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- All Subjects: engineering
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- Genre: Academic theses
- Creators: Ayyanar, Raja
- Creators: Buss, Ray
- Status: Published
Description
The high penetration of photovoltaic (PV) both at the utility and at the distribu-tion levels, has raised concerns about the reliability of grid-tied inverters of PV power systems. Inverters are generally considered as the weak link in PV power systems. The lack of a dedicated qualification/reliability standard for PV inverters is a main barrier in realizing higher level of confidence in reliability. Development of a well-accepted design qualification standard specifically for PV inverters will help pave the way for significant improvement in reliability and performance of inverters across the entire industry. The existing standards for PV inverters such as UL 1741 and IEC 62109-1 primarily focus on safety. IEC 62093 discusses inverter qualification but it includes all the balance of sys-tem components and therefore not specific to PV inverters. There are other general stan-dards for distributed generators including the IEEE1547 series of standards which cover major concerns like utility integration but they are not dedicated to PV inverters and are not written from a design qualification point of view. In this thesis, some of the potential requirements for a design qualification standard for PV inverters are addressed. The IEC 62093 is considered as a guideline and the possible inclusions in the framework for a dedicated design qualification standard of PV inverter are discussed. The missing links in existing PV inverter related standards are identified by performing gap analysis. Dif-ferent requirements of small residential inverters compared to large utility-scale systems, and the emerging requirements on grid support features are also considered. Electric stress test is found to be the key missing link and one of the electric stress tests, the surge withstand test is studied in detail. The use of the existing standards for surge withstand test of residential scale PV inverters is investigated and a method to suitably adopt these standards is proposed. The proposed method is studied analytically and verified using simulation. A design criterion for choosing the switch ratings of the inverter that can per-form reliably under the surge environment is derived.
ContributorsAlampoondi Venkataramanan, Sai Balasubramanian (Author) / Ayyanar, Raja (Thesis advisor) / Vittal, Vijay (Committee member) / Heydt, Gerald (Committee member) / Arizona State University (Publisher)
Created2011
Description
In modern electric power systems, energy management systems (EMSs) are responsi-ble for monitoring and controlling the generation system and transmission networks. State estimation (SE) is a critical `must run successful' component within the EMS software. This is dictated by the high reliability requirements and need to represent the closest real time model for market operations and other critical analysis functions in the EMS. Tradi-tionally, SE is run with data obtained only from supervisory control and data acquisition (SCADA) devices and systems. However, more emphasis on improving the performance of SE drives the inclusion of phasor measurement units (PMUs) into SE input data. PMU measurements are claimed to be more accurate than conventional measurements and PMUs `time stamp' measurements accurately. These widely distributed devices meas-ure the voltage phasors directly. That is, phase information for measured voltages and currents are available. PMUs provide data time stamps to synchronize measurements. Con-sidering the relatively small number of PMUs installed in contemporary power systems in North America, performing SE with only phasor measurements is not feasible. Thus a hy-brid SE, including both SCADA and PMU measurements, is the reality for contemporary power system SE. The hybrid approach is the focus of a number of research papers. There are many practical challenges in incorporating PMUs into SE input data. The higher reporting rates of PMUs as compared with SCADA measurements is one of the salient problems. The disparity of reporting rates raises a question whether buffering the phasor measurements helps to give better estimates of the states. The research presented in this thesis addresses the design of data buffers for PMU data as used in SE applications in electric power systems. The system theoretic analysis is illustrated using an operating electric power system in the southwest part of the USA. Var-ious instances of state estimation data have been used for analysis purposes. The details of the research, results obtained and conclusions drawn are presented in this document.
ContributorsMurugesan, Veerakumar (Author) / Vittal, Vijay (Committee member) / Heydt, Gerald (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2013
Description
Solar power generation is the most promising technology to transfer energy consumption reliance from fossil fuel to renewable sources. Concentrated solar power generation is a method to concentrate the sunlight from a bigger area to a smaller area. The collected sunlight is converted more efficiently through two types of technologies: concentrated solar photovoltaics (CSPV) and concentrated solar thermal power (CSTP) generation. In this thesis, these two technologies were evaluated in terms of system construction, performance characteristics, design considerations, cost benefit analysis and their field experience. The two concentrated solar power generation systems were implemented with similar solar concentrators and solar tracking systems but with different energy collecting and conversion components: the CSPV system uses high efficiency multi-junction solar cell modules, while the CSTP system uses a boiler -turbine-generator setup. The performances are calibrated via the experiments and evaluation analysis.
