The verification of power grids in modern integrated circuits must start early in the design process when adjustments can be most easily incorporated. We adopt an existing early verification framework. The framework is vectorless, i.e., it does not require input test patterns and does not rely on simulating the power grid subject to these patterns. In this framework, circuit uncertainty is captured via a set of current constraints that capture what may be known or specified from circuit behavior. Grid verification becomes a question of finding the worst-case grid behavior which, in turn, entails the solution of linear programs (LPs) whose size and number is proportional to the size of the grids. The thesis builds on this systematic framework for dealing with circuit uncertainty with the aim of improving efficiency and expanding the capabilities handled within. One contribution introduces an efficient method based on a sparse approximate inverse technique to greatly reduce the size of the required linear programs while ensuring a user-specified over-estimation margin on the exact solution. The application of the method is exhibited under both R and RC grid models. Another contribution first extends grid verification under RC grid models to also check for the worst-case branch currents. This would require as many LPs as there are branches. Then, it shows how to adapt the approximate inverse technique to speed up the branch current verification process. A third contribution proposes a novel approach to reduce the number of LPs in the voltage drop and branch current verification problems. This is achieved by examining dominance relations among node voltage drops and among branch currents. This allows us to replace a group of LPs by one conservative and tight LP. A fourth contribution proposes an efficient verification technique under RLC models. The proposed approach provides tight conservative bounds on the maximum and minimum worst-case voltage drops at every node on the grid.

The verification of power grids in modern integrated circuits must start early in the design process when adjustments can be most easily incorporated. We adopt an existing early verification framework. The framework is vectorless, i.e., it does not require input test patterns and does not rely on simulating the power grid subject to these patterns. In this framework, circuit uncertainty is captured via a set of current constraints that capture what may be known or specified from circuit behavior. Grid verification becomes a question of finding the worst-case grid behavior which, in turn, entails the solution of linear programs (LPs) whose size and number is proportional to the size of the grids. The thesis builds on this systematic framework for dealing with circuit uncertainty with the aim of improving efficiency and expanding the capabilities handled within. One contribution introduces an efficient method based on a sparse approximate inverse technique to greatly reduce the size of the required linear programs while ensuring a user-specified over-estimation margin on the exact solution. The application of the method is exhibited under both R and RC grid models. Another contribution first extends grid verification under RC grid models to also check for the worst-case branch currents. This would require as many LPs as there are branches. Then, it shows how to adapt the approximate inverse technique to speed up the branch current verification process. A third contribution proposes a novel approach to reduce the number of LPs in the voltage drop and branch current verification problems. This is achieved by examining dominance relations among node voltage drops and among branch currents. This allows us to replace a group of LPs by one conservative and tight LP. A fourth contribution proposes an efficient verification technique under RLC models. The proposed approach provides tight conservative bounds on the maximum and minimum worst-case voltage drops at every node on the grid.

