Doctor of Philosophy / Electrical and Computer Engineering / Steven Warren / Linear Systems (a.k.a., Signals and Systems) is an important class in an Electrical Engineering curriculum. A clear understanding of the topics in this course relies on a well-developed notion of lower-level mathematical constructs and procedures, including the roles these procedures play in system analysis. Students with an inadequate math foundation regularly struggle in this class, as they are typically able to perform sequences of the underlying calculations but cannot piece together the higher-level, conceptual relationships that drive these procedures. This dissertation describes an investigation to assess and improve students’ higher-level understanding of Linear Systems concepts. The focus is on the topics of (a) time-domain, linear time-invariant (LTI) system response visualization and (b) Fourier series conceptual understanding, including trigonometric Fourier series (TFS), compact trigonometric Fourier series (CTFS), and exponential Fourier series (EFS). Support data, including exam and online homework data, were collected since 2004 from students enrolled in ECE 512 - Linear Systems at Kansas State University. To assist with LTI response visualization, two online homework modules, Zero Input Response and Unit Impulse Response, were updated with enhanced plots of signal responses and placed in use starting with the Fall 2009 semester. To identify students’ conceptual weaknesses related to Fourier series and to help them achieve a better understanding of Fourier series concepts, teaching-learning interviews were applied between Spring 2010 and Fall 2012. A new concept-based online homework module was also introduced in Spring 2011. Selected final exam problems from 2007 to 2012 were analyzed, and these data were supplemented with detailed mid-term and final exam data from 77 students enrolled in the Spring 2010 and Spring 2011 semesters. In order to address these conceptual learning issues, two frameworks were applied: Bloom’s Taxonomy and APOS theory. The teaching-learning interviews and online module updates appeared to be effective treatments in terms of increasing students’ higher-level understanding. Scores on both conceptual exam questions and more traditional Fourier series exam questions were improved relative to scores received by students that did not receive those treatments.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Anil Pahwa / Shelli K. Starrett / Analysis of power system voltage stability has practical value in increasing wind penetration levels. As wind penetration levels increase in power systems, voltage stability challenges arise due to locating wind resources far away from load centers. This dissertation presents several different voltage stability methods for sizing new wind farms. Power system wind penetration levels depend on the available voltage stability margins (VSMs) of the existing power system and system load characteristics. Three new iterative methods have been developed to maximize wind penetration level in weak power systems based on systems’ VSMs. The first two methods use an iterative approach for increasing the size of each wind farm until reaching the collapse point. Wind farms with less negative impact on system VSMs are sized larger than others. A third wind farm sizing method has been developed using modal analysis in conjunction with the traditional voltage stability method (Q-V method). Wind farms are placed at buses in the power system which have the lowest negative impact on voltage instability modes (strong wind injection buses). By placing the wind farms at the strongest wind injection buses, higher amounts of wind power can be injected into the power system. To further increase wind penetration in weak power systems, two additional techniques are introduced and applied to the western Kansas power system. The first technique uses modes of voltage instability to place voltage support equipment like static var compensators at locations in the power system where they provide the needed reactive power support for increasing levels of wind penetration. The second technique uses the fact that wind patterns at a wind farm site may rarely allow the wind farm to produce its maximum capacity during the peak loading hours. Wind farm maximum sizes can be increased above their maximum voltage stable size limit without driving the power system into becoming voltage unstable. Preventing voltage collapse for the additional increases in wind farm sizes is accomplished by disconnecting some wind turbines inside the wind farm during critical times to reduce its power output to a voltage stable level.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas S. McGregor / A Micro-Pocket Fission Detector (MPFD) is a miniaturized type of fission chamber developed for use inside a nuclear reactor. Their unique design allows them to be located between or even inside fuel pins while being built from materials which give them an operational lifetime comparable to or exceeding the life of the fuel. While other types of neutron detectors have been made for use inside a nuclear reactor, the MPFD is the first neutron detector which can survive sustained use inside a nuclear reactor while providing a real-time measurement of the neutron flux. This dissertation covers the deployment of MPFDs as a large three-dimensional array inside the Kansas State University TRIGA Mark-II Nuclear Reactor for real-time neutron flux measurements. This entails advancements in the design, construction, and packaging of the Micro-Pocket Fission Detector Triads with incorporated Thermocouple, or MPFD[superscript]3-T. Specialized electronics and software also had to be designed and built in order to make a functional system capable of collecting real-time data from up to 60 MPFD[superscript]3-Ts, or 180 individual MPFDs and 60 thermocouples. Design of the electronics required the development of detailed simulations and analysis for determining the theoretical response of the detectors and determination of their size. The results of this research shows that MPFDs can operate for extended times inside a nuclear reactor and can be utilized toward the use as distributed neutron detector arrays for advanced reactor control systems and power mapping. These functions are critical for continued gains in efficiency of nuclear power reactors while also improving safety through relatively inexpensive redundancy.

