Power conversion system design issues are expanding their role in information technology equipment design philosophies. These issues include not only improving power conversion efficiency, but also increased concerns regarding the cost and complexity of the power conversion design techniques utilized to satisfy the host system's total performance requirements. In particular, in computer system (personal computers, workstations, and servers) designs, the power "supplies" are rapidly becoming a limiting factor in meeting overall design objectives. This dissertation addresses the issue of simplifying the architecture of distributed power systems incorporated into computing equipment. In the dissertation's first half, the subject of the design of the distributed power system's front-end converter is investigated from the perspective of simplifying the conversion process while simultaneously improving efficiency. This is initially accomplished by simplifying the second-stage DC/DC converter in the standard two-stage front-end design (PFC followed by DC/DC conversion) through the incorporation of secondary-side control. Unique modifications are then made to two basic topologies (the flyback and boost converter topologies) that enable the two-stage front-end design to be reduced to an isolated PFC conversion stage, resulting in a front-end design that features reduced complexity and higher efficiency. In the dissertation's second half, the overall DC distributed power system design concept is simplified through the elimination of power processing conversion steps - the result being the creation of a high-frequency (HF) AC distributed power system. Design techniques for generating, distributing, and processing HF AC power in this new system are developed and experimentally verified. Also, an experimental comparison between both DC and AC distributed power systems is performed, illustrating in a succinct fashion the merits and limitations of both approaches. / Ph. D.

Small-signal stability is of great concern for distributed power systems with a large number of regulated power converters. These converters are constant-power loads (CPLs) exhibit a negative incremental input resistance within the output voltage regulation bandwidth. In the case of dc systems, design requirements for impedances that guarantee stability have been previously developed and are used in the design and specification of these systems. In terms of three-phase ac systems, a mathematical framework based on the generalized Nyquist stability criterion (GNC), reference frame theory, and multivariable control is set forth for stability assessment. However, this approach relies on the actual measurement of these impedances, which up to now has severely hindered its applicability. Addressing this shortcoming, this research investigates the small-signal stability of three-phase ac systems using measured d-q frame impedances. Prior to this research, negative incremental resistance is only found in CPLs as a results of output voltage regulation. In this research, negative incremental resistance is discovered in grid-tied inverters as a consequence of grid synchronization and current injection, where the bandwidth of the phase-locked loop determines the frequency range of the negative incremental resistance behavior, and the power rating of inverter determines the magnitude of the resistance. Prior to this research, grid synchronization stability issue and sub-synchronous oscillations between grid-tied inverter and its nearby rectifier under weak grid condition are reported and analyzed using characteristic equation of the system. This research proposes a more design oriented analysis approach based on the negative incremental resistance concept of grid-tied inverters. Grid synchronization stability issues are well explained under the framework of GNC. Although stability and its margin of ac system can be addressed using source and load impedances in d-q frame, method to specify the shape of load impedances to assure system stability is not reported. This research finds out that under unity power factor condition, three-phase ac system is decoupled. It can be simplified to two dc systems. Load impedances can be then specified to guarantee system stability and less conservative design. / Ph. D.

The electric power grid is operated with exceptionally high levels of reliability, yet recent large-scale outages have highlighted areas for improvement in operation, control, and planning of power systems.  Synchrophasor technology may be able to address these concerns, and Phasor Measurement Units (PMUs) are actively being deployed across the Western Interconnection and North America.  Initiatives such as the Western Interconnection Synchrophasor Program (WISP) are making significant investments PMUs with the expectation that wide-area, synchronized, high-resolution measurements will improve operator situational awareness, enable advanced control strategies, and aid in planning the grid. This research is multifaceted in that it focuses on improved operator awareness and alarming as well as innovative remedial controls utilizing synchrophasors.  It integrates existing tools, controls, and infrastructure with new technology to propose applications and schemes that can be implemented for any utility.  This work presents solutions to problems relevant to the industry today, emphasizing utility design and implementation.  The Bonneville Power Administration (BPA) and Western Electricity Coordinating Council (WECC) transmission systems are used as the testing environment, and the work performed here is being explored for implementation at BPA.  However, this work is general in nature such that it can be implemented in myriad networks and control centers. A Phase Angle Alarming methodology is proposed for improving operator situational awareness.  The methodology is used for setting phase angle limits for a two-tiered angle alarming application.  PMUs are clustered using an adapted disturbance-based probabilistic rms-coherency analysis.  While the lower tier angle limits are determined using static security assessment between the PMU clusters, the higher tier limits are based on pre-contingency operating conditions that signify poorly damped post-contingency oscillation ringdown.  Data mining tools, specifically decision trees, are employed to determine critical indicators and their respective thresholds.  An application is presented as a prototype; however, the methodology may be implemented in online tools as well as offline studies. System response to disturbances is not only dependent on pre-contingency conditions but also highly dependent on post-contingency controls.  Pre-defined controls such as Special Protection Schemes (SPSs) or Remedial Action Schemes (RAS) have a substantial impact on the stability of the system.  However, existing RAS controls are generally event-driven, meaning they respond to predetermined events on the system.  This research expands an existing event-driven voltage stability RAS to a response-based scheme using synchrophasor measurements.  A rate-of-change algorithm is used to detect substantial events that may put the WECC system at risk of instability.  Pickup of this algorithm triggers a RAS that provides high-speed wide-area reactive support in the BPA area.  The controls have proved effective for varying system conditions and topologies, and maintain stability for low probability, high consequence contingencies generally dismissed in today's deterministic planning studies. With investments being made in synchrophasor technology, the path of innovation has been laid; it's a matter of where it goes.  The goal of this research is to present simple, yet highly effective solutions to problems.  Doing so, the momentum behind synchrophasors can continue to build upon itself as it matures industry-wide. / Ph. D.

