Nos dias de hoje, o aumento na demanda de energia no Brasil, associado a fatores econômicos e ambientais, tem dificultado a criação de novas usinas hidrelétricas, necessárias para suprir essa demanda adicional e aumentar a confiabilidade do sistema. Nesse contexto, a geração distribuída se destaca como uma solução adequada, pois economiza investimentos em redes de transmissão e distribuição, reduz perdas e diversifica a matriz energética do sistema elétrico, tornando-o mais robusto e eficiente. Dentre as fontes de energia utilizadas em sistemas de geração distribuída, a microturbina apresenta algumas vantagens em relação a outros modelos de GD, como por exemplo, a possibilidade da utilização de vários tipos de combustíveis. Para verificar as características de operação das microturbinas, foram realizadas simulações baseadas em modelos matemáticos presentes na literatura técnica. Porém, devido às altas velocidades de rotação das turbinas a gás, a energia gerada possui frequências muito altas para ser aproveitada diretamente pelos consumidores, sendo necessária uma interface eletrônica para adequação da energia elétrica. Neste trabalho é abordado o estudo, simulação e implementação da primeira etapa desta interface, um retificador trifásico com correção de fator de potência, para a geração de um barramento de corrente contínua com tensão estável, mantendo as correntes de entrada do retificador com formato senoidal e em fase com a tensão. / Nowadays, the increase in energy demand in Brazil, associated with economic and environmental factors, has hindered the creation of new power plants needed to provide this additional demand and improve system reliability. In this context, distributed generation stands out as an appropriate solution because it saves investments in transmission and distribution, reduces losses and diversify the energy matrix of the electrical system, making it more robust and efficient. Among the energy sources used in distributed generation systems, the microturbine has some advantages over other models of GD, such as the possibility of using various types of fuel. To verify the operating characteristics of microturbines, simulations were performed based on mathematical models present in literature. However, due to high rotation speeds of gas turbines, the energy generated has very high frequencies to be used directly by consumers, which requires an electronic interface to adequate the electricity. This work describe the study, simulation and implementation of the first stage of this interface, a three-phase rectifier with power factor correction, to generate a DC bus voltage stable, keeping the rectifier input current format sinusoidal and in phase with the voltage generated by the microturbine.

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More power semiconductors are applying to the aircraft power system to make the system smaller, lighter and more reliable. Average models provide a good solution to system simulation and can also serve as the basis to derive the small signal model for system-level study using linear control theory. A new average modeling approach for three-phase and nine-phase diode rectifiers with improved ac and dc dynamics is proposed in this dissertation. The key assumption is to model the load current using its first-order Taylor Series expansion throughout the entire averaging time span. A thorough comparison in the time domain is given of this model and two additional average models that were developed based on different load current assumptions, using the detailed switching models as the benchmark. The proposed average model is further verified by experimental results. In the frequency domain, the output impedance of a nine-phase diode rectifier is derived, and the sampling effect in the average model is investigated by Fourier analysis. The feeder's impedance before the rectifier is modeled differently in the output impedance in contrast in the equivalent commutation inductance. The average model is applied to the resonance study in a system composed of a synchronous generator, a nine-phase diode rectifier and a motor drive. The Thevenin's and Norton's equivalent circuits are derived to construct a linearized system. The equivalent impedance are derived from the average models, and the source are obtained from the switching circuit by short-circuit or open-circuit. Transfer functions are derived from the harmonic sources to the bus capacitor voltage for resonance study. The relationship between the stability and the resonance is analyzed, and the effect of controllers on the resonance is investigated. Optimization is another system-level application of the average model. A half-bridge circuit with piezoelectric actuator as its load is optimized using genetic algorithm. The optimization provides the possibility to design the actuator and its driving circuit automatically. / Ph. D.

