Thesis (M.A.)--University of North Carolina at Wilmington, 2006. / Includes bibliographical references (p. 62-66)

The power electronics market is valued at $23.25 billion in 2019 and is projected to reach $ 36.64 billion by 2027. Power electronic systems (PES) have been extensively used in a wide range of critical applications, including automotive, renewable energy, industrial variable-frequency drive, etc. Thus, the PESs' reliability and robustness are immensely important for the smooth operation of mission-critical applications. Power semiconductor switches are one of the most vulnerable components in the PES. The vulnerability of these switches impacts the reliability and robustness of the PES. Thus, switch-health monitoring and prognosis are critical for avoiding unexpected shutdowns and preventing catastrophic failures. The importance of the prognosis study increases dramatically with the growing popularity of the next-generation power semiconductor switches, wide bandgap switches. These switches show immense promise in the high-power high-frequency operations due to their higher breakdown voltage and lower switch loss. But their wide adaptation is limited by the inadequate reliability study. A thorough prognosis study comprising switch degradation modeling, remaining useful life (RUL) estimation, and degradation-aware controller development, is important to enhance the PESs' robustness, especially with wide bandgap switches. In this dissertation, three studies are conducted to achieve these objectives- 1) Insulated Gate Bipolar Transistor (IGBT) degradation modeling and RUL estimation, 2) cascode Gallium Nitride (GaN) Field-Effect Transistor (FET) degradation modeling and RUL estimation, and 3) Degradation-aware controller design for a PES, solid-state transformer (SST). The first two studies have addressed the significant variation in RUL estimation and proposed degradation identification methods for IGBT and cascode GaN FET. In the third study, a system-level integration of the switch degradation model is implemented in the SST. The insight into the switch's degradation pattern from the first two studies is integrated into developing a degradation-aware controller for the SST. State-of-the-art controllers do not consider the switch degradation that results in premature system failure. The proposed low-complexity degradation-aware and adaptive SST controller ensures optimal degradation-aware power transfer and robust operation over the lifetime.

The power consumption of smart camera in car black box varies significantly between light load and heavy load. The high efficiency voltage regulator is necessary in prolong the life of smart camera battery. Since the smart camera only recording the video when car is driving, the most time of the smart camera works in the sleep mode. Hence the light load efficiency is important in this application, however, conventional buck converter usually have high efficiency at heavy load but poor efficiency at light load. To increase the light load efficiency of buck converter, this research continues Yeago's two phase buck converter with optimum phase selection control and Zhao's two mode buck converter to further improve the light load efficiency for the target application. With 5V input voltage and 1.2V output voltage, the proposed two-mode synchronous buck converter can supply the load power from 12mW to 1.44W. To improve the light load efficiency of conventional buck converter, the proposed design applied Wei's baby buck concept to provide another light load power stage to reduce the switching loss and driving loss at light load. Then, the variable frequency ripple-based constant on-time control with discontinuous conduction mode (DCM) in light load is applied to the baby-buck mode to reduce the switching frequency to further reduce the switching loss. Also, the baby-buck mode uses the synchronous buck topology to remove the diode in asynchronous converter to increase the efficiency at light load. Finally, a sensorless mode selector remove the sensing resistor in power stage to increase the efficiency for entire load range, especially for the heavy load. The mode selector can select the optimum mode for different load condition, and the opposite mode would completely shut down to save the loss. The proposed design is implement in CMOS 0.25um technology. The proposed monolithic buck converter which include the power stage of heavy buck mode, baby-buck mode and the controller is fabricated. The measurement result shows the close loop efficiency varies from 70%-83% toward the entire load range. / Master of Science

The Norwegian Network Code FIKS from the Norwegian Transmission System Operator (TSO) Statnett, states that synchronous generators ≥ 25 MVA must have a static excitation system. It also includes requirements on the step time response and the available field winding ceiling voltage of the excitation system. An improved brushless excitation system is in operation in some pilot power plants. A rotating thyristor bridge is controlled via Bluetooth. The step time response is as fast as conventional static excitation systems. However, a ceiling voltage factor of 2 requires the thyristor bridge to operate at firing angles about 60 degrees. High torque pulsations, low power factor and low utilization of the exciter is the end result. New power electronic interfaces on the shaft results in a betterutilization of the designed exciter and improves the mechanical performance as well as the controllability of the generator field winding. Permanent magnet rotating exciters increase the field forcing strength of the synchronous generator, yielding improved transient stability (Fault Ride-Through req.). Brushless exciters also reduces regular maintenance of the generator. The thesis includes experiments on a state of the art synchronous generator test setup including constructed PM exciter and different power electronic solutions. Some investigations has been done on industrial power plants as well.

