O uso crescente de fontes alternativas de energia exige conversores de energia capazes de aumentar sua tensão nos terminais e conectá-los ao sistema de distribuição. Neste contexto, o conversor step-up clássico (conversor de potência CC/CC) e o inversor de fonte de tensão (VSI) são as soluções mais aplicadas para processar o fluxo de energia da fonte para a rede. No entanto, apresentam um baixo rendimento devido ao duplo estágio de conversão, isto é, a energia flui também através dos conversores de energia CC/CC e CC/CA. Para evitar esse tipo de desvantagem, no início da última década, o Z-Source-Inverter (ZSI) foi introduzido. Nesta nova solução, o conversor de energia CC/CC responsável por elevar a tensão nos terminais do conversor foi removido e uma rede de impedância LCLC foi adicionada com duas tarefas, ou seja, aumentar a tensão do terminal e melhorar a eficiência do ZSI. Infelizmente, os trabalhos da literatura não apresentaram um modelo matemático generalizado para apoiar os projetistas de conversores de potência na análise de estabilidade, projeto de controladores ou avaliar o ganho de tensão do conversor. Neste sentido, esta dissertação propõe o desenvolvimento de um modelo matemático completo e a análise de estabilidade da planta. Para suportar todo o desenvolvimento teórico, foi realizado um conjunto de análises no domínio do tempo e da frequência. Por fim, verificou-se o controle da tensão do elo CC para suportar todas as afirmações apresentadas neste trabalho (controle da tensão no capacitor da rede Z). / The growing use of alternative energy sources require power converters able to boost their terminal voltage and connect them to the distribution system. In this context, the classical step-up converter (DC/DC power converter) and the voltage source inverter (VSI) are the most applied solutions to process the power flow from the source to the grid. However, they present a low efficient because of the double stage of conversion, i.e. the power flows through the DC/DC and DC/AC power converters as well. To avoid this type of drawback, in the beginning of the last decade the impedance source inverter (ZSI) was introduce. In this new solution, the DC/DC power converter responsible for boosting the voltage at the DC-source terminals was removed and a Z (LCLC-network) was added with two tasks, i.e. boost the DC-source terminal voltage and improve the ZSI efficiency. Unfortunately, the papers in the literature did not present a generalized mathematical model to support designers of power converters in the analysis of stability, design of controllers or evaluate the voltage gain of the converter. In this sense, this thesis proposes the development of a complete mathematical model and the stability analysis of the plant. To support all the theoretical development a set of analysis in the time and frequency-domain was performed. Finally, the control of DC-link voltage was verified to support all the statements presented in this thesis (control on the Z-network voltage capacitance).

O uso crescente de fontes alternativas de energia exige conversores de energia capazes de aumentar sua tensão nos terminais e conectá-los ao sistema de distribuição. Neste contexto, o conversor step-up clássico (conversor de potência CC/CC) e o inversor de fonte de tensão (VSI) são as soluções mais aplicadas para processar o fluxo de energia da fonte para a rede. No entanto, apresentam um baixo rendimento devido ao duplo estágio de conversão, isto é, a energia flui também através dos conversores de energia CC/CC e CC/CA. Para evitar esse tipo de desvantagem, no início da última década, o Z-Source-Inverter (ZSI) foi introduzido. Nesta nova solução, o conversor de energia CC/CC responsável por elevar a tensão nos terminais do conversor foi removido e uma rede de impedância LCLC foi adicionada com duas tarefas, ou seja, aumentar a tensão do terminal e melhorar a eficiência do ZSI. Infelizmente, os trabalhos da literatura não apresentaram um modelo matemático generalizado para apoiar os projetistas de conversores de potência na análise de estabilidade, projeto de controladores ou avaliar o ganho de tensão do conversor. Neste sentido, esta dissertação propõe o desenvolvimento de um modelo matemático completo e a análise de estabilidade da planta. Para suportar todo o desenvolvimento teórico, foi realizado um conjunto de análises no domínio do tempo e da frequência. Por fim, verificou-se o controle da tensão do elo CC para suportar todas as afirmações apresentadas neste trabalho (controle da tensão no capacitor da rede Z). / The growing use of alternative energy sources require power converters able to boost their terminal voltage and connect them to the distribution system. In this context, the classical step-up converter (DC/DC power converter) and the voltage source inverter (VSI) are the most applied solutions to process the power flow from the source to the grid. However, they present a low efficient because of the double stage of conversion, i.e. the power flows through the DC/DC and DC/AC power converters as well. To avoid this type of drawback, in the beginning of the last decade the impedance source inverter (ZSI) was introduce. In this new solution, the DC/DC power converter responsible for boosting the voltage at the DC-source terminals was removed and a Z (LCLC-network) was added with two tasks, i.e. boost the DC-source terminal voltage and improve the ZSI efficiency. Unfortunately, the papers in the literature did not present a generalized mathematical model to support designers of power converters in the analysis of stability, design of controllers or evaluate the voltage gain of the converter. In this sense, this thesis proposes the development of a complete mathematical model and the stability analysis of the plant. To support all the theoretical development a set of analysis in the time and frequency-domain was performed. Finally, the control of DC-link voltage was verified to support all the statements presented in this thesis (control on the Z-network voltage capacitance).

