Dissertations / Theses on the topic 'DC Security'

The convenience of IEEE 802.11-based wireless access networks has led to widespread deployment. However, these applications are predicated on the assumption of availability and confidentiality. Error-prone wireless networks afford an attacker considerable flexibility to exploit the vulnerabilities of 802.11-based mechanism. Two of most famous misbehaviors are selfish and malicious attacks. In this thesis we investigate two attacks: Spurious CTS attack (SCTS) and Jamming ACK attack (JACK). In the SCTS, malicious nodes may send periodic Spurious CTS packets to force other nodes to update their NAV values and prevent them from using the channel. In the JACK, an attacker ruins legitimate ACK packets for the intention of disrupting the traffic flow and draining the battery energy of victim nodes quickly. Correspondingly, we propose solutions: termed Carrier Sensing based Discarding (CSD), and Extended Network Allocation Vector (ENAV) scheme. We further demonstrate the performance of our proposed schemes through analysis and NS2 simulations.

Geography
Ph.D.
Women worldwide carry out strategies to support themselves and their families that rely on connecting to physical resources, especially food, and to important social ties. This dissertation provides a nuanced understanding of the spatial implications of this connectivity as made visible through mobility and social networks in two cities. Everyday experiences of food security can be bolstered by access to greater mobility (e.g., access to a taxi/bus to go to the central market), which can be provided through social networks (e.g., sharing a ride with a family member or neighbor). At the same time, a lack of mobility may inhibit a person’s access to food (e.g., an inability to move beyond one’s neighborhood due to risk of violence), and is especially true when this need for mobility interferes with other social network obligations (e.g., needing to care for children). This mixed-methods research uses sketch mapping during in-depth interviews with 72 migrant women coping with food insecurity in Medellín, Colombia, and Washington, DC, USA. Based on this data, I use relational poverty’s emphasis on social relations to explain that food insecurity results from global political economic systems, especially a capitalist, corporate food regime (chapter 3). However, in moving beyond structural explanations, this dissertation also illustrates everyday survival strategies – such as relying on informal social networks – that act as resistance to these processes (chapter 4), are both social and mobile – for example, traveling with members of social networks to access emergency food providers (chapter 5), and are impacted locally by urban planning policies reflecting global norms (chapter 6). In doing so, this dissertation argues that food insecure individuals are powerful agents carrying out creative coping strategies that are constrained by political economic structures. Building on theoretical foundations from critical food studies, urban geography and feminist geography, this research contributes to these literatures through theorizing structure and agency dynamics evident in food insecurity, particularly from the perspective of those coping with food insecurity. It is important to attend to their complex, lived experience in order to better understand if strategies for alleviating food insecurity are appropriate. Additionally, focusing on different contexts of food insecurity allows illustrating how cities are similarly and differently integrated into globalized processes influencing experiences of poverty and governance in both the global north and south. It also contributes a more nuanced understanding of the food insecurity experiences of low-income women migrating into urban environments, enabling more effective scholarship as well as improved policy making and service provision by governments, relief agencies, and community organizations. For example, this dissertation provides critiques of policy approaches that singularly focus on increasing opportunities for consumption (chapters 3 and 5) and nutrition education programs emphasizing the ‘right’ kinds of consumption (chapters 4 and 5). These policy approaches ignore the structural causes of food insecurity (chapter 3) and the nutritional knowledge of food insecure migrants (chapter 4). Instead, I argue for policies and programs to be created with a better understanding of the lived experience of those they seek to support. This includes valuing their critiques of political economic systems (chapter 4), supporting their non-economic survival strategies – such as exchange in informal networks (chapters 4 and 5) and growing food (chapter 6), and increasing flexibility to accommodate ‘non-traditional’ mobility and (informal) work situations.
Temple University--Theses

L'intégration des Énergies Renouvelables pose aujourd'hui des problèmes de congestion et d'incertitude sur le réseau électrique vu l'intermittence et l'imprévisibilité de ce type d'énergie. De plus, pour des questions de rentabilité et d'efficacité, la puissance produite à partir du renouvelable est transmise sous forme de Haute Tension en Courant Continu (HVDC). Un nouveau concept a donc émergé, celui de la fusion d'interconnexions HVDC dans un réseau maillé existant et ceci apportera plus de flexibilité dans le fonctionnement du système global. Le résultat : une hybridation du système de transmission d'électricité avec des interactions mutuelles importantes entre système AC existant et DC intégré. Si les problèmes de stabilité du réseau AC sont aujourd'hui identifiés, ceux du système hybride doivent encore être étudiés puisque l'intégration de convertisseurs de puissance commandables et contrôlables rapidement pourrait modifier le comportement du système entier. De ce fait, ce projet de thèse cherche à établir une étude innovante englobant tout le système hybride AC/DC. Celle-ci portera tout d'abord sur une évaluation de la sécurité prenant en compte les contraintes opérationnelles et la capacité du système à atteindre un nouvel équilibre. En outre, cette thèse relèvera les défis de stabilisation du système hybride global. Pour cela, les missions consisteront en une étude préliminaire de l'état de l'art : quelles nature physique des problèmes d'instabilité du système AC ? Quels types et gammes de perturbations à considérer pour l'évaluation de la stabilité ? Finalement, quels modélisation et contrôle du système HVDC ? Tout cela permettra de développer un outil inclusif d'évaluation de la sécurité prenant en compte différentes méthodes de contrôle du système. Une analyse sera également faite pour comprendre l'influence des paramètres et des méthodes de contrôle adoptés. Cela nous aidera à mettre en place un moyen de contrôle systématique pour améliorer la sécurité du réseau et optimiser la distribution de la puissance à travers un réseau Multi-Terminal DC
Today, the integration of renewable energies poses problems of congestion and uncertainty on the electricity network, given the intermittency and unpredictability of this type of energy. What's more, for reasons of profitability and efficiency, the power generated from renewables is transmitted in the form of High Voltage Direct Current (HVDC). A new concept has therefore emerged, that of merging HVDC interconnections into an existing meshed network, which will bring greater flexibility to the operation of the overall system. The result is a hybrid electricity transmission system with significant mutual interactions between the existing AC system and the integrated DC system. While the stability problems of the AC network have now been identified, those of the hybrid system still need to be studied, since the integration of rapidly controllable power converters could modify the behaviour of the entire system. As a result, this thesis project seeks to establish an innovative study encompassing the entire AC/DC hybrid system. This will focus on a security assessment that takes into account operational constraints and the ability of the system to reach a new equilibrium. In addition, this thesis will address the stabilisation challenges of the overall hybrid system. To this end, the assignments will consist of a preliminary study of the state of the art: what is the physical nature of the instability problems of the AC system? What types and ranges of disturbances should be considered for stability assessment? Finally, what modelling and control of the HVDC system? All of this will enable the development of an inclusive security assessment tool that takes into account different system control methods. An analysis will also be carried out to understand the influence of the parameters and control methods adopted. This will help us to implement a systematic means of control to improve network security and optimise power distribution across a Multi-Terminal DC network

