factor in limiting power transfers in interconnected power systems. Poorly damped modes can trigger oscillatory instability, potentially leading to cascading blackouts in such systems. We consider a two-area system where DFIG based wind generation is integrated with conventional synchronous generators. A simple controller is proposed for the DFIG to improve damping of interarca oscillations. To support the proposition, case studies are conducted in Matlab/Simulink. The effectiveness of the proposed controller is then analyzed by eigenvalue analysis and verified with time domain simulation results. The results show that a properly tuned controller can increase the damping of dominant oscillatory mode by nearly 5% while improving the area transfer by about 200 MW of wind power. The results further show that with the proposed control strategy, damping of dominant oscillatory mode increased by more than 10%.
North Dakota State University. Graduate School
North Dakota State University. Department of Electrical and Computer Engineering

Security analysis of a power system requires a process called contingency analysis that analyzes results from all possible single contingencies (i.e. outages) in the system. The process of contingency analysis requires the definition of a parameter that is used to monitor a certain aspect of the system, which is called a performance index. The performance index definitions used traditionally have been highly nonlinear, and the results have not accurately predicted the outcome of the performance index in some cases. These incorrect results are referred to as misrankings since the contingency results are usually placed in order of severity so that the most severe cases are evident. This thesis considers a new definition of contingency ranking using a more linearized definition of the performance index. The construction of both the new, proposed definition and the classic definition both consider the current loading of circuits in the system as compared to their rated values. Specifically, the parameter measured by the proposed definition measures the difference, while the more nonlinear definition uses a ratio of the two quantities, which is then raised to a higher power. A small, four bus test system is used to demonstrate the benefits of the new, more linearized definition. The average percent error for all single line contingencies of the system decreased by over 9.5% using the proposed definition as compared to the previous one. This decrease in error allows this performance index to monitor a similar parameter (comparing current loading and current rating of the lines) and achieve a higher degree of accuracy. Further linearization of this proposed definition also shows a reduction in the average percent error by an additional 22% so that when compared to the original, highly nonlinear definition, the average error is reduced by almost 30%. By linearizing the definition of the performance index, the results are more accurate and misrankings are less likely to occur from the security analysis process.