Modelagem e análise dinâmica de um sistema de conversão de energia eólica dotado de gerador síncrono de imã permanente utilizando a plataforma ATP

Human development requires a broad balance between ecological, social and economic factors in order to ensure its own sustainability. In this sense, the search for new sources of energy generation, with low deployment and operation costs, which cause the least possible impact to the environment, has been the focus of attention of all society segments. To do so, the reduction in exploration of fossil fuels and the encouragement of using renewable energy resources for distributed generation have proved interesting alternatives to the expansion of the energy matrix of various countries in the world. In this sense, the wind energy has acquired an increasingly significant role, presenting increasing rates of power grid penetration and highlighting technological innovations such as the use of permanent magnet synchronous generators (PMSG). In Brazil, this fact has also been noted and, as a result, the impact of the inclusion of this source in the distribution and sub-transmission power grid has been a major concern of utilities and agents connected to Brazilian electrical sector. Thus, it is relevant the development of appropriate computational tools that allow detailed predictive studies about the dynamic behavior of wind farms, either operating with isolated load, either connected to the main grid, taking also into account the implementation of control strategies for active/reactive power generation and the keeping of adequate levels of voltage and frequency. This work fits in this context since it comprises mathematical and computational developments of a complete wind energy conversion system (WECS) endowed with PMSG using time domain techniques of Alternative Transients Program (ATP), which prides itself a recognized reputation by scientific and academic communities as well as by electricity professionals in Brazil and elsewhere. The modeling procedures performed allowed the elaboration of blocks representing each of the elements of a real WECS, comprising the primary source (the wind), the wind turbine, the PMSG, the frequency converter, the step up transformer, the load composition and the power grid equivalent. Special attention is also given to the implementation of wind turbine control techniques, mainly the pitch control responsible for keeping the generator under the maximum power operation point, and the vector theory that aims at adjusting the active/reactive power flow between the wind turbine and the power grid. Several simulations are performed to investigate the dynamic behavior of the wind farm when subjected to different operating conditions and/or on the occurrence of wind intensity variations. The results have shown the effectiveness of both mathematical and computational modeling developed for the wind turbine and the associated controls.

Ajustes de coeficientes integrantes de processos físicos e bioquímicos na autedepuração em curso de água de médio porte

The mathematical modeling in the simulation of self-purification capacity in lotic environment is an important tool in the planning and management of hydric resources in hydrographic basin scale. It satisfactorily deals with the self-purification process when the coefficients of physical and biochemical processes are calibrated from monitorated water quality data, which was the main focus of this study. The present study was conducted to simulate the behavior of the parameters OD, BOD5, total phosphorus, E. coli, ammonia, nitrite, nitrate and the total metals cadmium, chromium, copper, lead and zinc in the Uberabinha’s lower course (with an approximate annual growth flow between 4-35 m3/s), in a stretch of 19 km downstream of the treated effluent release by the WWTP of the city. The modelings, on the present study, show the importance of constant water quality parameters monitoration over the water course, based on the comparison of the simulations from calibrated coefficients and coefficients obtained in the literature for the period of June until November 2015. After coefficients calibration, there were good adjustments between simulated and measured data for the parameters OD, BOD, Ptotal, ammonia and nitrate and unsatisfactory adjust for the parameters nitrite and E. coli. About the total metals, the adjustments were not satisfactory on the reservoir’s vicinity of the Small Hydropower Plant Martins, due the considerable increase of the bottom sediment in lentic region. The greatest scientific contribution of this study was to calibrate the decay coefficient K and the quantification of the release by the fund S of total metals in watercourse midsize WWTP pollutant load receptor, justified by the lack of studies in the literature about the subject. For the metals cadmium, chromium, copper, lead and zinc, the borderline for K and S calibrated were: 0.0 to 13.0 day-1 and 0.0 to 1.7 g/m3.day; 0.0 to 0.9 day-1 and 0.0 to 7.3 g/m3.day; 0.0 to 25.0 day-1 and 0.0 to 1.8 g/m3.day; 0.0 to 7.0 day-1 and 0.0 to 40.3 g/m3.day; 0.0 to 30.0 day-1 and 0.0 to 70.1 g/m3.day.

Efeitos da internacionalização no desvio da estrutura de capital alvo e na velocidade de ajuste

This dissertation investigates the effects of internationalization in two gaps related to the capital structure that have not been discussed by the Brazilian literature yet. To this, were developed two independent sections. The first examined what the effects of internationalization on the deviation from the target capital structure. The second examined what the effects of internationalization on speed of adjustment (SOA) of the capital structure. It used data from Brazil, multinational and domestic companies, from 2006 to 2014. The results of the first analysis indicate that internationalization helps reduce the difference between the target and the current debt. That is, to the extent that the level of internationalization increases; whether only export or a combination of export, assets and employees abroad, the gap between the current structure and the target structure decreases. This reduction is given as a function of internationalization as a consequence of the upstream effect of the upstream-downstream hypothesis. Thus, as the Market Timing theory, it can be seen as an opportunity for adjustment of the capital structure, and with the reduction of deviation, there is also a reduction in the cost of capital of the firm. The result of the second analysis indicates that internationalization is able to significantly increase the speed adjustment, ensuring for the multinational a faster adjustment of its capital structure. Exports increase the SOA in 9 to 23%. And when also kept active assets and employees abroad the increase is 8 to 20%. In terms of time, while domestic company takes more than three years to reduce half of the deviation that has, while multinacional companies take on average one and a half year to reduce the same proportion of the deviation. The validity of the upstream-downstream hypothesis for the effect of internationalization in SOA was confirmed by comparing the results for US companies. Thus, the phenomenon of internationalization increases SOA when companies are from less stable markets, such as Brazil; and it has a less significcative effect when companies are derived from more stable markets, because they already have a high speed of adjustmennt. In addition, the adequacy analysis of the estimators also showed the model pooled OLS (Ordinary Least Squares) presents the highest quality in predicting the SOA than the system GMM (Generalized Method of Moments). For future studies it is suggested to analyze the effect of international event, by itself, and to validate the hypothesis using samples of different markets and the use of other estimators.