Three-phase rectifiers/inverters are widely used in grid-tied applications. Take the electric vehicle (EV) charging systems as an example. Within a certain space designated for the chargers, quick charging yet high efficiency are demanded. According to the current industry practice, with a power rating between 10 and 30 kW, the power density are limited by silicon (Si) power semiconductor devices, which make the systems operate at only up to around 30 kHz. The emerging wide bandgap (WBG) power semiconductor devices are considered as game changing devices to exceed the limits brought by their Si counterparts. Much higher switching frequency, higher power density and higher system efficiency are expected to be achieved with WBG power semiconductor devices. Among different types of WBG power semiconductor devices, Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors (SiC MOSFETs) are more popular in current research conducted for tens of kW power converter applications. However, the commonly adopted hard switching operation in this application still leads to significant switching loss at high frequency operation even for SiC-based systems. With the unique feature that the turn-off energy is almost negligible compared with the turn-on energy, critical conduction mode (CRM) based zero voltage soft switching turn-on operation is preferred for the SiC MOSFETs to eliminate the turn-on loss with small penalty on the conduction loss and on the turn-off loss. With this soft switching operation, switching frequency of SiC-based systems is able to be pushed to more than ten times higher than Si-based systems, and therefore higher power density yet even higher system efficiency can be achieved. The CRM-based soft switching is applied to three-phase rectifiers/inverters under the unity power factor operating condition first. Decoupled CRM-based control is enabled, and the inherent drawback of wide switching frequency variation range at CRM-based operation is overcome by the proposed novel modulation technique. It is the first time that CRM-based soft switching modulation is demonstrated in the most conventional three-phase H-bridge ac–dc converter, and more than three-time size reduction compared with current industry practice yet 99.0% peak efficiency are achieved at above 300 kHz switching frequency operation. Then this proposed soft switching modulation technique is extended to non-unity power factor operating conditions especially for grid-tied inverter system applications. With several improvements on the modulation, a generalized CRM-based soft switching modulation technique is proposed, which is applicable to both the unity and non-unity power factor conditions. With the power factor down to 0.8 lagging or leading according to commercial products, above 98.0% peak efficiency is achieved with the generalized soft switching modulation technique at above 300 kHz switching frequency operation. Furthermore from the aspect of electromagnetic interference (EMI), compared with the traditional Si-based design, CRM operation brings higher differential-mode (DM) EMI noise, and higher dv/dt with SiC MOSFETs brings higher common-mode (CM) EMI noise. What's more, hundreds of kHz switching frequency operation makes the main components of the system EMI spectrum located within the frequency range related to the EMI standard (150 kHz – 30 MHz). Therefore, several methods are adopted for the reduction of EMI noise. The total inductor current ripple is reduced with multi-channel interleaving control in order to reduce DM EMI noise. The balance technique is applied in order to reduce CM EMI noise. With PCB winding coupled inductors, the well-controlled parasitic parameters make the balance technique able to be effective for a uniform reduction of CM EMI noise from 150 kHz to above 20 MHz. In addition, PCB winding based magnetic designs are beneficial to achieving manufacture automation and reducing the labor cost. / Doctor of Philosophy / Power electronics and power conversion are crucial to many applications related to electricity, such as consumer electronics, domestic and commercial appliances, automobiles, data centers, utilities and infrastructure. In today's market, quality and reliability are usually considered as a given; high efficiency (low loss), high power density (small size and weight) and low cost are the main focuses in the design of power electronics products. In the past several decades, significant achievements in power electronics have been witnessed thanks to the silicon (Si) semiconductor technology, especially the Si power semiconductor devices. Nowadays, the development of Si power semiconductor devices is already close to the theoretical limits of the material itself. Therefore, in order to meet the increasing demands from customers in different applications, wide bandgap (WBG) based power semiconductor devices, namely Gallium Nitride (GaN) and Silicon Carbide (SiC), are becoming attractive because of its great potential compared with their Si counterparts. In literature, great contributions have already been made to understanding the WBG based power semiconductor devices. It is exciting and encouraging that some of the GaN-based power electronics products featuring high efficiency, high power density and low cost have been commercialized in consumer electronics applications. However, when pursuing these objectives, previous literature has not shown any applications of high frequency soft switching technology into the high power ac–dc conversion (usually three-phase ac–dc) in a simple way as the low power ac–dc conversion (usually single-phase ac–dc) in consumer electronics products. The key to achieving high efficiency, high power density and low cost is the high frequency soft switching operation. For single-phase ac–dc systems, the research on the realization of soft switching by control strategies instead of additional physical complexity has been intensively conducted, and this technology has also been adopted in the current industry practice. Therefore, the major achievement of this work is the development of a generalized soft switching control strategy for three-phase ac–dc systems, without adding any physical complexity, which is applicable to the simplest and most conventional three-phase ac-dc circuit topology. The proposed soft switching control strategy features bidirectional (rectifiers/inverters) power conversion, active/reactive power transfer, grid-tied/stand-alone modes, and scalability to multi-channel interleaved operation. Furthermore, with high frequency, the integration of magnetic components with embedded windings in the printed circuit board (PCB) becomes feasible, which is also beneficial to achieving electromagnetic compatibility (EMC) and manufacture automation. Based on the proposed control strategy and design methodology, a SiC-based 25-kW three-phase high frequency soft switching rectifier/inverter is developed for various applications such as electric vehicle (EV) charging stations, uninterruptible power supplies (UPS) and renewable energy based utilities.