Mestrado em Actuarial Science
Em Portugal, o envelhecimento da população desafia a sustentabilidade financeira do sistema de Segurança Social. Ao longo dos anos, muitas emendas legislativas foram introduzidas no sistema de Previdência Social com o objetivo de torná-lo auto-sustentável, todavia existe uma dificuldade para entregá-lo sem restringir os benefícios de aposentadoria devido a evolução demográfica. Inevitavelmente, isso leva a impactos negativos nas pensões de aposentadoria por idade. As administrações anteriores combinaram essas reformas com medidas que reforçam o estabelecimento de esquemas privados de fundos de pensões, dando-lhe um papel mais preponderante, de forma a diversificar as fontes de renda de aposentadoria. No contexto de aumento da responsabilidade individual pela adequação da renda de aposentadoria. Esta dissertação analisa a pensão de velhice com especial enfoque nas reformas antecipadas, dada a forte penalização que existe. Além disso, verifica-se a possibilidade de um plano de contribuição definida para mitigar totalmente essas reduções. Portanto, são descritos os dois sistemas, o público e o complementar.
In Portugal, population ageing is challenging the financial sustainability of the Social Security system. Throughout the years many legislative amendments have been introduced in the Social Security system, with the goal to make it self-sustainable, but it is struggling to deliver it without restricting old-age benefits due to the increase of the elderly population. Inevitably, this leads to negative impacts in the old-age retirement pensions. Past administrations have combined these reforms with measures to reinforce the establishment of the funded private pension sector, giving it a more prominent role, so as to diversify the sources of retirement income. In the context of increasing the individual responsibility for the adequacy of retirement income. This paper analyses the old-age benefits with special focus in the early retirement option, given the heavy penalties inherent to this option. Also, examines the possibility of fund a DC pension plan to fully mitigate those penalties.
info:eu-repo/semantics/publishedVersion

Modern power networks incorporate communications and information technology infrastructure into the electrical power system to create a smart grid in terms of control and operation. The smart grid enables real-time communication and control between consumers and utility companies allowing suppliers to optimize energy usage based on price preference and system technical issues. The smart grid design aims to provide overall power system monitoring, create protection and control strategies to maintain system performance, stability and security. This dissertation contributed to the development of a unique and novel smart grid test-bed laboratory with integrated monitoring, protection and control systems. This test-bed was used as a platform to test the smart grid operational ideas developed here. The implementation of this system in the real-time software creates an environment for studying, implementing and verifying novel control and protection schemes developed in this dissertation. Phasor measurement techniques were developed using the available Data Acquisition (DAQ) devices in order to monitor all points in the power system in real time. This provides a practical view of system parameter changes, system abnormal conditions and its stability and security information system. These developments provide valuable measurements for technical power system operators in the energy control centers. Phasor Measurement technology is an excellent solution for improving system planning, operation and energy trading in addition to enabling advanced applications in Wide Area Monitoring, Protection and Control (WAMPAC). Moreover, a virtual protection system was developed and implemented in the smart grid laboratory with integrated functionality for wide area applications. Experiments and procedures were developed in the system in order to detect the system abnormal conditions and apply proper remedies to heal the system. A design for DC microgrid was developed to integrate it to the AC system with appropriate control capability. This system represents realistic hybrid AC/DC microgrids connectivity to the AC side to study the use of such architecture in system operation to help remedy system abnormal conditions. In addition, this dissertation explored the challenges and feasibility of the implementation of real-time system analysis features in order to monitor the system security and stability measures. These indices are measured experimentally during the operation of the developed hybrid AC/DC microgrids. Furthermore, a real-time optimal power flow system was implemented to optimally manage the power sharing between AC generators and DC side resources. A study relating to real-time energy management algorithm in hybrid microgrids was performed to evaluate the effects of using energy storage resources and their use in mitigating heavy load impacts on system stability and operational security.