There are unique challenges and opportunities related to the integration of electric vehicles into the future power grid, especially the modern distribution grid since electric vehicle (EV) charging facilities and fast-charging stations are usually tied to low-voltage and medium-voltage power networks. The grid-connected EVs, if properly controlled, can operate as distributed energy storage and provide various ancillary services, such as peak shaving, fast-response reserve capacity, frequency regulation, voltage control and reactive supports. The purpose of this thesis is to integrate EVs to the power grid and provides suitable ancillary services to improve the grid reliability and stability. The larger future penetration of EVs and renewable energies is also taken into account to develop the vehicle-to-grid (V2G) control scheme with the constraints of EV charging and communication infrastructures. The main contents include: V2G mathematical model and system configuration; impact evaluation of EV integration and the V2G control framework; energy scheduling of EVs integration; V2G dynamic regulation services; control method of EV aggregator for dispatching a fleet of EVs; and the evaluation of V2G control scheme and hardware-in-the-loop experimental system design. 　　In the thesis, the impact of EV charging demand on the conventional distribution grid is firstly estimated to reveal the negative effects of the arbitrary EV charging and the necessity to control the EV charging process. The potential benefits EVs can bring into the power grid support are discussed and a V2G control framework is proposed to perform the V2G optimization and various regulation services. The current power electronics applied EV charging facilities and communication network are integrated into the V2G operation in the future distribution grid with microgrid and smaller installation of renewable generation units. 　　Next, mathematical model of V2G power control is formulated. Two optimization methods are proposed to schedule the EV charging and discharging energy to minimize the power losses and the operating cost while satisfying the mobility needs and the power system limitations. Subsequently, the dynamic regulation of V2G power is investigated to unleash the potential of EVs to provide multiple ancillary services simultaneously. In addition to V2G optimal energy scheduling, EVs can also be employed for dynamic power regulation which requires the fast response to the instantaneous imbalance between the power supply and demand. V2G power is controlled to mitigate the power fluctuation caused by the intermittent wind energy resources, and thus stabilize the system frequency and voltage. Finally, an EV-centric hybrid energy storage system is proposed, which combines the merits of V2G operation and superconducting magnetic energy storage (SMES) to enhance the power quality and system frequency stability. The critical issues in V2G applications are summarized in the end. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

In recent years, since the concept of smart grid rises and the existing power grids are continuously modernized, more and more electric vehicles (EVs) are integrated into the power grid. In the power grid, EVs are expected to provide various energy services, such as spinning reserves, regulation services, optimization services, stability improvement, reactive compensation and grid security. This thesis is to model, analyze and implement these energy services of EVs. 　　Firstly, a multilayer framework of a power system with vehicle-to-grid (V2G) and vehicle-to-vehicle (V2V) operation is proposed. Its fundamental components including batteries, renewable energy sources are modeled for system analysis. Moreover, a general model for multiply purposes is presented. 　　Secondly, based on the modeling of EVs and the power systems, the analysis on frequency regulation and transient stability of the V2G system can be carried out effectively. The objectives of the frequency regulation are to keep the system frequency constant, and eliminate the deviations fast and effectively. While, the transient stability is to observe the performances of the power systems integrated with EVs and superconducting magnetic energy storage (SMES) during emergency cases. The results illustrate that EVs are valuable for improve the frequency and transient stability of the power systems. 　　Finally, the coordination and optimization of the power systems with EVs are studied. Unit commitment involving EVs is analyzed, which uses EVs to replace some expensive generating units to achieve minimum operating cost and emissions. In addition, the optimal sizing of EV aggregations in the distribution power system is conducted to minimize the total power loss. And the individual EV in the aggregations is dispatched to achieve minimum charging cost by satisfying the optimal sized demand and the real-time pricing. The results verified that EVs can be used to achieve optimized goals, such as minimum costs, emissions and losses. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Electrical energy generation and distribution systems are good examples of complex systems. They include continuous, discrete, and social dynamics. They are operated by millions of human and non-human (or electro-mechanical) agents, and they show statistical properties found in other complex systems, such as power-law distributions in failure sizes. A number of recent large blackouts in Europe and North America have emphasized the societal importance of understanding these dynamics. Classical electromagnetic analysis alone frequently does not provide the insight required to characterize and mitigate risks in the electricity infrastructure. The objective of this thesis is to obtain insights into the dynamics of power grids using tools from the science of complex systems. In particular, this thesis will compare the topology, electrical structure, and attack/failure tolerance of power grids with those of theoretical graph structures such as regular, random, small-world, and scale-free networks. Simulation results in this thesis will describe the cost of the disturbances as a function of failure or attack sizes. The cost associated with network perturbations is often measured by changes on the diameter or average path length, whereas in the electricity industry, the loss of power demand (or blackout size) is the best indicator of the cost or impact of disturbances to electricity infrastructure.

