Resonant Behaviour of Pulse Generators for the Efficient Drive of Optical Radiation Sources Based on Dielectric Barrier Discharges

Dielectric barrier discharge (DBD) excimer lamps emit vacuum-UV optical radiation. This work presents novel methods for efficiently operating DBDs with short, high-voltage pulses. Transformer-less systems utilising SiC power semiconductor switches are presented. Pulse frequencies of up to 3.1 MHz and peak inverter efficiencies of 92 % were achieved. The work encloses both mathematical backgrounds of pulsed resonant circuits and practical implementation of low-inductive power stages

Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters

Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality.To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies.Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter.To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver

Switching dynamics of surface stabilized ferroelectric liquid crystal cells: effects of anchoring energy asymmetry

We study both theoretically and experimentally switching dynamics in surface stabilized ferroelectric liquid crystal cells with asymmetric boundary conditions. In these cells the bounding surfaces are treated differently to produce asymmetry in their anchoring properties. Our electro-optic measurements of the switching voltage thresholds that are determined by the peaks of the reversal polarization current reveal the frequency dependent shift of the hysteresis loop. We examine the predictions of the uniform dynamical model with the anchoring energy taken into account. It is found that the asymmetry effects are dominated by the polar contribution to the anchoring energy. Frequency dependence of the voltage thresholds is studied by analyzing the properties of time-periodic solutions to the dynamical equation (cycles). For this purpose, we apply the method that uses the parameterized half-period mappings for the approximate model and relate the cycles to the fixed points of the composition of two half-period mappings. The cycles are found to be unstable and can only be formed when the driving frequency is lower than its critical value. The polar anchoring parameter is estimated by making a comparison between the results of modelling and the experimental data for the shift vs frequency curve. For a double-well potential considered as a deformation of the Rapini-Papoular potential, the branch of stable cycles emerges in the low frequency region separated by the gap from the high frequency interval for unstable cycles.Comment: 35 pages, 15 figure

Investigation of multilayer magnetic domain lattice file

A theoretical and experimental investigation determined that current accessed self structured bubble memory devices have the potential of meeting projected data density and speed requirements. Device concepts analyzed include multilayer ferrimagnetic devices where the top layer contains a domain structure which defines the data location and the second contains the data. Current aperture and permalloy assisted current propagation devices were evaluated. Based on the result of this work more detailed device research was initiated. Detailed theoretical and experimental studies indicate that the difference in strip and threshold between a single bubble in the control layer and a double bubble which would exist in both the control layer and data layer is adequate to allow for detection of data. Detailed detector designs were investigated

A Tesla-Blumlein PFL-Bipolar pulsed power generator

A Tesla-Blumlein PFL-Bipolar pulsed power generator, has been successfully designed, manufactured and demonstrated. The compact Tesla transformer that it employs has successfully charged capacitive loads to peak voltages up to 0.6 MV with an overall energy efficiency in excess of 90%. The Tesla driven Blumlein PFL generator is capable of producing a voltage impulse approaching 0.6 MV with a rise time close to 2 ns, generating a peak electrical power of up to 10 GW for 5 ns when connected to a 30 Ω resistive load. Potentially for medical application, a bipolar former has been designed and successfully implemented as an extension to the system and to enable the generation of a sinusoid-like voltage impulse with a peak-to-peak value reaching 650 kV and having a frequency bandwidth beyond 1 GHz. This thesis describes the application of various numerical techniques used to design a successful generator, such as filamentary modelling, electrostatic and transient (PSpice) circuit analysis, and Computer Simulation Technology (CST) simulation. All the major parameters of both the Tesla transformer, the Blumlein pulse forming line and the bipolar former were determined, enabling accurate modelling of the overall unit to be performed. The wide bandwidth and ultrafast embedded sensors used to monitor the dynamic characteristics of the overall system are also presented. Experimental results obtained during this major experimental programme are compared with theoretical predictions and the way ahead towards connecting to an antenna for medical application is considered

Zenithal bistable device: comparison of modeling and experiment

A comparative modeling and experimental study of the zenithal bistable liquid crystal device is presented. A dynamic Landau de Gennes theory of nematic liquid crystals is solved numerically to model the electric field induced latching of the device and the results are compared with experimental measurements and theoretical approximations. The study gives a clear insight into the latching mechanism dynamics and enables the dependence of the device latching on both material parameters and surface shape to be determined. Analytical approximation highlights a route to optimize material selection in terms of latching voltages and the numerical model, which includes an accurate surface representation, recovers the complex surface shape effects. Predictions of device performance are presented as a function of both surface anchoring strength and surface shape and grating pitch. A measurement of the homeotropic anchoring energy has been undertaken by comparing the voltage response as a function of cell gap; we find the homeotropic anchoring energies can be varied in the range 0.5 to 4 (10-44 J m-2)

Теоретичні основи електротехніки[

The Theory of Electrical Engineering is presented in three parts: the Basic Theories of Steady-State and Transients in Electrical Circuits and the Basic Theory of Electromagnetic Field. For students of electrotechnical specialties of higher educational establishments, as well as for scientific and technical specialists dealing with modern problems in the theory and practice of electric power engineering and electromechanics.Викладено теоретичні основи електротехніки в трьох частинах: теорія стаціонарних процесів в електричних колах, теорія перехідних процесів в електричних колах і теорія електромагнітного поля. Для студентів електротехнічних спеціальностей вищих навчальних закладів, а також для науково-технічних фахівців, що займаються сучасними проблемами в теорії і практиці електроенергетики та електромеханіки

A Study of Medium and High Voltage Form-Wound Coil Turn-to-Turn Insulation of Converter Fed Rotating Machines

Converter fed medium voltage motors are increasingly being employed in industrial processes due to their higher efficiency and greater flexibility with respect to speed control. The increased use of motor adjustable speed drives has raised concerns about the adverse effects of the distorted voltage waveform of the converter on the insulation of the machine. Recent designs include a higher level of insulation than that are used in conventional AC-fed motors because of the presence of fast transients and harmonics in the voltage waveforms at the motor terminals. Many studies have focused on this problem, with most emphasizing on the stress-grading system and relatively a few investigating the form-wound turn insulation, with some contradictory reported results. Hence, the focus of the present research is to study the turn insulation of form-wound machines subjected to distorted voltage waveforms from converter pulses. The effect of pulse parameters such as rise time, pulse duty cycle, and switching frequency on the times-to-failure of turn insulation under unipolar and bipolar square pulses are investigated. Back-to-back turn insulation samples, with enamel insulation, were prepared based on IEC 60034-18-42 with improved insulation in the crotch region of the samples to prevent failures in this region. A high voltage pulse generator, and an antenna based PD measurement system, were implemented in order to investigate significant factors affecting insulation system using PD activity measurements and times-to-failure experiments. The experimental results were used to identify the significant parameters of aging as well as suggesting the aging mechanism involved. A point-to-plane setup having an insulation film representing a single defect in turn insulation system, was also implemented to investigate the PD features and their relationship to the times-to-failure of back-to-back samples in depth. Using this setup, a series of measurements were carried out to investigate the significance of charge accumulation on the times-to-failure of insulation samples. By conducting surface charge measurements, surface potential measurements, and COMSOL® simulations on the point-to-plane setup with different insulation films, the influence of accumulated charge in modifying the electric field and therefore the times-to-failure of insulation systems was studied for different pulse types and switching frequencies in order to explain the results of aging experiments and to validate the presented aging mechanism