A crescente demanda por fontes alternativas de energia, voltada principalmente a minimizar impactos ambientais provenientes do uso de combustíveis fósseis na geração de energia elétrica, tem impulsionado as pesquisas tanto no âmbito acadêmico como no setor privado. Dessa forma, estudos científicos vêm abordando painéis fotovoltaicos, aerogeradores, células combustível, dentre outros, no sentido de gerar energia limpa por meio de conversores estáticos CC-CC e CC-CA, conectados na rede de distribuição elétrica, configurando um cenário de Geração Distribuída. Devido ao uso de tais conversores, têm-se introduzido perturbações harmônicas nas redes de distribuição. Sendo assim, a qualidade de energia tornouse uma questão de suma importância no contexto energético contemporâneo, de tal modo que esta tese se apresenta um estudo voltado ao desenvolvimento e implementação de uma plataforma experimental de um Condicionador Unificado de Qualidade de Energia (UPQC) monofásico com compensação ativa de potência série e paralela, com uma potência de 1 kW, capaz de minimizar perturbações harmônicas em redes de distribuição. O sistema realiza a supressão de harmônicos e a compensação de afundamentos e elevações de tensão em redes elétricas, além de manter a tensão na carga regulada e com baixa taxa de distorção harmônica. Além disso, esse dispositivo realiza compensação de potência reativa e supressão de harmônicos da corrente de carga, o que resulta em uma efetiva correção do fator de potência. Nesse sentido, o dispositivo atua como um filtro ativo universal, realizando compensação da corrente de entrada, como também da tensão de saída. Para este fim, dois conversores monofásicos ANPC de 5 níveis são empregados, sendo estes o filtro ativo série (FAS), que atua como fonte de corrente senoidal, e o filtro ativo paralelo (FAP), que atua como fonte de tensão senoidal, em que ambos são controlados de tal forma a operar em fase com a tensão da rede elétrica. Com o objetivo de realizar as compensações harmônicas, é utilizado o algoritmo de extração de referência, conhecido como Compensação Cooperativa baseada na Teoria de Potência Conservativa. / The growing demand for alternative sources of energy, aimed mainly at minimizing environmental impacts from the use of fossil fuels in electric power generation, has driven research in both the academic and private sectors. Thus, scientific studies have addressed photovoltaic panels, aerogenerators, fuel cells, among others, in order to generate clean energy by means of static converters CC-CC and CC-CA, connected in the electric distribution network, configuring the Distributed Generation. Due to the use of such converters, harmonic disturbances have been introduced in the distribution networks. Thus, the quality of energy has become a matter of paramount importance in the contemporary energy context, such that this thesis presents a study aimed at the development and implementation of an experimental platform of a single-phase Unified Energy Quality Conditioner (UPQC) with active series and parallel power compensation, with a power of 1 kW, capable of minimizing harmonic disturbances in distribution networks. The system performs the suppression of harmonics and the compensation of sags and tensions in electrical networks, besides maintaining the voltage at the regulated load and with a low harmonic distortion rate. In addition, this device performs reactive power compensation and harmonic suppression of the load current, which results in an effective power factor correction. In this sense, the device acts as a universal active filter, performing compensation of the input current, as well as the output voltage. For this purpose, two 5-level ANPC single-phase converters are used, which are the series active filter (FAS), which acts as a sinusoidal current source, and the parallel active filter (FAP), which acts as a sinusoidal voltage source, in that both are controlled in such a way to operate in phase with the mains voltage. In order to perform the harmonic compensations, the reference extraction algorithm, known as Cooperative Compensation based on the Conservative Power Theory, is used.