Os modernos equipamentos elétricos de aquecimento de água de passagem, popularmente conhecidos como chuveiros, duchas ou aquecedores, possuem como elementos aquecedores resistências elétricas constituídas por um fio de liga metálica enrolado, geralmente em ferro-cromo-alumínio ou níquel-cromo. O controle da temperatura da água é usualmente realizado pelo controle do fluxo d'água e pela mudança das derivações ("taps") presentes na resistência. A simplicidade deste controle se opõe à sua falta de flexibilidade para impor ajuste simultâneo de temperatura e vazão d'água. Um controle eletrônico de potência é oferecido como diferencial nos modelos mais sofisticados. Os modelos atualmente existentes no mercado são implementados com controle eletrônico por ângulo de fase, e é sabido que esse tipo de controle gera problemas de distorção harmônica de corrente das redes de energia, com a presença de harmônicas superiores de corrente (acima da fundamental) cuja filtragem é de difícil implementação devido ao nível de potência envolvido e às dimensões físicas dos aparelhos de aquecimento. Como alternativa a esse tipo de controle existe o controle por ciclos inteiros, o qual não gera harmônicas superiores de corrente, mas traz outro inconveniente, que é a produção de variação de tensão da rede de energia, que acarreta variação de luminosidade nas lâmpadas da instalação em níveis de freqüência perceptíveis ao olho humano (fenômeno conhecido como cintilação ou "flicker"). O objetivo do presente trabalho é propor uma solução otimizada ao controle de potência por ciclos inteiros, onde o mesmo é implementado por semi ciclos inteiros "otimizados" de forma a não gerar distorção harmônica nem cintilação de luminosidade perceptível ao olho humano. / Modern electrical direct water heating (DWH) equipments use electrical resistances built with metal alloys (iron-chrome-aluminum or nickel-chrome) as heating elements. Water temperature control is usually made with water flow control, as well as with resistance tap changing. The simplicity of this approach conflicts with to the lack of flexibility to allow simultaneous control of both water flow and its temperature. Therefore, an electronic power control is usually found in more sophisticated models. Usually the electronic power control is implemented by using phase angle control, which causes higher order current harmonics distortion of AC line currents, and filtering is difficult due to the high level of power involved and to the limited dimensions of typical electrical DWH equipment. The alternative for this type of power control is the cycle-by-cycle power control, which does not generate higher order current harmonics but creates line voltage variation, which in turn provokes lighting level variation and resulting unsteadiness on visual sensation, also known as flicker. The aim of the present work is to present an optimized solution for a half-cycle power control, in a way that does not generate harmonic distortion nor eye perceptible level of flicker.

