The U. S. Navy is pursuing an all electric ship that will require enormous amounts of power for applications such as electric propulsion. Reliability and redundancy in the electronics are imperative, since failure of a critical system could leave a ship stranded and vulnerable. A parallel inverter drive topology has been proposed to provide reliability and redundancy through load sharing. The parallel architecture enables some functionality in the event that one of the inverters fails. This thesis explores paralleling current-mode inverters of different power levels and fidelities. A 50-kVA, three-phase hysteresis controlled inverter is designed, built, and tested at low power. The inverter is then tested in parallel with a low frequency, bulk inverter to demonstrate current sharing capability.

In order to limit global warming to 1.5-2 °C deployed solar photovoltaic (PV) power must increase from today's 0.228 terawatts to 2-10 terawatts installed by 2030, depending on demand. These goals require increasing manufacturing capacity, which, in turn, requires lowering the cost of electricity produced by PV. However, high demand scenarios will require greater cost reductions in order to make PV generated electricity <i> as competitive </i> as it needs to be to enable this growth. It is unclear whether established PV technologies — silicon, CdTe, GaAs, or CuInxGa1-xSe2 — can achieve the necessary breakthroughs in efficiency and price. A newer technology known as the &apos;perovskite solar cell&apos; (PSC) has recently emerged as promising contender. <br>     In the last seven years the efficiency of PSCs increased by the same amount covered by established technologies in the last thirty. However, PSCs suffer from chemical instability under operating conditions and hysteresis in current-voltage measurements used to characterize power output. Characterizing the defect structures formed by this material and how they interact with device performance and degradation may allow stabilization of PSCs. To that end, this work investigates defects in perovskite solar cells, the impact of these defects on performance, and the effect of alloying and degradation on the electronically active defect structure. Chapter I gives a brief introduction, motivating research in solar cells generally and perovskites in particular as well as introducing some challenges the technology faces. Chapter II gives some background in semiconductors and the device physics of solar cells. Chapter III introduces the performance and defect characterization methods employed. Chapter IV discusses results of these measurements on methylammonium lead triiodide cells correlating defects with device performance. Chapter V applies the some of the same techniques to a series of CH3NH3Pb(I1-xBrx)3 based perovskites aged for up to 2400 hours to explore the impact of alloying and aging on the defect structure. Chapter VI discusses implications for perovskite development and directions for future research. <br>     This dissertation includes previously published co-authored material.

The focus of this thesis is on the development of control systems for nano- positioning actuators using magnetostrictive materials. Magnetostrictive materials have large strokes and fast responses. However, they are less commonly used than other smart materials such as piezoceramics due to their highly nonlinear and hysteretic behaviour. It is necessary to arrive at an accurate model which can predict the material response at any magnetic field and load condition. Furthermore, due to the nonlinearity of the material, a closed-loop feedback system with a stabilizing controller is needed. Different hysteresis models for magnetostrictive materials are implemented and compared. Since load-dependence is one of the main features of hysteresis for magnetostrictive materials, load-dependent models are studied. An existing load- dependent model is implemented and compared with a new load-dependent hysteresis model which is developed by energy considerations. Passivity of the magnetostrictive system was shown using a physical argument. The results are used to develop a stabilizing controller. Using the properties of the Preisach model, an alternative approach for controller design is proposed. Tracking properties and stability of the controllers were shown. An experimental setup has been developed for data collection and model and controller evaluation.

The focus of this thesis is on the development of control systems for nano- positioning actuators using magnetostrictive materials. Magnetostrictive materials have large strokes and fast responses. However, they are less commonly used than other smart materials such as piezoceramics due to their highly nonlinear and hysteretic behaviour. It is necessary to arrive at an accurate model which can predict the material response at any magnetic field and load condition. Furthermore, due to the nonlinearity of the material, a closed-loop feedback system with a stabilizing controller is needed. Different hysteresis models for magnetostrictive materials are implemented and compared. Since load-dependence is one of the main features of hysteresis for magnetostrictive materials, load-dependent models are studied. An existing load- dependent model is implemented and compared with a new load-dependent hysteresis model which is developed by energy considerations. Passivity of the magnetostrictive system was shown using a physical argument. The results are used to develop a stabilizing controller. Using the properties of the Preisach model, an alternative approach for controller design is proposed. Tracking properties and stability of the controllers were shown. An experimental setup has been developed for data collection and model and controller evaluation.

It can not always be expected that ferroresonance happens.The ferroresonance is rarely seen on the nonlinear resonance of the power system. If the resonance is transient or steady it may result in overvoltage and over current and also degrade insulation of the equipment. It¡¦s been proved that the rare nonlinear resonance causes some unexplainable damages. Due to increasing power capacity, expanding transmission line and underground line of ferroresonance is increased. This thesis presents the three phase power system with analysis. The magnetic curve was obtained from field measurements and using many kinds of parameters which are from the magnetization characteristic and lines to analysis. Especially emphasized is the width of the hysteresis loop and the effects of magnetic hysteresis in the change of the operating point of the transformer. In the simulation, the thesis compares the effects of magnetic hysteresis with the non-effects of magnetic hysteresis, and compare the differences of parameter critical point to avoid ferroresonance. This thesis has presented some results in investigating the impact of different sets of initial condition on the models of behavior of a ferroresonance circuit.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Robert Ashton, Xiaoping Yun. Includes bibliographical references (p. 69-70). Also available online.

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Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [165]-183).

Thesis (M.A.), Psychology--University of Central Oklahoma, 2010. / Includes bibliographical references (leaves 23-25).