Switching patterns and steady-state analysis of grid-connected and stand-alone single-stage boost-inverters for PV applications

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

Caring and being cared -for: Perceptions of adolescent males at -risk for school failure

This qualitative study used grounded theory methods and purposeful sampling to explore perceptions on caring and being cared-for. Twenty-four adolescent male participants, identified as at-risk for school failure, completed a two phase interview process exploring these phenomena within three relationships; the relationship with the friend, with the most caring person they knew and with the teacher they felt cared for them. ^ Each participant was asked a predetermined set of open questions in an initial semi-structured interview. In addition each participant was encouraged to explore his own reflections on caring. A second interview allowed for member checking and for the participant to continue sharing his meaning of caring and being cared-for. ^ Line by line analysis with open, axial and selective coding was applied to interview transcripts along with a constant comparative method. Results indicated that the core category integrating all other categories was attachment bonding. Participants' stories manifested characteristics of proximity seeking, secure base, safe haven and distress upon involuntary separation from an attachment figure. ^ Strategies facilitating attachment bonding were influenced by the power positions of the relational players. Participants responded positively to the one-caring when they felt cared-for. Results further indicated that participants did not need to feel a sense of belonging in order to feel cared-for. Teacher behaviors indicating openness for authentic connections with students were specific to teacher's friendliness and professional competence. Teachers who nurtured feelings of being cared-for were uncommon in the participants' educational experience. ^ The number of adolescent males leaving high school prematurely is both a personal problem and a social problem. Despite a “mask” of indifference often exhibited by adolescent males at-risk for school failure, teachers might consider the social/emotional needs of these students when implementing the curriculum. In addition, policy makers might consider the social/emotional needs of this vulnerable population when developing programs meant to foster psychological well-being and connectedness for adolescent males at-risk for school failure. ^

Switching Patterns and Steady-State Analysis of Grid-Connected and Stand-Alone Single-Stage Boost-Inverters for PV Applications

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

Selecting a college or university: A study of students and their parents

This case study investigated the decision-making process of high-achieving high school students and their parents in selecting a college or university. The conceptual framework that guided this study included theoretical and empirical research framed around a three-phase model of college choice. Parental influence dominated the first phase of this model. The search phase, which was the second and the most crucial one, included financial considerations related to this decision, admissions considerations during the search phase, the psychology of decision making, and advertising strategies for teenagers. Once students completed the search phase they developed expectations of the institutions they considered prior to making the final decision. The study employed qualitative methods using individual interviews with students and their parents. ^ Six high-achieving high school seniors from a South Florida high school and their parents were selected to participate in this study. Of these students, four were female and two were male. Participants were individually interviewed on two separate occasions over a three-month period. Students and their parents were interviewed separately, with one exception, during the first set of interviews and together during the second. The data obtained from these interviews were transcribed and these transcripts were coded, categorized, analyzed, and sorted into major themes and submitted to interpretive analysis. ^ In-depth descriptions of participants' experiences during the decision-making process are described in the study. Financial factors—which included the cost of college, the socio-economic status of the family, and scholarship possibilities—drove the selection process for these students and their parents, most of whom reported their family incomes between the lower-middle to upper-middle class range. All of these students took advantage of the Bright Futures Scholarship Program, other scholarship opportunities, and the lower tuition costs of in-state public institutions. The effectiveness of recruitment techniques, such as brochures, campus visits, the development of college Web sites, and the overall impact of Internet resources, was assessed by the researcher. ^ As these students had progressed through the search phase, they developed perceptions of potential institutions as they were assisted by those around them. The value of familiarity with institutions and the use of heuristics were quite evident in the final analysis of this study, based on what the students communicated about how their knowledge of and comfort in these institutions affected their decisions. Parental influence played an important role in the selection process for the students in this study as the parents clearly directed the process, by the constant advice they gave their children and by the financial limitations they communicated to them. ^

The effects of cultural distance on student socialization and departure decisions