La sécurité de la couche physique consiste à permettre la transmission des données confidentielles via un réseau sans fil en présence d'utilisateurs illégitimes, sans s'appuyer sur un cryptage de couche supérieure. L'essence de la sécurité de la couche physique est de maximiser le taux de secret, qui est le taux maximal d'informations sans interception par les espions. De plus, la conception de la sécurité de la couche physique prend en compte la minimisation de la puissance de transmission. Ces deux objectifs sont souvent en conflit l'un avec l'autre. Ainsi, la recherche sur les conceptions de sécurité de la couche physique se concentre souvent sur les deux principales classes de problèmes d’optimisation : maximiser le taux de secret sous contrainte de puissance de transmission et minimiser la puissance de transmission sous contrainte de taux de secret. Ces problèmes sont non convexes, donc difficiles à résoudre. Dans cette thèse, nous nous concentrons sur le développement des méthodes d'optimisation pour résoudre ces deux classes de problèmes d'optimisation. Nos méthodes sont basées sur la programmation DC (Difference of Convex functions) et DCA (DC Algorithm) étant reconnues comme des outils puissants d'optimisation non convexe. Dans la première partie, nous considérons trois classes de problèmes de maximisation du taux de secret (chapitre 2, 3, 4). Le chapitre 2 étudie la transmission sécurisée des informations dans un système de relais MISO. Le relais utilise une combinaison de technique de formation de faisceau et de technique de bruit artificiel sous les modèles déterministes des canaux d'incertitude. Sans utiliser de relais, le chapitre 3 étudie le problème du transfert simultané d'information sans fil et de l’énergie dans un système sécurisé sous parfaite connaissance des canaux et imparfaite connaissance des canaux. Deux stratégies de transmission : formation de faisceaux avec bruit artificiel et sans bruit artificiel sont étudiés. Avec l'hypothèse du canal statistique des espions, chapitre 4 aborde le problème de maximisation du taux de secret sous la contrainte en probabilité dans un système SWIPT ("simultaneous wireless information and power transfer (SWIPT)" en anglais) multi-utilisateur. L'approche unifiée basée sur la programmation DC et DCA est proposée pour résoudre trois classes de problèmes d'optimisation. Le problème d'optimisation du chapitre 2 est reformulé comme deux programmes DC généraux. Les schémas DCA généraux sont proposés pour résoudre ces deux programmes DC. Dans le chapitre 3, nous considérons quatre problèmes d'optimisation conformément à quatre scénarios. Nous exploitons la structure particulière des problèmes considérés de les reformuler comme programmes DC généraux. Les schémas DCA généraux correspondants sont développés pour les résoudre. Dans le chapitre 4, nous transformons d’abord le problème considéré en une forme traitable. Nous développons ensuite un algorithme alternatif pour résoudre le problème transformé. Deux programmes DC généraux sont proposés à chaque itération du schéma alternatif. Pour résoudre ces programmes DC, nous étudions une variante de DCA général, à savoir le schéma DCA−ρ. La convergence de l’algorithme proposé est rigoureusement prouvée. La deuxième partie étudie le problème de minimisation de la puissance de transmission sous les contraintes de probabilité du taux de secret et de récolte l’énergie dans le réseau SWIPT (chapitre 5). Nous reformulons le problème d’origine comme trois programmes DC généraux pour lequel nous d´développons trois schémas DCA généraux correspondants. Les résultats numériques démontrent l’efficacité des algorithmes proposés
Physical layer security is to enable confidential data transmission through wireless networks in the presence of illegitimate users, without basing on higher-layer encryption. The essence of physical layer security is to maximize the secrecy rate, that is the maxi- mum rate of information without intercepted by the eavesdroppers. Besides, the design of physical layer security considers the transmit power minimization. These two objectives conflict with each other. Consequently, the research on physical layer security designs often focuses on the two main classes of optimization problems: maximizing secrecy rate under the transmit power constraint and minimizing power consumption while guaranteeing the secrecy rate constraint. These problems are nonconvex, thus, hard to solve. In this thesis, we focus on developing optimization approaches to solve these two optimization problem classes. Our methods are based on DC (Difference of Convex functions) programming and DCA (DC Algorithm) which well-known as one of the most powerful approaches in optimization. In the first part, we consider three classes of secrecy rate maximization problems (chapters 2, 3, 4). In particular, chapter 2 studies the secure information transmission in a multiple-input single-output (MISO) relay system by using joint beamforming and artificial noise strategy under the deterministic uncertainty channel models of all links. Without using a relay, chapter 3 addresses the problem of transfer wireless information and power simultaneously in MISO secure system where scenarios of perfect channel state information and deterministic uncertainty channel models are concerned. Transmit beamforming without artificial noise and that with artificial noise are investigated. Under the assumption of statistical channel state information to eavesdroppers, chapter 4 studies the probability constrained secrecy rate maximization problem in multiuser MISO simultaneous wireless information and power transfer (SWIPT) system. The unified approach based on DC programming and DCA is proposed to solve three classes of optimization problems. The optimization problem in chapter 2 is recast as two general DC programs. The general DCA schemes are proposed to solve these two DC programs. In chapter 3, we consider four optimization problems in accordance with four scenarios. Exploiting the special structures of these original optimization problems, we transform it into four general DC programs for which the corresponding general DCA based algorithms are developed. In chapter 4, we first transform the considered problem into a tractable form. We then develop an alternating scheme to solve the transformed problem. Two general DC programs are proposed in each step of the alternating scheme. For solving these DC programs, we study a variant of general DCA, namely, DCA−ρ scheme. The convergence of alternating general DCA−ρ scheme is proven. The second part studies the transmit power optimization problem under the probability constraints of secrecy rate and harvested energy in a MISO SWIPT system (chapter 5). We reformulate the original problem as three general DC programs for which the corresponding general DCA-based algorithms are investigated. Numerical results demonstrate the efficiency of the proposed algorithms

Freedom of speech and the right to privacy are maybe the most important elements of a modern society, yet the rights are often violated. This fact was the main reason for writing this thesis covering P2P network models, anonymity, censorship resistance and their use in real P2P networks and publishing systems. We discuss their effectiveness and suitability for specific purposes, but also the security considerations of their use. The second part of this thesis presents the LSPP publishing protocol, which is an library implementation of an anonymous censorship resistant P2P network. Finally, we analyze the proposed protocol and compare it with existing solutions.