Master of Science / Department of Electrical Engineering / Dwight Day / Power consumption has become a large concern in many systems including portable electronics and supercomputers. Creating efficient hardware that can do more computation with less power is highly desirable. This project proposes a possible avenue to complete this goal by hardware accelerating a conjugate gradient solve using a Field Programmable Gate Array (FPGA). This method uses three basic operations frequently: dot product, weighted vector addition, and sparse matrix vector multiply. Each operation was accelerated on the FPGA. A power monitor was also implemented to measure the power consumption of the FPGA during each operation with several different implementations. Results showed that a decrease in time can be achieved with the dot product being hardware accelerated in relation to a software only approach. However, the more memory intensive operations were slowed using the current architecture for hardware acceleration.

Master of Science / Department of Electrical and Computer Engineering / Anil Pahwa / In Afghanistan, electricity is mostly generated by hydroelectric, diesel and natural gas generators. A significant amount of electricity also is imported from neighboring countries. Accessibility of electricity is mostly limited to the capital and main towns. The government of Afghanistan and other development organizations, such as The United States Agency for International Development (USAID) and Deutsche Gesellschaft für Internationale Zusammenarbeit (German Agency for International Cooperation “GIZ”), are striving to develop accessibility of electricity to remote communities by supporting the local population of people to enhance living conditions. Although some of these remote communities are served by local diesel fuel generators for just a couple of hours during the night, still most communities do not have access to electricity and they are using wood and kerosene as major sources of energy in cooking, heating and lighting. For those remote communities who are served by local diesel fuel generators, the cost of electricity is much higher than from the national grid. On the other hand, grid extensions are too expensive and, in some cases, impossible for such communities because of the geographical features of Afghanistan. Afghanistan is a mountainous country which receives a significant amount of snow during the winter and once it melts the water runs into rivers, lakes and streams. Therefore mostly it does not face any shortage of running water during the year. Also Afghanistan has plentiful wind and solar energy. Therefore, small hydro-power, wind turbine and solar energy are attractive renewable energy sources for remote communities. The development of such a hybrid power system is a complex process and technical expertise is essential in design and construction phases. The main challenges are the high cost of civil works and equipment, technical expertise for design and construction and encouragement of local people for the support of the project. This report will give an insight into design, cost-effectiveness and feasibility of the system using HOMER in order to encourage private investors and local community people to take advantage of this potential available in Afghanistan and be convinced of the sustainability for investments in micro-hydropower, wind and solar.

Master of Science / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / Space-time coding (STC) schemes for Multiple Input Multiple Output (MIMO) systems have been an area of active research in the past decade. In this thesis, we propose a novel design of Space-Time Block Codes (STBCs) using Redundant Residue Number System (RRNS) codes, which are ideal for high data rate communication systems. Application of RRNS as a concatenated STC scheme to a MIMO wireless communication system is the main motivation for this work. We have optimized the link between residues and complex constellations by incorporating the “Direct Mapping” scheme, where residues are mapped directly to Gray coded constellations. Knowledge of apriori probabilities of residues is utilized to implement a probability based “Distance-Aware Direct Mapping” (DA) scheme, which uses a set-partitioning approach to map the most probable residues such that they are separated by the maximum possible distance. We have proposed an “Indirect Mapping” scheme, where we convert the residues back to bits before mapping them. We have also proposed an adaptive demapping scheme which utilizes the RRNS code structure to reduce the ML decoding complexity and improve the error performance. We quantify the upper bounds on codeword and bit error probabilities of both Systematic and Non-systematic RRNS-STBC and characterize the achievable coding and diversity gains assuming maximum likelihood decoding (MLD). Simulation results demonstrate that the DA Mapping scheme provides performance gain relative to a Gray coded direct mapping scheme. We show that Systematic RRNS-STBC codes provide superior performance compared to Nonsystematic RRNS-STBC, for the same code parameters, owing to more efficient binary to residue mapping. When compared to other concatenated STBC and Orthogonal STBC (OSTBC) schemes, the proposed system gives better performance at low SNRs.