Le développement du système électronique de puissance dans le transport électrique est poursuivi sous la forme de convertisseurs de puissance à haut rendement impliquant une topologie complexe.Bien que l'analyse et le contrôle d'un tel système soient souvent une tâche difficile en raison de l'environnement haute tension et haut courant, la simulation hardware-in-the-loop (HILs) offre un moyen sûr et rapide d'évaluer la stratégie de contrôle en simulant l'environnement externe du contrôleur dans le système embarqué.Au cours du processus, il y a deux exigences que nous devons relever dans le cadre de temps réel (i) Le processus de calcul doit être terminé avant que l'impulsion de déclenchement suivante de l'horloge en temps réel n'arrive; (ii) La latence dans le simulateur est assez petite pour être ignorée. Les périodes d'échantillonnage et de simulation dans les simulateurs basés sur CPU sont plus de 1 microseconde, il est difficile de prendre en compte l'ensemble des événements des commutateurs dans les systèmes d'entraînement modernes.En revanche, les FPGA (Field Programmable Gate Arrays) fournissent non seulement une vitesse d'échantillonnage rapide mais aussi une alternative viable pour accélérer le simulateur en temps réel. Cependant, la mise en œuvre d’un système électronique de puissance complexe dans les FPGA est l'une des limitations. Ainsi, dans cette thése, nous ferons des recherches sur la simulation en temps réel à base de FPGA avec la tentative de résoudre le problème en résolvant les questions suivantes,1.Comment pourrions-nous partitionner le système électronique de puissance et l'implémenter dans FPGA?2.Comment pouvons-nous tirer parti des fonctionnalités FPGA pour accélérer le processus de résolution de circuit3.Comment pourrions-nous optimiser les performances du FPGA?4.Comment exprimer la caractéristique de commutation non linéaire du système électronique de puissance dans le FPGA?La première question concerne la caractéristique hybride à l'intérieur du système électronique de puissance. Nous avons proposé une nouvelle méthode nodale et un solveur matriciel basé sur la décomposition de Cholesky essayant de garder la topologie du circuit fixe et de traiter chaque élément de commutation et de circuit indépendamment. La deuxième question est celle de savoir comment obtenir des approximations pour toutes sortes d’Équation différentielle (ODE). Nous avons utilisé une série de solveurs ODE parallèles pour accélérer le processus de résolution. La troisième question est d'utiliser des outils de synthèse de haut niveau (HLS) pour optimiser les performances du FPGA. De tels outils sont utilisés pour développer des unités de calcul haute performance pour des applications de simulation en temps réel. Enfin, afin de rechercher l'impact de la caractéristique de commutation non linéaire sur le système électronique de puissance, nous avons proposé un modèle IGBT ultra-rapide avec un temps de calcul en nanosecondes dans le FPGA.Dans l'ensemble, les méthodes présentées contribuent au développement du simulateur en temps réel par FPGA pour le système de transport électrique de trois façons: réduire le temps de calcul des matrices, proposer un solveur ODE parallèle dans le FPGA et optimiser les performances du FPGA. / The development of power electronic system in electrical transportation is being pursued in the form of high-efficiency power converters involving complex topology. Although analysis and control of such system is often a difficult task due to the high-voltage and high-current environment, the hardware-in-the-loop simulation (HILs) offers a time-saving and safe way to evaluate the control strategy by simulating the external environment of a controller in the embedded system.During the process, there are two requirements that we have to meet in the context of racing against real-time: (i) the computation process is necessary to the end before the next trigger impulse from the real-time clock arrives (ii) the latency in the simulator is small enough to ignore. The sampling and simulation period in today’s CPU-based HIL simulators can barely go under 1 us, it is hard to take into accounts the entire switch event from PWM (Pulse Width Modulation) in modern power drive systems. In contrast, Field Programmable Gate Arrays (FPGAs) provide not only an ultra-fast sampling speed but also a viable alternative for speeding up the real-time simulator. However, the implementing the complex power electronic system on FPGAs is one of the limitations in real time simulation. Thus, in this these, we will research the FPGA-based real-time simulation with the attempt to solve the following questions,1.How could we partition power electronic system and implement it in FPGA?2.How do we leverage FPGA features to accelerate circuit?3.How could we optimize the performance of FPGA?4.How do we express the nonlinear switch characteristic of power electronic system in the FPGA?The first question is about the hybrid characteristic inside the power electronic system. In the paper, we proposed a novel nodal method and a matrix solver based on Cholesky Decomposition trying to keep the circuit topology fixed and treat each switch and circuit element independently. The second question is one that how to obtain approximations for all kind of ordinary differential equations (ODEs). We utilized a series of parallel ODE solver to accelerate the solving process and deal with the stiff problem. The third question is to use high-level synthesis (HIL) tools to optimize the performance of FPGA. Such tools are employed for developing high-performance computing units, designated hereafter as hardware solvers (HS), for real-time simulation applications. At last, in order to research the impact of nonlinear switch characteristic on the power electronic system, we proposed an ultra-fast IGBT model with a calculation time in nanoseconds in the FPGA.Overall, the presented methods contribute to the development of FPGA-based real-time simulator in three ways: reducing the calculation time of matrix solving process, proposing parallel ODE solver in the FPGA and optimizing the performance of FPGA. Thus, with the FPGA solver we built, the model of power electronic system for electrical transportation can be solved within 50 nanoseconds in high accuracy.

