Dissertations / Theses on the topic 'Ship Power System'

CIVINS
Approved for public release, distribution unlimited
With the U.S. Navy's continued focus on Integrated Fight Thru Power (IFTP) there has been an ever increasing effort to ensure an electrical distribution system that maintains maximum capabilities in the event of system faults. Non-Intrusive Load Monitoring (NILM), which has been used extensively for condition based maintenance applications, could simultaneously be used to enhance the existing zonal protection system employed with Multi-Function Monitors (MFM). A test platform with three 5000 watt synchronous generators is being constructed to emulate a U.S. Navy DDG 51 FLT IIA class ship electric plant. This is being accomplished in order to evaluate the feasibility of improving the fault isolation capabilities of the MFM with NILM implementation. The first step in this endeavor will be to electrically relate the test platform to the DDG electric plant. In order to accomplish this step, the fault simulation results from the test platform will be compared to simulated faults using U.S. Navy data from DDG 51 electric plants. This will allow for the fault isolation results from the test platform to be related to the DDG 51electric plant.

Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.
Includes bibliographical references (p. 68).
With the U.S. Navy's continued focus on Integrated Fight Thru Power (IFTP) there has been an ever increasing effort to ensure an electrical distribution system that maintains maximum capabilities in the event of system faults. This is to ensure that the crew has the ability to complete real time tactical missions in the event of battle damage to any localized portions of the electrical distribution system. Fault isolation is a priority component of the U.S. Navy's Next Generation Integrated Power System (NGIPS) Roadmap, which lays out the framework as well as milestone dates for future development. Non-Intrusive Load Monitoring (NILM), which has been used extensively for condition based maintenance applications, could simultaneously be used to enhance the existing zonal protection system employed with Multi-Function Monitors (MFM). NILM may be able to, inexpensively, use the existing current and voltage sensors available from the MFM hardware to determine electrical loading which could allow for faster fault isolation capability. A test platform with three 5000 watt synchronous generators is being constructed to emulate a U.S. Navy DDG 51 FLT IIA class ship electric plant. This is being accomplished in order to evaluate the feasibility of improving the fault isolation capabilities of the MFM with NILM implementation. The first step in this endeavor will be to electrically relate the test platform to the DDG electric plant. In order to accomplish this step, the fault simulation results from the test platform will be compared to simulated faults using U.S. Navy data from DDG 51 electric plants.
(cont.) This will allow for the fault isolation results from the test platform to be related to the DDG 51 electric plant.
by Jeremy T. Leghorn.
S.M.
Nav.E.

Large marine vessels carry their loads all over the world. It can be a container ship carrying over 10 000 containers filled with foods, textiles and electronics or a bulk freighter carrying 400 000 tons of coal. Vessels usually have a ballast system that pumps water into ballast tanks to stabilize the vessel. The ballast system can be used to change the vessel’s trim and list angles. Trim and list are the ship equivalents of pitch and roll. By changing the trim angle the water resistance can be reduced and thus also the fuel consumption. Since the vessel is consuming a couple of hundred tons of fuel per day, a small reduction in fuel consumption can save a considerable amount of money, and it is good for the environment. In this thesis, the ship’s power consumption has been estimated using an artificial neural network, which is a mathematical model based on data. The name refers to certain structural similarities with the neural synapse system in animals. The idea with neural networks has been to create brain-like systems. For applications such as learning to interpret sensor data, artificial neural networks are an effective learning method. The goal is to estimate the ship power using a artificial neural network and then use it to calculate the trim angle, to be able to save fuel. The data used in the artificial neural network come from sensor systems mounted on a container ship sailing between Europe and Asia. The sensor data have been thoroughly preprocessed and this includes for example removing the parts when the ship is docked in harbour, data patching and synchronisation and outlier detection based on a Kalman filter. A physical model of a marine craft including wind, wave, hydrodynamic and hydrostatic effects, has also been introduced to help analyse the performance and behaviour of the artificial neural network. The artificial neural network developed in this thesis could successfully estimate the power consumption of the ship. Based on the developed networks it can be seen that the fuel consumption is reduced by trimming the ship by bow, i.e., the ship is angled so the bow is closer to the water line than the stern. The method introduced here could also be applied on other marine vessels, such as bulk freighters or tank ships.

Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, December 2001.
Thesis advisor(s): Ciezki, John G. ; Ashton, Robert W. "December 2001." Includes bibliographical references (p. 201-202). Also available in print.

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.

This Master of Science thesis was written based on the shipbuilder Kockums AB feasibility study regarding the development of an All- Electric Ship for the Swedish Navy. The thesis was aiming at addressing voltage stability issues in a dc system fed by PWM rectifiers operating in parallel when supplying constant power loads. A basic computer model was developed for investigating the influence from various parameters on the system. It was shown that the voltage stability is dependent upon the ability to store energy in large capacitors. It was also shown that a voltage droop must be implemented maintaining load sharing within acceptable limits. Different cases of operation were modelled, faults were discussed, and the principal behaviour of the system during a short-circuit was investigated. It was shown that the short-circuit current is much more limited in this type of system in comparison to an ac system. It was concluded that more research and development regarding the components of the system must be performed.

This doctoral thesis presents new ideas and research results on control of marine electric power system.

The main motivation for this work is the development of a control system, power management system (PMS) capable to improve the system robustness to blackout, handle major power system faults, minimize the operational cost and keep the power system machinery components under minimal stress in all operational conditions.

Today, the electric marine power system tends to have more system functionality implemented in integrated automation systems. The present state of the art type of tools and methods for analyzing marine power systems do only to a limited extent utilize the increased knowledge available within each of the mechanical and electrical engineering disciplines.

As the propulsion system is typically consisted of the largest consumers on the vessel, important interactions exists between the PMS and vessel propulsion system. These are interacted through the dynamic positioning (DP) controller, thrust allocation algorithm, local thruster controllers, generators' local frequency and voltage controllers. The PMS interacts with the propulsion system through the following main functions: available power static load control, load rate limiting control and blackout prevention control (i.e. fast load reduction). These functions serve to prevent the blackout and to ensure that the vessel will always have enough power.

The PMS interacts with other control systems in order to prevent a blackout and to minimize operational costs. The possibilities to maximize the performance of the vessel, increase the robustness to faults and decrease a component wear-out rate are mainly addressed locally for the individual control systems. The solutions are mainly implicative (for e.g. local thruster control, or DP thrust allocation), and attention has not been given on the interaction between these systems, the power system and PMS. Some of the questions that may arise regarding the system interactions, are as follows: how the PMS functionality may affect a local thruster control, how the local thruster control may affect the power system performance, how some consumers may affect the power system performance in normal operations and thus affect other consumers, how the power system operation may affect the susceptibility to faults and blackout, how various operating and weather conditions may affect the power system performance and thus propulsion performance though the PMS power limiting control, how propulsion performance may affect the overall vessel performance, which kind of faults can be avoided if the control system is re-structured, how to minimize the operational costs and to deal with the conflicting goals. This PhD thesis aims to provide answers to such questions.

The main contributions of this PhD thesis are:

− A new observer-based fast load reduction system for the blackout prevention control has been proposed. When compared to the existing fast load reduction systems, the proposed controller gives much faster blackout detection rate, high reliability in the detection and faster and more precise load reduction (within 150 miliseconds).

− New advanced energy management control strategies for reductions in the operational costs and improved fuel economy of the vessel.

− Load limiting controllers for the reduction of thruster wear-out rate. These controllers are based on the probability of torque loss, real-time torque loss and the thruster shaft

accelerations. The controllers provide means of redistributing thrust from load fluctuating thrusters to less load fluctuating ones, and may operate independently of the thrust allocation system. Another solution is also proposed where the load limiting controller based on thrust losses is an integrated part of DP thrust allocation algorithm.

− A new concept of totally integrated thrust allocation system, local thruster control and power system. These systems are integrated through PMS functionality which is contained within each thruster PLC, thereby distributed among individual controllers, and independent of the communications and dedicated controllers.

− Observer-based inertial controller and direct torque-loss controller (soft anti-spin controller) with particular attention to the control of machine wear-out rate. These controller contribute to general shaft speed control of electrical thrusters, generators and main propulsion prime movers.

The proposed controllers, estimators and concepts are demonstrated through time-domain simulations performed in MATLAB/SIMULINK. The selected data are typical for the required applications and may differ slightly for the presented cases.

Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. [100]-102).
Although propulsion and electric power systems selection is an important part of naval ship design, respective decisions often have to be made without detailed ship knowledge (resistance, propulsors, etc.). Propulsion and electric power systems have always had to satisfy speed and ship-service power requirements. Nowadays, increasing fuel costs are moving such decisions towards more fuel-efficient solutions. Unlike commercial ships, naval ships operate in a variety of speeds and electric loads, making fuel consumption optimization challenging. This thesis develops a flexible decision support tool in Matlab® environment, which identifies the propulsion and ship-service power generation systems configuration that minimizes fuel consumption for any ship based on its operating profile. Mechanical-driven propulsion systems with or without propulsion derived ship-service power generation, separate ship-service systems and integrated power systems are analyzed. Modeling includes hull resistance using the Holtrop-Mennen method requiring only basic hull geometry information, propeller efficiencies using the Wageningen B series and transmission and prime movers fuel efficiencies. Propulsion and ship-service power generation systems configuration is optimized using the genetic algorithm. US Navy's Advanced Surface Ship Evaluation Tool (ASSET) model for the DDG-51 Flight I destroyer was used for modeling validation. Optimal fuel consumption results are compared against the existing configuration for the DDG-51 Flight I destroyer using a representative operating profile.
by Emmanouil Sarris.
S.M.in Engineering and Management
Nav.E.

This work aims at providing a comprehensive and, as far as possible, standard and widely supported approach to a dependable design of all electric ship integrated power systems. The proposed approach is based upon latest development of dependability theory made recently available, from its founding lexicon and taxonomy to investigation tools and relevant international rules. In its first part, this work analyses present rule requirements governing the discipline of designing an integrated power system serving an all electric ship. Analysis covers system definitions (what is what) in terms of taxonomy and associated concepts; system required performances both in terms of delivered services and in terms of reaction to anticipated reactions to predetermined fault scenarios. In its second part, this work briefly presents latest developments in the theory and in the tools theory brings along: lexicon, taxonomy, system analysis, benchmarking and enforcing techniques. During this development, emphasis is posed on the fact that design documentation, be it owners’ technical specification, classification society rule book or international standard, often recall dependability concepts, without fully exploiting the potential theory is promising, or the completeness of its definition corpus. In its third part, this work applies dependability concepts to a real case scenario, an integrated power system installed on a recent cruise ship vessel. This application, albeit suffering from an important lack of information, due to copyrighting and industrial intellectual property rights, produces an informative example on the enquiring method and relevant deliverable: a system model, obtained in a strongly standardized way that permits a comprehensive and accurate dependability study, to be realized using tools and techniques defined in international standard. Results of this analysis are, as a consequence of method strong structure, repeatable and consistent, and allow quick verification of requirements. Analysis results, even though partial and superficial owing to already mentioned lack of accurate information, are offering some original view points. They are commented and classified according to indexes defined earlier. In its fourth part, this works presents proposals to be applied to systems which exhibited low values of indexes. Such proposals are briefly analyzed in terms of index value variations; in doing this a quantification of improvement that could be obtained is given. Finally, in its fifth part, this work shortly presents future research directions to improve investigation method. This work reports elements of project management and maritime law as well, this in force of the multidisciplinary nature of dependability theory, and its repercussion on different sector of the marine industry, besides engineering. It is show how present method can fit the actual engineering process, and can provide a common language serving as substrate for various disciplines, like the ones mentioned.
Questo lavoro si prefigge lo scopo di definire in maniera quanto piu’ possibile standardizzata e definita nel corpus delle regole internazionali la disciplina della progettazione volta alla fidatezza di impianti integrati di produzione, distribuzione ed utilizzo dell’energia elettrical a bordo di navi a propulsione elettrica. L’approccio proposto si fonda nei piu’ recenti sviluppi della teoria della fidatezza, che coinvolgono il lessico, la tassonomia, fino agli strumenti di analisi e di quantificazione degli attributi. Tali sviluppi sono al vaglio della comunita’ internazionale, ma gia’ un importante consenso e’ stato raggiunto. La prima parte contiene un’analisi dettagliata dello stato normativo attualmente in vigore che disciplina la progettazione di un impianto elettrico integrato. I documenti normativi analizzati sono principalmente: la specifica tecnica armatoriale, i regolamenti delle societa’ di classifica ed il corpus di regole degli enti internazionali. L’analisi si concentra sulla definizione dei sistemi, sia dal punto di vista tassonomico, funzionale e di requisiti in termini di reazione ad un predefinito insieme di condizioni di guasto. La seconda parte riporta un breve sunto della teoria della fidatezza, nella sua piu’ recente definizione. Si fa accenno al lessico, definito in maniera stringente, alla tassonomia ed alle tecniche di analisi e di sintesi della fidatezza. In questo contesto si attira l’attenzione sul fatto che i documenti analizzati nella parte precedente fanno sovente riferimento agli elementi della teoria della fidatezza, senza pero’ considerarne appieno il significato e le ricadute che la teoria offre. La teoria funge da substrato che integra la documentazione, altrimenti frammentaria e priva della necessaria precisione, in un unico insieme autocontenuto. La terza parte riporta un’applicazione dei concetti analizzati nella prima parte, rielaborati alla luce di quanto discusso nella seconda, ad un caso pratico: un impianto elettrico integrato di una nave da crociera di recente costruzione. L’applicazione, pur soffrendo di una importante mancanza d’informazioni, dovuta a vincoli di copyright e di protezione del know how aziendale, ha evidenziato la struttura del metodo e la sua esaustivita’. Il risultato dell’applicazione e’ un modello che permette lo studio preventivo della fidatezza del sistema in fase di progettazione e il rapido controllo del rispetto dei limiti imposti in termini di reazione ai guasti previsti dalle norme. Nonostante i vincoli posti, il modello ed il relativo sistema di indagine hanno offerto spunti interessanti ed innovativi rispetto a componenti il cui comportamento in caso di guasto era stato erroneamente trascurato. La quarta parte riprende i risultati ottenuti nella terza, ed offre implemetazioni alternative volte ad ottenere una maggiore fidatezza. Il raggiungimento di una maggiore fidatezza e’ vincolato al calcolo del relativo indice pertinente alla nuova proposta. In tal guisa il metodo offre la possibilita’ di comparare diverse archietture e di classificarle secondo un criterio univoco, ossia il valore dell’indice di fidatezza scelto. La quinta parte, infine, offre spunti per indirizzare la ricerca futura. L’analisi dei sistemi e dei loro requisiti ha reso evidente la necessita’ di muoversi su diversi fronti: dalla definizione sempre piu’ stringente ed esaustiva dei termini, inseriti nel loro contesto, allo sviluppo di nuovi componenti atti a svolgere un servizio piu’ completo, per quanto riguarda certi aspetti della loro fidatezza (rilevabilita’). Il lavoro riporta alcuni elementi di gestione dei progetti e di legislazione marittima che sono parte intergrante dell’ambiente in cui il progetto dei sistemi elettrici integrati si sviluppa. Cio’ e’ dovuto al fatto che la fidatezza e’ un insieme di attributi e qualita’ che travalica la pura ingegneria, ma sconfina nel campo della legislazione, dell’assicurazione dei rischi e financo nella gestione dei progretti. Si crede che il contesto creato dall’analisi di fidatezza possa costituire un comune sostrato per l’interazione di molteplici discipline, quali appunto la gestione di progetti, la legislazione e la gestione del rischio, tendente a favorire il dialogo e la reciproca comprensione.

