Diss. Teknillinen korkeakoulu, 2006. / Myös verkkojulkaisuna.

No description available.

The thesis is concerned with static frequency changers, using solid-state switching devices, capable of directly (i.e. without an intermediate dc link) converting polyphase ac power of a given frequency to single or polyphase power of a chosen frequency. The thesis consists of two parts. The first part, comprising five chapters, is devoted to the study of ideal frequency changers operated from ac Sources having zero internal impedance. The second part, comprising two chapters, considers sources with finite internal impedances . Chapter 1 introduces the basic concepts of static frequency conversion, outlines the basic mathematical models representing static frequency changers and defines the output and input performance indicators. Chapter 2 presents a detailed investigation of that class of three-pulse frequency changers which will be studied in the thesis. A large portion of the chapter is devoted to the study of output waveform generation. The mathematical tools of the investigation, existence matrices and modulating functions, are introduced and defined. Analytical expressions for output waveforms corresponding to various practical modulating functions are derived and the related performance indicators are computed. Assuming a given desired output performance, criteria for an optimal modulating function are established. It is proved that only one system can generate an output waveform conforming to the postulated prerequisites. This system is termed the "Unrestricted" Frequency Changer. Expressions for the input current waves are also derived in this chapter and the corresponding input performance indicators are determined . The concept of a new frequency changer having the unique property of providing unity input power factor, regardless of the load, is introduced. This system is termed the "Unity Power Factor" Frequency Changer. In Chapter 3 the previous results are extended to systems having pulse numbers which are integral multiples of three. Chapter 4 is devoted to the study of output voltage control. Three basic methods are analysed and detailed quantitative data for output voltage and input current waves, and the related performance indicators, are presented in graphical form. In Chapter 5 special aspects of static frequency changing are investigated. It is shown that the input displacement factor is variable. The concept of the "Controlled Displacement Factor" Frequency Changer is introduced It is proven that the naturally commutated cycloconvertor is theoretically equivalent to a particular "Controlled Displacement Factor" Frequency Changer. Chapter 6 presents a detailed analysis of the "Unrestricted" Frequency Changer, operated from an ac source with finite internal impedance. The basic conditions are defined and an outline is given of the techniques of symmetrical components used for the analysis. The input current, input terminal voltage and output voltage waveforms are expressed in terms of the input terminal impedance and the positive, negative and zero sequence components of the output currents. The equivalent sequence impedances and the output impedance matrix are derived . The output voltage unbalance is computed under various conditions and presented in graphical form. The relationships between the amplitudes of the unwanted components in the output waveform and the resonant frequency of the input terminal circuit are also graphically presented. The results obtained are verified by computer simulations. In Chapter 7 a similar analysis of the "Unity Power Factor" Frequency Changer is carried out . The computed data are also graphically presented. Again, the results are verified by appropriate computer simulations.

Typescript, etc.

This paper investigates the voltage and phase dynamics of a low inertia inverter based Microgrid in islanded operation. In such case, the network is less robust to disturbances due to the lack of associated inertia within an inverter. In islanded operation, the assumption of a stiff grid is no longer valid due to the voltage and phase adjustment based on conventional droop control have a resulting effect on the power flows throughout the network where voltage and frequency stability of the network may be compromised. Other approaches neglect the network dynamics when there are power imbalances in the system and how each node is affected and if the resulting increase in demand can be met with the available power generation. This paper uses the fact that the phase dynamics of coupled inverters that employ droop control closely resemble the phase dynamics proposed by the Kuramoto model. Using this model allows the network stability to be analyzed under the true nonlinear operation. It Is observed through the strong coupling impedance of the secondary distribution transmission lines and the implementation of proportional droop control will provide an appropriate means for rural and suburban neighborhoods to operate independently, given the proportional droop gain is tuned appropriately.

Ethylene propylene rubber (EPR) cable has been extensively used for distribution of power. The insulation of cable should withstand electrical, thermal, mechanical, and chemical stresses during its operation. It is imperative to measure the data providing dielectric strength of EPR cable for these stresses. Significant improvements on the quality of insulation have been progressing for better performance of cable under these stresses. This study deals with ac voltage stress imposed on the cable. The electrical breakdown strength of 5kV EPR cable under ac voltage has been measured by constructing a suitable test set in Mississippi State University High Voltage Lab.

No description available.

No description available.

