Harmonic distortion in a power system can excite non-characteristic harmonics from converter interfaced loads and generators which can then propagate back into the system, exciting other harmonics in the system. In this thesis, a harmonic analysis tool is presented that is designed to perform high accuracy, computationally efficient, steady-state harmonic analysis of distribution systems when multiple converter interfaced loads and generators exist in the system. The harmonic analysis tool requires less detail and engineering time than PSCAD/EMTDC while offering reliable assessment of harmonic coupling problems that are not captured by existing frequency-domain harmonic analysis tools. To do this, 5 harmonic models of common power electronic converter topologies were developed and implemented into this tool. The harmonic models are shown to be highly accurate; when tested in an unbalanced system with even and odd harmonic distortion, the harmonic models showed a maximum error of less than 0.4% when compared to PSCAD/EMTDC.

Shadows provide an important cue in computer graphics. In this thesis we focus on real-time soft shadow algorithms. Two new techniques are presented, both run entirely on modern graphics hardware. "Soft Shadows Using Precomputed Visibility Distance Functions" renders fake soft shadows in static scenes using precomputed visibility information. The technique handles dynamic local light sources and contains special computation steps to generate smooth shadows from hard visibility functions. The resulting images are not physically accurate, nevertheless the method renders plausible images that imitate global illumination. "Soft Projected Shadows" is a simple method for simulating natural shadow penumbra for projected grayscale shadow textures. Shadow blurring is performed entirely in image space and needs only a couple of special blurring passes on pixel shader 2.0 hardware. The technique treats shadow receivers as nearly planar surfaces and doesn’t handle self shadowing, but executes very fast and renders plausible soft shadows. Multiple overlapping shadow casters in a single shadow map are natively supported without any performance overhead.

This thesis describes the development of several small signal analysis methods for the modelling of power electronic converters. The methods are written generally and are intended to be able to be applied to all converter classes. In the penultimate chapter these general models are used to model the capacitor commutated converter. All the contained methods are based around a time domain small signal model. This time domain small model is a linearization of a power electronic system of passive components and ideal switches described as a hybrid system. The key problem in the derivation of the small signal model is the correct determination and description of the linearized effect of switching instant variation. Three analysis methods based upon the small signal model are advanced in this thesis, these are; time domain sensitivity matrices for use in a Newton determination of the cyclic steady state of a power electronic converter, partial waveform construction of harmonic sensitivity matrices for studying sensitivity of converters to harmonic disturbances, and harmonic state space models also for the construction of harmonic sensitivity matrices and for study of dynamic systems. Each modelling technique is applied to the more common converter topologies of the Buck-Boost converter and the Graetz Bridge before being finally applied to the capacitor commutated converter. Each technique is compared to PSCAD-EMTDC simulations for verification.

Darbe tiriami iškraipymai audio sistemose ir kaip žmogaus klausa juos suvokia. Autorius sistemina tyrimus, bibliografinius įrašus. Pateikiama alternatyvi tyrimo metodika. Tyrimo rezultatai reikšmingi tobulinant garsinio signalo traktą. / This research is about distortion in audio systems and how human hearing perceives it. Author collects together data from other researches and compares them. The main goal of this research is to find, what type of audio distortion is most audible. Results of the work can be used to improve audio equipment design with properties of human hearing in mind.

An expansion method for the stationary Schrodinger equation of a particle moving freely in an arbitrary axisymmeric three dimensional region defined by an analytic function is introduced. The region is transformed into the unit ball by means of coordinate substitution. As a result the Schrodinger equation is considerably changed. The wavefunction is expanded into a series of spherical harmonics, thus, reducing the transformed partial differential equation to an infinite system of coupled ordinary differential equations. A Fourier-Bessel expansion of the solution vector in terms of Bessel functions with real orders is employed, resulting in a generalized matrix eigenvalue problem. The method is applied to two particular examples. The first example is a prolate spheroidal billiard which is also treated by using an alternative method. The numerical results obtained by using both the methods are compared. The second exampleis a billiard family depending on a parameter. Numerical results concerning the second example include the statistical analysis of the eigenvalues.