This work discusses the implementation of a Unique Ships Grid design that utilizes Energy Storage. This Unique Ships Grid is used to enhance the efficiency of a Construction Single-Hull River Tender previously discussed and assessed by the Army Corps of Engineers and the United States Coast Guard (USCG). This Grid Design is shown to be both in compliance with applicable regulations and reliable due to built-in redundancy. Compliance with regulations and redundancy are both prized by the Maritime Community and the USCG. An applicable Heuristic Design Methodology is provided in conjunction with the Unique Ships Grid. This Design Methodology can be used with a simple load analysis and results in a Load Center breakdown and the sizing of Cables, Generators, Inverter, and required Energy Storage. This design process is shown to provide an inherent margin for growth and safety. This design process is quick and results in values necessary to do a cost analysis, environmental impact survey, and stability analysis (Ship Stability not Electrical Stability).
Master of Science

The Medium Voltage Direct Current (MVDC) distribution represents a promising technology for future shipboard power systems. In such a topic, during the last years, universities and reserch centers have proposed technical solutions to achieve the important targets of MVDC technology, for instance fuel saving, reducing power system weight/space, reconfigurability in case of fault and enhanced power quality. Conversely, the main challenge to face regards voltage control, which has to be capable for guaranteeing the paramount requirement of stability. In regards to this aspect, a possible instability may arise due to the presence of high-bandwidth controlled load converters, modeled as Constant Power Loads (CPLs). Such non-linear loads are seen from the system as negative incremental resistances which are the cause of voltage instability in presence of a perturbation (e.g. load connection, generating system disconnection). The thesis has been realized in the Laboratory of Grid Connected and Marine Electric Power Generation and Control (EPGC Lab.), at the University of Trieste. The aim is to develop voltage control strategies to solve the CPL issue in a realistic multi-converter MVDC Integrated Power System, which is conveniently designed considering a real cruise line MVAC distribution. In such a system, voltage instability may be engage by different approaches, exploiting plant solutions (addition of dedicated filters, addition of energy storage devices) or control solutions. The latter is followed in this thesis: in this case voltage actuators (DC/DC power converters) are used to compensate for the voltage instability: therefore, on one hand (load side) power converters are responsible for the non-linear loads’ issue but, on the other (generators side), they may be utilized to contribute in its solution, thus ensuring a stable behavior. The stabilizing approach foresees the employment of different control techniques, whose theory is focused in the thesis. Starting from the simplier State Feedback (SF), two techniques are mostly studied in the multi-converter arrangement, i.e the Active Damping (AD) and the Linearization via State Feedback (LSF). The AD is a control method to transiently increase the filter resistances in order to damp the voltage oscillations: one of the main pros is the simple implementation on digital controllers, whereas the drawback regards its limited stabilizing action. Therefore, strategies based on Active Damping are to be used to stabilize non-critical systems. Conversely, LSF is a well-performing technique to obtain a notable cancellation of the non-linearities related to CPLs, by exploiting the DC/DC converters to apply a proper non-linear control function. Against the notable capability in stabilizing critical systems, great attention is to be paid in control function’s estimation: inaccurate system parameters or errors in controller’ feedbacks may invalidate the LSF approach, determining a partial loop-cancellation, therefore a non-linear resulting power system. Final simulations are aimed in testing AD and LSF, implemented in global and local control strategies: the former strategy has the purpose to solve the instability directly on CPLs, whereas the second one ensures the bus stability.
La distribuzione in media tensione continua (Medium Voltage Direct Current, MVDC) rappresenta una tecnologia promettente per i sistemi elettrici navali del futuro. A tal riguardo, negli ultimi anni, università e centri di ricerca hanno proposto soluzioni tecniche tali da raggiungere gli obiettivi propri della tecnologia MVDC: fra gli altri, risparmio di carburante, riduzione del peso/ingombro dell’impianto elettrico, riconfigurabilità a fronte di guasti e miglioramento della power quality. D’altra parte, la più grande sfida da affrontare riguarda la regolazione della tensione che deve risultare in grado di garantire il requisito fondamentale della stabilità. Relativamente a questo aspetto, una possibile instabilità si manifesta in presenza di convertitori di carico a banda elevata, modellizzabili come carichi a potenza costante (Constant Power Loads, CPLs). Tali carichi non-lineari vengono visti dal sistema come resistenze incrementali negative, le quali rappresentano la causa dell’instabilità della tensione a fronte di un disturbo (per esempio connessione di carico, disconnessione di un sistema di genenerazione). La tesi è stata realizzata presso il Laboratorio Grid Connected and Marine Electric Power Generation and Control (EPGC Lab.), presso l’Università degli Studi di Trieste. Lo scopo è quello di sviluppare strategie per il controllo della tensione in grado di risolvere la questione CPL, considerando un possibile impianto elettrico integrato (multi-convertitore) in MVDC, convenientemente progettato a partire dalla distribuzione reale MVAC di una nave da crociera. Nel sistema visto, l’instabilità di tensione può essere affrontata secondo diversi approcci, sfruttando soluzioni impiantistiche (aggiunta di filtraggio dedicato, aggiunta di energy storage) oppure soluzioni controllistiche. Il secondo approccio è quello seguito nella presente tesi: gli attuatori di tensione (convertitori DC/DC) vengono usati in questo caso per compensare l’instabilità di tensione. Quindi, da una parte (lato carico) i convertitori sono responsabili del problema dei carichi non-lineari, dall’altro (lato generatori) possono essere utilizzati per contribuire alla sua soluzione, garantendo un comportamento stabile. L’approccio stabilizzante previsto prevede l’utilizzo di diverse tecniche di controllo, analizzate nella tesi dal punto di vista teorico. A partire dalla tecnica semplice State Feedback (SF), altre due tecniche sono state studiate per il caso di sistema multi-converter, ovvero l’Active Damping (AD) e il Linearization via State Feedback (LSF). L’AD è un metodo di controllo per incrementare transitorialmente la resistenza dei filtri, in modo tale da smorzare le oscillazioni di tensione: uno dei principali vantaggi è quello relativo alla semplice ingegnerizzazione su controllori digitali, mentre lo svantaggio riguarda la limitata azione stabilizzante. Pertanto, strategie basate sull’AD devono considerarsi valide per stabilizzare sistemi non critici. D’altra parte, LSF è una tecnica molto valida per ottenere una buona cancellazione delle non-linearità dei CPL, per mezzo dell’azione di convertitori DC/DC in grado di applicare un’opportuna funzione di controllo non-lineare. A fronte di una notevole capacità nello stabilizzare sistemi critici, grande attenzione va posta nella stima della funzione di controllo: conoscenza inaccurata dei parametri o errori nei feedback ai controllori possono invalidare l’approccio LSF, causando una parziale cancellazione, quindi un sistema risultante non-lineare. Le simulazioni finali hanno lo scopo di testare le tecniche AD e LSF, implementate in strategie di controllo locale e globale: la prima strategia ha lo scopo di risolvere l’instabilità direttamente sui CPL, mentre la seconda assicura la stabilità del bus.

The ever-growing intercontinental maritime trade and transporthave identified the need for the ship and passengerssafety, energy efficiency and environmental pollution to be considered as dominant issues within shipping industry and academia. Recently introduced safety regulations, known as Safe-Return-to-Port, and ‘green’ regulations, by the IMO, came into force to address and, indirectly, couple the above objectives through the enforcement of specific safety performance requirements of ship systems after a casualty and mandatory environmental measures for GHG emissions limitation, for the former and the latter regulations respectively. This thesis focus is on improving the safety and the energy efficiency of ships during design and operation by adopting approaches assessing the safety critical systems availability at emergencies and estimating performance requirements of electrical energy onboard ships over their life cycle. Through the adoption of methodologies successfully applied in damage stability, the probabilistic assessment of systems safety is employed with the logical modelling of the system into the ship environment and the application of statistical flooding damages to be initiated. Critical zones for the systems location are investigated with topological and geometrical optimisation to be performed identifying ‘enhanced-availability areas’ onboard targeting, also,the components redundancies reduction. First principles were introduced for the numerical modelling of the electrical energy systems onboard aiming to evaluate the energy performance of the ship. However, the great number of input parameters and computational problems shown up during the systems development, especially for larger vessels such as passenger, triggered necessary simplification considerations for the design. Investigation was considered for the identification of the key design parameters, with a verification process based on energy simulations to have been used for constructing guidelines and indicating acceptable assumptions. Investigation results were used for the systems optimisation in energy efficiency and cost perspectives during the design through the development of the Power Management System, with the latter’s functionality to be extended also during operation aiming fuel consumption minimisation. The amount of consumed fuel were quantified for both case, and results were used to create design and operation guidelines for power generation sets sizing and loading respectively. All findings were used to form methodology for the design of the electrical energy systems aiming to increase the energy efficiency through the appropriate sizing of the power generation sets and also, for the case of passenger vessels, to increase systems safety through the optimisation of their onboard location. Implementation of the methodology was exhibited with two case studies, one for a cargo and one for a passenger ship. The work undertaken and the derived results clearly demonstrate the applicability of probabilistic assessment for the quantification of systems availability post-casualty not only for rules compliance but also for the increased results accuracy and the integration to ship survivability concept. In addition, the introduction of Dynamic Energy Modelling concept as a platform in shipping to support life-cycle energy management were concluded through the electrical energy systems simulations during operation and design considering simplification during the latter’s process. Those concepts could be applied under the multi-objective optimisation platform in order to explore the whole design space concerning systems common parameters. All these constitute significant developments in shipping.