碩士
國立宜蘭大學
多媒體網路通訊數位學習碩士在職專班
105
Maintaining leading position in the networking appliance requires not only the best technology and production capabilities but also technological innovation and strategies, realizing the market position of the entry level networking security application is essential, Being aware of market position of its own product can avoid the low cost competition caused by other Taiwan ODM competitors, moving forward to innovation is the right path and essential. Previous product, entry level network security appliance, adopted one 250W ATX power supply to be the main power source that is not capable to have another backup power supply. It also has limitations from physical size and cost as well that can’t use redundant power supply, once the PSU (Power Supply) is malfunction; high maintenance fee is caused by disassembling the system to replace new PSU (Power Supply). The research is to find the opportunity to prevent the disadvantages of the previous product by public procurement tender. It can bring redundant DC-DC converter device to entry level network security appliance and makes it become cost effective and modularized.

碩士
國立高雄海洋科技大學
輪機工程研究所
95
In contrast with traditional AC radial distribution systems, significant giants can be realized in terms of supply quality, weight, manning, and cost from a shipboard DC zonal electric distribution system (DC ZEDS). The DC ZEDS is predicted on having starboard and port DC buses feeding electrical zones delineated by watertight bulkhead compartments. The main bus DC voltage is stepped down within the zone and then converted to three-phase AC and lower voltage DC by power converters. Security assessment of the shipboard DC ZEDS under different fault conditions is important for real-time secure operation of the system. This thesis aims for security analysis of the shipboard DC ZEDS by probabilistic methodologies. The power converter operation and power generation and load variations are handled by AC/DC load flow and probabilistic load flow techniques to compute possible AC/DC load flow solution distributions, including bus voltages, phase angles, network flows, and power converter operation parameters. Stochastic contingency analysis of the system is also performed to compute the probability of the occurrence of the system insecurity and determine the critical contingency.

Test coverage criteria, including logical coverage, such as Modified Condition / Decision Coverage (MC/DC) have been increasingly used in safety-critical or mission-critical domains, complementing the more popularly used structural coverage criteria such as branch coverage. However, existing automated test-generation approaches such as concolic test generation often target at branch coverage for test generation and selection. Therefore, they do not support testing against logical coverage. Existing test-generation approaches fail to strategically choose input values to achieve high or complete logical coverages. To address these issues, we propose some source code pre-processing (program transformation) techniques to generate test inputs that achieve logical coverage for the program under test. In Particular, we use code instrumentation to assist an existing test-generation approach(Concolic Testing) that targets, at achieving logical coverage such as MC/DC. We present code transformation techniques that enable concolic testing execution to achieve increased MC/DC percentage. The transformation techniques introduce several new branches in the program under test. However, we do not modify any existing code of the program. We only insert nested conditional statements with empty branches in the program. These new branches contain constraints that need to be satisfied to achieve an increase in MC/DC. We then supply the transformed program to the concolic tester for dynamic symbolic testing. The generation of input values for the transformed program achieves an increase in MC/DC for the program under test. We have proposed our first code transformation technique named Program Code Transformer (PCT). We use Boolean logic simplification techniques that help generate equivalent simple conditional statements. The equivalent simple conditions for a predicate are inserted in the program under test with empty branches before the particular predicate. We use Boolean algebra properties to solve the Boolean expressions to frame into the Sum of Product (SOP) form. Then, the Boolean expression may become complex. To address this issue, we have applied Quine-McCluskey(QM) technique. After using PCT, MC/DC percentage is still low and insufficient. Hence, it requires some more test input values to achieve an increase in MC/DC percentage. Therefore,we propose another transformer named Exclusive-NOR Code Transformer (EX-NCT). We use Boolean derivative method to generate additional conditional statements for the complex Boolean expressions in the program. These additional conditions contain constraints which show the independent effect of component conditions on the evaluation of a complex condition. The additional conditional statements are inserted in the program under test with empty branches before the particular predicate. We have fused PCT and Ex-NCT to get some more test data, and observed that it really works. We have named this third type of code transformer as Double Refined Code Transformer (DRCT), due to its double transformation nature. We have set up a client-server mesh-topology of the computer systems and executed distributed concolic testing to generate more number of useful test cases. Since, now-a-days many programs are written in object-oriented programming languages, so we have extended our proposed techniques to handle object-oriented language such as Java. We have also extended our proposed techniques to handle multithreaded Java programs. During experimentation using concolic testers, we found that there are some test inputs with large integer values. We have replaced those values with “0”(Zero) a neutral value and created new test inputs. Then, we observed significant increase in MC/DC percentage. Subsequently, we propose a technique to minimize the number of test cases and another technique to prioritize the test cases. We have developed some tools to measure MC/DC percentage of the program under test.From the experimental results, it is observed that we have achieved higher MC/DC than that of the existing methods/approaches.

碩士
國立交通大學
電機工程學系
106
As far as Internet-of-Everything (IoE) devices are concerned, strong hardware security and low electromagnetic interference (EMI) are design requirements for power management to guarantee personal data protection. Conventional linear feedback shift register (LFSR) based loop randomization technique has the ability to avoid the power side channel attacks (PSCA), but the power injection attack (PIA) results in limited random number (RN) due to the predictability and reproducibility of the LFSR, and thus cause the loop randomization cracked and vulnerable to the PSCA. Besides, the PIA not only narrows the LFSR based random switching frequency but also reduces the triangular modulation frequency to around 1/N times of the switching frequency. Consequently, the EMI noise floor fails to meet the specification of EN 55032 Class B. Other techniques offer counter-measures to improve resistance against malicious attacks but result in either greatly increased power consumption or large hardware overhead. In this thesis, the true random number (TRN) based pseudo hysteresis controller (PHC) and the enhanced security randomizer (ESR) are proposed to avoid both PSCA and PIA simultaneously and reduce EMI without degrading performance. The ESR is capable of generating input-supply-independent RN correctly under PSCA and PIA. The TRN based PHC converts the RN to the hysteresis window that constitutes a true random modulated switching frequency, thereby ensuring suitable spread spectrum and low EMI. Besides, fast transient response is maintained due to inherent hysteresis control. Experimental results show peak EMI noise is reduced from 89.72dBμV to 54.32dBμV and meets the specification of EN 55032 Class B even under the PIA interference up to 1V. Furthermore, transient performance achieves 7.3μs recovery time and 53mV drop of output voltage in case of 0.2A-to-0.8A load step at the switching frequency around 1MHz and peak efficiency is 92.4%.