Este trabalho apresenta o estudo de um inversor NPC de 6 kW e 380 V, trifÃsico, para interconexÃo de sistemas de geraÃÃo distribuÃda à rede elÃtrica. O inversor à estudado nas frequÃncias de chaveamento de 3, 4 e 6 kHz, sendo interligado à rede elÃtrica atravÃs dos filtros L e LCL. Para identificar qual filtro passivo, L ou LCL, se adequa melhor ao inversor em estudo foram realizadas simulaÃÃes numÃricas para diferentes situaÃÃes, validando o projeto do inversor e a modelagem vetorial desenvolvida. A resposta do controle à satisfatÃria, pois o inversor à capaz de controlar o fluxo de potÃncia ativa e reativa entregues à rede elÃtrica. Diante dos resultados obtidos percebeu-se que o filtro LCL apresentou um menor conteÃdo harmÃnico para as trÃs frequÃncias estudadas em relaÃÃo ao filtro L. Ambos os filtros atenderam aos requisitos da norma Std IEEE 1543, no entanto o filtro L à o mais indicado para o inversor em estudo, pois alÃm de atender a norma, o mesmo apresenta um menor custo quando comparado ao filtro LCL. / This paper presents the study of a 6 kW, 380 V, three phase NPC inverter for interconnecting distributed generation unit to the grid. The inverter is studied with switching frequency of 3, 4 and 6 kHz, and it is interconnected to the grid through L and LCL filters. To identify which passive filter, L or LCL, is best suited to the inverter under study, a mathematical model has been proposed and several numerical simulations have been carried out to validate the design of the inverter and vector model developed. The control response is satisfactory, since the inverter is able to control the flow of active and reactive power delivered to the grid. Based on these results it was noticed that the LCL filter showed a lower harmonic content for the three frequencies studied in relation to the filter L. Both filters met the requirements of the standard IEEE Std 1543, however the filter L is the most suitable for the inverter under study, because the filter L not only meet the standard but also it presents a lower cost when compared to the LCL filter.

The global requirement for sustainable energy provision will become increasingly important over the next fifty years as the environmental effects of fossil fuel use become apparent. Therefore, the issues surrounding integration of renewable energy supplies need to be considered carefully. The focus of this work was the development of an innovative computer aided design of a 3 Dimensional renewable energy platform for Togo’s smart grid power system infrastructure. It demonstrates its validation for industrial, commercial and domestic applications. The Wind, Hydro, and PV system forming our 3 Dimensional renewable energy power generation systems introduces a new path for hybrid systems which extends the system capacities to include, a stable and constant clean energy supply, a reduced harmonic distortion, and an improved power system efficiency. Issues requiring consideration in high percentage renewable energy systems therefore includes the reliability of the supply when intermittent sources of electricity are being used, and the subsequent necessity for storage and back-up generation The adoption of Genetic algorithms in this case was much suited in minimizing the THD as the adoption of the CHB-MLI was ideal for connecting renewable energy sources with an AC grid. Cascaded inverters have also been proposed for use as the main traction drive in electric vehicles, where several batteries or ultra-capacitors are well suited to serve as separate DC sources. The simulation done in various non-linear load conditions showed the proportionality of an integral control based compensating cascaded passive filter thereby balancing the system even in non-linear load conditions. The measured total harmonic distortion of the source currents was found to be 2.36% thereby in compliance with IEEE 519-1992 and IEC 61000-3 standards for harmonics This work has succeeded in developing a more complete tool for analysing the feasibility of integrated renewable energy systems. This will allow informed decisions to be made about the technical feasibility of supply mix and control strategies, plant type, sizing and storage sizing, for any given area and range of supply options. The developed 3D renewable energy platform was examined and evaluated using CAD software analysis and a laboratory base mini test. The initial results showed improvements compared to other hybrid systems and their existing control systems. There was a notable improvement in the dynamic load demand and response, stability of the system with a reduced harmonic distortion. The derivatives of this research therefore proposes an innovative solution and a path for Togo and its intention of switching to renewable energy especially for its smart grid power system infrastructure. It demonstrates its validation for industrial, commercial and domestic applications.