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Advanced power semiconductor devices have consistently proven to be a major force in pushing the progressive development of power conversion technology. The emerging wide-band-gap (WBG) material based power semiconductor devices are considered as gaming changing devices which can exceed the limit of silicon (Si) and be used to pursue groundbreaking high-frequency, high-efficiency, and high-power-density power conversion. The switching performance of cascode GaN HEMT is studied at first. An accurate behavior-level simulation model is developed with comprehensive consideration of the impacts of parasitics. Then based on the simulation model, detailed loss breakdown and loss mechanism analysis are studied. The cascode GaN HEMT has high turn-on loss due to the reverse recovery charge and junction capacitor charge, and the common source inductance (CSI) of the package; while the turn-off loss is extremely small attributing to unique current source turn off mechanism of the cascode structure. With this unique feature, the critical conduction mode (CRM) soft switching technique is applied to reduce the dominant turn on loss and significantly increase converter efficiency. The switching frequency is successfully pushed to 5MHz while maintaining high efficiency and good thermal performance. Traditional packaging method is becoming a bottle neck to fully utilize the advantages of GaN HEMT. So an investigation of the package influence on the cascode GaN HEMT is also conducted. Several critical parasitic inductance are identified, which cause high turn on loss and high parasitic ringing that may lead to device failure. To solve the issue, the stack-die package is proposed to eliminate all critical parasitic inductance, and as a result, reducing turn on loss by half and avoiding potential failure mode of the cascode GaN device effectively. Utilizing soft switching and enhanced packaging, a GaN-based MHz totem-pole PFC rectifier is demonstrated with 99% peak efficiency and 700 W/in3 power density. The switching frequency of the PFC is more than ten times higher than the state-of-the-art industry product while it achieves best possible efficiency and power density. Integrated power module and integrated PCB winding coupled inductor are all studied and applied in this PFC. Furthermore, the technology of soft switching totem-pole PFC is extended to a bidirectional rectifier/inverter design. By using SiC MOSFETs, both operating voltage and power are dramatically increased so that it is successfully applied into a bidirectional on-board charger (OBC) which achieves significantly improved efficiency and power density comparing to the best of industrial practice. In addition, a novel 2-stage system architecture and control strategy are proposed and demonstrated in the OBC system. As a continued extension, the critical mode based soft switching rectifier/inverter technology is applied to three-phase AC/DC converter. The inherent drawback of critical mode due to variable frequency operation is overcome by the proposed new modulation method with the idea of frequency synchronization. It is the first time that a critical mode based modulation is demonstrated in the most conventional three phase H-bridge AC/DC converter, and with 99% plus efficiency at above 300 kHz switching frequency. / Ph. D.

The objective of this thesis is to design, analyze, and fabricate an innovative backpack energy harvester for human walking. To model human walking with backpack energy harvester, a simple dual-mass model has been developed and studied first. Dual-mass model for three types of distinct harvesters were investigated, pure damping, traditional rack pinion energy harvester and our MMR based energy harvester. A comparison in the output power and human comfort between the three types of harvesters is discussed. However, the dual-mass model could not effectively represent human walking in real situation with sinusoidal input, like M shaped Ground Reaction Force (GRF), vertical Center of Mass (COM) motion, etc. Thus, a bipedal walking model has been proposed to simulate human walking with backpack harvester. Experiments were conducted to compare power output and efficiency of MMR based backpack energy harvester with traditional rack pinion backpack energy harvester, and verify conclusions from the bipedal walking model that the proposed backpack energy harvester using mechanical motion rectifier (MMR) mechanism has larger power output than traditional backpack energy harvester at different walking speed. In human treadmill test, subjects were asked to wear the backpack frame which embedded with harvesters walking on a treadmill. Two walking speed, 3mph and 3.5mph, and four resistor values has been tested. The test results showed that the MMR based backpack energy harvester generated more power regardless of resistor values and walking speed. Up to 4.84W average power and instant power of 12.8W could be obtained while the subject walking on the treadmill at 3.5mph speed with MMR based backpack energy harvester. / Master of Science