The ship emission already occupy the eighth position in the world biggest emitters ranking. This happens because the ship operations have a huge demand variation therefore in order to reduce the ship emissions is required an efficient operation of the generators. This work aims at integrating advanced storage systems into the operation of diesel generators. The variation of the operation point has a direct interference on the emissions and on the diesel consumption, this variation is allowed through the frequency and voltage control. The use of lithium batteries for various operation points of the generators is analyzed. The use of an energy storage system allowed the operation of the generators in a better operation point therefore there was a reduction in diesel consumption and in CO2 emissions when the diesel generators. The main result of this work could also shed light in the operation of isolated power systems equipped with advanced storage systems and diesel generators.
As emissões dos navios já ocupam a oitava posição entre os países com maior emissão no mundo. Isso pode ser explicado pelo fato de que as operações dos navios têm uma grande variação de demanda de potência, com isso a operação inteligente dos geradores a diesel é fundamental para a redução das emissões. A abordagem desenvolvida nesse trabalho integra o uso de sistemas de armazenamento avançados na operação dos geradores a diesel. A variação do ponto de operação dos geradores a diesel interfere diretamente no consumo e nas emissões, essa variação só é possível por meio do controle de frequência e tensão providos pelo sistema de armazenamento de energia. Nesse trabalho foram analisados o uso de baterias de lítio para diferentes pontos de operação do gerador a diesel. O uso das baterias possibilitou a operação dos geradores num melhor ponto de carga com isso houve uma redução das emissões e do consumo de combustível. Os resultados encontrados nesse trabalho podem ser extrapolados qualitativamente para outros sistemas de potência offshore, como plataformas de petróleo e de perfuração, que operem com sistemas de baterias avançadas e geradores a diesel.

A study into the environmental impact of marine power systems was performed in proximity with the defined research objectives: (i) present an overview on Annex VI The International Convention for the Prevention of Pollution from Ships, cargo ships, marine power systems and technologies; (ii) review life cycle assessment (LCA) methodology development; (iii) develop an LCA framework for marine power systems; (iv) carry out case studies to determine environmental impact, significant components and critical processes; (v) apply scenario analysis to investigate the sensitivity of the results to selected parameters; and (vi) compare power systems under study to verify their environmental benefits. Built upon literature and the proposed LCA framework, LCA case studies on conventional, retrofit and new-build power systems were performed using a bottom-up integrated system approach, where data were gathered and LCA models were created for individual technologies using GaBi software. Life cycle impact assessment was performed using CML2001, International Reference Life Cycle Data System (ILCD) and Eco-Indicator99 to estimate the environmental impact of the systems. It was found that disposing metal scrap of significant components was the principal cause of ecotoxicity potential, which was the impact category that showed the top two highest indicator results; and operating diesel engines and auxiliary generators or diesel gensets was mainly accounted for other impact categories. When compared with the conventional system, both retrofit and new-build systems consumed less fuels and released less emissions during operation but involved more materials and energy during other life cycle phases, leading to a decline in most impact categories to the detriment of a few burdens. The life cycle of marine power systems must be planned, managed and monitored appropriately for reduced environmental implications. Further research should address limitations presented in this study and explore other factors that might affect the environmental burdens of marine power systems.

Power electronics applications in high power are normally large, expensive, spatially distributed systems. These systems are typically complex and have multiple functions. Due to these properties, the control algorithm and its implementation are challenging, and a different approach is needed to avoid customized solutions to every application while still having reliable sensor measurements and converter communication and control.

This thesis proposes a synchronous digital control architecture that allows for the communication and control of devices via a fiber optic communication ring using digital technology. The proposed control architecture is a multidisciplinary approach consisting of concepts from several areas of electrical engineering. A review of the state of the art is presented in Chapter 2 in the areas of power electronics, fieldbus control networks, and digital design. A universal controller is proposed as a solution to the hardware independent control of these converters. Chapter 3 discusses how the controller was specified, designed, implemented, and tested. The power level specific hardware is implemented in modules referred to as hardware managers. A design for a hardware manager was previously implemented and tested. Based on these results and experiences, an improved hardware manager is specified in Chapter 4. A fault tolerant communication protocol is specified in Chapter 5. This protocol is an improvement on a previous version of the protocol, adding benefits of improved synchronization, multimaster support, fault tolerant structure with support for hot-swapping, live insertion and removals, a variable ring structure, and a new network based clock concept for greater flexibility and control. Chapter 6 provides a system demonstration, verifying the components work in configurations involving combinations of controllers and hardware managers to form applications. Chapter 7 is the conclusion. VHDL code is included for the controller, the hardware manager, and the protocol. Schematics and manufacturing specifications are included for the controller.
Master of Science

Thesis (M.S. in Systems Engineering Management)--Naval Postgraduate School, March 2005.
Thesis Advisor(s): Scott Carlson, Benjamin Roberts. Includes bibliographical references (p. 145-152) Also available online.

In this work, the data analysis of oscillating flapping fins is conducted for mathematical model. Data points of heave and surge force obtained by the CFD (Computational Fluid Dynamics) for different geometrical kinds of flapping fins. The fin undergoes a combination of vertical and angular oscillatory motion, while travelling at constant forward speed. The surge thrust and heave lift are generated by the combined motion of the flapping fins, especially due to the carrier vehicle’s heave and pitch motion will be investigated to acquire system identification with CFD data available while the fin pitching motion is selected as a function of fin vertical motion and it is imposed by an external mechanism. The data series applied to model unsteady lifting flow around the system will be employed to develop an optimization algorithm to establish an approximation transfer function model for heave force and obtain a predicting black box system with nonlinear theory for surge force with fin motion control synthesis.

Nowadays a regulatory framework regarding the pollutant emissions abatement, both at international and local level, significantly interests the maritime sector. To comply with the latest environmental rules, a new approach to ship design and a renewed way to operate the ship are need both in navigation and in harbour. This PhD Thesis aims to investigate on the positive features offered by the LNG fuel, more eco-friendly than the traditional marine fuel oils. In the first part of the research, the performance comparison between two marine engines, fuelled by natural gas and diesel oil respectively is reported. Two different simulation codes, one for each engine, validated by means of geometrical and performance data provided by the manufacturer have been developed to extend the comparison to the whole working area of the examined engines. In the second part of the research, a LNG-repowering study of a cruise ferry is presented. The study is enhanced by the investigation on possible Waste Heat Recovery (WHR) systems aiming at the reduction of Green House Gas (GHG), pollution, and money saving. A computational code has been developed to carry out the sizing and to analyse the energetic performance and economical aspects of the several examined WHR layout systems. The more eco-friendly layout for the considered ship is proposed to comply with in force rules. The third part of the PhD Thesis is focused on studying some maritime technical solutions for the electric energy generation and delivery to ships moored in port, by means of LNG fuelled generators installed on board a floating unit. Two different scenarios, regarding the LNG supply chain, are considered and some options for producing cleaner electric energy are then investigated. The reference area examined in this study is the old port of Genoa, where the traffic of both passenger and cargo ships takes place. The analysis is carried out by means of a MATLAB numerical code to calculate the most important features of the floating unit, as dimensions and weights and the most significant characteristics of the electric generation equipment, as the average load factor, fuel consumption and energy cost. From an economical point of view, the externalities costs abatement, thanks to the technical solution proposed are investigated. The study also focuses on the estimation of governmental incentives to promote and sustain the use of the proposed power supply barge, resulting into a fully positive technical solution.

