No description available.

No description available.

No description available.

Silicon micromachining techniques were developed and used to batch fabricate a new type of heavily doped p-type (or p") silicon etch stop structure on glass that could be suitable for implementation of a condenser microphone. This involved study, development and use of techniques such as mask design, lithography, oxidation, diffusion, thin film deposition, electrostatic bonding, many different etching techniques, freeze drying, packaging/interfacing and testing. The condenser microphone structure consisted of a thin conductive diaphragm suspended above a back plate electrode in order to form a capacitive device. A narrow gap between the two plates constituted the capacitor plate separation and the air occupying the gap was the dielectric material. Two versions of this condenser microphone structure were fabricated with over all dimensions of 2mm2 x 8-12 Jlm, air gap sizes of 0.5-1.5 Jlm and lum thick diaphragms. The first design utilised a square diaphragm with an area of lrnm" while the second incorporated a circular diaphragm with a diameter of lrnm. Fabrication of the back chambers was implemented with an innovative double thermal oxidation technique. Signals of up to ImVIPa were obtained in the audio range for one of the circular p+ silicon microphone structures, but the frequency response measured was not consistent with the desired frequency response for a condenser microphone. Thin film thicknesses, silicon etch rates and electrode metallisation conductivity were characterised using specially designed test structures and innovative electrical and opticalmeasurement techniques so that fabrication accuracy and reproducibility could be monitored. As a result of the investigations carried out to develop novel p" silicon microphone structures, this thesis also identifies important areas which warrant further research, and provides a foundation, in terms of theory and fabrication, for future development of more advanced and appropriate p + microstructures for application as condenser microphones.

The suitability of electromagnetic actuating devices for application to machines with ever more demanding response time specifications is discussed, with the proposal that piezoelectric actuator technology can produce practical devices with faster response times than solenoids, for example. This thesis discusses and validates the proposition that the performance of piezoelectric ceramic actuators makes them viable devices for inclusion in high-speed machine applications, where rapid clutching using two-state actuation is required. Further, techniques are devised and explored for the design and application of these devices using displacement amplifying structures, which lead to the utilisation of engineering methods of relatively low precision. This is highly advantageous as to date, the piezoelectric multilayer actuator has usually been associated with high precision engineering. Applications of piezoelectric ceramic technology are reviewed, and the mechanical and electrical properties of these materials are discussed. Literature covering applications of piezoelectric actuators in relation to clutches, motors and positioners is also reviewed. This data search revealed many devices or systems where the displacement amplification of piezoelectric actuators was exploited in some way, but failed to show any devices where the high efficiency of these amplifying structures was either primary or even necessarily achieved. Indeed, it was concluded that in the absence of such applications or methodologies, a fruitful area of research might be to explore these methodologies. This work is a core element of this thesis. Using two basic topologies, devices producing efficient transformation of high-force, small movement two-state actuation, to larger movement with lower force, have been designed (using flexural hinge methods), manufactured, tested and analyzed. Hydraulic transformers have been briefly investigated and ultimately rejected on the grounds of comparative complexity. For any displacement amplifying or transforming device, applications for these systems are widely varying, but criteria for advantageous employment of the piezoelectric approach, as opposed to electromagnetic, are established. Design techniques which are partially analytical and partially experiential are proposed, which in practice exhibit adeptness for producing well-optimised designs. These methods are incorporated into special purpose structure-designer computer programs. Several design examples are detailed, and their performance analyzed in comparison with the modelling techniques and design program predictions. The application of these displacement amplifiers is discussed by example, to two discrete motion machines, both of which have been designed specifically to demonstrate the possibilities of using piezoelectric technology to regulate discrete motion drives. It is shown that the speed of response of the devices is such, that the concept of zero-velocity clutching with the intention of minimising wear, is feasible.