Organizational socialization theory and university student retention literature support the concept that social integration influences new recruits' level of satisfaction with the organization and their decision to remain. This three-phase study proposes and tests a Cultural Distance Model of student retention based on Tinto's (1975) Student Integration Model, Louis' (1980) Model of Newcomer Experience, and Kuh and Love's (2000) theory relating cultural distance to departure from the organization. ^ The main proposition tested in this study was that the greater the cultural distance, the greater the likelihood of early departure from the organization. Accordingly, it was inferred that new recruits entering the university culture experience some degree of social and psychological distance. The extent of the distance correspondingly influences satisfaction with the institution and intent to remain for subsequent years. ^ The model was tested through two freshman student surveys designed to examine the effects of cultural distance on non-Hispanics at a predominantly Hispanic, urban, public university. The first survey was administered eight weeks into their first Fall semester and the second at the end of their first year. Student retention was determined through their re-enrollment for the second Fall semester. Path analysis tested the viability of the hypothesis relating cultural distance to satisfaction and retention as suggested in the model. Logistic regression tested the model's predictive power. ^ Correlations among variables were significant, accounting for 54% of variance in students' decisions to return for the second year with 96% prediction accuracy. Initial feelings of high cultural distance were related to increased dissatisfaction with social interactions and institutional choice at the end of the first year and students' intention not to re-enroll. Path analysis results supported the view that the construct of culture distance incorporates both social and psychological distance, and is composed of beliefs of institutional fit with one's cultural expectations, individual comfort with the fit, and the consequent sense of “belonging” or identifying with the institution. ^

Perceptions of character education in a Seventh-day Adventist school

Character education has been viewed by many educators as having significant historical, academic, and social value. Many stakeholders in education argue for character development as a curricular experience. While understanding the degree to which character education is of worth to stakeholders of institutions is important, understanding students, teachers, and administrators perspectives from their lived experiences is likewise significant. The purpose of this phenomenological study was to gain a deeper understanding of character education within a Biblical framework environment by examining the lived experiences of students, administrators, and teachers of a Seventh-day Adventist School. Phenomenology describes individuals' daily experiences of phenomena, the manner in which these experiences are structured, and focuses analysis on the perspectives of the persons having the experience (Moustakas, 1994). This inquiry was undertaken to answer the question: What are the perceptions of students, teachers, and an administrator toward character education in a Seventh-day Adventist school setting? Ten participants (seven students and three adults) formed the homogeneous purposive sample, and the major data collection tool was semi-structured interviews (Patton, 1990; Seidman, 2006). Three 90-minute open-ended interviews were conducted with each of the participants. Data analysis included a three-phase process of description, reduction and interpretation. The findings from this study revealed that participants perceived that their involvement in the school's character education program decreased the tendency to violence, improved their conduct and ethical sensibility, enhanced their ability to engage in decision-making concerning social relationships and their impact on others, brought to their attention the emerging global awareness of moral deficiency, and fostered incremental progress from practice and recognition of vices to their acquisition of virtues. The findings, therefore, provide a model for teaching character education from a Seventh-day Adventist perspective. The model is also relevant for non-Seventh day Adventists who aspire to teach character education as a means to improving social and moral conditions in schools.

Gaining insight into teaching: A phenomenological exploration of the lived experience of Teachers of the Year

What qualities, skills, and knowledge produce quality teachers? Many stake-holders in education argue that teacher quality should be measured by student achievement. This qualitative study shows that good teachers are multi-dimensional; their effectiveness cannot be represented by students' test scores alone. The purpose of this phenomenological study was to gain a deeper understanding of quality in teaching by examining the lived experiences of 10 winners or finalists of the Teacher of the Year (ToY) Award. Phenomenology describes individuals' daily experiences of phenomena, examines how these experiences are structured, and focuses analysis on the perspectives of the persons having the experience (Moustakas, 1994). This inquiry asked two questions: (a) How is teaching experienced by recognized as outstanding Teachers of the Year? and (b) How do ToYs feelings and perceptions about being good teachers provide insight, if any, about concepts such as pedagogical tact, teacher selfhood, and professional dispositions? Ten participants formed the purposive sample; the major data collection tool was semi-structured interviews (Patton, 1990; Seidman, 2006). Sixty to 90-minute interviews were conducted with each participant. Data also included the participants' ToY application essays. Data analysis included a three-phase process: description, reduction, interpretation. Findings revealed that the ToYs are dedicated, hard-working individuals. They exhibit behaviors, such as working beyond the school day, engaging in lifelong learning, and assisting colleagues to improve their practice. Working as teachers is their life's compass, guiding and wrapping them into meaningful and purposeful lives. Pedagogical tact, teacher selfhood, and professional dispositions were shown to be relevant, offering important insights into good teaching. Results indicate that for these ToYs, good teaching is experienced by getting through to students using effective and moral means; they are emotionally open, have a sense of the sacred, and they operate from a sense of intentionality. The essence of the ToYs teaching experience was their being properly engaged in their craft, embodying logical, psychological, and moral realms. Findings challenge current teacher effectiveness process-product orthodoxy which makes a causal connection between effective teaching and student test scores, and which assumes that effective teaching arises solely from and because of the actions of the teacher.