Nowadays electric propulsion has become a valid alternative to mechanical propulsion for large ships that require high speed. The electric propulsion advantages are well known and widely documented in the literature: higher dynamic performance of the electric propulsion motors; internal combustion engines separation from shafts; increased flexibility in space/zones subdivision; increased efficiency through the modulation of number of running generators; noise and vibration reduction; increasing in automation, with a consequent crew reduction. The use of electric propulsion along with the progressive increase, in number and power, in electrical loads used for ship services, led to the development of the All Electric Ship (AES) concept. Over the last years, the All Electric Ships (AESs) concept has begun to be adopted by the most important Navies, principally by the U.S. Navy, giving a boost to the technological research. An AES is a ship where all onboard electrical loads (including propulsion) are powered by a single electrical system, called Integrated Electrical System (IPS). The IPS requires careful design and management in order to ensure both high Power Quality standard and the continuity of the service. With the technological progress, the shipboard electrical systems have changed considerably, rising from few MW of installed power to values of the order of hundred MW, both in cruises and military ships. Especially in military vessels, considering the number of special devices that are present on board (weapon systems, communication equipment, radar, sonar, and missile guidance systems), a performing and reliable electrical systems is required. Moreover, it is necessary to notice that some of the new electrical pulsed loads specific to military applications (e.g. radar, electromagnetic launchers, etc.) together with electric drives for propulsion engines can cause strong disturbances to the system, thus causing the malfunction of other electric utilities that may endanger the continuity of the service. The penetration of power electronics converters is the main issue for the contribution of harmonic distortion in AC grids, which must be limited not to increase system power losses, and to allow the correct operation of system and user devices. Standards dictate the maximum admissible values of the total voltage harmonic distortion and of the individual harmonics amplitudes, as a function of the rated system voltage. The relatively limited short-circuit power available on board also exposes the IPS to significant voltage sags and flickers caused by switching and/or intermittent loads. In this scenario, DC electrical distribution systems can be very attractive, thanks to their intrinsic immunity to harmonic problems. If DC micro-grids are interfaced to AC networks by means of Front End Converters (FECs), both AC/DC grid decoupling and considerable AC-side harmonic distortion reduction can be achieved. In addition, they simplify the power supply of converter-fed loads and the interfacing of storage systems. The latter can perform several tasks, including ensuring power supply in case of AC grid loss, peak-shaving and levelling pulsating loads further improving both the quality and the continuity of supply to DC islands loads. In the light of the above, it is evident that the electric power system is of primary importance for a modern ship. Moreover, if high-performance is required, careful analysis of the disturbances in the power system is mandatory. In fact, in order to achieve a reliable and performing power system, together with a high-Power Quality, it is necessary to assess this situation and propose guidelines to be observed for the solution of various problems. The definition and evaluation of possible IPS architectures should take into account AC/DC protection devices in order to carry out an integrated analysis of the system. Different MVAC/MVDC electrical distribution layouts coupling with all-electric or hybrid propulsion (electric/diesel/gas turbine) needs to be accurately investigated to show its advantages in terms of reliability, safety and quality of power. The thesis focusses on the Naval Smart Grid (NaSG) research project completed in partnership with the University of Trieste and the Polytechnic University of Milan. The aim of the research is to produce useful results for the design of a new ship, equipped with the following innovative features: modular power system; subsystem flexible integration; efficiency improvement; security improvement; new weapon systems; survivability improvement and high Power Quality standard. The main focus was the study of methodologies/solutions able to improve and define the onboard Power Quality (PQ). The research project reports Power Quality analysis about aspects of continuity of service, harmonic disturbances, pulsed power loads impact on the system, electromechanical transient evaluation and use of power and energy storage systems. An exhaustive investigation was carried out on system architectures in frequency domain to identify resonances and non-linear loads to detect disturbance frequencies. Moreover, the guidelines for the correct coordination of all the elements of the power system design affecting system performance (protections, converters, control systems, energy storage systems, etc.) are reported. A brief abstract for each Chapter is reported. Chapter 1 and 2 - Overview of Electrical Naval Systems and Integrated Power System in Military Ships The chapter reports the complete state of the art on naval electrical system and a brief description of naval classification, showing technological improvements and historical evolution. Details about electric propulsion, electrical generation on board, energy distribution and network layout are carried out. A complete description of the main IPS military ships with their own architecture and features is reported. Chapter 3 - Methodologies for Harmonic Disturbances Analysis and Power Quality (Service Continuity) In the field of Power quality (harmonic content, asymmetries, voltage sags, power factor), methodologies applied for the analysis/detection of harmonic disturbances are reported with an overview of electrical systems dependability in order to evaluate the service continuity of the system. Harmonic distortion could affect equipment on shipboard causing its outages, consequently, in an island system, power distribution network should ensure high re-configurability after faults, damage or untimely switch off. However, the increased interest in system’s safety and resilience generates, in turn, an increase in design burden necessary to analyze the consequences of faults and demonstrate the system’s compliance with the relevant regulations. The chapter presents the models and calculation code used for simulation activities. A Simulink model for time domain analysis and for time varying non-linear load, as well as a Fortran model for harmonic domain are described. Chapter 4 and 5 - Characterization of a military aircraft carrier and Aircraft Cavour – Measurement campaign A measurement campaign onboard the ship Cavour was carried out with the aim to characterize the relevant electric loads on board military vessel and to validate the models of the system’s components to be used. The analysis of data collected, allows to model the behavior of loads in terms of time and frequency domains, thus permitting their use for the required studies. Some specific electrical loads, such as new electrically pulsed loads specific for military applications (e.g. radar, electromagnetic launchers, etc.) with high distorted current absorption were identified. Their characterization was carried out in order to define their contribution to harmonic disturbances and their impact on the network. A model validation based on a measurement campaign is carried out. Chapter 6 - A New layout for an Integrated Power System Naval Unit-All Electric/Hybrid Different IPS architectures are defined: a full MVAC (Medium Voltage Alternate Current) power system, a hybrid MVAC plus MVDC/LVDC islands (Medium/Low Voltage Direct Current) and a MVAC 50-60 Hz, with a hybrid (electric/diesel/gas turbine) propulsion. In the architecture of the latter, the power of the installed engines is much lower than the first two cases. Chapter 7 - Network Equivalents in Harmonic Domain The needs to easily represent a complex network with high accuracy, lead to the development of a methodology based on aggregation of loads, creating a simplified network to carry out harmonic analysis. Different equivalent network models have been proposed that show their accuracy, through network impedances, and compare them with the overall representation of the network. The influence of cables was also studied. The best radial equivalent network was identified. Chapter 8 - Harmonic Analysis In order to propose appropriate solutions designed to improve power quality, the study of system impedance and power systems in frequency domain were studied. This analysis, carried out on the basis of the schematics and data load obtained in cooperation with the IT Navy, revealed some criticalities in the frequency range for both the systems architectures. As to full MVAC (Medium Voltage Alternate Current) power system and hybrid MVAC plus MVDC/LVDC islands, the aim was to evaluate whether or not the inclusion of capacitors (on shore, for power factor correction in shore connections) or filters (onboard, to reduce harmonic disturbances produced by propulsion systems) cause special issues, because of the high power of installed propulsion engines. Moreover, the advantages of DC island on electrical distribution in order to ensure high reliability and quality of service, in addition to the need to increase the efficiency of the ships’ power systems are highlighted. For the MVAC 50-60 Hz layout, the goal is to show how the use of hybrid (electric/diesel/gas turbine) propulsion where the power of engines is significantly reduced as compared to previous cases could solve some issues relating to power quality aspects. Chapter 9 - Reliability Analysis Preliminary studies about dependability, re-configurability and some top-events relevant for the vessel, were evaluated for all electric MVAC/MVAC "hybrid" models. The analysis of electrical disconnection of load areas due to a fault or an untimely tripping of the switches caused by harmonic disturbances was carried out. Chapter 10 - Three-Phase Short Circuit Analysis For MVAC 50-60 Hz Layout Preliminary evaluations were performed by analyzing the system within the perspective of given faults to perform system analysis in both permanent and short-circuit conditions. To highlight possible protection issues, the steady state condition and the three-phase short-circuit faults were studied and simulated under different load conditions for the MVAC architecture plus rotary converters, with hybrid (electric/diesel/gas turbine) propulsion.

