The dissertation presents a new control strategy for two terminal HVDC systems embedded in an AC network. The control is based upon real-time measurements performed on the AC/DC system. Use is made of a technique for high speed accurate measurement of positive sequence voltages and currents, first developed in the field of computer relaying. The real-time measurements provides a term in the control law to compensate for inaccuracies following departure from the operating point. The control criterion is to damp out the electromechanical oscillations following a disturbance. The main contribution of the dissertation is to describe a new optimal controller formulation which contains a measurement based component. Optimal controllers are commonly constructed using linearized equations of the system around the operating point. In DC systems this approach is of a very limited value because of a highly nonlinear nature of the system. With the controller developed in this dissertation, it becomes possible to describe the system as a nonlinear dynamic system. The approximation resulting from the usual linearization of the system equations is thus avoided, and leads to a better controller design. The control technique is illustrated with a small AC/DC system. However, the equations formulated are sufficiently general, so that the technique can be applied to a larger system. Simulation results are included to represent the effectiveness of the developed controller. / Ph. D.

No description available.

In a VLSI design environment, a more efficient test generation algorithm is definitely needed. This thesis evaluates a test generation algorithm, PODEM, as mechanism to generate the goal states in a sequential circuit test search system, SCIRTSS. First, a hardware description language, AHPL, is used to describe the behavior of a sequential circuit. Next, SCIRTSS is used to generate the test vectors. Several circuits are evaluated and experimental results are compared with data from a previous version of SCIRTSS which was implemented with the D-Algorithm. Depending on the number of reconvergent fanouts in a circuit, it is found that PODEM is 1 to 23 times faster than the D-Algorithm.

Os circuitos ou modelos elétricos equivalentes destinam-se à modelagem de transdutores piezoelétricos, incluindo todo seu comportamento eletromecânico. Os modelos elétricos convencionais e clássicos foram elaborados inicialmente para materiais cerâmicos e cristalinos e só posteriormente adaptados para a simulação de polímeros piezoelétricos. Seguindo estes estudos, este trabalho apresenta um circuito elétrico equivalente para transdutores construídos com a tecnologia dos piezoeletretos termo-formados, desenvolvida no Grupo de Alta Tensão e Materiais da Escola de Engenharia de São Carlos (EESC-USP). Este circuito, baseado em um modelo proposto por Fiorillo (2000) para simular um transdutor curvo de fluoreto de polivinilideno (PVDF), foi aprimorado para melhor representar o comportamento em baixas frequências. Nele existem dois ramos: um mecânico e um elétrico. Os parâmetros do ramo mecânico foram calculados nas proximidades da frequência de ressonância das amostras, enquanto que os componentes do ramo elétrico foram determinados pelos ajustes das curvas de condutância e de susceptância para frequências distantes da ressonância. Esta etapa compreendeu o desenvolvimento de um algoritmo baseado na taxa de variação da condutância pela frequência, o qual permitiu determinar um método para separação do espectro de frequência em uma região próxima e outra distante da frequência de ressonância. Após a determinação de todos os parâmetros do modelo elétrico, circuitos para simulação no software Pspice foram elaborados para cada transdutor. Os resultados das simulações da condutância, da susceptância, do módulo da impedância e do ângulo de fase dos circuitos mostraram relevante concordância com as medições quando comparados grafica e numericamente. Esta última análise foi feita através da expressão de erro relativo percentual médio. Neste trabalho, empregou-se a metodologia fundamentada nas medidas da condutância e da susceptância de diferentes amostras, incluindo filmes de polipropileno (PP), de PVDF e de piezoeletretos de canais tubulares abertos de Teflon®FEP. / Equivalent electric circuits or models are regularly employed in piezoelectric transducers modeling, including its electromechanical behavior. Conventional and classic electric models were initially developed for ceramic and crystalline materials and later adapted for simulating piezoelectric polymers. Following these studies, this work presents an equivalent electric circuit for transducers built with the piezoelectret thermo-formed technology, developed by the High Voltage and Materials Group of São Carlos Engineering School (EESC-USP). This circuit, based on a model proposed by Fiorillo (2000) for simulating a curved polyvinylidene fluoride (PVDF) transducer, was improved to represent the behavior at low frequencies. There are two branches in this circuit: a mechanical and an electrical branches. The mechanical branch parameters were calculated in the vicinity of the resonance frequency, whereas the components of the electrical branch were determined by conductance and susceptance curves fittings for frequencies far from resonance. This stage included the development of an algorithm based on the rate of change of conductance, which allowed determining a method to separate the frequency spectrum in near resonance and far from resonance. After determining all parameters, electrical circuits were designed to perform simulations using Pspice software. The results for conductance, susceptance, impedance magnitude and phase angle simulations presented relevant agreement with measurements when compared graphically and numerically. This latter analysis was done by error relative expression. In this work, the methodology was based on conductance and susceptance measurements for different samples, including porous polypropylene (PP), PVDF and Teflon®FEP piezoelectrets with open-tubular channels films.

