Overcoming electro-thermal barriers to achieve extreme performance power conversion for more electric aircraft

The National Aeronautics and Space Administration (NASA), in addition to an increasing number of privately funded ventures, has demonstrated growing interest in more electric aircraft (MEA) - flight vehicles where propulsion is partially or totally supplied by electric motors. While hybrid or turbo-electric MEA concepts would still rely on a jet engine power plant to provide electrical power to these electric motors, NASA studies indicate these concepts can result in cleaner, quieter, and more fuel-efficient flight compared to current best-in-class passenger jet aircraft. To achieve this new paradigm in flight, major engineering challenges must be overcome to improve the thermal management, efficiency and power density of the propulsion electronics as well as ensure the high reliability necessary for aviation. This thesis focuses on these challenges in the scope of one block of this electrical system: a high-performance dc-ac converter designed to drive the type of electric machine engineered for electric flight from a high-voltage dc bus that would be present on some MEA concepts. The flying capacitor multilevel topology is demonstrated as an enabling technology for simultaneously achieving high-efficiency and high power-density, with specific consideration given to packaging and implementation. Reliability of the converter is addressed through discussion of on-line health management through the use of a real-time hardware-in-the-loop (HIL) observer

High-Performance Architectures for Vehicle Propulsion: An Unconventional Approach to Design, Fabrication and Analysis using Scalable Flying Capacitor Multilevel Converter Modules

The consequences of climate change grow more pronounced each year as carbon emissions continue unabated. Decarbonizing all aspects of the transportation sector is a major requirement for a sustainable pathway to mitigate these consequences. However, this requires overcoming substantial engineering challenges, not the least of which are the power density and efficiency requirements of the inverter system in future electric drivetrains. This work examines a high-performance and scalable approach for modeling, designing, fabricating and testing an architecture that meets aggressive industry targets through innovative techniques and the use of an unconventional topology. Several prominent and promising topologies are reviewed, and an unconventional approach using the flying-capacitor multilevel topology is introduced to drive the order-of-magnitude improvements required by the industry targets. A 10-level, 1 kV, dual-interleaved converter module serves as the platform for an in-depth study of the electrical and thermal design and performance attained using this approach, where a peak power of 18.9 kW and a peak efficiency of 98.95 % is experimentally demonstrated. Scalability and reliability of the proposed architecture is discussed and tested using individual modules as well as an array paralleling nine of these 38.4 kW/kg, 24.4 kW/L modules. Finally, potential extensions to the work in future studies are reviewed

A Retrospective Review of Morbidity and Mortality Associated with Acute Benzodiazepine Withdrawal at a Midwestern Academic Medical Center: Acute Benzodiazepine Withdrawal

Introduction. There is concern that acute benzodiazepine (BZP) withdrawal may result in morbidity and mortality. However, there is a paucity of medical literature regarding clinical characteristics and outcomes of acute BZP withdrawal. We sought to characterize acute BZP withdrawal at a midwestern academic medical center. Methods. This was a retrospective study. The medical records of the University of Kansas Hospital, a tertiary academic medical center, were queried for patients with a diagnosis of BZP withdrawal, drug withdrawal, sedative-hypnotic withdrawal or withdrawal-NOS from 1/1/2009 to 1/1/2016. Data collected included: age, sex, month/year of encounter, initial vital signs, type of drug withdrawal (alcohol, opioid, BZP or other), type of BZP withdrawing from, disposition, duration of hospitalization, seizures, endotracheal intubation, mortality and pharmacological treatment. Results. 82 cases of were identified. Cases per year increased over the study period. Thirty-one (38%) cases involved concurrent drug withdrawal with opioids most common (n=25). Alprazolam (n=32) was the most common BZP implicated in BZP withdrawal. Thirty-nine cases (47%) were admitted including 7 to the ICU. Seizures were reported in 8 (10%) cases. Endotracheal intubation occurred in 3 (3.6%). Sixty-seven patients (81%) were treated with a BZP with lorazepam (n=42) most commonly used. There were no deaths. Upon discharge 40 (49%) patients received a prescription for a benzodiazepine. Conclusions. Cases of acute BZP withdrawal increased over the study period but were associated with only occasional morbidity and no mortality. Further multi-center studies are warranted to better characterize the incidence and characteristics of acute BZP withdrawal

Low-Power Maximum Power Point Tracker with Digital Control for Thermophotovoltaic Generators

This paper describes the design, optimization, and evaluation of the power electronics circuitry for a low-power portable thermophotovotaic (TPV) generator system. TPV system is based on a silicon micro-reactor design and low-bandgap photovoltaic (PV) diodes. We outline critical system-level challenges associated with TPV power generation, and propose a power electronics architecture that addresses these challenges. We present experimental data from a compact, highly efficient peak power tracker and show how the proposed architecture enables increased energy extraction compared to conventional methods. The operation of the power tracker is verified with low-bandgap PV cells illuminated by a quartz halogen lamp producing a PV diode output power of 0.5 W, and above 99% tracking efficiency is demonstrated. Additionally, the complete system operation is verified with the power tracker connected to GaInAsSb PV diodes and a silicon micro-reactor, producing 150 mW of electrical power.United States. Army Research OfficeMassachusetts Institute of Technology. Institute for Soldier Nanotechnologie

Securitisation from Below: The Relationship between immigration and foreign policy in South Africa's Approach to the Zimbabwe Crisis

The political and economic debacle in Zimbabwe has led to a large-scale influx of Zimbabweans into neighbouring South Africa. This article argues that there is a complex and significant link between the domestic response to this immigration influx and South Africa’s foreign policy towards Zimbabwe. South Africa’s foreign and security policy elite preferred to use an immigration approach of benign neglect as a tool to promote its ‘quiet diplomacy’ approach towards the Zimbabwean regime, treating the influx as a ‘non-problem’. But increased xenophobic violence, vigilantism and protests in townships and informal settlements against Zimbabwean and other African immigrants, culminating in widespread riots across the country in 2008, contributed to a change not only in immigration policy but also in the mediation efforts towards the Zimbabwean parties. I argue that this foreign policy change was pushed by a process of ‘securitisation from below’, where the understanding of Zimbabwean immigrants as a security threat were promoted not by traditional security elites but by South Africa’s marginalised urban poor