Perceptions of Character Education in a Seventh-Day Adventist School

Character education has been viewed by many educators as having significant historical, academic, and social value. Many stakeholders in education argue for character development as a curricular experience. While understanding the degree to which character education is of worth to stakeholders of institutions is important, understanding students, teachers, and administrators perspectives from their lived experiences is likewise significant. The purpose of this phenomenological study was to gain a deeper understanding of character education within a Biblical framework environment by examining the lived experiences of students, administrators, and teachers of a Seventh-day Adventist School. Phenomenology describes individuals’ daily experiences of phenomena, the manner in which these experiences are structured, and focuses analysis on the perspectives of the persons having the experience (Moustakas, 1994). ). This inquiry was undertaken to answer the question: What are the perceptions of students, teachers, and an administrator toward character education in a Seventh-day Adventist school setting? Ten participants (seven students and three adults) formed the homogeneous purposive sample, and the major data collection tool was semi-structured interviews (Patton, 1990; Seidman, 2006). Three 90-minute open-ended interviews were conducted with each of the participants. Data analysis included a three-phase process of description, reduction and interpretation. The findings from this study revealed that participants perceived that their involvement in the school’s character education program decreased the tendency to violence, improved their conduct and ethical sensibility, enhanced their ability to engage in decision-making concerning social relationships and their impact on others, brought to their attention the emerging global awareness of moral deficiency, and fostered incremental progress from practice and recognition of vices to their acquisition of virtues. The findings, therefore, provide a model for teaching character education from a Seventh-day Adventist perspective. The model is also relevant for non-Seventh day Adventists who aspire to teach character education as a means to improving social and moral conditions in schools.

Gaining Insight into Teaching: A Phenomenological Exploration of the Lived Experience of the Teachers of the Year

What qualities, skills, and knowledge produce quality teachers? Many stake-holders in education argue that teacher quality should be measured by student achievement. This qualitative study shows that good teachers are multi-dimensional; their effectiveness cannot be represented by students’ test scores alone. The purpose of this phenomenological study was to gain a deeper understanding of quality in teaching by examining the lived experiences of 10 winners or finalists of the Teacher of the Year (ToY) Award. Phenomenology describes individuals’ daily experiences of phenomena, examines how these experiences are structured, and focuses analysis on the perspectives of the persons having the experience (Moustakas, 1994). This inquiry asked two questions: (a) How is teaching experienced by recognized as outstanding Teachers of the Year? and (b) How do ToYs feelings and perceptions about being good teachers provide insight, if any, about concepts such as pedagogical tact, teacher selfhood, and professional dispositions? Ten participants formed the purposive sample; the major data collection tool was semi-structured interviews (Patton, 1990; Seidman, 2006). Sixty to 90-minute interviews were conducted with each participant. Data also included the participants’ ToY application essays. Data analysis included a three-phase process: description, reduction, interpretation. Findings revealed that the ToYs are dedicated, hard-working individuals. They exhibit behaviors, such as working beyond the school day, engaging in lifelong learning, and assisting colleagues to improve their practice. Working as teachers is their life’s compass, guiding and wrapping them into meaningful and purposeful lives. Pedagogical tact, teacher selfhood, and professional dispositions were shown to be relevant, offering important insights into good teaching. Results indicate that for these ToYs, good teaching is experienced by getting through to students using effective and moral means; they are emotionally open, have a sense of the sacred, and they operate from a sense of intentionality. The essence of the ToYs teaching experience was their being properly engaged in their craft, embodying logical, psychological, and moral realms. Findings challenge current teacher effectiveness process-product orthodoxy which makes a causal connection between effective teaching and student test scores, and which assumes that effective teaching arises solely from and because of the actions of the teacher.