Insulated Gate Bipolar Transistor (IGBT) based voltage source converter (VSC) applica-tions embedded in power systems are growing. Optimal design of thermal management systems for such converters requires estimation of IGBT losses under various operating conditions, both normal and abnormal. Therefore, development of tools for estimating IGBT losses in EMT simulators is important as converters embedded in large power sys-tems are simulated in EMT simulators. Two circuit models are developed to simulate turn-on and turn-off transients using a be-havioral approach. These circuit models mimic the observed behavior in distinct phases of the turn-on and turn-off transients under the inductive load switching. In this model, the nonlinear nature of the circuit model of the IGBT is treated and converter specific in-fluential parameters are taken in to account. An excellent correlation between the meas-ured and simulated waveforms as well as measured and estimated switching losses is ob-served. Finally, an efficient method to incorporate switching loss calculation in an EMT program in the form of a lookup table created using the developed transient model is pro-posed.

M.A. (African Languages) / Please refer to full text to view abstract

Soft-switching techniques can significantly reduce the switching loss and switching stresses of the power semiconductor devices in a power converter. This work presents several soft-switching topologies for high power PWM converters. These new topologies achieve soft-switching functions with minimum increase of device voltage/current stresses and converter circulating energy, and thus have advantages over conventional techniques in efficiency, power density, reliability, and cost of power converters. The improved zero-current transition (ZCT) converters achieve zero-current switching at both turn-on and turn-off for all main switches and auxiliary switches. These converters significantly reduce the switching loss and stress of the power semiconductor devices, while have a voltage/current stress and circulating energy similar to a PWM converter’s. The analysis, design, and experimental verification are presented. The three-phase zero-voltage transition (ZVT) boost rectifiers/voltage source inverters are developed with simple auxiliary circuits. Unlike most existing three-phase soft-switching techniques, these new topologies achieve soft-switching functions without overcharging the resonant inductors, and realize the benefits of soft-switching operation with minimum extra main switch turn-offs and fixed auxiliary circuit control timing. The operation principles of the developed techniques are experimentally verified, and their efficiency performances are evaluated with experiments and computer simulation. The three-phase ZVT buck rectifier topologies developed in this work achieves zero-voltage turn-on for all main switches with an optimum modulation schemes and simple auxiliary circuits. The auxiliary circuits, which are connected directly to each main switch, can also absorb the parasitic resonance of the bridge arms, and keep the voltage stress of the power devices at the minimum. The analysis and simulation results are presented to verify the converter operation. New ZVT dc-link schemes for three-phase ac-dc-ac converters are investigated. With coordinated control of the ac-dc converter and the dc-ac converter, a set of simple auxiliary circuit can provide soft-switching function for all switches in both the ac-dc converter and the dc-ac converter. The power loss in the auxiliary circuit is also significantly lower than existing dc-link soft-switching schemes. Simulation with experimentally obtained device switching loss data proves that significant efficiency improvement can be achieved with the new ZVT dc-link techniques. New ZVT and ZCT techniques for three-level converters are also developed. The auxiliary circuits are not in the main power path, and allow the converters to be controlled with optimum PWM schemes. Analysis and simulation results are presented to demonstrate the operation principles and advantages of soft switching in three-level converters. / Ph. D.

Output queues in network switches are known to provide a suitable architecture for scheduling disciplines that need to provide quality of service (QoS) guarantees. However, today’s memory technology is incapable of meeting the speed requirements. Combined input and output queued (CIOQ) switches have emerged as one alternative to address the problem of memory speed. When a switch of this architecture uses a stable matching algorithm to transfer packets across the switch fabric, an output queued (OQ) switch can be mimicked exactly with a speedup of only two. The use of a stable matching algorithm typically requires complex and time-consuming calculations to ensure the behaviour of an OQ switch is maintained. Stable matching algorithms are well studied in the area in which they originally appeared. However, little is presently known on how the stable matching algorithm performs in CIOQ switches and how key parameters are affected by switch size, traffic type and traffic load. Knowledge of how these conditions affect performance is essential to judge the practicability of an architecture and to provide useful information on how to design such switches. Until now, CIOQ switches were likely to be dismissed due to the high complexity of the stable matching algorithm when applied to other applications. However, the characteristics of a stable matching algorithm in a CIOQ switch have not been thoroughly analysed. The principal goal of this thesis is to identify the conditions the stable matching algorithm encounters in a CIOQ switch under realistic operational scenarios. This thesis provides accurate mathematical models based on Markov chains to predict the value of key parameters that affect the complexity and runtime of a stable matching algorithm in CIOQ switches. The applicability of the models is then backed up by simulations. The results of the analysis quantify critical operational parameters, such as the size and number of preference lists and runtime complexity. These provide detailed insights into switch behaviour and useful information for switch designs. Major conclusions to be drawn from this analysis include that the average values of the key parameters of the stable matching algorithm are feasibly small and do not strongly correlate with switch size, which is contrary to the behaviour of the stable matching ii algorithm in its original application. Furthermore, although these parameters have wide theoretical ranges, the mean values and standard deviations are found to be small under operational conditions. The results also suggest that the implementation becomes very versatile as the completion time of the stable matching algorithm is not strongly correlated to the network traffic type; that is, the runtime is minimally affected by the nature of the traffic.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / The development of network-based data acquisition systems has resulted in a new architecture for supporting flight instrumentation that has the potential to revolutionize the way we test our aircraft. Unlike conventional flight test instrumentation, networks provide for a two-way communication path between all elements of the system, utilize packetized data, support communication protocols, have dynamic quality of service levels, can be subject to loss of data, utilize asynchronous transmission behavior and provide an even higher level of time synchronization. Different flight test architectures can be realized which combine each of the previous attributes in different ways; finding the best architecture for a set of given applications while minimizing cost and complexity is a very difficult problem. For the last 3 years, the Network Products Division at Teletronics has been involved in the design and evaluation of aircraft instrumentation networks for both customers and the iNET program. This paper describes the result of these efforts by discussing the high-level design of a modular architecture for an aircraft instrumentation network.