Electrical energy is one of the most common forms of energy these days. Consequently, electric power system is an indispensable part of any society. However, due to the deregulation of electricity markets and the growth in the share of power generation by uncontrollable renewable energies such as wind and solar, power system simulations are more challenging than earlier. Thus, new techniques for simplifying these simulations are needed. One important example of such simplification techniques is the power system reduction. Power system reduction can be used at least for four different purposes: a) Simplifying the power system simulations, b) Reducing the computational complexity, c) Compensating the data unavailability, and d) Reducing the existing uncertainty. Due to such reasons, power system reduction is an important and necessary subject, but a challenging task to do. Power system reduction is even more essential when system operators are facing very large-scale power systems and when the renewable energy resources like hydro, wind, and solar have a high share in power generation. This thesis focuses on the topic of large-scale power system reduction with high penetration of renewable energy resources and tries to pursue the following goals: • The thesis first reviews the different methods which can be used for simplifying the power system studies, including the power system reduction. A comparison among three important simplification techniques is also performed to reveal which simplification results in less error and more simulation time decrement. • Secondly, different steps and methods for power system reduction, including network aggregation and generation aggregation, are introduced, described and discussed. • Some improvements regarding the subject of power system reduction, i.e. on both network aggregation and generation aggregation, are developed. • Finally, power system reduction is applied to some power system problems and the results of these applications are evaluated. A general conclusion is that using power system simplification techniques and specially the system reduction can provides many important advantages in studying large-scale power systems with high share of renewable energy generations. In most of applications, not only the power system reduction highly reduces the complexity of the power system study under consideration, but it also results in small errors. Therefore, it can be used as an efficient method for dealing with current bulk power systems with huge amounts of renewable and distributed generations. / <p>The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively. QC 20150116</p>

No description available.

Hurricanes are a threat to power and telecommunication infrastructure. This work summarizes a method for hurricane characterization using the proposed Localized Tropical Cyclone Intensity Index(LTCII) as a model for estimating damages to Electric power infrastructure. The model considers the effect of storm surge, maximum sustained wind speeds, the duration of time for which the system has been under tropical storm conditions and the area swept by hurricane over land. The measurements focus on major load centers in the system. The validation of the outage data is discussed. The model is evaluated for hurricanes from 2004, 2005 and 2008 hurricane seasons. The degree of influence of various hurricane parameters on the damages suffered by electric power systems are discussed using case studies. The maximum outages are observed to follow a logistic regression curve with respect to log(LTCII), with a correlation of 0.85. The observed restoration times fit a 6th degree polynomial with an R2 = 0.6. The effects of time under tropical storm winds were observed to have great significance in the damage profile observed with the model. / text

Wind power generation influences on the quality of the power grid. Because wind velocity is consistently changing this change causes unstable wind power generation. Since more wind power is expected to be used in the future, it is crucial to study the influence of the wind penetration level on normalized-damping ratio and damped-resonant frequency. In this thesis three types of calculated data were used to analyze the effect of wind penetration level on the Texas power grid: the percentage of wind power generation in Texas, generator-unit trip damping coefficient, and damped-resonant frequency. The percentage of wind energy was calculated from wind data provided by the Electric Reliability Council of Texas. The damping coefficient and damped-resonant frequency values are the indicators of power system stability and were calculated from synchronized phase data from the Texas power grid. The synchronized phase measurements were collected from the University of Texas at Austin and the wind farm near the Mc-Donald observatory. The data analyzed in this paper were from September 2009 to February 2010. The wind data were correlated to the grid-stability indicators which allowed us to interpret the status of the power grid according to the wind penetration level. When the wind penetration level increased over 11 %, five generator trip events occurred with damping coefficient values ten times higher than those of the regular unit trips. Moreover, during those events, damped-resonant frequency values rose nearly four times higher than the frequency values of other events. The results of this study may lead us to the conclusion that simply increasing the capacity of wind power generation will cause the power system to become unstable, and this will result in low quality of electricity. Therefore, further study is needed to determine the optimum amount of wind power generation without causing instability in the power grid. / text