ContributorsJin, Zhilei (Author) / Hui, Yu (Thesis advisor) / Ayyanar, Raja (Committee member) / Rodriguez, Armando (Committee member) / Arizona State University (Publisher)
Created2013
Description
The National Association of Community College Teacher Education Programs (NACCTEP) was established to promote the community college role in the recruitment, preparation, retention, and renewal of teachers. NACCTEP is led by a 13-member executive board consisting of community college teacher education administrators and faculty members from across the United States. Board members expressed concern that their first year consisted of them trying to learn their role as a board member including how to participate in board activities. By the time they became fully knowledgeable about their role and became more active participants, their two-year term was completed. They also indicated that initially they felt disconnected from veteran board members. To address this issue, an orientation/leadership suite was developed for new board members to assist them in transitioning from peripheral roles to full active roles. The suite included activities such as an association orientation web page, participation in monthly board conference calls, a face-to-face leadership session, and mentoring by veteran board members. The communities of practice (CoP) framework shaped this action research study and the activities of the suite were designed to foster a CoP. This action research study utilized a mixed-method research approach in which both qualitative and quantitative instruments were used to gather data. The descriptive statistics indicated that on average, new board members perceived mentoring was effective, understood their role on the board, experienced a sense of a community of practice, considered themselves as active on the board, and believed the leadership orientation suite was effective. An analysis of the qualitative data resulted in four themes: community, communication, participation, and efficacy. Overall, the findings indicated that the new board member orientation/leadership suite assisted new board members transition from peripheral roles to active leadership roles through developing a sense of community; facilitating and sustaining communication; defining, supporting, and encouraging participation; and increasing efficacy in their roles. Through the learning of their roles, the new board members became knowledgeable, comfortable, and confident in serving as board members, which facilitated their participating in the NACCTEP board's CoP.
ContributorsOstos, Ray A (Author) / Buss, Ray (Thesis advisor) / Barnett, Joshua (Committee member) / De Los Santos, Gerardo (Committee member) / Arizona State University (Publisher)
Created2013
Description
The Smart Grid initiative describes the collaborative effort to modernize the U.S. electric power infrastructure. Modernization efforts incorporate digital data and information technology to effectuate control, enhance reliability, encourage small customer sited distributed generation (DG), and better utilize assets. The Smart Grid environment is envisioned to include distributed generation, flexible and controllable loads, bidirectional communications using smart meters and other technologies. Sensory technology may be utilized as a tool that enhances operation including operation of the distribution system. Addressing this point, a distribution system state estimation algorithm is developed in this thesis. The state estimation algorithm developed here utilizes distribution system modeling techniques to calculate a vector of state variables for a given set of measurements. Measurements include active and reactive power flows, voltage and current magnitudes, phasor voltages with magnitude and angle information. The state estimator is envisioned as a tool embedded in distribution substation computers as part of distribution management systems (DMS); the estimator acts as a supervisory layer for a number of applications including automation (DA), energy management, control and switching. The distribution system state estimator is developed in full three-phase detail, and the effect of mutual coupling and single-phase laterals and loads on the solution is calculated. The network model comprises a full three-phase admittance matrix and a subset of equations that relates measurements to system states. Network equations and variables are represented in rectangular form. Thus a linear calculation procedure may be employed. When initialized to the vector of measured quantities and approximated non-metered load values, the calculation procedure is non-iterative. This dissertation presents background information used to develop the state estimation algorithm, considerations for distribution system modeling, and the formulation of the state estimator. Estimator performance for various power system test beds is investigated. Sample applications of the estimator to Smart Grid systems are presented. Applications include monitoring, enabling demand response (DR), voltage unbalance mitigation, and enhancing voltage control. Illustrations of these applications are shown. Also, examples of enhanced reliability and restoration using a sensory based automation infrastructure are shown.
