The architecture and control strategies of computing environments able to provide decision-support, together with software selection, are described. In the area of engineering design, the need to provide both a knowledge base and a database, and direct communication between the two, is recognised as an essential pre-requisite to the successful development of decision-support software. The role of expert systems in developing and maintaining the knowledge base, and factors influencing the choice of expert system, are discussed. An integrated software network in which to build computer-aided design tools is described and fully realised. The network is based on Crystal, a commercially-available expert system shell, and Lotus 123, which provides data support and management. The expert system can interrogate directly the database via a custom interface while a second interface allows the user direct access. Library facilities are also available to permit the filing of designs produced by the system. Assessment of the interface is achieved by comparing it with a commercially-available database interface. Finally, using the software network developed, two rule-based expert decision-support systems for the design of power transformers and inductors carrying direct current, operating at frequencies up to 100 kHz, are developed. The relevant component-design methodology, and the scope and operation of the design software, are explained.

The cycloconverter as a direct frequency converter without a d.c. link is well known as a power amplifier in low speed a.c. drives. If continuous circulating current operation can be maintained, reversible energy flow and regenerative braking can be achieved in an induction motor drive without a change in the gate pulse sequence. Continuous circulating current operation also reduces the output harmonic content of the cycloconverter and increases the speed range of the drive. This dissertation describes the use of an induction motor stator as an inter-group reactor maintaining continuous circulating current in the cycloconverter. The same stator winding sets up the conventional rotating air gap-flux and the reactor machine has standard torque-speed characteristics. In the multi-machine drive designed and constructed in this work, one machine requires a special stator winding. Conventional squirrel-cage machines can then be added for tandem speed control and the utilisation of copper improved. Closed-loop speed control and air gap flux control are incorporated on the reactor machine. The standard induction motors added in addition to the reactor machine are shown to be essentially operating under open-loop conditions but a "hard supply" is maintained by closed-loop control.

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A converter is proposed which is based on <i>parallel-resonant</i> technology, incorporating a capacitive filter. The convertor complies with a high-power, low voltage load specification, and is required to operate with a fixed switching frequency. The topology uses a combination of resonant tanks, and a clamped voltage technique, to maintain the advantages of more standard square-wave converters, whilst exploiting the desirable features of resonant conversion. The purpose of the proposed converter is threefold: 1. -to reduce the converter size by operating without an output filter choke; 2. -to reduce component stresses by clamping internal voltages, and so limiting voltage and current peaks; 3. -to reduce switching losses by limiting the volt-current product during the switching transient. The shape of the internal waveforms define the power transferred and are determined by values of resonant components positioned within a standard bridge circuit. As a result of these resonant components the converter efficiency at full load approaches 93%, and the characteristics of the EMI spectrum are favourable. Low power resonant techniques are well understood, however, operation at higher output powers requires careful construction techniques and consideration of various engineering compromises. An explanation of these is presented and justification for their choice is discussed. Three prototype converters are built and tested, and problems encountered during their development are highlighted. Results of two simulation techniques correlate well with the observed results, and a numerical modelling technique is developed as a design aid. As a result of the work at low output voltages it is shown that the converter is better suited to operation as the front-end of a <i>distributed power</i> power system, converting voltage from 270 V to 48 V.

The thesis begins by describing the experimental determination of the hydrodynamic coefficients of two test models; an Edinburgh duck and a semi-submerged, horizontal right circular cylinder. The impedance and wave force coefficient matrices are measured for these two models, and in the case of the cylinder are checked against exact analytical results. The radiation and scattering pattern matrices are also measured. Synthesis of optimal (complex-conjugate) control is achieved for the cylinder in one and two degrees-of-freedom, and for the duck in one, two and three degrees-of-freedom. Synthesis is defined as the pre-computation of drive signals to simulate control using prior knowledge of the incident wave and the device hydrodynamics. The concept of complex-conjugate control with amplitude constraint is introduced, and synthesised for the cylinder. This is compared with the results for control without constraint. A discrepancy is found between efficiency calculated at the duck axis and efficiency calculated from the wave amplitudes. This is traced to physical losses in the system. These losses are due to the scale of the test models, and may not be present at full-scale. Having accounted for these losses, the results for the synthesis runs agree well with predictions based on the model coefficients and hydrodynamics. This suggests that the linear model can be used to predict the effect of changes in shape on the forces, displacements and velocities of an optimally controlled device. Full-scale performance is predicted for a 10m diameter duck in unidirectional mixed seas. Two pseudo-optimal control strategies are defined which are based on the impedance measurements. Four different physical configurations are considered. It is found that changing the configuration will roughly determine the effectiveness of the device, and choosing the correct control strategy for that configuration fine tunes performance. The two pseudo-optimal strategies are simple to implement, but are nearly as effective as complex-conjugate control.

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The mathematical analysis of static electromagnetic devices such as transformers, voltage stabilisers, etc., is complicated by the nonlinear, multi-valued relationship between flux density and field strength in the ferromagnetic core. Initially, vdrious methods of analysis are discussed, with emphasis on the importance of incorporating a means of adequately representing the influence of the magnetisation characteristic, and the physical structure of the core. The single-valued exponential series representation of the flux density / field strength relationship which was developed in an earlier investigation into transient currents in transformers due to switching of the supply, is modified and extended to cater for the non-unique nature of the B/H relationship. This new representation is then incorporated into the mathematical models of single-phase and three-limb, three-phase transformers, which are utilised in the study of residual core conditions in these devices. The ways in which residual conditions are established, and the influence of such factors as load and primary circuit configuration are examined, both experimentally and theoretically, and the results used in devising a simple graphical technique for estimating the magnitude and polarity of remanent flux and m. m. f. A study is also made of the effect of residual conditions on the transient currents which occur on reapplication of the supply. An example of the extension of the range of application of the transformer model is demonstrated in a brief study of ferroresonance in single- and three-phase systems. The processes involved in the initiation of a stable resonant condition are considered, and a comparison of computed and recorded steady-state current, voltage and flax density waveforms is made. Finally, general conclusions are drawn, and some suggestions are made as to how the transformer model might be improved, together with examples of other areas of interest in which the analytical techniques developed for the transformer may be applied.

No description available.

No description available.

No description available.