Most power market structures have been developed and implemented without being tested, causing major problems such as shortages and blackouts. The main cause for these problems is the inability of some markets to provide adequate stimulus for new generation investments. The installed generation capacity goes through boom and bust cycles, exposing consumers to potential shortages during long bust periods. With the realisation that the power market has a strong interaction with generation investment, a System Dynamics (SD) model is developed to study how the market interacts with generation expansion. The SD model also allows for market structures and policies to be evaluated before being implemented. It can be an important tool in ensuring that generation expansion is done optimally without the expense of energy security. New Zealand’s generation capacity is no exception to the boom and bust trend. Since the commencement of the New Zealand Energy Market (NZEM) in October 1996, energy shortages occurred in the winters of 2001, 2003 and 2008. As a case study, an SD model is developed to study the NZEM. The results show that under some forecasted scenarios, New Zealand is susceptible to future energy shortages due to boom and bust cycles in the generation capacity.

To date, the potential of on-line Dynamic Security Assessment (DSA) to monitor, alert, and enhance system security is constrained by the longer computational cycle time. Traditional techniques requiring extensive numerical computations make it challenging to complete the assessment within an acceptable time. Longer computational cycles produce obsolete security assessment results as the system operating point evolves continuously. This thesis presents a DSA algorithm, based on Transient Energy Function (TEF) method and machine learning, to enable frequent computational cycles in on-line DSA of power systems. The use of selected terms of the TEF as pre-processed input features for machine learning demonstrated the ability to successfully train a contingency-independent classifier that is capable of classifying stable and unstable operating points. The network is trained for current system topology and loading conditions. The classifier can be trained using a small dataset when the TEF terms are used as input features. The prediction accuracy of the proposed scheme was tested under the balanced and unbalanced faults with the presence of voltage sensitive and dynamic loads for different operating points. The test results demonstrate the potential of using the proposed technique for power system on-line DSA. Power system devices such as HVDC and FACTS can be included in the algorithm by incorporating the effective terms of a corresponding TEF. An on-line DSA system requires the integration of several functional components. The practicality of the proposed technique in terms of a) critical data communications aspects b) computational hardware requirements; and c) capabilities and limitations of the tools in use was tested using an implementation of an on-line DSA system. The test power system model was simulated using a real-time digital simulator. The other functional units were distributed over the Local Area Network (LAN). The implementation indicated that an acceptable computational cycle time can be achieved using the proposed method. In addition, the work carried out during this thesis has produced two tools that can be used for a) web-based automated data generation for power system studies; and b) testing of on-line DSA algorithms. / February 2017

Following the introduction of the microprocessor into the power system protection field, modern microprocessor based numeric relays have developed very rapidly in the last 20 years, and modern power system protection schemes are virtually all based on microcomputers technology. The International Electro-technical Commission (IEC) recently launched the standard IEC61850, “Communication Networks and System in Substation”, which is having a major impact on the structure of new protection systems and schemes. In itself it describes the concepts for sub-station communications covering protection, control and metering functions. However, although it is going to have a major impact on the power systems communications, it will also influence the design of future protection systems. There will also be a host of other opportunities and advantages that can be realised. These include easier upgrading, refurbishment and replacement of sub-station protection. They also provide for greater use of general purpose Intelligent Electronics Devices (IEDs), self-healing systems, and plug and play type facilities. The Ethernet based communication network for data transfer between process level switchyard equipment and bay level IEDs, the process bus, is defined in IEC61850 Section 9-2. This process bus facilitates the communication of two types of real-time, peer-to-peer communication messages. Generic object-oriented substation event messages, the GOOSE messages and the data sample values, SVs which include the measured currents and voltages. Although this standard describes the message structures and the timing requirements, it does not describe the process bus topology. This work describes different LAN topologies that can be used in the design of process bus for protection systems. It considers the implications of the different structures on the operation of the protection scheme and how these relate to the operational strategy of different operators. It provides an assessment of the data handling capabilities of the system and how the demands of the protection system can be met. Several potential problem areas are identified and analyzed. The probabilistic nature of these systems is discussed and the implications explained. It also provides an insight into the implementation of the alternative topologies and their performance when applied to a transmission line feeder protection and transformer protection. The digital substation and the implementation of IEC61850 are fundamental to the future of protection ‘relays’. There are many pointers to the potential directions that these systems will develop and the skills required for the protection engineers of the future. This project is seeking to overcome some of the ownership challenges presented by modern protection and control (P&C) devices, which have an inherent short life due to their dependence on modern electronics and software.