This thesis is a systematic investigation of preparatory reorienting of task-relevant spatial attention. Task switching experiments typically report a performance overhead when the current task is different to that performed on the previous trial relative to when the task repeats. This ‘switch cost’ tends to reduce as participants are given more time to prepare (consistent with an active reconfiguration process) but a ‘residual’ switch cost usually remains even at very long preparation intervals (often interpreted as evidence of carryover of response selection parameters from the previous trial which are immune to preparation). Although attentional selection of perceptual attributes is often considered to be part of task-set and is included in some models of task-set control, little research has investigated the dynamics of this component in detail. Over a series of seven experiments in which tasks were consistently mapped to screen locations, eye-tracking was used to systematically investigate task-relevant spatial selection of perceptual attributes during the preparation interval and early after stimulus onset. Experiment 1 revealed a switch-induced delay in appropriate attention orientation and a measure of ‘attentional inertia’ which could not be explained by task-independent re-orienting to locations or low-level oculomotor phenomena but were markers of task-relevant spatial selection. Experiment 2 provided a sensitive measure of both of these attentional handicaps and demonstrated that they both contribute to the switch cost (including its residual component). Although attentional inertia reduced with preparation, both handicaps were present at the longest preparation intervals. The constancy of the delay in attending to the relevant attribute reflects the effort to re-allocate attention, rather than peculiarities of spatial orienting when the cue and stimulus are presented near-simultaneously on trials with short cue-stimulus intervals. The presence of attentional inertia in blocks with long preparation intervals suggested some component of inertia immune to preparation (though see Experiments 5 and 6 below). Experiments 3 and 4 investigated the extent to which attentional selection can be decoupled from other task-set components. Cues which explicitly provided location information reduced (or eliminated) the attentional effects found in Experiment 2 indicating that attentional selection can be decoupled from other task-set components. However, Experiment 3 found that the ‘natural’ state is for attentional selection to be coupled at least to a degree (and accessed via) task-set. Experiment 5 combined eye-tracking with ERPs to investigate the relative order of attentional selection and reconfiguration of other task-set components. A well-documented ERP marker of task-set preparation always followed onset of the first fixation on the currently relevant stimulus element indicating that (at least some) task-set components are reconfigured in a serial order with spatial selection preceding other components (e.g., loading of S-R rules or other parameters into working memory). Experiments 6 and 7 investigated the nature of attentional inertia. In Experiment 6 participants were given ultimate control over the duration of the preparation interval which eliminated attentional inertia (at least as indexed by preferential fixation of the previously relevant element on switch trials). In Experiment 7 the stimulus comprised three items which were from perceptually distinct classes (digits, letters, objects) to investigate whether the presence of task-specific features would elicit extra attentional inertia and whether early spatial selection was effective enough to block the processing of task-irrelevant features once the stimulus was presented. Although there was some evidence that the previously relevant stimulus element ‘captured’ attention, this tendency was modest in the fixations and absent in performance measures (response congruence effects).

Even though there had been extensive research in Switching Mode Power Amplifier design their applications at industry level are quite limited. This is because a Fully-Integrated Switching Mode Power Amplifier using conventional active devices such as Bipolar Junction Transistors (BJT) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is challenging due to the inherent design challenges in the Switching Power Amplifier design. A Fully-Integrated Differential Class-F2,3 Power Amplifier design is explored for this Thesis research. This Power Amplifier has a maximum theoretical efficiency of 90.7% but this value is reduced because of the switching nature of the active device, parasitic effects associated with layout and the quality factor of the passive components used. Waveform shaping required for a Class-F Power Amplifier is done using the stray inductances within a non-ideal transformer instead of individual inductors. This techniques effective reduces the foot prints of two inductors for the tuning network design and make a Fully-Integrated solution more practical.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / An agile RF routing system has been developed which utilizes phasing techniques to direct signal power to any one of four orthogonally mounted antennae, or either set of two antennae mounted 180° apart on a launch vehicle. The system has been integrated into a telemetry transmitter and has shown superior performance to traditional methods of antennae switching. The unit is self-correcting to maintain maximum RF power at the desired antenna port(s) across a dynamic mission environment. Due to its low loss and high reliability, this method of antennae switching provides a robust RF link.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / Switches are a critical component in any networked FTI data acquisition system in order to allow the forwarding of data from the DAU to the target destination devices such as the network recorder, PCM gateways, or ground station. Commercial off the shelf switches cannot meet the harsh operating conditions of FTI. This paper describes a hardware implementation of a crossbar switching architecture that meets the reliability and performance requirements of FTI equipment. Moreover, by combining the crossbar architecture with filtering techniques, the switch can be configured to achieve sophisticated forwarding operations. By way of illustration, a Gigabit network tap application is used to demonstrate the fundamental concepts of switching, forwarding, crossbar architecture, and filtering.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy