126 research outputs found
Control aspects of synchronous machines in power systems applications
No full textDevelopments in control design methods for power systems have continually been made during the last ten years, and the present thesis seeks to make its contribution to this pattern of work. In so doing, it develops electrical machine mathematical models on which the subsequent designs are based. The formulations relate specifically to those from which computer programs may be readily developed and particular importance has been attached to the systematic marshalling of plant and network equations for the subsequent and efficient solution by computer methods. Methods of model reduction and state transformation are described and these are used to manipulate the system models into the form appropriate to the regulator design algorithm. The regulator-design algorithm is described in which a systematic numerical technique is used to predetermine the performance criterionJ = C(xtQx + u )dt. The constraints imposed on the system response by the design specification are associated with the movement of the eigenvalue locations to give actual values for the elements of Q. The algorithm described, for the linear single-input system, is based on the sensitivity of the elements of Q to shifts in the eigenvalue locations to produce a performance criterion for improved system stability. The resulting algorithm is applied to the design of an a.c. turbo generator excitation control and is shown to give a system that has advantages over a controller designed using conventional techniques. The thesis is supported by four published papers in which the author of the present thesis is joint author. One reports on the development of the design algorithm and the others deal with computational aspects of control design and its-application to power systems; computer listings are presented in the papers. In addition, the author's work has been presented at two conferences for which published records exist.</p
Non-Hydride Group V Sources for Omvpe
No full textAbstractA major limitation to the continuing development of organometallic vapor phase epitaxy (OMVPE) for the growth of II/V semiconductor materials is the hazard posed by the hydride sources, AsH3 and PH3, which are virtually universally used, in high pressure cylinders, as the group V source materials for the growth of the highest quality materials. The set of stringent requirements for an organometallic group V source, which includes a high vapor pressure (>50 Torr) and freedom from undesirable carbon contamination, eliminates most commonly available non-hydride group V sources. Recent research on newly developed sources has shown considerable promise. The entire area of group V sources, including the elemental sources, for OMVPE growth of II/V materials will be reviewed. The sources with no hydrogen atoms attached to the group V atom, the elemental, trimethyl-V, and triethyl-V, sources all appear to give unacceptably high carbon incorporation, as does dimethylarsine. Diethylarsine, which has one H attached to the As, produces high quality GaAs. Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) appear to be promising source materials. TBP has a very low toxicity, a vapor pressure ideal for OMVPE growth, and the pyrolysis occurs at lower temperatures than for PH3. No carbon contamination can be attributed to the TBP. Control of the As/P ratio in OMVPE grown GaAsP is much improved for TBP as compared with PH3 due to the more rapid pyrolysis. TBAs has similar attributes including a favorable vapor pressure and lower pyrolysis temperature than AsH3. The substitution of TBAs for AsH3 results in no observable increase in carbon in the epitaxial GaAs. Phenylarsine is a similar source, with a phenyl radical substituted for a single H atom on AsH3. The vapor pressure of phenylarsine is quite low and the pyrolysis temperature is expected to be some what lower than that for AsH3. Limited results indicate that carbon incorporation in GaAs is acceptable only when TEGa is the group V source.</jats:p
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