The simultaneous estimation of multi-mode heat transfer properties, conductive and radiative, is investigated for materials that include significant heat transfer by radiation. The focus is on insulative type materials with a relatively large optical thickness. Two basic models were developed for the combined conduction and radiation heat transfer: a diffusion solution and a more exact absorbing and isotropically scattering solution. Both solutions were written for one-dimensional heat transfer in gray, isotropically scattering materials. Different experimental setups were compared through a sensitivity analysis of the parameters to determine the best experiment for estimating the properties. An experiment was performed to collect real data to verify estimation procedures. The material used for the experiment was Styrofoam and the experiment consisted of a heat flux supplied by a thin film heater on one boundary and a constant temperature on the other boundary. The thermal capacitance of the heater proved to have an effect on the temperature measurements at the heated surface and had to be incorporated into the model. The estimation procedure involved the use of two methods, the modified Box Kanemasu algorithm and a genetic algorithm. Difficulties were encountered in simultaneously estimating all the properties due to correlation between the thermal conductivity and the radiation parameters, as well as some correlation between the heat capacity of the Styrofoam and the heat capacity of the heater. However, the genetic algorithm did provide fairly narrow and well-defined property ranges and confirmed that radiation transfer was significant in the Styrofoam. / Ph. D.

The critical conduction mode (CRM) power factor correction converters (PFC) are widely used in industry for low power offline switching mode power supplies. For the CRM PFC, the main advantage is to reduce turn-on loss of the main switch. However, the large inductor current ripple in CRM PFC creates huge DM EMI noise, which requires a big EMI filter. The switching frequency of the CRM PFC is variable in half line cycle which makes the EMI characteristics of the CRM PFC are not clear and have not been carefully investigated. The worst case of the EMI noise, which is the baseline to design the EMI filter, is difficult to be identified. In this paper, an approximate mathematical EMI noise model based on the investigation of the principle of the quasi-peak detection is proposed to predict the DM EMI noise of the CRM PFC. The developed prediction method is verified by measurement results and the predicted DM EMI noise is good to evaluate the EMI performance. Based on the noise prediction, the worst case analysis of the DM EMI noise in the CRM PFC is applied and the worst case can be found at some line and load condition, which will be a great help to the EMI filter design and meanwhile leave an opportunity for the optimization of the whole converter design. What is more, the worst case analysis can be extended to 2-channel interleaved CRM PFC and some interesting characteristics can be observed. For example, the great EMI performance improvement through ripple current cancellation in traditional constant frequency PFC by using interleaving techniques will not directly apply to the CRM PFC due to its variable switching frequency. More research needs to be done to abstract some design criteria for the boost inductor and EMI filter in the interleaved CRM PFC. / Master of Science

Within the "forbidden" range of electron energies between the valence and conduction bands of titanium dioxide, crystal lattice irregularities lead to the formation of electron trapping sites. These sites are known as shallow trap states, where "shallow" refers to the close energy proximity of those features to the bottom of the semiconductor conduction band. For wide bandgap semiconductors like titanium dioxide, shallow electron traps are the principle route for thermal excitation of electrons into the conduction band. The studies described here employ a novel infrared spectroscopic approach to determine the energy of shallow electron traps in titanium dioxide nanoparticles. Mobile electrons within the conduction band of semiconductors are known to absorb infrared radiation. As those electrons absorb the infrared photons, transitions within the continuum of the conduction band produce a broad spectral signal across the entire mid-infrared range. A Mathematical expression based upon Fermi–Dirac statistics was derived to correlate the temperature of the particles to the population of charge carriers, as measured through the infrared absorbance. The primary variable of interest in the Fermi – Dirac expression is the energy difference between the shallow trap states and the conduction band. Fitting data sets consisting of titanium dioxide nanoparticle temperatures and their associated infrared spectra, over a defined frequency range, to the Fermi–Dirac expression is used to determine the shallow electron trap state energy. / Master of Science

We consider the design of finite element methods for inverse problems with full-field data governed by elliptic forward operators. Such problems arise in applications in inverse heat conduction, in mechanical property characterization, and in medical imaging. For this class of problems, novel finite element methods have been proposed (Barbone et al., 2010) that give good performance, provided the solutions are in the H^1(Ω) function space. The material property distributions being estimated can be discontinuous, however, and therefore it is desirable to have formulations that can accommodate discontinuities in both data and solution. Toward this end, we present a mixed variational formulation for this class of problems that handles discontinuities well. We motivate the mixed formulation by examining the possibility of discretizing using a discontinuous discretization in an irreducible finite element method, and discuss the limitations of that approach. We then derive a new mixed formulation based on a least-square error in the constitutive equation. We prove that the continuous variational formulations are well-posed for applications in both inverse heat conduction and plane stress elasticity. We derive a priori error bounds for discretization error, valid in the limit of mesh refinement. We demonstrate convergence of the method with mesh refinement in cases with both continuous and discontinuous solutions. Finally we apply the formulation to measured data to estimate the elastic shear modulus distributions in both tissue mimicking phantoms and in breast masses from data collected in vivo.

La fibrilación auricular (FA) es una de las arritmias cardiacas más comunes, la cual afecta alrededor del 10% de la población de más de 70 años. En FA, los impulsos eléctricos auriculares generados por el nodo sinusal son sustituidos por impulsos eléctricos desorganizados. Esto esta asociado con un bombardeo irregular de activaciones auriculares hacia el nodo AV. Dado que el nodo AV no puede conducir todas estas activaciones, algunas de ellas son bloqueadas en el nodo. Esta propiedad de filtrado que tiene el nodo es fundamental para mantener el ritmo cardiaco en un rango compatible con la vida. Sin embargo, la respuesta ventricular durante FA presenta intervalos RR (tiempo entre dos activaciones) más cortos e irregulares que durante ritmo sinusal. Al ser el nodo AV la única estructura responsable para la conducción de los latidos auriculares hacia los ventrículos, las estrategias terapéuticas para controlar el ritmo cardiaco durante FA tratan de utilizar y ajustar las propiedades de conducción del nodo. Sin embargo, sigue sin estar suficientemente entendido el papel que dichas propiedades de conducción juegan para controlar y modular la respuesta ventricular durante FA. Durante el desarrollo de la presente tesis se han investigado en diferentes especies y con diversas técnicas algunas de las principales características de la conducción del nodo AV con la intención de aportar mayor conocimiento sobre esta intrigante estructura del corazón. Específicamente, se ha analizado uno de los fenómenos más enigmáticos de la respuesta ventricular durante FA: la aparición de patrones de respuesta ventricular multimodales al construir histogramas de RR obtenidos a partir de registros de larga duración. En la literatura se han sugerido diversas teorías que pudiesen explicar la aparición de estos múltiples intervalos RR predominantes. En el desarrollo de la presente disertación se mostrarán algunos resultados incompatibles con dichas teorías, razón por la cual se presenta y defiende una nueva hipótesis que sugiere que los intervalos RR predominantes están relacionados con el proceso fibrilatorio auricular. / Martínez Climent, BA. (2011). Characterization and Modeling of Atrioventricular Conduction during Atrial Fibrillation [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10985

An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been previously investigated, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer. A parametric study was conducted considering three non-dimensional probe geometric ratios (vent location to shield length (0.029-0.806), sensor diameter to shield inner diameter (0.252-0.672), and shield outer diameter to strut/mount thickness (0.245-0.759)) and three operating conditions (total temperature (70, 850, 2500°F) and pressure (1, 1, 10 atm), respectively) at a moderate Mach number of 0.4. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for evaluating radiation and transient influences on sensor performance. These new flow and heat transfer correlations together with the new Reduced Order Modeling technique developed here greatly enhance the capabilities of designers to evaluate performance of current and future probe designs, with higher accuracy and with significant reductions in computational resources. / Doctor of Philosophy / An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been thoroughly described and quantified in the past, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer (CHT) capabilities. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling (ROM) technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for readily predicting the impact of radiation environment and transient errors on sensor performance.