ContributorsHaughton, Daniel Andrew (Author) / Heydt, Gerald T (Thesis advisor) / Vittal, Vijay (Committee member) / Ayyanar, Raja (Committee member) / Hedman, Kory W (Committee member) / Arizona State University (Publisher)
Created2012
Description
The constant scaling of supply voltages in state-of-the-art CMOS processes has led to severe limitations for many analog circuit applications. Some CMOS processes have addressed this issue by adding high voltage MOSFETs to their process. Although it can be a completely viable solution, it usually requires a changing of the process flow or adding additional steps, which in turn, leads to an increase in fabrication costs. Si-MESFETs (silicon-metal-semiconductor-field-effect-transistors) from Arizona State University (ASU) on the other hand, have an inherent high voltage capability and can be added to any silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) CMOS process free of cost. This has been proved at five different commercial foundries on technologies ranging from 0.5 to 0.15 μm. Another critical issue facing CMOS processes on insulated substrates is the scaling of the thin silicon channel. Consequently, the future direction of SOI/SOS CMOS transistors may trend away from partially depleted (PD) transistors and towards fully depleted (FD) devices. FD-CMOS are already being implemented in multiple applications due to their very low power capability. Since the FD-CMOS market only figures to grow, it is appropriate that MESFETs also be developed for these processes. The beginning of this thesis will focus on the device aspects of both PD and FD-MESFETs including their layout structure, DC and RF characteristics, and breakdown voltage. The second half will then shift the focus towards implementing both types of MESFETs in an analog circuit application. Aside from their high breakdown ability, MESFETs also feature depletion mode operation, easy to adjust but well controlled threshold voltages, and fT's up to 45 GHz. Those unique characteristics can allow certain designs that were previously difficult to implement or prohibitively expensive using conventional technologies to now be achieved. One such application which benefits is low dropout regulators (LDO). By utilizing an n-channel MESFET as the pass transistor, a LDO featuring very low dropout voltage, fast transient response, and stable operation can be achieved without an external capacitance. With the focus of this thesis being MESFET based LDOs, the device discussion will be mostly tailored towards optimally designing MESFETs for this particular application.
ContributorsLepkowski, William (Author) / Thornton, Trevor (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Goryll, Michael (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2010
Description
It is common for graduate programs to be plagued by delays in on-time student completion or to experience student attrition. Students have experienced such delays in a local program at the University where I am employed as a lecturer. Therefore, this dissertation was undertaken with the aim of supporting university students at the graduate level toward successful on-time completion of their programs. This action research study was multi-phased in its approach; with data collection, and reflection driving the process for intervention delivery and subsequent evaluation. A dynamic approach which included some components of greater structure than was previously seen in the program, was designed for implementation. It was envisaged that this approach would serve as a model of support for students. The following chapters written in article format details the cycles of action research undertaken as part of this dissertation. The first article tells a story written for a wider audience. While the second article presents a more direct look at the implementation of the dynamic structured approach, and lessons learned through the experiential stories of the students. The dynamic structured approach is a framework which was created from a synergetic review of studies on the issues of attrition and delayed completion in graduate programs. The approach was therefore discussed in hopes that it can be used as a model in other graduate programs to ensure that students are supported in a holistic manner. Further, recommendations were made to bolster the approach based on the lessons learned from its initial implementation as well as through the reflections of the researcher-practitioner. The approach has built-in flexibility and is open to refinement and modification to suit the needs of varying institutions for future use.
ContributorsLord, Kara Tamara (Author) / Basile, Carole (Thesis advisor) / Buss, Ray (Committee member) / Smith, Stephanie (Committee member) / Bissessar, Charmaine (Committee member) / Arizona State University (Publisher)
Created2022
Description
The community college leadership pipeline is a source for concern in the face of anticipated retirements, yet most administrators come only from the ranks of classroom faculty, not from the full spectrum of all faculty. Librarians, whose experiences lend themselves to many administrative duties, seldom advance into administrative positions. This study was centered on the development of a career coaching intervention by which participants from a subset of California community college libraries received guidance from administrators who had previously been librarians. The aim was to see whether such an intervention could increase administrative skills, improve self-efficacy to perform in administrative roles, increase perceptions of the desirability of attaining such positions, and lead to greater intent to move onto such career pathways. The study found that a career coaching program had mixed success at addressing the study aims, but that it also opened space for librarians alone to explore other leadership and professional growth opportunities. The research argues for the restaging of such a career coaching program, centered on librarians only, so as to encourage their advancement, whether into administrative ranks at their community colleges or otherwise.