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta contribuições para algoritmos de controle utilizados em filtros ativos e híbridos conectados em redes elétricas trifásicas a 3 ou a 4 fios. Em relação aos algoritmos de controle para filtros ativos, a contribuição consiste em estender o conceito da filtragem harmônica seletiva para compensação de correntes harmônicas e desequilibradas em uma rede trifásica a 4 fios. Esses algoritmos derivam dos conceitos utilizados na teoria da potência instantânea (teoria pq), em conjunto com um circuito de sincronismo PLL. É importante ressaltar que estes algoritmos não utilizam as correntes consumidas pelas cargas, ou seja, apenas as tensões no ponto da rede onde o filtro está conectado são utilizadas para determinação das correntes harmônicas de referência. Apenas as correntes na saída do conversor são utilizadas como realimentação do controle PWM. Estes algoritmos também foram utilizados no filtro híbrido para compensação de correntes harmônicas em uma rede trifásica a 3 fios. Por fim foi feito uma alteração nesses algoritmos de controle que permite eliminar as correntes utilizadas na realimentação do controle PWM. Resultados de simulação são apresentados com objetivo de observar o comportamento desses algoritmos tanto no filtro ativo quanto no híbrido nas condições mencionadas. / This work presents some contributions involving control algorithms for active and hybrid filters connected in 3 or 4-wire three-phase electrical grids. In relation to the control algorithms for active filters, the contribution results from the extension involving the concepts of selective harmonic filtering to compensate unbalanced and harmonic currents in a 4-wire three-phase electrical grid. These algorithms derive from the instantaneous power theory (pq theory) together with a synchronizing PLL-circuit. It is important to mention that these algorithm do not use the currents consumed by the loads, i.e, only the voltages at the point common coupling (PCC) are used to determine the reference harmonic currents. Only the output converter currents were used as a feedback to the PWM control. These algorithms were also employed in a hybrid filter to compensate harmonic currents in a 3-wire three-phase electrical grid. Finally, some improvements on these control algorithms were done, such that the output converter currents used as a feedback of the PWM control were eliminated. Simulations results were provided in order to analyze the behavior of the active and hybrid filters in the aforementioned conditions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta contribuições para algoritmos de controle utilizados em filtros ativos e híbridos conectados em redes elétricas trifásicas a 3 ou a 4 fios. Em relação aos algoritmos de controle para filtros ativos, a contribuição consiste em estender o conceito da filtragem harmônica seletiva para compensação de correntes harmônicas e desequilibradas em uma rede trifásica a 4 fios. Esses algoritmos derivam dos conceitos utilizados na teoria da potência instantânea (teoria pq), em conjunto com um circuito de sincronismo PLL. É importante ressaltar que estes algoritmos não utilizam as correntes consumidas pelas cargas, ou seja, apenas as tensões no ponto da rede onde o filtro está conectado são utilizadas para determinação das correntes harmônicas de referência. Apenas as correntes na saída do conversor são utilizadas como realimentação do controle PWM. Estes algoritmos também foram utilizados no filtro híbrido para compensação de correntes harmônicas em uma rede trifásica a 3 fios. Por fim foi feito uma alteração nesses algoritmos de controle que permite eliminar as correntes utilizadas na realimentação do controle PWM. Resultados de simulação são apresentados com objetivo de observar o comportamento desses algoritmos tanto no filtro ativo quanto no híbrido nas condições mencionadas. / This work presents some contributions involving control algorithms for active and hybrid filters connected in 3 or 4-wire three-phase electrical grids. In relation to the control algorithms for active filters, the contribution results from the extension involving the concepts of selective harmonic filtering to compensate unbalanced and harmonic currents in a 4-wire three-phase electrical grid. These algorithms derive from the instantaneous power theory (pq theory) together with a synchronizing PLL-circuit. It is important to mention that these algorithm do not use the currents consumed by the loads, i.e, only the voltages at the point common coupling (PCC) are used to determine the reference harmonic currents. Only the output converter currents were used as a feedback to the PWM control. These algorithms were also employed in a hybrid filter to compensate harmonic currents in a 3-wire three-phase electrical grid. Finally, some improvements on these control algorithms were done, such that the output converter currents used as a feedback of the PWM control were eliminated. Simulations results were provided in order to analyze the behavior of the active and hybrid filters in the aforementioned conditions.