This dissertation explores the characteristics of Monotonic-Static CMOS and its potential applications in leakage reduction in ultra scaled Bulk-Si technology with significant gate leakage currents. Using test circuits consisting of different configurations of 16-bit lookahead adders, we performed a comparison among static, monotonic static and domino logic in terms of various properties including power, delay, noise margin and area. Comparisons were done over a wide range of possible transistor widths to fully characterize the tradeoffs for each circuit type. Experimental results show that MS-CMOS has potential advantages in some situations in terms of stand-by power, evaluation speed and noise margin in such a technology.

Demand for wireless network capacity keeps growing exponentially every year, as a result a 1000-fold increase in data traffic is projected over the next 10 years in the context of 5G wireless networks. Solutions for delivering the 1000-fold increase in capacity fall into three main categories: deploying smaller cells, allocating more spectrum and improving spectral efficiency of wireless systems. Smaller cells at RF frequencies (1-6GHz) are unlikely to deliver the demanded capacity increase. On the other hand, millimeter-wave spectrum (frequencies over 24GHz) offers wider, multi-GHz channel bandwidths, and therefore has gained significant research interest as one of the most promising solutions to address the data traffic demands of 5G. Another disruptive technology is full-duplex which breaks a century-old assumption in wireless communication, by simultaneous transmission and reception on the same frequency channel. In doing so, full-duplex offers many benefits for wireless networks, including an immediate spectral efficiency improvement in the physical layer. Although FD promises great benefits, self-interference from the transmitter to its own receiver poses a fundamental challenge. The self-interference can be more than a billion times stronger than the desired signal and must be suppressed below the receiver noise floor. In recent years, there has been some research efforts on fully-integrated full-duplex RF transceivers, but mm-wave fully-integrated full-duplex systems, are still in their infancy. This dissertation presents novel architectures, antenna and circuit techniques to merge two exciting technologies, mm-wave and full-duplex, which can potentially offer the dual benefits of wide bandwidths and improved spectral efficiency. To this end, two different antenna interfaces, namely a wideband reconfigurable T/R antenna pair with polarization-based antenna cancellation and an mm-wave fully-integrated magnetic-free non-reciprocal circulator, are presented. The polarization-based antenna cancellation is employed in conjunction with the RF and digital cancellation to design a 60GHz full-duplex 45nm SOI CMOS transceiver with nearly 80dB self-interference suppression. The concepts and prototypes presented in this dissertation have also profound implications for emerging applications such as vehicular radars, 5G small-cell base-stations and virtual reality.

Electrical Impedance Tomography is a non-invasive, non-ionizing, non-destructive and painless imaging technology that can distinguish between cancerous and non-cancerous cells by reproducing tomographic images of the electrical impedance distribution within the body. The primary scope of this thesis is the study of hardware modules required for an EIT system. The key component in any EIT system is the excitation system. Impedance measurement can be performed by applying either a current or voltage through emitting electrodes and then measuring the resulting voltages or current on receiving electrodes. In this research, both types of excitation systems are investigated and developed for the Sussex EIM system. Firstly, a current source (CS) excitation system is investigated and developed. The performance of the excitation system degrades due to the unwanted capacitance within the system. Hence two CS circuits: Enhance Howland Source (EHS) and EHS combined with a General impedance convertor (GIC: to minimise the unwanted capacitance) are evaluated. Another technique (guard-amplifier) has also been investigated and developed to minimise the effect of stray capacitance. The accuracy of both types of CS circuits are evaluated in terms of its output impedance along with other performance parameters for different loading conditions and the results are compared to show their performance. Both CS circuits were affected by the loading voltage problem. A bootstrapping technique is investigated and integrated with both CS circuits to overcome the loading voltage problem. The research shows that both CS circuits were unable to achieve a high frequency bandwidth (i.e. ≥10MHz) and were limited to 2-3MHz. Alternatively, a discrete components current source was also investigated and developed to achieve a high frequency bandwidth and other desirable performance parameters. The research also introduces a microcontroller module to control the multiplexing involved for different CS circuit configurations via serial port interface software running on a PC. For breast cancer diagnosis, the interesting characteristics of breast tissues mostly lie above 1MHz, therefore a wideband excitation source covering high frequencies (i.e. ≥1-10MHz) is required. Hence, a second type of the excitation system is investigated. A constant voltage source (VS) circuit was developed for a wide frequency bandwidth with low output impedance. The research investigated three VS architectures and based on their initial bandwidth comparison, a differential VS system was developed to provide a wide frequency bandwidth (≥10MHz). The research presents the performance of the developed VS excitation system for different loading configurations reporting acceptable performance parameters. A voltage measurement system is also developed in this research work. Two different differential amplifier circuits were investigated and developed to measure precise differential voltage at a high frequency. The research reports a performance comparison of possible types of excitation systems. Results are compared to establish their relationship to performance parameters: frequency bandwidth, output impedance, SNR and phase difference over a wide bandwidth (i.e. up to 10MHz). The objective of this study is to investigate which design is the most appropriate for constructing a wideband excitation system for the Sussex EIM system or any other EIT based biomedical application with wide a bandwidth requirement.