abstract: Power management circuits are employed in most electronic integrated systems, including applications for automotive, IoT, and smart wearables. Oftentimes, these power management circuits become a single point of system failure, and since they are present in most modern electronic devices, they become a target for hardware security attacks. Digital circuits are typically more prone to security attacks compared to analog circuits, but malfunctions in digital circuitry can affect the analog performance/parameters of power management circuits. This research studies the effect that these hacks will have on the analog performance of power circuits, specifically linear and switching power regulators/converters. Apart from security attacks, these circuits suffer from performance degradations due to temperature, aging, and load stress. Power management circuits usually consist of regulators or converters that regulate the load’s voltage supply by employing a feedback loop, and the stability of the feedback loop is a critical parameter in the system design. Oftentimes, the passive components employed in these circuits shift in value over varying conditions and may cause instability within the power converter. Therefore, variations in the passive components, as well as malicious hardware security attacks, can degrade regulator performance and affect the system’s stability. The traditional ways of detecting phase margin, which indicates system stability, employ techniques that require the converter to be in open loop, and hence can’t be used while the system is deployed in-the-field under normal operation. Aging of components and security attacks may occur after the power management systems have completed post-production test and have been deployed, and they may not cause catastrophic failure of the system, hence making them difficult to detect. These two issues of component variations and security attacks can be detected during normal operation over the product lifetime, if the frequency response of the power converter can be monitored in-situ and in-field. This work presents a method to monitor the phase margin (stability) of a power converter without affecting its normal mode of operation by injecting a white noise/ pseudo random binary sequence (PRBS). Furthermore, this work investigates the analog performance parameters, including phase margin, that are affected by various digital hacks on the control circuitry associated with power converters. A case study of potential hardware attacks is completed for a linear low-dropout regulator (LDO).
Dissertation/Thesis
Masters Thesis Electrical Engineering 2019

Traditionally energy has been generated with large synchronous generators. These large plants have characteristics that are well understood and are the basis for the operation of the electricity grid. Most grid codes are based on the assumption that new plant will be composed of synchronous generators. Most of these plants are powered by non-renewable fuels that come with significant carbon emissions. The realisation that there is not an infinite supply of these fuels and their emissions are harming the world’s environment has resulted in policies being implemented aiming at reducing these sources of emissions. This energy is to be replaced with energy from renewable sources. There are many renewable generator types available but wind generation has the highest focus in most countries. As of 2013 there is approximately 318 GW of wind energy installed worldwide. Integrating all of this wind generation into the synchronous power system presents many challenges to grid companies. Wind generation usually does not have the same characteristics as synchronous plant as it is asynchronous. Many of the services that are assumed to be provided by synchronous plant such as inertia or fault contribution are unavailable or come with additional cost. Compounding this wind generation will displace synchronous plant, reducing the system strength further. It is important for grid companies to gain an understanding of the impact of wind generation on the electrical system before the wind integration becomes an issue. Usually when issues begin to arise it is too late to alter existing plant. This means any mitigation of system issues will be expensive or result in an inefficient market. This means that new generators would be required to meet much higher connection standards as there is little system strength left to allocate to the new generators. Ireland has tacked this integration issue by adopting a simple wind integration metric System Non Synchronous Penetration (SNSP) to flag when the system is approaching critical non-synchronous generation levels. This thesis aims to investigate wind generation integration issues in small power systems, in particular ones that are not connected or only weakly connected to other larger grids. It will: • Develop a wind integration metric similar to that used in Ireland or determine application guidelines for the Irish SNSP; • Determine what regulatory approach may reduce the impact of new wind generation minimising the requirement for the integration metric; and • Determine what effect wind generation may have on other plant, particularly those that will not be mitigated by the first two points. For this study the power system of Tasmania is used as the case study. Tasmania is a relatively small (~1700 MW peak load, ~900 MW minimum load) power system connected weakly to the much larger mainland Australia power system via a single HVDC interconnector. This interconnector has a transfer capability of 500 MW into Tasmania and 630 MW out of Tasmania. Additionally this connector is monopolar and can lose all transfer capability in a single fault. This means that during low load approximately half of Tasmania’s generation needs to be able to be tripped at any moment. This is before any response from wind farms is taken into account. Tasmanian generation is predominantly hydro. This type of plant is very flexible. It can be started and shut down very quickly and has no real minimum operating level. This means that when wind generation is high it will tend to shut down rather than operate at a minimum level. This thesis is presented in five sections: Chapter 1. Introduction: This chapter introduces this thesis and its objectives. It also summarises the experiences of other jurisdictions and how they may be similar to the study case. Chapter 2. Mathematical description of a wind plant: This chapter describes a wind plant in mathematical terms, and then it shows how a wind plant responds differently to grid disturbances. Chapter 3. Impact of wind generation on a small power system: This chapter studies the impact of wind generation on the case study power system and investigates how this impact may be mitigated. Chapter 4. Conclusion: This chapter summarises this thesis and explains its outcomes.