Syfte: Företags kassaflöden och vinster samt staters inkomster påverkas av hur mycket skatt som betalas av företag. Resultat i tidigare forskning om företagsstorlekens betydelse för effektiva skattesatser är motstridiga. Utelämnande av andra variabler som i vissa studier har visats ha signifikanta effekter på effektiva skattesatser kan vara en anledning till denna motstridighet. Sådan forskning har inte genomförts i Sverige enligt författarnas kännedom. Därför undersöks i denna studie effekterna av variabler som mäter storlek, skuldsättning, kapitalintensitet, forsknings- och utvecklingsintensitet samt lönsamhet på effektiva skattesatser hos företag med svensk företagsledning eller koncernledning. Syftet med detta är att ge en bild av vilka faktorer som kan förklara variationer mellan dessa företags skattebörda. Metod: Fem hypoteser om samband mellan variabler deduceras utifrån teorier och tidigare forskning. 3 593 kvantitativa observationer från 702 noterade företag och 6 år samlas in från databasen Retriever Business. Den longitudinella datan används i en regressionsanalys som testar de fem hypoteserna. Resultat: Denna studie bidrar med empiriskt bevis för ett positivt och signifikant samband mellan företagsstorlek och effektiva skattesatser. Däremot visas inte effekterna av skuldsättning, kapitalintensitet, FoU-intensitet och lönsamhet på effektiva skattesatser vara signifikanta. Slutsatser: Den slutsats som dras är att företagsstorlek är en indikation på storleken på effektiva skattesatser för företag med svensk företagsledning eller koncernledning. Teorin om politiska kostnader kan användas för att förklara sambandets riktning. / Aim: Cash flows and profits in firms as well as government revenue are affected by how much is paid in corporate taxes. Results in prior research concerning the effect of firm size on effective tax rates are inconsistent. Omitting other variables that have in some studies been proven to have significant effects on effective tax rates can be one cause of this inconsistency. Such research has not been conducted in Sweden to the extent of the authors’ knowledge. Therefore, this study examines the effects of variables that measure size, leverage, capital intensity, research and development intensity, and profitability on effective tax rates for firms with Swedish management or group management. The aim of this is describing which factors that can explain variations between these firms’ tax burdens. Method: Five hypotheses regarding associations between variables are deduced from theories and prior research. 3 593 quantitative observations from 702 publicly listed firms and 6 years are collected from the database Retriever Business. The longitudinal data is used in a regression analysis that tests the five hypotheses. Results: This study provides empirical evidence for a positive and significant association between firm size and effective tax rates. However, the effects of leverage, capital intensity, R&D intensity, and profitability on effective tax rates are not shown to be significant. Conclusions: It is concluded that firm size is an indicator of the size of effective tax rates for firms with Swedish management or group management. The political cost theory can be used in explaining the direction of the association.

The intentions of the so-called "More Electrical Aircraft" (MEA) are higher efficiency and lower weight. A main topic here is the application of electrical instead of hydraulical, pneumatical and mechanical systems. The necessary power electronic devices have intermediate DC-links, which are typically supplied by a three-phase system with active B6 and passive B12 rectifiers. A possible alternative is the B6 diode bridge in combination with an active power filter (APF). Due to the parallel arrangement, the APF offers a higher power density and is able to compensate for harmonics from several devices. The use of the diode bridge rectifier alone is not permitted due to the highly distorted phase current. The following investigations are dealing with the development of an active power filter for a three-phase supply with variable frequency from 360 to 800 Hz. All relevant components such as inductors, EMC-filters, power modules and DC-link capacitor are designed. A particular focus is put on the customized power module with SiC-MOSFETs and SiC-diodes, which is characterized electrically and thermally. The maximum supply frequency slope has a value of 50 Hz/ms, which requires a high dynamic and robustness on the control algorithm. Furthermore, the content of 5th and 7th harmonics must be reduced to less than 2 %, which demands a high accuracy. To cope with both requirements, a two-stage filter algorithm is developed and implemented in two independent signal processors. Simulations and laboratory experiments confirm the performance and robustness of the control algorithm. This work comprehensively presents the design of aerospace rectifiers. The results were published in conferences and patents. / Hauptziele des sogenannten "More Electrical Aircraft" (MEA) sind Effizienzerhöhung und Gewichtseinsparung. Ein Schwerpunkt hierbei ist die Nutzung von elektrischen statt hydraulischen, pneumatischen und mechanischen Systemen. Die notwendigen Leistungselektroniken haben DC-Zwischenkreise, welche mittels aktiven B6 und passiven B12 Gleichrichtern aus dem Dreiphasennetz gespeist werden. Eine mögliche Alternative ist die B6 Diodenbrücke in Kombination mit einem aktiven Netzfilter, welcher aufgrund der parallelen Anordnung eine höhere Leistungsdichte aufweist und darüber hinaus mehrere Geräte gleichzeitig entstören kann. Die alleinige Nutzung einer Diodenbrücke ist aufgrund des hohen Anteils von Stromharmonischen nicht zulässig. Diese Arbeit beschäftigt sich mit der Entwicklung eines aktiven Filters für ein Dreiphasensystem mit variabler Frequenz von 360 bis 800 Hz. Es werden alle relevanten Bauteile wie Induktivitäten, EMV-Filter, Leistungsmodule und Zwischenkreiskondensator ausgelegt. Besonderes Augenmerk liegt auf dem kundenspezifischen Modul mit SiC-Dioden und SiCMOSFETs, welches vollständig elektrisch und thermisch charakterisiert wird. Die Änderung der Netzfrequenz beträgt bis zu 50 Hz/ms, was eine hohe Dynamik und Robustheit von der Filterregelung verlangt. Weiterhin ist im statischen Fall eine hohe Genauigkeit gefordert, da die 5. und 7. Harmonische auf unter 2% geregelt werden müssen. Um beiden Anforderungen gerecht zu werden, wird ein zweistufiger Regelungsalgorithmus entwickelt der auf zwei digitalen Signalprozessoren implementiert wird. Simulationen und Labormessungen bestätigen die Robustheit des Regelungskonzeptes. Diese Arbeit stellt umfassend die Entwicklung von Luftfahrtgleichrichtern dar. Die Ergebnisse wurden in Konferenzen und Patenten veröffentlicht.