Os circuitos ou modelos elétricos equivalentes destinam-se à modelagem de transdutores piezoelétricos, incluindo todo seu comportamento eletromecânico. Os modelos elétricos convencionais e clássicos foram elaborados inicialmente para materiais cerâmicos e cristalinos e só posteriormente adaptados para a simulação de polímeros piezoelétricos. Seguindo estes estudos, este trabalho apresenta um circuito elétrico equivalente para transdutores construídos com a tecnologia dos piezoeletretos termo-formados, desenvolvida no Grupo de Alta Tensão e Materiais da Escola de Engenharia de São Carlos (EESC-USP). Este circuito, baseado em um modelo proposto por Fiorillo (2000) para simular um transdutor curvo de fluoreto de polivinilideno (PVDF), foi aprimorado para melhor representar o comportamento em baixas frequências. Nele existem dois ramos: um mecânico e um elétrico. Os parâmetros do ramo mecânico foram calculados nas proximidades da frequência de ressonância das amostras, enquanto que os componentes do ramo elétrico foram determinados pelos ajustes das curvas de condutância e de susceptância para frequências distantes da ressonância. Esta etapa compreendeu o desenvolvimento de um algoritmo baseado na taxa de variação da condutância pela frequência, o qual permitiu determinar um método para separação do espectro de frequência em uma região próxima e outra distante da frequência de ressonância. Após a determinação de todos os parâmetros do modelo elétrico, circuitos para simulação no software Pspice foram elaborados para cada transdutor. Os resultados das simulações da condutância, da susceptância, do módulo da impedância e do ângulo de fase dos circuitos mostraram relevante concordância com as medições quando comparados grafica e numericamente. Esta última análise foi feita através da expressão de erro relativo percentual médio. Neste trabalho, empregou-se a metodologia fundamentada nas medidas da condutância e da susceptância de diferentes amostras, incluindo filmes de polipropileno (PP), de PVDF e de piezoeletretos de canais tubulares abertos de Teflon®FEP. / Equivalent electric circuits or models are regularly employed in piezoelectric transducers modeling, including its electromechanical behavior. Conventional and classic electric models were initially developed for ceramic and crystalline materials and later adapted for simulating piezoelectric polymers. Following these studies, this work presents an equivalent electric circuit for transducers built with the piezoelectret thermo-formed technology, developed by the High Voltage and Materials Group of São Carlos Engineering School (EESC-USP). This circuit, based on a model proposed by Fiorillo (2000) for simulating a curved polyvinylidene fluoride (PVDF) transducer, was improved to represent the behavior at low frequencies. There are two branches in this circuit: a mechanical and an electrical branches. The mechanical branch parameters were calculated in the vicinity of the resonance frequency, whereas the components of the electrical branch were determined by conductance and susceptance curves fittings for frequencies far from resonance. This stage included the development of an algorithm based on the rate of change of conductance, which allowed determining a method to separate the frequency spectrum in near resonance and far from resonance. After determining all parameters, electrical circuits were designed to perform simulations using Pspice software. The results for conductance, susceptance, impedance magnitude and phase angle simulations presented relevant agreement with measurements when compared graphically and numerically. This latter analysis was done by error relative expression. In this work, the methodology was based on conductance and susceptance measurements for different samples, including porous polypropylene (PP), PVDF and Teflon®FEP piezoelectrets with open-tubular channels films.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-12T20:28:48Z No. of bitstreams: 1 SegundoCabanillas.pdf: 2228720 bytes, checksum: a6e02304416e03c2afc432c9a11f24f2 (MD5) / Made available in DSpace on 2017-06-12T20:28:48Z (GMT). No. of bitstreams: 1 SegundoCabanillas.pdf: 2228720 bytes, checksum: a6e02304416e03c2afc432c9a11f24f2 (MD5) Previous issue date: 2016-10-10 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / This dissertation was prepared in order to provide subsidies to mathematics teachers to improve the performance of high scholl students of Y Bacanga college of the State of Maranhãao, specifically the students of three years in math discipline, subject refers to the study of complex numbers. The main idea is to use the Geogebra software and using the various features that the software offers facilitate student learning, and motivate their participation in the classroom, making reference to the theory of complex numbers is used in the study and analysis of electrical circuits. Thus, it presents a brief history of advancing the theory of complex numbers and how the structure was completed, using the Geogebra we study their different forms of representation and its operations are carried out, it shows how subject of complex numbers are used in the study of electrical circuits with emphasis on alternating current AC, solving practical exercises and finally it present a basic concept regarding the way to estimate the power electric consumption in a residence. / Este trabalho de dissertação foi elaborado com o objetivo de fornecer subsídios aos professores de matemática, para melhorar o rendimento dos alunos do Ensino Médio do colégio Y Bacanga do Governo do Estado do Maranhão, especificamente dos alunos do 3o ano, na disciplina de matemática, no assunto que se refere ao estudo dos números complexos. A ideia principal é utilizar o software Geogebra e utilizando os diversos recursos que o software oferece facilitar o aprendizado dos alunos, assim como motivar a sua participação na sala de aula, fazendo referência de como a teoria dos números complexos é utilizada no estudo e análise dos circuitos elétricos. Assim, apresenta-se uma breve história do avanço da teoria dos números complexos e a forma como a sua estrutura foi concretizada, utilizando o Geogebra estudam-se as suas diferentes formas de representação e como são efetuadas as suas operações, mostra-se como o assunto dos números complexos é utilizado no estudo dos circuitos elétricos, com ênfase na corrente alternada CA, resolvem-se alguns exercícios de aplicação e por último apresenta-se uma noção básica em relação é forma de estimar o consumo de energia elétrica em uma residência.