Accurately measuring the total temperature of a high-speed fluid flow is a challenging task that is required in many research areas and industry applications. The difficulty in total temperature measurement generally stems from attempting to minimize measurement error or accurately predict error so it can be accounted for. Conduction error and aerodynamic error are two very common sources of error in total temperature probe measurements. Numerous studies have been performed in prior literature to account for simple cases of both errors. However, the impacts of a mounting strut and freestream flow angle on conduction error and aerodynamic error have not been previously modeled. Both of these effects are very common in gas-turbine applications of total temperature probes. Therefore, a fundamental study was performed to analyze the impact of mount interference and freestream flow angle on a probe's conduction error and aerodynamic error. An experimental study of aerodynamic error was performed using strut-mounted thermocouples in a high-speed jet at Mach numbers ranging from 0.25-0.72. This study showed that a strut stagnation point can provide aerodynamic error reductions and insensitivity to approach Mach number. An off-angle experimental study of conduction error was also performed using strut-mounted thermocouples at pitch angles ranging from -30° to 30°. High-fidelity Computational Fluid Dynamics (CFD) simulations with Conjugate Heat Transfer (CHT) were performed in conjunction with the experiments to provide key heat transfer information and flow visualizations. It was identified that unshielded total temperature probes have reduced conduction error at off-angles, but are sensitive to changes in the freestream flow angle. A low-order method was developed to account for mount interference and flow angle effects. The developed low order method utilizes a local Mach number for aerodynamic error predictions and a local Reynolds number for conduction error predictions. This developed low-order method was validated against experiment and 3D, CFD results, and was shown to accurately capture flow angle trends, mount interference effects, and the impacts of varying probe geometry. / Master of Science / Accurately measuring the total temperature of a high-speed fluid flow is a challenging task that is required in many research areas and industry applications. Many methods exist for measuring total temperature, but the use of thermocouple based probes immersed into a flow remains a common and desirable measurement technique. The difficulty in using thermocouple based probes to acquire total temperature stems from attempting to minimize or accurately predict the probe’s measurement error. Conduction, convection, and radiation heat transfer between the fluid flow and probe create challenges for minimizing measurement error so that the accurate total temperature can be obtained. Numerous studies have been performed in prior literature to account for simple cases of each error source. However, there are many complex, practical applications in which the influence of each error source has not been studied. The impacts of a freestream flow angle and the total temperature probe’s mounting structure have not been previously modeled. Both of these effects are very common in gas-turbine applications of total temperature probes. This Thesis will present a fundamental study analyzing the impact that freestream flow angle and a probe’s mount have on a total temperature probe’s measurement error. The influence of conduction and convection heat transfer was studied experimentally for numerous probe geometries, and the impacts of a mounting strut and freestream flow angle were analyzed. A low-order method was developed to predict conduction error and aerodynamic error for total temperature probes in offangle conditions with the presence of mount interference. The developed low-order method was shown to accurately capture the effects of a mounting strut, varying probe geometry, and varying flow angle. Additionally, the low-order method was validated against experimental and 3D, CFD/CHT results.