ContributorsHepburn, Peter (Author) / Gee, Elisabeth (Thesis advisor) / Buss, Ray (Committee member) / Aguiñaga, José (Committee member) / Arizona State University (Publisher)
Created2021
Description
Studies of discourse are prevalent in mathematics education, as are investigations on facilitating change in instructional practices that impact student attitudes toward mathematics. However, the literature has not sufficiently addressed the operationalization of the commognitive framework in the context of Calculus I, nor considered the inevitable impact on students’ attitudes of persistence, confidence, and enjoyment of mathematics. This study presents an innovation, founded, designed, and implemented, utilizing four frameworks. The overarching theory pivots to commognition, a theory that asserts communication is tantamount to thinking. Students experienced a Calculus I class grounded on four frames: a theoretical, a conceptual, a design pattern, and an analytical framework, which combined, engaged students in discursive practices. Multiple activities invited specific student actions: uncover, play, apply, connect, question, and realize, prompting calculus discourse. The study exploited a mixed-methods action research design that aimed to explore how discursive activities impact students’ understanding of the derivative and how and to what extent instructional practices, which prompt mathematical discourse, impact students’ persistence, confidence, and enjoyment of calculus.
This study offers a potential solution to a problem of practice that has long challenged practitioners and researchers—the persistence of Calculus I as a gatekeeper for Science, Technology, Engineering, and Mathematics (STEM). In this investigation it is suggested that Good and Ambitious Teaching practices, including asking students to explain their thinking and assigning group projects, positively impact students’ persistence, confidence, and enjoyment. Common calculus discourse among the experimental students, particularly discursive activities engaging word use and visual representations of the derivative, warrants further research for the pragmatic utility of the fine grain of a commognitive framework. For researchers the work provides a lens through which they can examine data resulting from the operationalization of multiple frameworks working in tandem. For practitioners, mathematical objects as discursive objects, allow for classrooms with readily observable outcomes.
ContributorsChowdhury, Madeleine Perez (Author) / Judson, Eugene (Thesis advisor) / Buss, Ray (Committee member) / Reinholz, Daniel (Committee member) / Arizona State University (Publisher)
Created2022
Description
The current model of teaching where one teacher works individually with a group of learners in a classroom in an alternative educational setting promoted unrealistic expectations by assuming individual teachers working alone could meet the needs of all students. To address this problem, I conducted an action research study in which I explored the outcomes of a team-based teaching approach that was implemented to make the dramatic shift away from a traditional, industrial-like, one-teacher, one-classroom model that existed in the school. In the intervention, a teams-based approach was implemented where teachers worked in teams of four to collaborate on professional learning, determine students’ needs, then plan and implement instruction for the same, group of students. A sample of nine educators at Riverview High School completed the Teacher Self-Efficacy Scale (TSES) and the Professional Learning and Teacher Attitude (PLTA) survey to assess self-efficacy for instruction, classroom management, and student engagement, and professional learning and attitudes in a team-based setting. Qualitative data consisted of interview data and data from four focus groups. Findings indicated teachers using the team-based model demonstrated increases in mean scores across the five constructs. Additionally, analysis of the interview and focus group data revealed four themes emerged, including a new school culture, meaningful professional learning, collegiality through collaboration, and increased professional attitudes. The discussion focused on complementarity of the quantitative and qualitative data and how use of the team-based model transformed how education was conceived and delivered at an alternative school for at-risk students. In addition, I described limitations, implications for practice and research, and concluding thoughts.
ContributorsMendez, Gregory (Author) / Buss, Ray (Thesis advisor) / Basile, Carole (Committee member) / Oliver, Michael (Committee member) / Arizona State University (Publisher)
Created2023