The objective of this research is to introduce a neural network based solution for the problem of measuring the actual amount of harmonic current injected into a power network by an individual nonlinear load. Harmonic currents from nonlinear loads propagate through the system and cause harmonic pollution. As a result, voltage at the point of common coupling (PCC) is rarely sinusoidal. The IEEE 519 harmonic standard provides customer and utility harmonic limits and many utilities are now requiring their customers to comply with IEEE 519. Measurements of the customer’s current at the PCC are expected to determine the customer’s compliance with IEEE 519. However, results in this research show that the current measurements at the PCC are not always reliable in that determination. In such a case, it may be necessary to determine what the customer’s true current harmonic distortions would be if the PCC voltage could be a pure sinusoidal voltage. However, establishing a pure sinusoidal voltage at the PCC may not be feasible since that would mean performing utility switching to reduce the system impedance. An alternative approach is to use a neural network that is able to learn the customer’s load admittance. Then, it is possible to predict the customer’s true current harmonic distortions based on mathematically applying a pure sinusoidal voltage to the learned load admittance. The proposed method is called load modeling. Load modeling predicts the true harmonic current that can be attributed to a customer regardless of whether a resonant condition exists on the utility power system. If a corrective action is taken by the customer, another important parameter of interest is the change in the voltage distortion level at the PCC due to the corrective action of the customer. This issue is also addressed by using the dual of the load modeling method. Topologies of the neural networks used in this research include multilayer perceptron neural networks and recurrent neural networks. The theory and implementation of a new neural network topology known as an Echo State Networks is also introduced. The proposed methods are verified on a number of different power electronic test circuits as well as field data. The main advantages of the proposed methods are that only waveforms of voltages and currents are required for their operation and they are applicable to both single and three phase systems. The proposed methods can be integrated into any existing power quality instrument or can be fabricated into a commercial standalone instrument that could be installed in substations of large customer loads, or used as a hand-held clip on instrument.

The limiter is a commonly used device in communication receiving systems to remove the amplitude variations of the received signal, but it is usually observed that limiter degrades the envelope detection performance of a single tone. In this thesis, it is demonstrated that the limiter-generated third harmonic can be used to improve the envelope detection performance of a single tone over that of the linearly processed fundamental. Differences in the probability distributions of the limiter-generated harmonics cause differences in their detection probabilities, which lead to differences in the performance of subsequent envelope detection. Comparison of the envelope detection performance of the limiter-generated third harmonic and the input to the limiter shows a maximum detection probability gain of 1.12 and also error probability gain of 2.4 in linear scale, whereas the fundamental harmonic does not show any practically significant gain. The envelope detection performance of the vector sum of the limiter-generated fundamental and third harmonics is also evaluated. This combination provides better performance than do the individual harmonics, especially for a large clipping parameter of the limiter. The combined harmonics shows a maximum detetction probability gain of 1.15 and error probability gain of 14, over that of the envelope detection performance of a tone without limiter. It is also observed that the envelope detection performance of a tone with limiter-generated higher harmonics shows non-monotonic behaviour as functions of either noise or the limiter-clipping parameter, which is a signature of stochastic resonance. The theoretical results from earlier research on the envelope detection of a single tone embedded in additive white Gaussian noise, both with and without a limiter, are presented and shown to match our simulation results. In previous work when a limiter was used in the envelope detection of a single tone, only the envelope of the fundamental harmonic was considered under very specific conditions. By contrast we also take notice of the limiter-generated higher harmonics and obtain improved envelope detection performance in the detection of a single tone.

Thesis (Ph. D.)--Ohio University, August, 1993. / Title from PDF t.p.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.S.)--Ohio University, June, 1997. / Title from PDF t.p.