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.

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.

School desegregation in Broward County, Florida, 1970--1998: A historical study of power

This is a historical case study on school desegregation and power in Broward County, Florida from 1970 to 1998. The purpose of this study is to describe, explain and analyze types of power used by the School Board of Broward County, Florida and community activists, in their efforts to influence desegregation decisions from 1970 to 1998. In addition, this study explains who benefited and who won from the School Board's desegregation decisions and who governed those decisions? ^ A historical case study approach was used as the method for conducting this study. Data sources included 11 interviews of individuals who were involved in school desegregation issues as either School Board officials or community activists and 10 archival data sources. ^ The theoretical models of Russell, Galbraith, Wartenberg and Domhoff were used to determine the different types of power techniques used by School Board officials and community activists and to answer the questions: who benefited and who won from the School Board's desegregation decisions and who governed those policies and practices? ^ The primary beneficiaries of school desegregation policies and practices in Broward County were: white, affluent communities and the builders, developers, realtors and other businesses in the western suburban communities. All of the data sources indicated that the black community did not benefit from the School Board's desegregation policies. ^ The primary power techniques used by School Board officials to influence desegregation policies and practices was “power over opinions” and compensation. These power techniques were manifested by the School Board publicly disputing the allegations raised by community activists and by compensating those who supported and promoted the School Board's desegregation policies and practices. ^ The power techniques primarily used by community activists were coercive force and “power over opinions.” They effectively used these power techniques to change the School Board's policies and practices they felt were detrimental to black children and the black community. ^ Based on the analysis of the qualitative data, it can be concluded that black children did not benefit from school desegregation in Broward County, Florida and the community continues to suffer residual effects from past desegregation policies and practices. ^

School desegregation in Broward County, Florida 1970-1998 : a historical study of power

This is a historical case study on school desegregation and power in Broward County, Florida from 1970 to 1998. The purpose of this study is to describe, explain and analyze types of power used by the School Board of Broward County, Florida and community activists, in their efforts to influence desegregation decisions from 1970 to 1998. In addition, this study explains who benefited and who won from the School Board's desegregation decisions and who governed those decisions? A historical case study approach was used as the method for conducting this study. Data sources included 11 interviews of individuals who were involved in school desegregation issues as either School Board officials or community activists and 10 archival data sources. The theoretical models of Russell, Galbraith, Wartenberg and Domhoff were used to determine the different types of power techniques used by School Board officials and community activists and to answer the questions: who benefited and who won from the School Board's desegregation decisions and who governed those policies and practices? The primary beneficiaries of school desegregation policies and practices in Broward County were: white, affluent communities and the builders, developers, realtors and other businesses in the western suburban communities. All of the data sources indicated that the black community did not benefit from the School Board's desegregation policies. The primary power techniques used by School Board officials to influence desegregation policies and practices was "power over opinions" and compensation. These power techniques were manifested by the School Board publicly disputing the allegations raised by community activists and by compensating those who supported and promoted the School Board's desegregation policies and practices. The power techniques primarily used by community activists were coercive force and "power over opinions." They effectively used these power techniques to change the School Board's policies and practices they felt were detrimental to black children and the black community. Based on the analysis of the qualitative data, it can be concluded that black children did not benefit from school desegregation in Broward County, Florida and the community continues to suffer residual effects from past desegregation policies and practices.

Can Compensation Committees Effectively Mitigate the CEO Horizon Problem? The Role of Co-opted Directors

Extant research finds inconclusive evidence about the CEO horizon problem. One possibility is that compensation committees design CEO compensation in a way that discourages retiring CEOs from opportunistic earnings management and R&D reduction. However, compensation committees dominated by co-opted directors may not be as effective as those with fewer co-opted directors in mitigating the CEO horizon problem, because directors co-opted by the CEO tend to bias their decisions in favor of the CEO. I find that compensation committees dominated by co-opted directors are associated with higher CEO compensation packages. I document R&D reduction and accruals management in firms with retiring CEOs and compensation committees dominated by co-opted directors, and find that R&D reduction and income-increasing accruals are less discouraged by compensation committees dominated by co-opted directors when deciding CEO compensation. I also examine the effect of boards of directors and compensation committee characteristics on CEO compensation and on mitigating the CEO horizon problem. I find that CEO compensation positively associates with CEO power, director independence, and the percentage of busy directors, and negatively associates with board of directors and committee size and director ownership. Moreover, I find that retiring CEOs are more likely to reduce R&D expenditures when CEOs have more power, and director tenure is longer; retiring CEOs in firms with large boards of directors and compensation committees are less likely to manage accruals.