Achieving a low carbon economy has been the focus of Hong Kong in recent years. Strategies are put forth to support sustainable energy, because Hong Kong has inadequate local and renewable energy reserves. Smart grid technologies have benefited many countries in the world, and countries such as the United States, the United Kingdom, China, and South Korea are exploring this new green energy strategy. Hong Kong’s power companies have considered smart grid technologies, conducting pilot projects to test their local feasibility. In this research, stakeholders’ perspectives of the current status of smart grids are overviewed in Hong Kong from the angle of policy aspect. Stakeholder theory is utilized as the framework for understanding and analyzing the perceptions of stakeholder groups. An integrated and modified stakeholder power-interest matrix was developed for analyzing level of power and interest of stakeholder groups on smart grid from policy dimension. Through the course of this research project, qualitative interviews were conducted for 11 interviewees with subjectsfrom1six stakeholder groups, including: academics, advisory bodies, business, government, non-governmental organizations, and power companies. Follow-up quantitative questionnaires were distributed to the same target group for stakeholder analysis and to map the level of power and interest of stakeholder groups regarding smart grid policy development in Hong Kong. The data collected from interviews were compared with and contrasted against each stakeholder groups and other countries, with a view to identifying common motivations, barriers, and policy suggestions. The findings reveal that the six stakeholder groups hold medium to high power and interest in smart grid policy development in Hong Kong. Common motivations identified by local stakeholder groups include: the right to choose their own energy mix for power generation, potential behavioural change via smart meter and tariff restructuring, possible energy savings and emissions reductions for the environment, and corporate social responsibility. The most significant motivation for smart grid development shared with other countries is the goal of achieving low carbon economy and energy efficiency. Shared barriers perceived by the six stakeholder groups are: unreliable renewable power supplies, significant capital investments required, impracticalities of supplying electricity back to the grid, transfers of additional power generation costs to consumers, and limited smart grid knowledge by the public. The most significant barrier shared with international countries is funding mechanism, yet it may be difficult for Hong Kong to secure funding from the government because of problems of trust. Three stages of recommendations are suggested. Short-term recommendations centre on the policy development direction of smart grid in Hong Kong, and include implementing dynamic pricing, undertaking a large-scale pilot program and establishing an awareness campaign (funded by the government)for educating the general public. Medium-term recommendation is to establish a joint green fund with the contributions of companies with large carbon footprints. Long-term recommendations include market liberalization and increases in market competition. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

Electromigration is re-emerging as a significant problem in modern integrated circuits (IC). Especially in power-grids, due to shrinking wire widths and increasing current densities, there is little or no margin left between the predicted EM stress and that allowed by the EM design rules. Statistical Electromigration Budgeting estimates the reliability of the grid by considering it as a series system. However, a power grid with its many parallel paths has much inherent redundancy. In this work, we propose a new model to estimate the MTF and reliability of the power grid under the influence of EM, which accounts for these redundancies. To implement the mesh model, we also develop a framework to estimate the change in statistics of an interconnect as its effective-EM current varies. The results indicate that the series model gives a pessimistic estimate of power grid MTF by a factor of 3-4.

Electromigration is re-emerging as a significant problem in modern integrated circuits (IC). Especially in power-grids, due to shrinking wire widths and increasing current densities, there is little or no margin left between the predicted EM stress and that allowed by the EM design rules. Statistical Electromigration Budgeting estimates the reliability of the grid by considering it as a series system. However, a power grid with its many parallel paths has much inherent redundancy. In this work, we propose a new model to estimate the MTF and reliability of the power grid under the influence of EM, which accounts for these redundancies. To implement the mesh model, we also develop a framework to estimate the change in statistics of an interconnect as its effective-EM current varies. The results indicate that the series model gives a pessimistic estimate of power grid MTF by a factor of 3-4.