碩士
國立臺灣海洋大學
河海工程學系
104
Marine transportation played an important role in global economic development, due to the trend of globalization of world economic activity. As the carrier ship transport of goods was growing rapidly and cruise market was also booming, so the development of ship oriented toward the large-scale and shipping sailings also increased substantially at the same time. But the exhaust emissions from ships also caused a lot of air pollution and had a huge impact punch to the environmental of port and coastal areas. Because of the terrain environment that Keelung Harbor goes deep into Keelung downtown area and port area is close to the urban, the above problems affect us seriously. The air quality issues are more worthy of attention. In recent years, the number of Keelung inbound and outbound vessels and total tonnage of vessels remained stablely, no significant growth, but the number of cruise passengers to Keelung increased steadily. Comparing the numbers of visitors who were inbound and outbound at different international harbor in Taiwan,the numbers of visitors in Keelung were always majority except that in Kaohsiung was majority in 2006. It shows the booming trend of cruise industry in Keelung Harbor. For reducing air pollution and greenhouse gas emissions at harbor area, one important way is to use the shore power system when ship berthing. This study explores the technical feasibility and cost benefit analysis of the cruise ship shore power system, oil analysis, load analysis, contract capacity, electricity and pollution reduction benefit assessment by using of shore power system for cruise ship at the ferry terminal of Keelung harbor.

碩士
國立臺灣科技大學
電機工程系
106
This thesis is about a power supply system applied in deep sea exploration ship, including a 350V/300V DC/DC converter, a 350V/24V DC/DC converter and a driver system of 4-polar conductivity meter. The DC/DC converter is structured by Full-Bridge LLC circuit with two paralleled module to increase the output power up to 2 kW. The digital controller captures the voltage, current feedback and calculates the variations. In order to stabilize the output voltage, the frequency modulation technique is used to reach the required level, and duty control is employed to balance the output current of two power module. Also, the thesis uses the resonant inductor, resonant capacitor and parasitic components in transformer to form a resonant tank. It can achieve the zero-voltage switching to decrease the power loss of switching under desired load conditions. Finally, the testing result shows that the efficiency of the whole system is above 80 %, and the maximum is up to 95.7 %. Moreover, a 24V/1.2V DC/DC converter is implemented to drive the four-polar conductivity meter. We can sense the current of the current electrode, and the voltage of the voltage electrode and convert these signals to digital codes by ADC. After that, these converted information will be delivered throughout SCI (serial communication interface) and be sent to the ship for reading and storing the conductivity of seawater.

The goal of the work reported herein has been to model aspects of the electrical distribution system of an all-electric ship (AES) and to couple electrical load behavior with the thermal management network aboard the ship. The development of a thermally dependent electrical network has built upon an in-house thermal management simulation environment to replace the existing steady state heat loads with dynamic, thermally dependent, electrical heat loads. Quantifying the close relationship between thermal and electrical systems is of fundamental importance in a large, integrated system like the AES. This in-house thermal management environment, called the Dynamic Thermal Modeling and Simulation (DTMS) framework, provided the fundamental capabilities for modeling thermal systems and subsystems relevant to the AES. The motivation behind the initial work on DTMS was to understand the dynamics of thermal management aboard the ship. The first version, developed in 2007, captured the fundamental aspects of system-level thermal management while maintaining modularity and allowing for further development into other energy domains. The reconfigurable nature of the DTMS framework allowed for the expansion into the electrical domain with the creation of an electrical distribution network in support of thermal simulations. The dynamics of the electrical distribution system of the AES were captured using reconfigurable and physics-based circuit elements that allow for thermal feedback to affect the behavior of the system. Following the creation of the electrical network, subsystems and systems were created to simulate electrical distribution. Then, again using the modularity features of DTMS, a thermal resistive heat flow network was created to capture the transient behavior of heat flow from the electrical network to the existing thermal management framework. This network provides the intimate link between the thermal management framework and the electrical distribution system. Finally, the three frameworks (electrical, thermal resistive, and thermal management) were combined to quantify the impact that each system has relative to system-level operation. Simulations provide an indication of the unlimited configurations and potential design space a user of DTMS can explore to explore the design of an AES.
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All-electric ship power systems have limited generation capacity and finite rotating inertia compared with large power systems. Moreover, all-electric ship power systems include large portions of nonlinear loads and dynamic loads relative to the total power capacity, which may significantly reduce the stability margin. Pulse loads and other high-energy weapon loads in the system draw a large amount of power intermittently, which may cause significant frequency and voltage oscillations in the system. Thus, an effective real-time load management technique is needed to dynamically balance the load and generation to operate the system normally. Multi-agent systems, inspired by biological phenomena, aim to cooperatively achieve system objectives that are difficult to reach by a single agent or centralized controller. Since power systems include various electrical components with different dynamical systems, conventional homogeneous multi-agent system cooperative controllers have difficulties solving the real-time load management problem with heterogeneous agents. In this dissertation, a novel heterogeneous multi-agent system cooperative control methodology is presented based on artificial potential functions and reduced-order agent models to cooperatively achieve real-time load management for all-electric ship power systems. The technique integrates high-order system dynamics and various kinds of operational constraints into the multi-agent system, which improves the accuracy of the cooperative controller. The multi-agent system includes a MVAC multiagent system and a DC zone multi-agent, which are coordinated by an AC-DC communication agent. The developed multi-agent system framework and the notional all-electric ship power system model were simulated in PSCAD software. Case studies and performance analysis of the MVAC multi-agent system and the DC zone multi-agent system were performed. The simulation results indicated that propulsion loads and pulse loads can be successfully coordinated to reduce the impact of pulse loads on the power quality of all-electric ship power systems. Further, the switch status or power set-point of loads in DC zones can be optimally determined to dynamically balance the generation and load while satisfying the operational constraints of the system and considering load priorities. The method has great potential to be extended to other isolated power systems, such as microgrids.

In this dissertation, we present the theory and application of polyspectral signal analysis techniques for interharmonics in shipboard power systems. Interharmonics are generated from various kinds of adjustable speed drives (ASD) in such power systems. ASDs are highly nonlinear devices due to the use of rectifiers and inverters. Since interharmonics can seriously hamper the normal operation of electric ships in many different ways (e.g., excitation of undesirable electrical and/or mechanical resonances, misoperation of control devices, and light flicker), the detection and analysis of interharmonic-related events is a critical issue in assessing power quality in an all-electric ship. Standard signal analysis techniques for regular harmonics are not immediately applicable to interharmonics due to their small amplitude and uncertain frequency of occurrence. Hence, we propose the use of alternative polyspectral analysis techniques such as higher-order spectra (the cross bispectrum/bicoherence) for the detection and analysis of the ASD-generated interharmonics. First, we develop the interharmonic application specific definitions of the cross bispectrum and the cross bicoherence. The statistical characteristics and frequency domain symmetries are also investigated. We apply the modified cross bispectrum to interharmonic detection problems. Due to their small amplitudes, the detection of interharmonics is sensitive to many undesirable factors such as spectral leakage and measurement error. Our analysis results demonstrate that the detection performance of the conventional DFT-based method is seriously degraded in the presence of noise. Hence, we develop a constant false alarm rate (CFAR) interharmonic detector based on the modified cross bispectrum. Our analysis and experimental results show that our method can provide more robust detection performance than conventional methods in the presence of noise. We also develop an ASD condition monitoring method based on the cross bicoherence. The key idea is to diagnose the status of the load side of an ASD from observations made at the source side. In this dissertation, we apply our method to detection and analysis of phase imbalance at the load side of the ASD. Our experimental results demonstrate that the proposed method provides a unique interharmonic signature for detection and classification of asymmetric impedance associated with the phase imbalance. Furthermore, the proposed method shows a more sensitive detection performance compared to the conventional imbalance measurement method, which enables prognosis of potential faults. A novel quadratic phase coupling detector for a single data record with coherent interharmonics is developed. The traditional bicoherence definition fails when its ’phase randomization’ assumption is not satisfied. This assumption is not appropriate for certain applications such as continuous monitoring of rotating machines. Therefore, we propose a novel quadratic phase coupling detector and compare it with previous techniques. It is shown that our detector is superior to previous detectors at high SNRs, and can also address partially coherent cases which previous approaches could not properly address. Flicker issues related to interharmonics are also discussed. We present a newly found limitation of the current IEC flickermeter regarding detecting flicker caused by low frequency interharmonics. We also present observation results of flicker responses of various lamps including light-emitting-diode (LED) lamps. Our observation results confirm that compact fluorescent and LED lamps are sensitive to high frequency interharmonics, although the IEC flickmeter can not detect flicker caused by such interharmonics. Hence, we develop an alternative flicker detection method based on down-up sampling. Our experiment results show that our method can detect flicker regardless of the value of the interharmonic frequencies. Independent of interharmonic topics, we also present our additional achievement involving application of wavelet denoising techniques to network congestion monitoring problems. This was a collaboration with researchers at the Department of Computer Sciences in the University of Texas at Austin, and mainly completed before becoming engaged in the electric ship project. By applying wavelet techniques, we could drastically enhance shared congestion detection performance over previously proposed methods.
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The requirements for power quality in ship power systems have been increasing over the years. This is an essential consequence of improving the efficiency of the onboard power network and reduce emissions in the long term. The connection of sophisticated navigation and measuring instruments into the grid has also necessitated a higher quality of power to ensure optimal operating conditions for all the loads and avoid malfunction of equipment onboard a ship. The most significant challenge to maintain power quality for the shipboard power system is to mitigate the transient conditions that arise due to the widely varying load conditions imposed by varying sea conditions as well as fluctuating onboard power demands. This work has attempted to illustrate the extent of the transient phenomena due to load changes in the case of vessels with hybrid mechanical and electrical propulsion. Subsequently, control solutions to limit and reduce such transient conditions and their propagation that include energy storage devices such as the capacitor and battery have been developed. A shipboard power system with hybrid propulsion has been modeled and the transient responses to various types of load changes during the course of different modes of operation possible for the hybrid system have been analyzed. An active damping strategy has been developed to reduce the torsional vibrations at the drive shaft of the thruster due to extreme load conditions while avoiding overdesign of the shaft itself. The strategy has been extended further to incorporate a capacitor clamped inverter to reduce the electrical transients that are caused by propagation of these transients from the mechanical portion of the hybrid propulsion system into the electrical system. A Model Predictive Control (MPC) strategy has also been developed for a Battery Energy Storage System (BESS) to mitigate the electrical transients arising as a result of propulsion and service load transients while keeping the main engine in the optimum operating range. The MPC power converter control allows for the battery to smoothen the electrical frequency profile during different types of extreme load change conditions and allows for charging and discharging the battery repeatedly. The findings of this research work have significant implications in defining the extent of transient conditions in hybrid power systems. In addition, the efficacy of integrating an energy storage system into the hybrid electric propulsion power network in order to reduce the transients has also been proven.

