Determination and dynamic compensation of fictitious power in electric power systems

D.Ing. (Electrical & Electronic Engineering)Please refer to full text to view abstrac

Low-Threshold AlGaN-based UVB VCSELs enabled by post-growth cavity detuning

The performance of vertical-cavity surface-emitting lasers (VCSELs) is strongly dependent on the spectral detuning between the gain peak and the resonance wavelength. Here, we use angle-resolved photoluminescence spectroscopy to investigate the emission properties of AlGaN-based VCSELs emitting in the ultraviolet-B spectral range with different detuning between the photoluminescence peak of the quantum-wells and the resonance wavelength. Accurate setting of the cavity length, and thereby the resonance wavelength, is accomplished by using doping-selective electrochemical etching of AlGaN sacrificial layers for substrate removal combined with deposition of dielectric spacer layers. By matching the resonance wavelength to the quantum-wells photoluminescence peak, a threshold power density of 0.4 MW/cm2 was achieved, and this was possible only for smooth etched surfaces with a root mean square roughness below 2 nm. These results demonstrate the importance of accurate cavity length control and surface smoothness to achieve low-Threshold AlGaN-based ultraviolet VCSELs

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm)

Electric energy : a prerequisite for prosperity

Electric energy is a fundamental prerequisite for prosperity in any community, moreso for South Africa. Energy is needed for existence at large, while electric energy is a prerequisite for the development of any community. The earth has a continuous power input of nearly 20 million Terrawatt from the sun. This large amount of energy is in fact ten thousand times larger than the current annual world energy consumption, if the power input is taken over one year. It seems that we have a lot of energy, unfortunately the energy is spread over a large area, the peak power density form the sun is reasonably low and interrupted by daily cycles. There is therefore a great number of oportunities, in energy technology, open to electrical engineers. The challenges and contraints of the electrical engineer in a decade and century of multiple technology innovations are described. The emphasis is placed on energy technology and the associated creation of prosperity within South Africa. The intervening of engineers to energy careers is addressed with reference to opportunities in research activities and selfrealization. Aspects of the training of electrical engineers, curricula, and properties of electrical engineers are discussed, with reference to the role of the electrical engineer in the South African industry.Item was scanned at 300 dpi. Scanner used HP Scanjet 5590Pp. 27-35: Publikasies van die Universiteit van Pretoria (Nuwe Reeks)http://explore.up.ac.za/record=b174389

Design, analysis and experimental evaluation of a vibration energy generator

MEng (Mechanical Engineering), North-West University, Potchefstroom CampusGenerating energy from ambient vibration is a method of harvesting green energy. Harvesting energy in this manner is similar to that of solar and wind energy harvesting. The vibration energy generator discussed in this dissertation illustrates a thorough example of a method to harvest green energy and the required components for the design of a vibration energy generator. Through the investigation of the design, and further analysis and experimental evaluation, the technical behaviour of an electromagnetic vibration energy generator is predicted and determined. The design of a vibration energy harvester is considered in literature - more specifically, the design of an electromagnetic vibration generator. Multitudes of concepts have been published and compared in studies. For the mechanical system in this study, the design of the vibration energy generator is obtained through the use of a subwoofer (loudspeaker). The mechanical system is studied to determine the typical mechanical properties under varying electrical load. The parameters, for this study, were determined by different methods with aid of mathematical models for characterization and verification. The electrical components were simply measured and implemented into mathematical models. The electrical properties together with the mechanical properties are incorporated for analysis of the generator in context of the mechanical and electrical response. The generator design is analysed in the form of mathematical models. Two mathematical models predict the usable electrical power to be harvested at specific load conditions. The usable electrical power is determined from both a mechanical and an electrical perspective. To evaluate the mathematical models, measurements were made to record the usable electrical power from the systems. The measured values under varying electrical loads are compared to the predicted values from the mechanical and electrical models respectively. To arrive at a design for a vibration energy generator it is essential to address certain design considerations proactively for each specific application, as harmonic tuning and optimal electrical load choice have intricate effects on both the mechanical and electrical systems for performance of the system to produce usable power. Furthermore, it is shown that a loudspeaker can be used as a vibration energy generator. However, changes will be required for use as a vibration energy generator.Master

The electrical resistivity method of geophysical prospecting and its practical application to geological problems of economic importance in the Union of South Africa

Thesis (D. Sc. Physics) -- University of Stellenbosch, 1944.Full text to be digitised and attached to bibliographic record

Transformation of conventional transformers for enhanced DC mitigation in AC power networks with advanced grid support

The flow of quasi-DC or DC in AC networks may trigger half-cycle saturation of electrical grid transformers that could lead to their internal heating or grid collapse. Apart from the requirement of DC mitigation measures, the conversion of conventional power grid into an intricate network demands the need for power equipment with dynamic control capability. The transformers provide the most strategic point in the grid for the introduction of DC protection and grid-support features. This paper proposes a fractionally rated power-electronics module coupled to neutral and ground terminals of conventional transformers that delivers efficient power network protection against quasi-DC or DC flow with different advanced grid-support features injected on the transformer primary. The proposed concept is validated on an experimental hardware prototype employing power hardware-in-the-loop (P-HIL) configuration of Typhoon HIL-402 and compared with the simulation results in this paper. Also, a transformer and associated module protection approach employing a hybrid bypass switch has been suggested and experimentally validated in this work. The experimental results validate the capability of the module to counter DC injection, perform harmonics mitigation, voltage control or unbalance compensation, impedance matching and power flow control at the same injection point

DC-side harmonic compensation in DC traction applications

A problem associated with dc traction substations, is the non-robustness of the passive filters used for the filtering of the harmonics induced by the 12-pulse rectifiers. These harmonics cause problems with the communications and the signaling on the dc railway lines. Interference with the railway signaling system can have serious and sometimes fatal effects. Therefore, a method is being devised by which the problematic harmonics can be compensated for by means of an Active Power Filter (APF) on the dc-side of the 12-pulse rectifiers.Conference Pape