The intentions of the so-called "More Electrical Aircraft" (MEA) are higher efficiency and lower weight. A main topic here is the application of electrical instead of hydraulical, pneumatical and mechanical systems. The necessary power electronic devices have intermediate DC-links, which are typically supplied by a three-phase system with active B6 and passive B12 rectifiers. A possible alternative is the B6 diode bridge in combination with an active power filter (APF). Due to the parallel arrangement, the APF offers a higher power density and is able to compensate for harmonics from several devices. The use of the diode bridge rectifier alone is not permitted due to the highly distorted phase current. The following investigations are dealing with the development of an active power filter for a three-phase supply with variable frequency from 360 to 800 Hz. All relevant components such as inductors, EMC-filters, power modules and DC-link capacitor are designed. A particular focus is put on the customized power module with SiC-MOSFETs and SiC-diodes, which is characterized electrically and thermally. The maximum supply frequency slope has a value of 50 Hz/ms, which requires a high dynamic and robustness on the control algorithm. Furthermore, the content of 5th and 7th harmonics must be reduced to less than 2 %, which demands a high accuracy. To cope with both requirements, a two-stage filter algorithm is developed and implemented in two independent signal processors. Simulations and laboratory experiments confirm the performance and robustness of the control algorithm. This work comprehensively presents the design of aerospace rectifiers. The results were published in conferences and patents. / Hauptziele des sogenannten "More Electrical Aircraft" (MEA) sind Effizienzerhöhung und Gewichtseinsparung. Ein Schwerpunkt hierbei ist die Nutzung von elektrischen statt hydraulischen, pneumatischen und mechanischen Systemen. Die notwendigen Leistungselektroniken haben DC-Zwischenkreise, welche mittels aktiven B6 und passiven B12 Gleichrichtern aus dem Dreiphasennetz gespeist werden. Eine mögliche Alternative ist die B6 Diodenbrücke in Kombination mit einem aktiven Netzfilter, welcher aufgrund der parallelen Anordnung eine höhere Leistungsdichte aufweist und darüber hinaus mehrere Geräte gleichzeitig entstören kann. Die alleinige Nutzung einer Diodenbrücke ist aufgrund des hohen Anteils von Stromharmonischen nicht zulässig. Diese Arbeit beschäftigt sich mit der Entwicklung eines aktiven Filters für ein Dreiphasensystem mit variabler Frequenz von 360 bis 800 Hz. Es werden alle relevanten Bauteile wie Induktivitäten, EMV-Filter, Leistungsmodule und Zwischenkreiskondensator ausgelegt. Besonderes Augenmerk liegt auf dem kundenspezifischen Modul mit SiC-Dioden und SiCMOSFETs, welches vollständig elektrisch und thermisch charakterisiert wird. Die Änderung der Netzfrequenz beträgt bis zu 50 Hz/ms, was eine hohe Dynamik und Robustheit von der Filterregelung verlangt. Weiterhin ist im statischen Fall eine hohe Genauigkeit gefordert, da die 5. und 7. Harmonische auf unter 2% geregelt werden müssen. Um beiden Anforderungen gerecht zu werden, wird ein zweistufiger Regelungsalgorithmus entwickelt der auf zwei digitalen Signalprozessoren implementiert wird. Simulationen und Labormessungen bestätigen die Robustheit des Regelungskonzeptes. Diese Arbeit stellt umfassend die Entwicklung von Luftfahrtgleichrichtern dar. Die Ergebnisse wurden in Konferenzen und Patenten veröffentlicht.

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