The objective of an Energy Control Center (ECC) is to ensure secure and economic operation of power system. The challenge to optimize power system operation, while maintaining system security and quality of power supply to customers, is increasing. Growing demand without matching expansion of generation and transmission facilities and more tightly interconnected power systems contribute to the increased complexity of system operation. Rising costs due to inflation and increased environmental concerns has made transmission, as well as generation systems to be operated closure to design limits, with smaller safety margins and hence greater exposure to unsatisfactory operating conditions following a disturbance. Investigations of recent blackouts indicate that the root cause of most of these major power system disturbances is voltage collapse. Information gathered and preliminary analysis, from the most recent blackout incident in North America on 14th August 2003, is pointing the finger on voltage instability due to some unexpected contingency. In this incident, reports indicate that approximately 50 million people were affected interruption from continuous supply for more than 15 hours. Most of the incidents are related to heavily stressed system where large amounts of real and reactive power are transported over long transmission lines while appropriate real and reactive power resources are not available to maintain normal system conditions. Hence, the problem of voltage stability and voltage collapse has become a major concern in power system planning and operation. Reliable operation of large scale electric power networks requires that system voltages and currents stay within design limits. Operation beyond those limits can lead to equipment failures and blackouts. In the last few decades, the problem of reactive power control for improving economy and security of power system operation has received much attention. Generally, the load bus voltages can be maintained within their permissible limits by reallocating reactive power generations in the system. This can be achieved by adjusting transformer taps, generator voltages, and switchable Ar sources. In addition, the system losses can be minimized via redistribution of reactive power in the system. Therefore, the problem of the reactive power dispatch can be optimized to improve the voltage profile and minimize the system losses as well. The Instability in power system could be relieved or at least minimized with the help of most recent developed devices called Flexible AC Transmission System (FACTS) controllers. The use of Flexible AC Transmission System (FACTS) controllers in power transmission system have led to many applications of these controllers not only to improve the stability of the existing power network resources but also provide operating flexibility to the power system. In the past, transmission systems were owned by regulated, vertically integrated utility companies. They have been designed and operated so that conditions in close proximity to security boundaries are not frequently encountered. However, in the new open access environment, operating conditions tend to be much closer to security boundaries, as transmission use is increasing in sudden and unpredictable directions. Transmission unbundling, coupled with other regulatory requirements, has made new transmission facility construction more difficult. In fact, there are numerous technical challenges emerging from the new market structure. There is an acute need for research work in the new market structure, especially in the areas of voltage security, reactive power support and congestion management. In the last few decades more attention was paid to optimal reactive power dispatch. Since the problem of reactive power optimization is non-linear in nature, nonlinear programming methods have been used to solve it. These methods work quite well for small power systems but may develop convergence problems as system size increases. Linear programming techniques with iterative schemes are certainly the most promising tools for solving these types of problems. The thesis presents efficient algorithms with different objectives for reactive power optimization. The approach adopted is an iterative scheme with successive power-flow analysis using decoupled technique, formulation and solution of the linear-programmingproblem with only upper-bound limits on the state variables. Further the thesispresents critical analysis of the three following objectives, Viz., •Minimization of the sum of the squares of the voltage deviations (Vdesired) •Minimization of sum of the squares of the voltage stability L indices (Vstability) •Minimization of real power losses (Ploss) Voltage stability problems normally occur in heavily stressed systems. While the disturbance leading to voltage collapse may be initiated by a variety of causes, the underlying problem is an inherent weakness in the power system. The factors contributing to voltage collapse are the generator reactive power /voltage control limits, load characteristics, characteristics of reactive compensation devices, and the action of the voltage control devices such as transformer On Load Tap Changers (OLTCs). Power system experiences abnormal operating conditions following a disturbance, and subsequently a reduction in the EHV level voltages at load centers will be reflected on the distribution system. The OLTCs of distribution transformers would restore distribution voltages. With each tap change operation, the MW and MVAR loading on the EHV lines would increase, thereby causing great voltage drops in EHV levels and increasing the losses. As a result, with each tap changing operation, the reactive output of generators throughout the system would increase gradually and the generators may hit their reactive power capability limits, causing voltage instability problems. Thus, the operation of certain OLTCs has a significant influence on voltage instability under some operating conditions. These transformers can be made manual to avoid possible voltage instability due to their operation during heavy load conditions. Tap blocking, based