The outstanding features of modular multilevel converters (MMC) have recently gained much attention in the high-voltage direct-current (HVDC) transmission field. Power quality, converter cost and system performance are three crucial aspects of HVDC MMCs which are directly linked to the converter modulation and switching schemes. High power quality and performance require high switching frequency and large cell capacitor whereas low switching frequency and small cell capacitor are needed to reduce the converter cost. The main objective of this thesis is to propose a practical switching method for HVDC MMCs which balances the aforementioned contradictory requirements. A mathematical analysis of the converter switching pattern, against the power quality and converter cost, has been conducted to formulate an optimization problem for MMCs. Different objective functions are studied for the formulated optimization problem such as converter loss minimization, voltage imbalance minimization and computational burden minimization. This thesis proposes three methods to address different objective functions. Ultimately, a real-time simulator has been built to practically verify and investigate the performance of the proposed methods in a realistic point-to-point HVDC link. The most significant outcome of this thesis is the tolerance band-based switching scheme which offers a direct control of the cell capacitor voltage, low power losses, and robust dynamic performance. As a result, the converter switching frequency can reach frequencies as low as 70 Hz (with the proposed cell tolerance band (CTB) method). A modified optimized CTB method is proposed to minimize the converter switching losses and it could reduce the converter switching losses by 60% in comparison to the conventional phase shifted carrier modulation method. It is concluded intelligent utilization of sorting algorithm can enable efficient HVDC station operation by reducing the converter cost. / <p>QC 20160916</p>

Made available in DSpace on 2015-04-09T12:28:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-12-01Bitstream added on 2015-04-09T12:48:14Z : No. of bitstreams: 1 000813588.pdf: 5039777 bytes, checksum: 5cf7448ce5632b008c0f6ddc5804f4c6 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As smart grids e os smart meters, ou redes inteligentes, respectivamente, tornam-se uma realidade cada vez mais próxima dos consumidores residenciais mundo afora. Diversos paises vêm desenvolvendo estudos com foco nos impactos relacionados à introdução destas novas tecnologias, e a eficiência energética é um dos grandes objetivos a serem alcançados. Os ganhos relacionados à eficiência energética poderão ser percebidos diretamente pelo consumidor através da economia nas contas de energia elétrica. Também serão observados pelas concessionárias através da minimização das perdas de transmissão e distribuição, pelo aumento na estabilidade do sistema, na minimização do carregamento durante os horários de pico, entre outros. Para demonstrar o potencial de eficiência energética serão apresentadas duas referências, uma focando em medidores inteligentes e suas interfaces com os usuários, e a outra relacionando as smart grids a novos conceitos como o demand response. Os smart meters são a base para implantação das smart grids, além de serem indispensáveis na realização de testes como os apresentados. Existem no mercado diversos modelos de medidores eletrônicos disponíveis bem como kits didáticos para desenvolvimento, entretanto, dependendo da aplicação podem se tornar limitados ou inflexíveis quanto à modificações. Assim é apresentado o desenvolvimento de um smart meter de baixo custo com estrutura flexível, tendo com objetivo obter precisão e exatidão nas medidas além da capacidade de armazenar os dados coletados, possibilitando análises posteriores. O smart meter desenvolvido alcançou seus objetivos, mostrando-se uma ferramenta bastante interessante para o monitoramento da rede e também do comportamento dos consumidores / The smart grids and smart meters become a reality closer to residential consumers worldwide. Several countries are developing studies with focus on impacts related to the introduction of these new technologies and energy efficiency is one of the major objectives to be achieved. Gains related to energy efficiency will be felt directly by the consumer through the economy in electricity bills. Will also be noted by the concessionaires by minimizing transmission and distribution losses, by the increased system stability, minimizing the load during peak hours, among others. To demonstrate the potential of energy efficiency will be presented two references, one focusing on the introduction of smart meters and their interfaces with users and other relating the smart grids and new concepts such as demand response. The smart meters are the basis for the implementation of the smart grids, and are indispensable to conducting tests as presented. There are many electronic meters as well as educational kits for development available in the market, however, depending on the application may become limited or inflexibe regarding to modifications. Finally it is presented the development of a low cost smart meter, with a flexibe structure, aiming to achieve accuracy and precision in the measurements plus the ability to store the collected data, allowing further analysis. The smart developed achieved it objectives and proved to be a very interesting tool to monitor the network and also the behavior of consumers