This thesis intends to examine the principles of operation for switched reluctance machines (SRM) and examine the power electronic drive circuits that control them, in order provide a basis of understanding for evaluating total drive efficiency and responsiveness potential. This document specifically examines the characteristics of a motor drive circuit which affect motor and converter efficiency and driving performance. A drive topology suited for efficient operation and excellent responsiveness is proposed. Finally, a SRM drive system model for evaluating these systems in simulation is described as a tool for comparative evaluations in future work. The end goal of this work is to provide a foundation of knowledge for future work, developing in-wheel, SRM-based, high performance hybrid electric drivetrains in future ground combat vehicles which are modular, possess an open architecture for upgrades, and operate with high efficiency and improved mobility. / text

This thesis introduces a power electronic interface for a kinetic hydropower generation platform that enables extraction of electric power from a free-flowing water source such as a river or a stream. The implemented system transfers power from a high-frequency permanent magnet synchronous generator (PMSG) to a 60-Hz load. Special configurations and control techniques were developed to cater for the long distance between the generator and the power interface; and also to address the wide range of the PMSG frequency and voltage variations. The proposed power-electronic interface was constructed and tested in the laboratory as well as in the field. The thesis also introduces two feasible methods for controlling a hydrokinetic plant to supply islanded loads or to deliver the maximum power available from the turbine-generator to the utility network. Application of multiple turbines in a kinetic farm was also investigated, and different approaches to controlling hydrokinetic turbines were developed.

With the desire for energy conservation and lower costs, the application of pulse-width modulated (PWM) voltage source converter (VSC) drives has grown at an exponential rate. However, due to their high switching frequency and high dv/dt, increased dielectric stresses and thermal stresses are applied to the insulation system of the motors, which may lead to the failure of the insulation. In order to test the performance of the motor insulation under the above complex stress conditions, an IGBT-based pulse voltage generator which can produce high voltage square wave and PWM waveforms has been successfully developed in this research. The generator consists of IGBT switches and other wave shaping components. The special cascade connection circuit design enables the generator to produce the stable high voltage square wave and PWM waveforms. A microcontroller-based trigger signal generator is used to trigger the power electronic switches in the generator. In order to avoid false triggering from electromagnetic interference (EMI), optical fibre cables are used to connect the trigger signal generator to the switches which are located in a high electric potential area. The generator can produce square wave and PWM waveforms with a peak voltage up to 15 kV and with a switching frequency of 600 Hz to 6 kHz. The fundamental frequency of the PWM waveform is 20 Hz to 1200 Hz, the rise time is less than 200 ns, and the pulse width can be varied up to several milliseconds. A 4 kVrms form wound model stator coil was tested under different voltage waveforms: power frequency, exponential decay pulse, square wave, and sinusoidal pulse-width modulated (SPWM) waveform. Infrared images and the maximum temperature rise of the coil under different electrical stresses were recorded. The results show that both the square and SPWM voltage waveforms cause a significantly higher temperature rise than the power frequency and exponential decay pulse voltage waveforms. Since the actual VSCs generate transients similar to those of the square and PWM voltage waveforms, it is recommended that the stator coil insulation be analyzed using PWM voltage waveforms in order to simulate actual conditions.

This thesis introduces a power electronic interface for a kinetic hydropower generation platform that enables extraction of electric power from a free-flowing water source such as a river or a stream. The implemented system transfers power from a high-frequency permanent magnet synchronous generator (PMSG) to a 60-Hz load. Special configurations and control techniques were developed to cater for the long distance between the generator and the power interface; and also to address the wide range of the PMSG frequency and voltage variations. The proposed power-electronic interface was constructed and tested in the laboratory as well as in the field. The thesis also introduces two feasible methods for controlling a hydrokinetic plant to supply islanded loads or to deliver the maximum power available from the turbine-generator to the utility network. Application of multiple turbines in a kinetic farm was also investigated, and different approaches to controlling hydrokinetic turbines were developed.