on local measurement of high voltage side of load tap changers, is a common practice of power utilities to prevent voltage collapse. The great advantage of this method is that it can be easily implemented, but does not guarantee voltage stability. So a proper approach for identification of critical OLTC s based on voltage stability criteria is essential to guide the operator in ECC, which has been proposed in this thesis. It discusses the effect of OLTCs with different objectives of reactive power dispatch and proposes a technique to identify critical OLTCs based on voltage stability criteria. The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as High Voltage DC transmission (HVDC) and Flexible AC Transmission System (FACTS), which can be applied in transmission and distribution systems. The technical and economicalBenefits of these technologies represent an alternative to the application in AC systems. Deregulation in the power industry and opening of the market for delivery of cheaper energy to the customers is creating additional requirements for the operation of power systems. HVDC and FACTS offer major advantages in meeting these requirements. .A method for co-ordinated optimum allocation of reactive power in AC/DC power systems by including FACTS controller UPFC, with an objective of minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization.minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization. As power systems grow in their size and interconnections, their complexity increases. For secure operation and control of power systems under normal and contingency conditions, it is essential to provide solutions in real time to the operator in ECC. For real time control of power systems, the conventional algorithmic software available in ECC are found to be inadequate as they are computationally very intensive and not organized to guide the operator during contingency conditions. Artificial Intelligence (AI) techniques such as, Expert systems, Neural Networks, Fuzzy systems are emerging decision support system tools which give fast, though approximate, but acceptable right solutions in real time as they mostly use symbolic processing with a minimum number of numeric computations. The solution thus obtained can be used as a guide by the operator in ECC for power system control. Optimum real and reactive power dispatch play an important role in the day-to-day operation of power systems. Existing conventional Optimal Power Flow (OPF) methods use all of the controls in solving the optimization problem. The operators can not move so many control devices within a reasonable time. In this context an algorithm using fuzzy-expert approach has been proposed in this thesis to curtail the number of control actions, in order to realize real time objectives in voltage/reactive power control. The technique is formulated using membership functions of linguistic variables such as voltage deviations at all the load buses and the voltage deviation sensitivity to control variables. Voltage deviations and controlling variables are translated into fuzzy set notations to formulate the relation between voltage deviations and controlling ability of controlling devices. Control variables considered are switchable VAR compensators, OLTC transformers and generator excitations. A fuzzy rule based system is formed to select the critical controllers, their movement direction and step size. Results show that the proposed approach is effective for improving voltage security to acceptable levels with fewer numbers of controllers. So, under emergency conditions the operator need not move all the controllers to different settings and the solution obtained is fast with significant speedups. Hence, the proposed method has the potential to be integrated for on-line implementation in energy management systems to achieve the goals of secure power system operation. In a deregulated electricity market, it may not be always possible to dispatch all of the contracted power transactions due to congestion of the transmission corridors. System operators try to manage congestion, which otherwise increases the cost of the electricity and also threatens the system security and stability. An approach for alleviation of network over loads in the day-to-day operation of power systems under deregulated environment is presented in this thesis. The control used for overload alleviation is real power generation rescheduling based on Relative Electrical Distance (RED) concept. The method estimates the relative location of load nodes with respect to the generator nodes. The contribution of each generator for a particular over loaded line is first identified , then based on RED concept the desired proportions of generations for the desired overload relieving is obtained, so that the system will have minimum transmission losses and more stability margins with respect to voltage profiles, bus angles and better transmission tariff. The results obtained reveal that the proposed method is not only effective for overload relieving but also reduces the system power loss and improves the voltage stability margin. The presented concepts are better suited for finding the utilization of resources generation/load and network by various players involved in the day-to-day operation of the system under normal and contingency conditions. This will help in finding the contribution by various players involved in the congestion management and the deviations can be used for proper tariff purposes. Suitable computer programs have been developed based on the algorithms presented in various chapters and thoroughly tested. Studies have been carried out on various equivalent systems of practical real life Indian power networks and also on some standard IEEE systems under simulated conditions. Results obtained on a modified IEEE 30 bus system, IEEE 39 bus New England system and four Indian power networks of EHV 24 bus real life equivalent power network, an equivalent of 36 bus EHV Indian western grid, Uttar Pradesh 96 bus AC/DC system and 205 Bus real life interconnected grid system of Indian southern region are presented for illustration purposes.

The objective of an Energy Control Center (ECC) is to ensure secure and economic operation of power system. The challenge to optimize power system operation, while maintaining system security and quality of power supply to customers, is increasing. Growing demand without matching expansion of generation and transmission facilities and more tightly interconnected power systems contribute to the increased complexity of system operation. Rising costs due to inflation and increased environmental concerns has made transmission, as well as generation systems to be operated closure to design limits, with smaller safety margins and hence greater exposure to unsatisfactory operating conditions following a disturbance. Investigations of recent blackouts indicate that the root cause of most of these major power system disturbances is voltage collapse. Information gathered and preliminary analysis, from the most recent blackout incident in North America on 14th August 2003, is pointing the finger on voltage instability due to some unexpected contingency. In this incident, reports indicate that approximately 50 million people were affected interruption from continuous supply for more than 15 hours. Most of the incidents are related to heavily stressed system where large amounts of real and reactive power are transported over long transmission lines while appropriate real and reactive power resources are not available to maintain normal system conditions. Hence, the problem of voltage stability and voltage collapse has become a major concern in power system planning and operation. Reliable operation of large scale electric power networks requires that system voltages and currents stay within design limits. Operation beyond those limits can lead to equipment failures and blackouts. In the last few decades, the problem of reactive power control for improving economy and security of power system operation has received much attention. Generally, the load bus voltages can be maintained within their permissible limits by reallocating reactive power generations in the system. This can be achieved by adjusting transformer taps, generator voltages, and switchable Ar sources. In addition, the system losses can be minimized via redistribution of reactive power in the system. Therefore, the problem of the reactive power dispatch can be optimized to improve the voltage profile and minimize the system losses as well. The Instability in power system could be relieved or at least minimized with the help of most recent developed devices called Flexible AC Transmission System (FACTS) controllers. The use of Flexible AC Transmission System (FACTS) controllers in power transmission system have led to many applications of these controllers not only to improve the stability of the existing power network resources but also provide operating flexibility to the power system. In the past, transmission systems were owned by regulated, vertically integrated utility companies. They have been designed and operated so that conditions in close proximity to security boundaries are not frequently encountered. However, in the new open access environment, operating conditions tend to be much closer to security boundaries, as transmission use is increasing in sudden and unpredictable directions. Transmission unbundling, coupled with other regulatory requirements, has made new transmission facility construction more difficult. In fact, there are numerous technical challenges emerging from the new market structure. There is an acute need for research work in the new market structure, especially in the areas of voltage security, reactive power support and congestion management. In the last few decades more attention was paid to optimal reactive power dispatch. Since the problem of reactive power optimization is non-linear in nature, nonlinear programming methods have been used to solve it. These methods work quite well for small power systems but may develop convergence problems as system size increases. Linear programming techniques with iterative schemes are certainly the most promising tools for solving these types of problems. The thesis presents efficient algorithms with different objectives for reactive power optimization. The approach adopted is an iterative scheme with successive power-flow analysis using decoupled technique, formulation and solution of the linear-programmingproblem with only upper-bound limits on the state variables. Further the thesispresents critical analysis of the three following objectives, Viz., •Minimization of the sum of the squares of the voltage deviations (Vdesired) •Minimization of sum of the squares of the voltage stability L indices (Vstability) •Minimization of real power losses (Ploss) Voltage stability problems normally occur in heavily stressed systems. While the disturbance leading to voltage collapse may be initiated by a variety of causes, the underlying problem is an inherent weakness in the power system. The factors contributing to voltage collapse are the generator reactive power /voltage control limits, load characteristics, characteristics of reactive compensation devices, and the action of the voltage control devices such as transformer On Load Tap Changers (OLTCs). Power system experiences abnormal operating conditions following a disturbance, and subsequently a reduction in the EHV level voltages at load centers will be reflected on the distribution system. The OLTCs of distribution transformers would restore distribution voltages. With each tap change operation, the MW and MVAR loading on the EHV lines would increase, thereby causing great voltage drops in EHV levels and increasing the losses. As a result, with each tap changing operation, the reactive output of generators throughout the system would increase gradually and the generators may hit their reactive power capability limits, causing voltage instability problems. Thus, the operation of certain OLTCs has a significant influence on voltage instability under some operating conditions. These transformers can be made manual to avoid possible voltage instability due to their operation during heavy load conditions. Tap blocking, based on local measurement of high voltage side of load tap changers, is a common practice of power utilities to prevent voltage collapse. The great advantage of this method is that it can be easily implemented, but does not guarantee voltage stability. So a proper approach for identification of critical OLTC s based on voltage stability criteria is essential to guide the operator in ECC, which has been proposed in this thesis. It discusses the effect of OLTCs with different objectives of reactive power dispatch and proposes a technique to identify critical OLTCs based on voltage stability criteria. The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as High Voltage DC transmission (HVDC) and Flexible AC Transmission System (FACTS), which can be applied in transmission and distribution systems. The technical and economicalBenefits of these technologies represent an alternative to the application in AC systems. Deregulation in the power industry and opening of the market for delivery of cheaper energy to the customers is creating additional requirements for the operation of power systems. HVDC and FACTS offer major advantages in meeting these requirements. .A method for co-ordinated optimum allocation of reactive power in AC/DC power systems by including FACTS controller UPFC, with an objective of minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization.minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization. As power systems grow in their size and interconnections, their complexity increases. For secure operation and control of power systems under normal and contingency conditions, it is essential to provide solutions in real time to the operator in ECC. For real time control of power systems, the conventional algorithmic software available in ECC are found to be inadequate as they are computationally very intensive and not organized to guide the operator during contingency conditions. Artificial Intelligence (AI) techniques such as, Expert systems, Neural Networks, Fuzzy systems are emerging decision support system tools which give fast, though approximate, but acceptable right solutions in real time as they mostly use symbolic processing with a minimum number of numeric computations. The solution thus obtained can be used as a guide by the operator in ECC for power system control. Optimum real and reactive power dispatch play an important role in the day-to-day operation of power systems. Existing conventional Optimal Power Flow (OPF) methods use all of the controls in solving the optimization problem. The operators can not move so many control devices within a reasonable time. In this context an algorithm using fuzzy-expert approach has been proposed in this thesis to curtail the number of control actions, in order to realize real time objectives in voltage/reactive power control. The technique is formulated using membership functions of linguistic variables such as voltage deviations at all the load buses and the voltage deviation sensitivity to control variables. Voltage deviations and controlling variables are translated into fuzzy set notations to formulate the relation between voltage deviations and controlling ability of controlling devices. Control variables considered are switchable VAR compensators, OLTC transformers and generator excitations. A fuzzy rule based system is formed to select the critical controllers, their movement direction and step size. Results show that the proposed approach is effective for improving voltage security to acceptable levels with fewer numbers of controllers. So, under emergency conditions the operator need not move all the controllers to different settings and the solution obtained is fast with significant speedups. Hence, the proposed method has the potential to be integrated for on-line implementation in energy management systems to achieve the goals of secure power system operation. In a deregulated electricity market, it may not be always possible to dispatch all of the contracted power transactions due to congestion of the transmission corridors. System operators try to manage congestion, which otherwise increases the cost of the electricity and also threatens the system security and stability. An approach for alleviation of network over loads in the day-to-day operation of power systems under deregulated environment is presented in this thesis. The control used for overload alleviation is real power generation rescheduling based on Relative Electrical Distance (RED) concept. The method estimates the relative location of load nodes with respect to the generator nodes. The contribution of each generator for a particular over loaded line is first identified , then based on RED concept the desired proportions of generations for the desired overload relieving is obtained, so that the system will have minimum transmission losses and more stability margins with respect to voltage profiles, bus angles and better transmission tariff. The results obtained reveal that the proposed method is not only effective for overload relieving but also reduces the system power loss and improves the voltage stability margin. The presented concepts are better suited for finding the utilization of resources generation/load and network by various players involved in the day-to-day operation of the system under normal and contingency conditions. This will help in finding the contribution by various players involved in the congestion management and the deviations can be used for proper tariff purposes. Suitable computer programs have been developed based on the algorithms presented in various chapters and thoroughly tested. Studies have been carried out on various equivalent systems of practical real life Indian power networks and also on some standard IEEE systems under simulated conditions. Results obtained on a modified IEEE 30 bus system, IEEE 39 bus New England system and four Indian power networks of EHV 24 bus real life equivalent power network, an equivalent of 36 bus EHV Indian western grid, Uttar Pradesh 96 bus AC/DC system and 205 Bus real life interconnected grid system of Indian southern region are presented for illustration purposes.