The general trends in the past decade of increasing solar cell efficiency, decreasing PV system costs, increasing government incentive programs, and several other factors have all combined synergistically to reduce the barriers of entry for PV systems to enter the market and expand their contribution to the global energy portfolio. The shortcomings of current inverter functions which link PV systems to the utility network are becoming transparent as PV penetration levels continue to increase. The solution this thesis proposes is an approach to control the inverters real and reactive power output to help eliminate the problems associated with PV systems at their origin and in addition provide the grid with ancillary support services. The design, modeling, and analysis of a grid-tied PV system was performed in the PSCAD software simulation environment. Results indicate that in the presence of grid disturbances the smart inverter can react dynamically to help restore the power system back to its normal state. A harmonic analysis was also performed indicating the inverter under study met the applicable power quality standards for distributed energy resources.

<p>Low-sensitivity switched capacitor filters imitating 'R','L' and 'C' can be built by means of capacitances, ordinary switches and voltage inverter switches (VIS). These structures carry the inherent bilinear transformation of their doubly resistively terminated ladder reference filters. This one to one correspondence between the 's-domain' and the 'z-domain' results in the Nyquist criterion being the only limitation on the sampling frequency. This eliminates the necessity for oversampling and VIS filters can be designed for high operating rates.</p><p>Filters based on VIS principle were analysed in previous literatures in the 'phi-domain'. In this thesis work, a successful attempt has been made to formulate an analysis procedure for discrete-time filters based on VIS principle in the 'z-domain'. Significant details have been brought out in comparison with the respective reference filter. A fifth-order lowpass filter has been designed and implemented to exhibit the closeness to the bilinearly transformed continuous-time reference filter. Settling time analysis has been done to justify the need for filters using VIS principle as compared to the filters employing integrator based switched capacitor filter. It is shown that VIS filter can be made to settle within half the period required for a conventional integrator based switched capacitor filter.</p>

Distributed energy resources (DE) with power electronics interfaces and logic control using local measurements are capable of providing reactive power related to ancillary system services. In particular, local voltage regulation has drawn much attention in regards to power system reliability and voltage stability, especially from past major cascading outages. This dissertation addresses the challenges of controlling the DEs to regulate the local voltage in distribution systems. First, an adaptive voltage control method has been proposed to dynamically modify the control parameters of a single DE to respond to system changes such that the ideal response can be achieved. Theoretical analysis shows that a corresponding formulation of the dynamic control parameters exists; hence, the adaptive control method is theoretically solid. Also, the field experiment test results at the Distributed Energy Communications and Controls (DECC) Laboratory in single DE regulation case confirm the effectiveness of this method. Then, control methods have been discussed in the case of multiple DEs regulating voltages considering the availability of communications among all the DEs. When communications are readily available, a method is proposed to directly calculate the needed adaptive change of the DE control parameters in order to achieve the ideal response. When there is no communication available, an approach to adaptively and incrementally adjust the control parameters based on the local voltage changes is proposed. Since the impact from other DEs is implicitly considered in this approach, multiple DEs can collectively regulate voltages closely following the ideal response curve. Simulation results show that each method, with or without communications, can satisfy the fast response requirement for operational use without causing oscillation, inefficiency or system equipment interference, although the case with communication can perform even faster and more accurate. Since the proposed adaptive voltage regulation method in the case of multiple DEs without communication, has a high tolerance to real-time data shortage and can still provide good enough performance, it is more suitable for broad utility applications. The approach of multiple DEs with communication can be considered as a high-end solution, which gives faster and more precise results at a higher cost

