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In the time of rapid growth, there is an increase of demand for a reliable and stable power supply. Due to this, utility companies are forced to operate their power system nearer to its maximum capabilities since system expansion may be a costly option. As a result, the power system will be at risk to voltage collapse. Voltage collapse phenomenon is known to be complex and localised in nature but with a widespread effect. The ultimate effect of voltage collapse would be total system collapse which would incur high losses to utility companies. This thesis discusses the voltage collapse phenomenon, its causes, effects and its analytical tools. Looking into its analytical tools, it is observed that it relies upon system equations and models. Published results from these techniques are accurate but may require long computation time for a big and complex system. As a possible solution, this thesis looks into combining machine learning techniques with fuzzy logic in creating a fuzzy decision tree (FDT) tool for voltage collapse analysis. The algorithm utilises static power flow solution as data sets in partitioning the power system into strong and weak areas. From several test results and algorithm development, this research concludes with a possible voltage collapse analytical tool using a hybrid FDT approach based upon multiple attribute partitioning. This thesis concludes with discussions on test results highlighting the FDT performance and ends with a discussion on possible future development on the FDT in creating a more complete tool for voltage collapse analysis.

Almost all mobile devices nowadays are enabled with IEEE 802.11 Wireless Local Area Network (WLAN), which is also known as WiFi. One of the most important considerations when choosing an 802.11 device is its battery life. To allow mobile devices to conserve energy, IEEE 802.11 standard specifies a power save mode (PSM). A station/device in PSM, i.e. PSM-STA, will wake up at a predefined listen interval (LI) to receive frames buffered at the access point (AP) while it is sleeping. In this thesis, we focus on enhancing the basic PSM mechanisms in the standard. In particular, two new power saving schemes, delayed wakeup and dynamic listen interval, are proposed. Unlike many existing schemes, our schemes are fully standard compliant, and legacy devices can support them via a firmware upgrade. In our delayed wakeup (DW) scheme, we assume that all PSM-STAs use the same listen interval of one. That is all PSM-STAs wake up at every beacon frame broadcast, or beacon interval (BI). From the traffic indication map (TIM) in the beacon, a PSMSTA learns if there are any buffered frames at AP. If yes, it will stay awake until all buffered frames are retrieved. This creates a rush hour on the shared channel right after a beacon broadcast. If the channel is congested, having all PSM-STAs staying awake will not improve the system delay performance but consume more power. Aiming at saving battery power while not affecting delay-throughput performance, our DWscheme divides a BI into n sub-BIs. Then based on the amount of buffered frames, AP identifies and instructs “excess” stations to sleep immediately and wake up at a non-congested sub-BI later on. “Instructions” are judiciously encoded inside the modified TIM. We show that our modifications are fully transparent to legacy stations. In order to more accurately identify the amount of excess stations, an analytical model is also constructed to derive the saturated throughput of a WLAN consisting of PSM-STAs. In our dynamic listen interval (DLI) scheme, we aim at minimizing unnecessary wakeups while without sacrificing delay performance. Note that when a PSM-STA wakes up to receive a beacon and found that there are no buffered frames at AP, the PSM-STA experiences an unnecessary wakeup. Accordingly, the associated mode transition energy is wasted. According to the IEEE 802.11 standard, each STA chooses its fixed LI at the time of association. If LI=1, a STA wakes up at every beacon interval (as that in DW scheme). Although packet delay is minimized in this case, the chance of unnecessary wakeups can be high. On the other hand, a larger LI can reduce the chance of unnecessary wakeups but the delay will be increased. Our DLI scheme addresses this problem by dynamically adjusting the LI value according to traffic load. Specifically, each unnecessary wakeup will increase a STA’s LI by one, and a necessary wakeup will immediately reset LI to one. Simulations show that when traffic is bursty, mode transition energy consumption can be reduced without noticeable degradation in delay performance. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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Bibliography: pages 168-174. / The Emergency Electric Power Supply Systems at Pressurized Water Reactor Nuclear Power Plants are reviewed, problem areas are identified, and recommendations are made for existing and future Nuclear Power Plants. A simplified introduction to a typical Pressurized Water Nuclear Reactor is given and the problems associated with the commercial use of nuclear power are discussed. An overview of the Nuclear industry's solutions is presented and covers the Reliability of equipment and the American Regulatory requirements. The alternating and direct current power supply systems are examined in terms of plant operational state and equipment type (Diesel generators, Grid network, Lead-acid batteries, Battery chargers, Inverters, and Power Distribution networks). The trends in the design of Emergency Electric Power supply systems at Nuclear Power Plants are presented. The loss of all alternating current power, known as Station Blackout, is discussed and the American and European response to this. problem is presented. Problems experienced in the direct current systems are discussed and solutions are presented. The experience at Koeberg Nuclear Power station with Lead-acid batteries is included in the discussion. The thesis concludes with recommendations for designers and operators of the Electric Power Supply Systems at Nuclear Power Stations.

ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / During the program researching on airborne telemetering transmitter of a certain remote telemetry system, small size and a variety of voltage on board are design difficulties. Due to the above important factors, the performance of power supply makes a big affect to the parameters of BPSK modulated signal, especially the EVM (Error Vector Magnitude). The author analyzes the cause of power supply noise and puts forward some suggestions to damp the noise. With these methods, the EVM of modulated signal is improved. Finally, we can conclude the related principles about the suppression of power supply noise.

This thesis proposes an uninterruptible power supply, UPS for high availability servers with fuel cells as its back up energy source. The system comprises a DC to DC converter designed to accommodate the fuel cellâ s wide output voltage range. A server power supply is specified, designed and simulated for use with this UPS. The UPS interfaces internal to the server power supply, instead of providing standard AC power. This topology affords enhanced protection from faults and increases overall efficiency of the system by removing power conversions. The UPS is simulated with the designed power supply to demonstrate its effectiveness.

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It is estimated that 1.6 billion people today live without access to electricity. Most of these people live in remote rural areas in developing countries. One economic solution to this problem is the deployment of small domestic photovoltaic (PV) systems called solar home systems (SHS). In order to improve the performance and reduce the life cycle cost of these systems, accurate monitoring data of real SHSs is required. To this end, two SHSs typical of those found in the field were designed and installed, one in a rural area of the Eastern Cape of South Africa and the other in the laboratory. Monitoring systems were designed to record energy ows in the system and important environmental parameters. A novel technique was developed to correct for measurement errors occurring during the utilization of pulse width modulation charge control techniques. These errors were found to be as large as 47.6 percent. Simulations show that correction techniques produce measurement errors that are up to 20 times smaller than uncorrected values, depending upon the operating conditions. As a tool to aid in the analysis of monitoring data, a PV performance model was developed. The model, used to predict the maximum power point (MPP) power of a PV array, was able to predict MPP energy production to within 0.2 percent over the course of three days. Monitoring data from the laboratory system shows that the largest sources of energy loss are charge control, module under performance relative to manufacturer specifications and operation of the PV array away from MPP. These accounted for losses of approximately 18-27 percent, 15 percent and 8-11 percent of rated PV energy under standard test conditions, respectively. Energy consumed by loads on the systems was less than 50 percent of rated PV energy for both the remote and laboratory systems. Performance ratios (PR) for the laboratory system ranged from 0.38 to 0.49 for the three monitoring periods. The remote system produced a PR of 0.46. In both systems the PV arrays appear to have been oversized. This was due to overestimation of the energy requirements of the loads on the systems. In the laboratory system, the loads consisting of three compact fluorescent lamps and one incandescent lamp, were used to simulate a typical SHS load pro le and collectively consumed only 85 percent of their rated power. The 8 predicted load profile for the remote system proved to be signi cantly overestimated. The results of the monitoring project demonstrate the importance of acquiring an accurate estimation of the energy demand from loads on the system. Overestimations result in over-sized arrays and energy lost to charge control while under-sized systems risk damaging system batteries and load shedding. Significant under-performance of the PV module used in the laboratory system, underlines the importance of measuring module IV curves and verifying manufacturer specifications before system deployment. It was also found that signi cant PV array performance gains could be obtained by the use of maximum power point tracking charge controllers. Increased PV array performance leads to smaller arrays and reduced system cost.

In the fall of 1986 the Galactic Radio Patrol began total power observations with the new seven feed system on the 91 metre radio telescope at Green Bank, W. Virginia. The data were taken at a wavelength of 6 cm, with Nyquist sampling intervals, in the region of the galactic plane corresponding to the coordinate ranges of 1=25 to 225 degrees, and |b| ≤ 5.5 degrees. Existing surveys at 6 cm provide a coverage of the galactic plane over the galactic longitude range 190 to 60 (through 360) degrees. This work is largely complementary in that its coverage is over the galactic longitude range of 25 to 225 degrees. A mapping technique has been developed to fully exploit this data. This technique will allow the mapping of the galactic region with a sensitivity several times that of previously available surveys and with reliable structural information on angular scales of ≤ 1 degree. The above technique was applied to a test region centred upon the supernova remnant G109.1-1.0. The resultant maps were compared to a previously published map of this supernova remnant in order to determine the strengths and reliability of the present reduction method. / Science, Faculty of / Physics and Astronomy, Department of / Graduate