Thesis (MSc. (Physics)) --University of Limpopo, 2015 / This study investigated the extent to which learners from rural and peri-urban areas understand what the symbols represent and their roles in simple direct current resistive electrical circuits. The emphasis was on simple direct current resistive electrical circuits that consist of batteries and bulbs. The study was carried out with Grade 12 learners at high school level in the Limpopo Provincial Department of Education. It used both qualitative and quantitative data collection methods to investigate learners’ understanding of direct current resistive electrical circuits at rural and peri-urban schools. It used questionnaires and structured interviews to collect the data so that the results could provide in-depth understanding and generalizability. The results revealed that learners knew the symbols used in direct current resistive circuits, however, when the circuit was populated with a number of known symbols it became complex to such an extent that some learners struggled to identify the symbols. As it appeared, learners could not conceptualize the role played by a battery, conductor, ammeter and voltmeter in direct current resistive electrical circuit. In addition, the study also revealed that learners experience difficulties when translating a real circuit to a schematic circuit. This study suggests that deeper focus has to be directed towards developing leaners’ understanding of the working and role played by each symbol in a schematic circuit. Learners were operating at far lower conceptual basis and thought of conductor as a hollow pipe like material. Results were also compared in terms of geographical location of the school, and findings indicate that the rural school was performing better than peri-urban school. The results highlight a number of the frequently encountered alternative frameworks which learners come across when they are faced with schematic circuit diagrams. Most of the alternative frameworks found are well documented in literature (for example current consumption, difficulty with understanding electric concepts, difficulty with concept differentiation, and no firm alternative frameworks). vi The participants in this study were not exposed to practical work. This suggests the results might be different with learners exposed to practical work. It is therefore recommended that future studies look at the understanding of the role played by individual electrical components with learners who had practical experience with real electrical circuits. Majority of learners in this study could not communicate their scientific conclusions using English, as the English is their second language.