碩士
國立高雄海洋科技大學
輪機工程研究所
96
Abstract More and more power electronic converter equipment such as adjustable speed drivers (ASDs) and single/three phase power converters are used in a shipboard for electric motor driver and various power supply applications due to advanced technology in power semiconductor switching devices in the recent years. These power converters that are nonlinear loads can produce non-sinusoidal distorted currents and these currents are then delivered and broadcasted through the power network and therefore bus voltages are distorted. This thesis aims to build a set of analysis model for analysis and improvement of power harmonics in the shipboard. A harmonic power flow analysis technology is used to estimate each order and total harmonic distortion (THD) of harmonic voltages in the ship with distorted current injections at different locations. Based on the analysis results, suitable passive filters are designed to reduce the harmonic distortion according to shipboard harmonic regulations. Two practical power systems of electric propulsion and container vessels under different operating situations are used for the study. The test results and proposed analysis model can provide electrical engineers useful information in planning or designing shipboard harmonic mitigation measures. Keywords: Shipboard electric power system, Power Electronics, Power Converter, Harmonics, Harmonic power flow, Filter.

碩士
國立高雄海洋科技大學
輪機工程研究所
102
Ship shore power connection issue is essential and important for green port and clean harbor city around the world. From a whole grid point of view, the ship electric power system is connected to the onshore grid to become a part of onshore power networks through the shore power connection, which has increased the complexity of the short-circuit current analysis of ship power systems. To exactly calculate short-circuit currents at different fault points in the system for determining proper breaking capacity protection devices, this paper proposes a set of analysis model for the short-circuit current analysis for ship shore power connections. Two possible calculation methods, which include IEC std. 60909-0 and combining with IEC std. 60909-0 and IEC std. 61363-1, are developed and used to calculate the short-circuit currents in the system connected to onshore power grids. A practical ship shore power connection system is selected to ensure and demonstrate the performance of proposed methods.

碩士
崑山科技大學
電機工程研究所
101
With the consequences of trade growth and economic development, ships are getting bigger with size and equipped with automatic devices resulting in consuming a lot of electrical power. Usually, the ship is equipped with 2 or 4 power generators and operates them depending on the need through single operation or parallel operation. Ships’ Power Distribution Systems is an independent working component in a ship, where in the power consumption from small devices to heavy machines are loaded on electrical power system, and could thus cause variations on current, voltage and frequency there of. The main motivation for this work is the operational analysis of marine power system; the analysis shows that two turbine generators run in parallel in accordance with three common operational conditions, and it models dynamic response with the application of Matlab / Simullnk. This thesis presents a model on dynamic response analysis in Ships’ Power Distribution Systems for builders to design a Turbine-Generator system in ship.

碩士
國立高雄海洋科技大學
輪機工程研究所
104
Among the demonstration systems of green ports and clean harbor cities promoted around the world, the vessel high voltage shore connection (HVSC) system is one of the most important. In terms of overall power grid, when the vessel power system becomes a part of the onshore power grid, the onshore power distribution system exhibits voltage fluctuations due to line or load variation, thus influencing service performance and life of the electrical equipment. In a ship-to-shore power connection system, if the voltage fluctuation or line voltage drop is too large, then the service performance and life of the equipment on the ship are also impacted, and a parallel arrangement for vessel power and shore power will fail in a parallel connection or disconnection due to excessive voltage fluctuations. To design effective shore power connection equipment with adequate capacity and power quality for port construction, a set of analysis model for line voltage drop calculation is proposed in this thesis. Test results of a practical shore power connection system are presented to validate and demonstrate the performance of proposed method. Test results show that the line voltage drop in the shore power connection is influenced by ship load, the power factor, cable length, and cable diameter, and the line voltage drop is proportional to ship load, line length, and cable diameter and inversely proportional to the power factor. Comparing these influential factors, the power factor has a stronger effect on the line voltage drop, followed by ship load and line length, while the cable diameter has a slight effect on the line voltage drop.

Analysis was performed to quantify and compare the reliability of several different notional shipboard DC distribution system topologies in serving their equipment loads. Further, the relationship between the relative placement of loads and generators within a distribution system and the system’s reliability was investigated, resulting in an algorithmically-derived optimal placement configuration in the system topology found to be the most reliable in the initial analysis. Using Markov models and fault-tree analysis, system reliability indices were derived from distribution system component reliability indices, and these values were compared between competing topologies and equipment configurations. A distribution system based on the breaker-and-a-half topology often used in terrestrial utility substations was found to be superior in terms of reliability to the currently-standard ring bus topology. Expected rates of service interruptions to equipment systems served by the breaker-and-a-half system were reduced overall, in some cases dropping dramatically to less than one expected interruption per 10,000 years. This improvement, however, came at the expense of requiring more circuit breakers in the distribution system’s construction. Within this breaker-and-a-half distribution system, an optimal placement of loads and generators was algorithmically derived, which further improved the reliability of the system. This improvement over the base case was marginal, but the optimized placement configuration was able to reduce the expected interruption rate of the ship’s radar system by over 40%.
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碩士
國立高雄海洋科技大學
輪機工程研究所
96
Abstract The ship automation and large-scale developments have forced more and more electrical equipment to be installed for enhancing the marine shipping economic competition. On the other hand, many ship building corporations worldwide has paid more attentions to all-electric ships due to the significant gains in terms of a more flexible solution for energy shortage, exhaust emission and large-scale cargos realized from this type of ship. Since larger capacities of power generations and electric loads are used in these two types of ships, large short circuit currents can degrade the system security when the system faulted. When the existing power protection devices cannot accommodate the fault currents or the suitable devices are not available, how to reduce the fault currents becomes an important task for the shipboard power system design and operations. Many countries have studied the advantages of fault current limiters (FCLs) that are one of the effective strategies for system protection and short circuit improvement and used them to reduce fault currents in a power network for system security purpose. This thesis aims to investigate the application of FCLs to shipboard fault current improvement. The benefits and placement of FCLs installation for the ship application are studied. The suitable FCLs locations are determined by simulations and the impedance matrix modify method is used for FCLs design. Test results of two different types of ship power systems are reported to illustrate the FCLs placement and improvement effectiveness. Keywords: Shipboard electric power system, All-electric ship, Short circuit current, Fault current limiter.