A system-on-chip (SoC) with near-threshold supply voltage (NTV) operation has received a significant amount of attention. Its high energy-efficiency supports a number of low-power emerging applications such as wireless sensor networks and Internet-of-Thing edge devices. Integrating various digital, analog, mixed-signal, and power sub-systems, such SoC designs need to employ tens of voltage domains to push the envelope of energy-efficiency, performance, and robustness. A low-drop-out (LDO) regulator is a key building block for creating voltage domains on a chip thanks to its high power density. In particular, its digital implementation, i.e., digital LDO, recently has emerged as a popular topology since it can support a wide range of input voltage from super-threshold to near-threshold voltage regimes, while conventional analog LDOs become less effective. One of the critical overheads in existing digital LDO designs is a requirement of off-chip output capacitor for stabilizing the output voltage, due to inadequate latency in active control paths. It is possible to employ higher clock frequency in a digital LDO; however such solutions inevitably increase power dissipation. This off-chip capacitor overhead can significantly increase chip pin count and printed circuit board (PCB) space, thus limiting the number of power domains that an SoC can have. This thesis presents my research on fully-integrated digital LDO designs based on event-driven control architecture. My research focuses on scaling down the output capacitor size to the integrable level and improving transient performance such as maximum voltage change and settling time. To shrink the output capacitor size, we introduced the event-driven control and the binary digital PI controller in our first event-driven LDO design. Thanks to the event-driven control, we achieved control loop latency reduction without compromising power consumption, leading to output capacitor size reduction. The first design shows 2.7x improvement over the previous digital LDO designs in Figure-of-Merit with a 400pF of output capacitor. To further reduce output capacitor size and support larger load current, we implemented the second event-driven digital LDO designs with fine-grained parallelism. The parallel structure of its PI controller reduces the latency of the proportional part, which mainly regulates output voltage, so it achieves better transient performance with reduced size of capacitor. Also, the parallel-shift-register-based integration part lowers computation and area overheads. The second design outperforms the state of the arts by over 17x in Figure-of-Merits with only a 100pF of output capacitor. In the last design, we introduced initialization and self-triggering control. The initialization estimates load current change in the beginning of regulation process and sets the controller output close to the desired value. This leads to substantial reduction of settling time. Also, thanks to self-triggering control, the hardware overhead from counting the event interval is removed without the first response time degradation, achieving high current density. The last design with a 100pF of output capacitor improves settling time and current density by 3.8x and 6.7x, respectively, while achieving comparable transient performance in terms of Figure-of-Merit.

Power quality is an issue of ever increasing importance, and with ever increasingcustomer expectations on such issues, the significance of supplying customers withhigh quality power can never be underestimated. One of the most important mattersthat define power of good quality is the voltage level each customer is supplied with.Most appliances are designed to operate satisfactorily only within a narrow range ofsupply voltages. Inappropriate supply voltages can not only result in poor performingappliances, it can also cause equipment damage, increase distribution losses anddecrease the revenue for the power supplier.The point that is electrically closest to the consumers, where the voltage is activelyregulated and monitored, is usually in a zone substation, where on load tap changerson the zone substation transformers ensure that the voltage in the distribution networkis kept within appropriate limits. The supply voltage is therefore directly reliant oncorrect operation and functionality of the on load tap changers and their controllingautomatic voltage regulators. The main objective that this thesis seeks to achieve is todetermine the most effective method of voltage control to be utilised with differenttypes of zone substations, primarily with respect to the algorithms utilised in theautomatic voltage regulator.Metering data from the distribution network has been utilised to examine the presentvoltage performance of the distribution network. Different reasons that can causevoltage fluctuations and unpredictable voltage performance are investigated anddiscussed. Voltage levels that are investigated are steady-state voltages, hencetransients, flicker, and sags and swells of short duration have not been taken intoconsideration. The present voltage levels are also examined in network models, withthe aim to investigate the impact of altered methods of voltage control in zonesubstations. The accuracy of the utilised network models is also investigated, bycomparing metering data to modelled voltage levels.This thesis is undertaken with the assistance of Ergon Energy Corporation Limited, acorporation owned and operated by the Queensland Government. Ergon Energy ownsand operates the subtransmission and distribution network in regional Queensland. Itis intended that this thesis will aid understanding of the voltage performance of thedistribution network, and that it will bring clarity to how the voltage in thedistribution network should be controlled in order to achieve optimum voltageperformance. / Uppsatsnivå: C