In electric power systems, the existence of constant power loads such as output-regulated power converters may bring instability problem to AC or DC distributed systems. Impedance based stability criteria has been proven a good tool for small-signal stability analysis. This works focuses on the developing of a comprehensive software tool which can extract DC or three phase AC impedances, and apply stability analysis. An algorithm is designed to select FFT window and adjust perturbation frequencies. This feature enables the software to accurately measure impedances even in existence of system line harmonics. Furthermore, multi-tone approach is developed to improve simulation time. The complete software tool is tested with simulation models and experiment results, to show the effectiveness. When multi-tone approach is applied on nonlinear loads, it gives incorrect results. The reason is that perturbation frequency will have overlapping with side-band harmonics. An algorithm is designed to avoid this problem. The algorithm is tested with 12-pulse diode rectifier simulation model, and 6-pulse diode rectifier simulation model and experimental test bed. Both simulation and experiment results verifies the concept. / Master of Science

Yes / Electrophysiological properties and molecular background of the zebrafish (Danio rerio) cardiac inward rectifier current (IK1) were examined. Ventricular myocytes of zebrafish have a robust (−6.7±1.2 pA pF−1 at −120 mV) strongly rectifying and Ba2+-sensitive (IC50=3.8 μM) IK1. Transcripts of six Kir2 channels (drKir2.1a, drKir2.1b, drKir2.2a, drKir2.2b, drKir2.3, and drKir2.4) were expressed in the zebrafish heart. drKir2.4 and drKir2.2a were the dominant isoforms in both the ventricle (92.9±1.5 and 6.3±1.5 %) and the atrium (28.9±2.9 and 64.7±3.0 %). The remaining four channels comprised together less than 1 and 7 % of the total transcripts in ventricle and atrium, respectively. The four main gene products (drKir2.1a, drKir2.2a, drKir2.2b, drKir2.4) were cloned, sequenced, and expressed in HEK cells for electrophysiological characterization. drKir2.1a was the most weakly rectifying (passed more outward current) and drKir2.2b the most strongly rectifying (passed less outward current) channel, whilst drKir2.2a and drKir2.4 were intermediate between the two. In regard to sensitivity to Ba2+ block, drKir2.4 was the most sensitive (IC50=1.8 μM) and drKir2.1a the least sensitive channel (IC50=132 μM). These findings indicate that the Kir2 isoform composition of the zebrafish heart markedly differs from that of mammalian hearts. Furthermore orthologous Kir2 channels (Kir2.1 and Kir2.4) of zebrafish and mammals show striking differences in Ba2+- sensitivity. Structural and functional differences needs to be taken into account when zebrafish is used as a model for human cardiac electrophysiology, cardiac diseases, and in screening cardioactive substances.

A monolithically integrated smart rectifier has been presented first in this work. The smart rectifier, which integrates a power MOSFET, gate driver and control circuitry, operates in a self-synchronized fashion based on its drain-source voltage, and does not need external control input. The analysis, simulation, and design considerations are described in detail. A 5V, 5-µm CMOS process was used to fabricate the prototype. Experimental results show that the proposed rectifier functions as expected in the design. Since no dead-time control needs to be used to switch the sync-FET and ctrl-FET, it is expected that the body diode losses can be reduced substantially, compared to the conventional synchronous rectifier. The proposed self-synchronized rectifier (SSR) can be operated at high frequencies and maintains high efficiency over a wide load range. As an example of the smart rectifier's application in isolated DC-DC converter, a synchronous flyback converter with SSR is analyzed, designed and tested. Experimental results show that the operating frequency could be as high as 4MHz and the efficiency could be improved by more than 10% compared to that when a hyper fast diode rectifier is used. Based on a new current-source gate driver scheme, an integrated gate driver for buck converter is also developed in this work by using a 0.35µm CMOS process with optional high voltage (50V) power MOSFET. The integrated gate driver consists both the current-source driver for high-side power MOSFET and low-power driver for low-side power iv MOSFET. Compared with the conventional gate driver circuit, the current-source gate driver can recovery some gate charging energy and reduce switching loss. So the current-source driver (CSD) can be used to improve the efficiency performance in high frequency power converters. This work also presents a new implementation of a power supply in package (PSiP) 5MHz buck converter, which is different from all the prior-of-art PSiP solutions by using a high-Q bondwire inductor. The high-Q bondwire inductor can be manufactured by applying ferrite epoxy to the common bondwire during standard IC packaging process, so the new implementation of PSiP is expected to be a cost-effective way of power supply integration.