碩士
國立高雄海洋科技大學
輪機工程研究所
99
Service restoration during a fault in ship electric power systems due to external forces or internal faults is an important task for future ship power systems design. To enhance the system reliability, this thesis aims to utilize a multi-agent system (MAS) based technique to build an effective service restoration strategy for performing fault isolation and restoration by feeder reconfigurations. When a fault in the system is detected and isolated, an appropriate restoration plan is derived by power electronic building blocks (PEBBs) used in the MAS to determine the restoration priority of feeders and sectionalizing loads according to the system emergency operation standard. To ensure the performance of the proposed method, two common ship distribution systems including radial and ring schemes and a practical ship electric distribution system are used for computer simulations. Simulation results have shown that with the MAS based ship service power restoration, the appropriate strategy can be promptly determined and executed for service restoration for enhancing system reliability.

An approach to parallelize the simulation of AC-Radial Shipboard Power Systems (SPSs) using multicore computers is presented. Time domain simulations of SPSs are notoriously slow, due principally to the number of components, and the time-variance of the component models. A common approach to reduce the simulation run-time of power systems is to formulate the electrical network equations using modified nodal analysis, use Bergeron's travelling-wave transmission line model to create subsystems, and to parallelize the simulation using a distributed computer. In this work, an SPS was formulated using loop analysis, defining the subsystems using a diakoptics-based approach, and the simulation parallelized using a multicore computer. A program was developed in C# to conduct multithreaded parallel-sequential simulations of an SPS. The program first represents an SPS as a graph, and then partitions the graph. Each graph partition represents a SPS subsystem and is computationally balanced using iterative refinement heuristics. Once balanced subsystems are obtained, each SPS subsystem's electrical network equations are formulated using loop analysis. Each SPS subsystem is solved using a unique thread, and each thread is manually assigned to a core of a multicore computer. To validate the partitioning approach, performance metrics were created to assess the speed gain and accuracy of the partitioned SPS simulations. The simulation parameters swept for the performance metrics were the number of partitions, the number of cores used, and the time step increment. The results of the performance metrics showed adequate speed gains with negligible error. An increasing simulation speed gain was observed when the number of partitions and cores were augmented, obtaining maximum speed gains of <30x when using a quadcore computer. Results show that the speed gain is more sensitive to the number partitions than is to the number of cores. While multicore computers are suitable for parallel-sequential SPS simulations, increasing the number of cores does not contribute to the gain in speed as much as does partitioning. The simulation error increased with the simulation time step but did not influence the partitioned simulation results. The number of operations caused by protective devices was used to determine whether the simulation error introduced by partitioning SPS simulations produced a inconsistent system behavior. It is shown, for the time step sizes uses, that protective devices did not operate inadvertently, which indicates that the errors did not alter RMS measurement and, hence, were non-influential.

The focus of this research is on identification, location, interruption, characterization and overall management of faults in conventional AC distribution systems as well as isolated MVDC power systems. The primary focus in AC distributions systems is on identifying and locating underground cable faults using voltage and current waveforms as the input data. Cable failure process is gradual and is characterized by a series of single-phase sub-cycle incipient faults with high arc voltage. They often go undetected and eventually result in a permanent fault in the same phase. In order to locate such incipient cable faults, a robust yet practical algorithm is developed taking into account the fault arc voltage. The algorithm is implemented in the time-domain and utilizes power quality monitor data to estimate the distance to the fault in terms of the line impedance. It can be applied to locate both sub-cycle as well as permanent faults. The proposed algorithm is evaluated and proved out using field data collected from utility distribution circuits. Furthermore, this algorithm is extended to locate evolving faults on overhead distribution lines. Evolving faults are faults beginning in one phase of a distribution circuit and spreading to another phase after a few cycles. The algorithm is divided into two parts, namely, the single line-to-ground portion of the fault and the line-to-line-to-ground portion of the fault. For the single line-to-ground portion of the fault, the distance to the fault is estimated in terms of the loop or self-reactance between the monitor and the fault. On the other hand, for the line-to-line-to-ground and line-to-line portion of the fault the distance is estimated in terms of the positive-sequence reactance. The secondary focus of fault management in AC distribution systems is on identifying fault cause employing voltage and current waveform data as well as meteorological information. As the first step, unique characteristics of cable faults are examined along with methods to identify such faults with suitable accuracy. These characteristics are also used to distinguish underground cable faults from other overhead distribution line faults. The overhead line faults include tree contact, animal contact and lightning induced faults. Waveform signature analysis, wavelet transforms and arc voltages during the fault event are used for fault cause identification and classification. A statistical based classification methodology to identify fault cause is developed by utilizing promising characteristics. Unlike the AC system infrastructure which is already in place, the DC system considered in this document is that of a notional electric ship. The nature of DC current, with the absence of a current zero as well as the presence of power electronic devices influencing the current behavior, makes interrupting DC fault currents challenging. As a part of this research an innovative DC fault interruption scheme is proposed for rectifier- fed MVDC systems. A fault at the terminals of a phase-controlled rectifier results in a high magnitude current impulse caused by the filter capacitor discharging into the fault resistance. It is proposed to use a series inductor to limit the magnitude of this current impulse. The addition of the inductor results in an underdamped series RLC circuit at the output terminals of the rectifier which causes the fault current to oscillate about zero. Furthermore, it is proposed to utilize a conventional AC circuit breaker to interrupt this fault current by exploiting the zero crossings resulting from the oscillations. Using the proposed scheme for the example case, the peak fault current magnitude as well as the interruption time is significantly reduced.
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碩士
義守大學
電機工程學系碩士班
98
Ship-to-shore container cranes are not only the major equipment of shipment of ocean transportation but also their processes are important to reduce freight time. Container cranes use inverters to control large AC/DC motors to achieve various actions of loading or unloading containers. However large inverters and large AC/DC motors have non-linear load characteristics, those characteristics will produce large amounts of harmonic currents when the equipment works. The harmonic currents produced will propagate through power systems, affect other electrical equipment, make the voltage waveform distorted and influence the wharf power quality. Besides, the movements of ship-to-shore crane have stochastic characteristics; the stochastic characteristics must be considered in the harmonic analysis. This thesis investigates the behaviors of stochastic harmonic sources caused by container cranes and their penetrations to power supply systems. In order to analyze the stochastic behaviors of container cranes in detail, the movements of container crane are divided into ten stages. A power quality recorder is used to record the voltage, current, power, harmonic etc. of each stage. The time distribution of each stage can also be investigated accordingly. Base on the measured data and time distribution of each stage, a comprehensive analysis can be achieved. Test results demonstrate the significance of the proposed method.

American jurisprudence currently applies two incompatible validity standards to determine which laws are enforceable. The natural law tradition evaluates validity by an uncertain standard of divine law, and its methodology relies on contradictory views of human reason. Legal positivism, on the other hand, relies on a methodology that commits the analytic fallacy, separates law from its application, and produces an incomplete model of law. These incompatible standards have created a schism in American jurisprudence that impairs the delivery of justice. This dissertation therefore formulates a new standard for legal validity. This new standard rejects the uncertainties and inconsistencies inherent in natural law theory. It also rejects the narrow linguistic methodology of legal positivism. In their stead, this dissertation adopts a pragmatic methodology that develops a standard for legal validity based on actual legal experience. This approach focuses on the operations of law and its effects upon ongoing human activities, and it evaluates legal principles by applying the experimental method to the social consequences they produce. Because legal history provides a long record of past experimentation with legal principles, legal history is an essential feature of this method. This new validity standard contains three principles. The principle of reason requires legal systems to respect every subject as a rational creature with a free will. The principle of reason also requires procedural due process to protect against the punishment of the innocent and the tyranny of the majority. Legal systems that respect their subjects' status as rational creatures with free wills permit their subjects to orient their own behavior. The principle of reason therefore requires substantive due process to ensure that laws provide dependable guideposts to individuals in orienting their behavior. The principle of consent recognizes that the legitimacy of law derives from the consent of those subject to its power. Common law custom, the doctrine of stare decisis, and legislation sanctioned by the subjects' legitimate representatives all evidence consent. The principle of autonomy establishes the authority of law. Laws must wield supremacy over political rulers, and political rulers must be subject to the same laws as other citizens. Political rulers may not arbitrarily alter the law to accord to their will. Legal history demonstrates that, in the absence of a validity standard based on these principles, legal systems will not treat their subjects as ends in themselves. They will inevitably treat their subjects as mere means to other ends. Once laws do this, men have no rest from evil.