Most existing synchronous machine stability studies are based on the assumption that the machine is operating on an infinite busbar of constant voltage and frequency. The present study however, is concerned Mainly with the dynamic stability of the type of gas-turbine generating unit commonly used in remote sites, such as off-shore oil rigs and desert areas, where the' grid is far from stiff and is liable to become unstable in the event of a severe system disturbance. Because of this, there is a pressing need for an accurate representation of the system, to enable investigations to be made into problems concerned with the system response and to consider any improvements that may be effected in the associated control scheme. The initial stage of the investigation involves the development of digital models for a synchronous machine, using both direct-phase co-ordinates and a stationary 2-axis representation. Symmetrical and unsymmetrical faults at the generator terminals are simulated and comparisons with test results are made. Despite being more restricted in its range of application than the direct-phase representation, the 2-axis model is used throughout the remainder of the investigations described in the thesis, Mainly because of its computational convenience. The increasing use of large induction motor drives makes it necessary to study their effect on system stability, especially in the case of small gas-turbine power systems. Various types of switching transients on both small and large squirrel-cage induction motors are therefore studied. The successful development of the synchronous and induction machine models is followed by a fault simulation of a composite system containing both types of machines. The machine investigation is followed by the simulation of a conventional steam turbo-alternator unit operating on an infinite grid system. Various types of system disturbances are simulated and the effect of generator saturation on the system response is considered. Following this study, a mathematical model of a gas-turbine generating unit is developed, with emphasis given to operation in an isolated grid situation. To validate this model, correlations between predicted and test results on a typical installation are presented.

No description available.

This thesis is concerned with the use of all-electric systems for the closed loop position control of mechanical (valve) actuators. It embraces a wide range of topics including * the use of 3-phase induction motors and their speed/torque control using Pulse Width Modulation techniques * implementation of both analogue and digital (PID) controllers * Using computer simulation methods for the development of digital control algorithms and tuning techniques * the use of Computer Assisted Tuning methods for tuning up the position control loop. The major hardware activities described here are concerned with the design, development and construction of a 3-phase 115 volt inverter unit, an analogue controller, and interfaces to a single board microcomputer (SBC). The construction and test of the SBC is also described in the text. Details of the use of an analog controller to study and determine the transfer function of the inverter/actuator system is presented. Digital implementation of PID control (for actuator's position) by microcomputer is also described, together with the theoretical development of the control algorithm. Software activities consist of two major parts, plant simulation and software development for the microprocessor (embedded) controller. The derivation of a plant model from the results of on-line testing is given; from this a computer simulation is developed to study the effects of controller tuning parameters on the loop performance. Software development for the embedded controller covers Man-Machine Interfacing, tuning, and control functions. A new approach to the tuning of control systems is developed here, that of computer assisted tuning. Test results are given showing the effectiveness of CAT techniques for the tuning of the actuator position control loop; these tests also demonstrate the performance achieved using a digital PID controller. It is concluded that, provided plant parameters can be established, Computer Aided Tuning enables plant tuning to be carried out to meet specific performance targets (e.g. rise time, overshoot) set by the plant operator. Furthermore this can be carried out by a relatively unskilled operator.

No description available.

The main tasks of power electronics in power transmission and distribution systems is to process and control the flow of electric energy by supplying voltages and currents in a form that is suitable for user loads. In recent years, the field of power electronics has experienced a large growth. Electric utilities expected that by the year 2000 over half of the electrical load may be supplied through power electronic systems. In order to take advantage of this highly developed technology a number of detailed modelling procedures and simulation facilities are needed. The work in this thesis is concentrated on modelling, control and design of various power electronic based models for use within transmission and distribution systems. The overall objective is to provide effective methods and tools for assessing the impact of the latest technology based on power electronic devices in the reinforcement of power system networks. The thesis clarifies modelling and control of various variable speed drive models, such as the six-step, PWM and vector control and gives a detailed account of the systematic derivation of equations that are necessary for the dynamic and transient analysis of a multi-machine multi-node power system with associated adjustable speed drives. Simulation of Flexible AC Transmission Systems (FACTS) models has also been developed for a number of devices including: the SVC (Static Var Compensator), the STATCON (Static Condenser) and the UPFC (Unified Power Flow Controller). The methodologies for development of the models are described and a number of case studies are included in order to give a broad overview of the applications and to prove the usefulness of the results. The last part of the thesis includes simulation, control and design of Custom Power Devices for use within distribution system architectures. It starts with a complete control system strategy for the modelling of a solid-state switch and continues with the modelling of a Dynamic Voltage Restorer model, using an innovative control system. The creation of the power electronics models library provides several opportunities for future developments, which are discussed in the concluding sections of the thesis.