In the past, distribution systems were characterized by a unidirectional power flow where power flows from the main power generation units to consumers. However, with changes in power system regulation and increasing incentives for integrating renewable energy sources, Distributed Generation (DG) has become an important component of modern distribution systems. However, when a portion of the system is energized by one or more DG and is disconnected from the grid, this portion becomes islanded and might cause several operational and safety issues. Therefore, an accurate and fast islanding detection technique is needed to avoid these issues as per IEEE Standard 1547-2003 [1]. Islanding detection techniques are dependent on the type of the DG connected to the system and can achieve accurate results when only one type of DG is used in the system. Thus, a major challenge is to design a universal islanding technique to detect islanding accurately and in a timely manner for different DG types and multiple DG units in the system. This thesis introduces an efficient universal islanding detection method that can be applied to both Inverter-based DG and Synchronous-based DG. The proposed method relies on extracting a group of features from measurements of the voltage and frequency at the Point of Common Coupling (PCC) of the targeted island. The Random Forest (RF) classification technique is used to distinguish between islanding and non-islanding situations with the goals of achieving a zero Non-Detection Zone (NDZ), which is a region where islanding detection techniques fail to detect islanding, as well as avoiding nuisance DG tripping during non-islanding conditions. The accuracy of the proposed technique is evaluated using a cross-validation technique. The methodology of the proposed islanding detection technique is shown to have a zero NDZ, 98% accuracy, and fast response when applied to both types of DGs. Finally, four other classifiers are compared with the Random Forest classifier, and the RF technique proved to be the most efficient approach for islanding detection.

As the costs of large-scale power generation and transmission rise, distributed generation is becoming a prevalent alternative used by a growing number of both residences and businesses. Distributed generation systems typically consist of two main components: a small-scale, often high-efficiency or renewable power source, such as a fuel cell, solar panel, or wind turbine, and a power electronic converter to convert the raw power produced by the source to a usable form. In North America, the majority of power used in residential and light commercial locations is provided in a form known as single-phase three-wire, or split-phase. This consists of two half-phase AC voltages, each of 110 to 120V rms, and one combined AC voltage of 220 to 240V rms. It is therefore necessary for distributed generation systems to supply power in this same form so that it can be used by standard loads such as lighting or appliances, and the excess power can be fed back into the distribution grid. The most common type of converter used to make this conversion is the voltage-sourced inverter (VSI). There are, however, some advantages to using a current-sourced inverter (CSI) instead. These include improved output voltage waveform quality, built-in voltage boost, and built-in overcurrent protection. However, there are also two obstacles that have prevented the adoption of current-sourced inverters to date. The first obstacle to the use of current-sourced inverters is that they require a DC current input to operate. Therefore, a circuit and control algorithm must be developed to produce a DC current from a low DC voltage source. The first part of this thesis deals with the generation of a suitable DC current. The second major obstacle to adopting current-sourced inverters is that no algorithm for producing single-phase three-wire outputs with a CSI presently exists in literature. The second part of this thesis develops such a switching algorithm, using a three-leg current-sourced inverter. The algorithm is demonstrated using simulation and experimental results, which show that the proposed system is able to successfully generate balanced output voltages under unbalanced loading conditions while equalizing switch utilization and minimizing output voltage ripple.

En av Glimek AB:s mest förekommande maskiner är SD-180 som används för degavvägning. Den finns i flera olika varianter. Den enklaste har enbart start- och stoppknapp och en potentiometer för att ställa hastigheten och en mer avancerad variant har en operatörspanel där olika möjligheter till inställningar finns. Konstruktionen på denna maskin hade inte uppdaterats på många år och behövde en uppdatering av användargränssnitt, programvara och elkonstruktion. Arbetet har framförallt koncentrerat sig på användargränssnittet till panelen. En del av arbetet var att undersöka om det var möjligt att utesluta PLC ur konstruktionen och använda en mer avancerad programmerbar frekvensomformare. Eftersom det blev problem med lanseringen av programvara till frekvensomformaren och enbart en mindre bra fungerande demoversion fanns tillgänglig så var detta tyvärr inte möjligt. I arbetet har olika varianter på operatörspaneler utretts. Exempel på flödesdiagram till PLC har också gjorts. / One of Glimek AB's most common machines is the dough divider, SD-180. It is available in many different variants. The simplest has only a start- and stop button and a potentiometer to set the speed. A more advanced version has an operator panel with various options. The design of this machine had not been updated in many years and needed an update of the user interface, software and electrical construction. The thesis has mainly concentrated on the human machine interface. A part of the work was to investigate whether it was possible to exclude the PLC from the design and use a more powerful and programmable frequency inverter.Unfortunately problems arose with the release of the software for the frequency converter. Only a demo version of the software where available and it was not possible to this study because of that. Different variants of human machine interface have been investigated. An example flowchart diagram to the PLC has also been made.