Doctor of Philosophy / Department of Electrical & Computer Engineering / Steve Warren / The U.S. health care system is one of the most advanced and costly systems in the world. The health services supply/demand gap is being enlarged by the aging population coupled with shortages in the traditional health care workforce and new information technology workers. This will not change if the current medical system adheres to the traditional hospital-centered model. One promising solution is to incorporate patient-centered, point-of-care test systems that promote proactive and preventive care by utilizing technology advancements in sensors, devices, communication standards, engineering systems, and information infrastructures. Biomedical devices optimized for home and mobile health care environments will drive this transition. This dissertation documents research and development focused on biomedical device design for this purpose (including a wearable wireless pulse oximeter, motion sensor, and two-thumb electrocardiograph) and, more importantly, their interactions with other medical components, their supporting information infrastructures, and processing tools that illustrate the effectiveness of their data. The GumPack concept and prototype introduced in Chapter 2 addresses these aspects, as it is a sensor-laden device, a host for a local body area network (BAN), a portal to external integration frameworks, and a data processing platform. GumPack sensor-component design (Chapters 3 and 4) is oriented toward surface applications (e.g., touch and measure), an everyday-carry form factor, and reconfigurability. Onboard tagging technology (Chapters 5 and 6) enhances sensor functionality by providing, e.g., a signal quality index and confidence coefficient for itself and/or next-tier medical components (e.g., a hub). Sensor interaction and integration work includes applications based on the GumPack design (Chapters 7 through 9) and the Medical Device Coordination Framework (Chapters 10 through 12). A high-resolution, wireless BAN is presented in Chapter 8, followed by a new physiological use case for pulse wave velocity estimation in Chapter 9. The collaborative MDCF work is transitioned to a web-based Hospital Information Integration System (Chapter 11) by employing database, AJAX, and Java Servlet technology. Given the preceding sensor designs and the availability of information infrastructures like the MDCF, medical platform-oriented devices (Chapter 12) could be an innovative and efficient way to design medical devices for hospital and home health care applications.

Master of Science / Department of Electrical and Computer Engineering / Sanjoy Das / Noel Schulz / In a shipboard power system (SPS) there are many possible locations for faults along power lines. It is important to identify the location and isolate these faults in order to protect the equipment and loads. The shipboard systems represented in this research are based on an all-electric ship that is presented by Corzine and a simplified version of the same ship. This research considers faults at the ends on the lines. Sensors collect data in order to determine where the fault has occurred. The fault location identification algorithm being presented uses data collected from simulations of different switch configurations and different loads. After the data is collected, Bayesian techniques are used to determine where the fault is located. An online training technique is presented to adjust to changes in loads over time to increase the accuracy of the algorithm.

Master of Science / Department of Electrical and Computer Engineering / Noel N. Schulz / Wind energy is becoming one of the most widely implemented forms of renewable energy worldwide. Traditionally, wind has been considered a non-dispatchable source of energy due to the uncertainty of wind speed and hence the variable availability of wind power. Advances in technology allow the consideration of the impact of distributed wind turbines and farms on distribution systems. It is possible to combine the clean energy attributes of wind with the quickly dispatchable nature of a storage facility in order to provide the maximum amount of locally available power economically to the loads present on the distribution feeder. However, a monitoring and control system needs to be provided that is capable of detecting the changes associated with the distribution feeder load and also the variable generation output from the wind farms. This task can be accomplished using a Phasor Measurement Unit (PMU) which has very high sampling rates and hence can measure very rapid and dynamic changes in power levels associated with distribution feeder load and wind generation. The data which is obtained from these PMUs can be used to calculate the amount of distributed generation and storage that can be dispatched locally at the distribution feeder, thus resulting in a reduction in the peak load levels associated with the distribution feeder as seen by the substation monitoring system. Simulations will work to balance load requirements, wind generation output, and distributed storage providing a stable system utilizing maximum renewable resources. The standard IEEE 37-node distribution test feeder is used in the study. Probabilistic models are implemented for distribution feeder load, and the models are analyzed through simulations. Four different combinations of charging and discharging methods have been investigated. Two analytically different algorithms have been used for wind and battery dispatch, one based on forecasted load information and the other based on historical measurements obtained from PMUs. The strategies being investigated can also be used to implement other important applications such as distribution system state estimation, protection and instability prediction.

Master of Science / Department of Electrical and Computer Engineering / Ruth Douglas Miller / This thesis presents the design of two models for permanent-magnet direct-drive wind turbines. The models are of a 10 kW and a 5 MW wind turbine, which are representative of residential scale and commercial scale turbines respectively. The models include aerodynamic and mechanical simulations through the FAST software, as well as concurrent electrical simulations through the SimPowerSystems toolbox for MATLAB/Simulink. The aim is to provide wind turbine designers and researchers with a comprehensive simulation tool that they can use to design and test many different aspects of a wind turbine. The particular novelty of these models is their high level of detail in electromechanical simulations. For each model, a generator speed controller was designed in a reference frame attached to the generator’s rotor, and was executed with a 3-phase active rectifier using space-vector pulse-width modulation. Also for each model, active and reactive power controllers were designed in a reference frame synchronous with the grid, and were executed with a 3-phase inverter using space-vector pulse-width modulation. Additionally, a blade pitch controller was designed for the 5 MW model. Validation of the models was carried out in the MATLAB/Simulink environment with satisfactory results.