One of the greatest technological challenges of the world today is reducing the size and weight of the existing products to make them portable. Specifically, in electric vehicles such as electric cars, UAVs and aero planes, the size of battery chargers and inverters needs to be reduced so as to make space for more parts in these vehicles. Electromagnetic Interference (EMI) filters take up a more than 80 % of these power converters, the size of these filters can be reduced by pushing the switching frequency higher. High frequency operation (> 300 kHz) leads to a size in reduction of EMI filters though it also leads to an increase in switching losses thus compromising on efficiency. Thus, soft switching becomes necessary to reduce the losses, adding more electrical components to the converter to achieve soft switching is a common method. However, it increases the physical complexity of the system. Hence, advanced control methods are adopted for today's power converters that enable soft switching for devices specifically ZVS turn-on as the turn-off losses of next generation WBG devices are negligible. Thus, the goal of this research is to discover novel switching algorithms for soft turn-on. The state-of the-art control methods namely CRM and TCM achieve soft turn-on by enabling bi-directional current such that the anti-parallel body diode starts conducting before the device is turned on. CRM and TCM result in variable switching frequency which leads to asynchronous operation in multi-phase and multi-converter systems. Hence, TCM is modified in this dissertation to achieve constant switching frequency, as the goal of this research is to be able to achieve ZVS turn-on for a three-phase converter. Further, Triangular Current Mode (TCM) to achieve soft switching and phase synchronization for three-phase two-level converters is proposed. It is shown how soft switching and sinusoidal currents can be achieved by operating the phases in a combination of discontinuous conduction mode (DCM), TCM and clamped mode. The proposed scheme can achieve soft switching ZVS turn-on for all the three phases. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kW with a density of 110 W/in3. The discussion of TCM in current literature is limited to unity power factor assumption, however this limits the algorithm's adoption in real world applications. It is shown how proposed TCM algorithm can be extended to accommodate phase shift with all the three phases operating in a combination of DCM+TCM+Clamped modes of operation. The algorithm is tested and validated on a GaN converter, 99% efficiency is achieved at 0.7 kVA with a density of 110 W/in3. TCM operation results in 33 % higher rms current which leads to higher conduction losses, as WBG devices have lower on-resistance, these devices are the ideal candidates for TCM operation, hence to accurately obtain the device parameters, a detailed device characterization is performed. Further, proposed TCM+DCM+Clamped control algorithm is extended to three-level topologies, the control is modified to extract the advantage of reduced Common Mode Voltage (CMV) switching states of the three-level topology, the switching frequency can thus be pushed to 3 times higher as compared to state-of-the-art SVPWM control while maintaining close to 99 % efficiency. Two switching schemes are presented and both of them have a very small switching frequency variation (6%) as compared to state-of-the-art methods with >200% switching frequency variation. / Doctor of Philosophy / Power supplies are at the heart of today's advanced technological systems like aero planes, UAVs, electrical cars, uninterruptible power supplies (UPS), smart grids etc. These performance driven systems have high requirements for the power conversion stage in terms of efficiency, density and reliability. With the growing demand of reduction in size for electromechanical and electronic systems, it is highly desirable to reduce the size of the power supplies and power converters while maintaining high efficiency. High density is achieved by pushing the switching frequency higher to reduce the size of the magnetics. High switching frequency leads to higher losses if conventional hard switching methods are used, this drives the need for soft switching methods without adding to the physical complexity of the system. This dissertation proposes novel soft switching techniques to improve the performance and density of AC/DC and DC/AC converters at high switching frequency without increasing the component count. The concept and the features of this new proposed control scheme, along with the comparison of its benefits as compared to conventional control methodologies, have been presented in detail in different chapters of this dissertation.

The proposed circuit intends to harvest kinetic energy from ElectroMagnetic Generators (EMGs). In order to extract maximum power from an EMG, an AC-DC boost rectifier is designed to match the impedance of the EMG. Rather than operate a buck-boost converter in Discontinuous Conduction Mode (DCM) in other impedance matching cases, the proposed method is running the boost topology in Boundary Conduction Mode (BCM). So it would perform resistive input matching, while reducing the converter power loss. The boost rectifier also merges a rectifier and a boost converter to reduce power loss for rectification. It also utilizes the internal inductance of the EMG to eliminate the impedance matching error and reduce the off-chip inductor size. An optional buck converter regulates the output voltage to 5 V to power devices through USB ports. The proposed circuit is designed and fabricated in BiCMOS 0.18 μm technology. Its functionality is shown through simulation results. The measurement of the IC is also performed. However, since the IC only work partially, test result is gathered using some discrete components as substitutes. It indicates the circuit can realize the proposed control method. / Master of Science / The development of energy-efficient semiconductor devices has reduced the power requirements of electronic circuits. As the electronics’ scale decreases, so does the energy consumption. In this sense, batteries were also produced in smaller size providing more energy storage availability. However, due to technical and technological issues, the batteries have not been followed by the same evolutionary trend limiting the operational time and performance of portable devices as it need to be recharged or replaced periodically. On the other hand, portable electronic devices such as cell phones, GPS, cameras, etc. are powered only by batteries. For circumstances that power supplies are not accessible, energy harvesting (EH) from human or environmental sources has proven to be an effective alternative or complement. Light, thermal, mechanical and RF are major sources in EH. Among them, mechanical energy from wind, waves, vibrations, etc. is commonly existed in our daily life. The energy is harvested by using micro generators and the various types include electromagnetic, piezoelectric and electrostatic. In particular, the ElectroMagnetic Generator (EMG) is of great interest for its potentially high energy density and efficiency. Since EMG is an AC voltage generator while portable devices usually require a stable DC supply, an EH circuit as a rectifier ought to be designed. At the same time, for EH application, we would like to harvest as much power as possible from EMGs. This research project addresses the development of a unique EH circuit capable of fulfilling the distinct needs illustrated above.