The inherent advantages of the induction motor in variable speed drive applications can now be realised in a cost-effective manner as a result of recent advances in power electronics and microelectronics. This thesis is devoted to the advancement of the use of induction motors in variable speed applications, and describes the analysis, simulation and implementation of a variable speed induction motor drive. The state-space method lends itself as an ideal approach both for digital computer modelling and design of modem controller and was therefore adopted for the analysis and simulation of the drive system. The simulation was developed by means of a low cost personal computer package called MATLAB that has been designed to facilitate matrix operations. The use of such a specialized software package provided a 'user-friendly' operating environment with error messages identifying problem areas during program development. The resulted computer model of the drive system offers high flexibility and modularity and can be readily incorporated into further analysis and real-time controller design. Experimental results of the drive demonstrated good correlation with the model at both steady and transient states and the validity of the model is therefore confirmed. The experimental drive system was developed by means of transputers and its associated programming language occam. It was a flexible and comprehensive drive system comprising: (i) an on-line user interactive environment facilitated by the Transputer Development System; (ii) a 3-phase inverter bridge as the power conditioning unit; and (iii) a signal processing unit by means of a multi-transputer network system. The adoption of the transputer and occam enabled parallel processing to be achieved cost effectively in the drive system. The specifications of the drive system developed included on-line speed change, dynamic braking and programmable soft-start. Vector-control was also incorporated for good dynamic response. Experimental results of the specified functions of the drive are provided to confirm the proposed specifications of the drive. Further research areas on the present system are proposed, so that a viable industrial implementation may be contemplated.

This thesis is mainly devoted to the investigation of speed control methods of three phase, cage rotor induction motors with particular emphasis being given to vector control and direct torque control techniques. Modern control strategies such as vector control and direct torque control are investigated as well as the conventional methods such as open loop (constant V/f) operation. A number of different pulse width modulation (p.w.m.) waveform generation strategies are simulated and discussed and their application to the above speed control systems fully investigated. A 3kW, three phase induction motor drive has been designed and experimental data obtained from it in order to verify the results achieved by simulation. It is shown that direct torque control achieves decoupling of the motor torque and the motor flux without the use of a co-ordinate transform. A variation of the direct torque control algorithm has also been developed and implemented. It is shown, that by using different switching tables for the selection of voltage vectors, the performance of direct torque control can be further improved. Further insight into the nature of direct torque control has been gained from the study of the effect of the application of inverter switch settings, or the application of corresponding voltage vectors, on the motor flux and torque. It has been found that the range of torque variation of the motor drive system depends strongly on both the motor load torque and the motor speed. The results of the work reported indicate that the range of torque variation for a drive system which strongly depends on motor load torque and motor speed is considerably reduced by the novel direct torque control system resulting from the research. The control algorithms have been implemented on 32 bit micro processors which facilitate the use of parallelism in both the hardware and the software design. The resulting system is capable of controlling a three phase induction motor with variable voltage and variable frequency with control strategies such as six step operation, symmetric and asymmetric regular and natural sampled p.w.m. waveforms, sigma delta modulation methods, space vector modulation techniques, flux vector control and direct torque control.

A general model is developed describing the performance of positive displacement flowmeters. This model allows to predict the performance of any positive displacement meter if 8 coefficients describing the meter design are known. The logic is that a flowmeter performs at a defined pressure loss for a given speed. This pressure loss times flowrate is then energy balanced against all internal loses. Pressure loss and speed are the reasons for leakage. Rotational speed times the theoretical swept volume is the theoretical flowrate and this flowrate, when combined with leakage flow can be used to calculate the effective or true flowrate. The 8 coefficients describe the influence of the design of a meter on laminar leakage flow, turbulent leakage flow, speed related leakage flow, viscous friction, mechanical friction, constant friction, impulse energy losses and ball bearing friction, respectively. This model was applied to a twin-screw type displacement flowmeter which uses two helical rotors which form separate pockets and allow the flow-rate of the fluid to be measured. Based on the general prediction model it was found that for this type of flowmeter mainly two coefficients are the reasons for deviation from linearity. These are the constant friction power losses KC produced by mechanical sliding and the turbulent leakage flow losses Kt ur . When the values of KC and Ktur are zero then the error against flowrate is constant. A complete model of an actual twin-screw type displacement flowmeter was realised, determining all 8 loss coefficients. In order to do so, tests with a twin-screw type displacement flowmeter have been carried out on the overall meter performance, leakage flow losses and bearing friction. The theoretical work includes the determination of all 8 coefficients based on a study of the rotor geometry of the meter and a calculation of the fluid forces and torques acting on the rotors. The theoretical results of the final performance prediction model were compared with experimental results and show a good accordance. It was found that one optimal circumference clearance value can be determined for every different fluid property and flowrate. The flowmeter performance may be increased by minimising mechanical sliding and turbulent leakage flow losses.

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I have used practice as method to investigate the creative potential of portable projectors, and theoretical approaches to reflect on: 1. the perception of the environment and its textures, 2. the sense of place-making and being while in motion, 3. the portability and collective mediation of the environment, and 4. the collaborative process of participation. These four themes emerged from the four video walks I developed during the research: The Surface Inside (2011), I-Walk (2012), Walk-itch (2013), and (wh)ere land (2014). To delve into the philosophical nuances and practical outcomes, I have paired the four video walks with the four themes. This research approach resembles the design process, where practice develops in the action of reflection (Schon, 1983). The thesis and portfolio are the result of an iterative practice-reflection process which is based on the thread metaphor. The experience of being and walking in the environment is proprioceptive (J. J. Gibson, 1986) and can only be partially conveyed through audiovisual records. People experience the complex texture of the environment in motion (i.e. accretion of surfaces). While moving, they thread their own paths into the environment (Ingold, 2007) and establish links with the environment, technology and others. As they move, people experience the texturality of the surfaces they encounter. Video records captured with visual apparatuses (Flusser, 2000) are a fraction of the points of observation a person may have adopted while walking in and experiencing the environment. These records are likely to be created with PEDs, shared in digital environments and accessed on digital screens. When these records are experienced on digital screens, the texture of the environment is reduced to a flat surface. PEDs, with their digital screens, are carried around everyday and enable people to communicate with others, to collect and share audiovisual material, and to experience hybrid environments where tangible and digital realms converge (Coyne, 2010). Audiovisuals can be accessed anywhere and are no longer dependent on the architectures that hosted them in the past. Yet, PEDs may also isolate people from their immediate surroundings and favour introspective engagement with audiovisual content, digital others and digital environments (Turkle, 2011). The size of PEDs limits the number of people that can engage with the content at only one time. Pocketsize devices tend to be used individually, and their audiovisual content played through digital screens and headphones which foster cocoon-like engagement. Through the four video walks, I investigate how portable projectors may be used to challenge this inward looking mode of experiencing audiovisuals on flat digital screens, and to devise participatory events where people thread their paths in the environment, and project and engage with audiovisuals together. In the video walks, I invite people to move with projections and explore mediated public environments. Instead of sitting in front of fixed projections or looking at digital screens, people experience and share visuals while walking and projecting them in the environment. Portable projectors are starting to be embedded in mobile phones and other portable electronic devices (PEDs), and this presents new challenges and opportunities to creative practitioners. Thus, I study the affordances of portable projectors and develop artworks where participants walk, project visuals and explore textures in the environment collectively.

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This thesis describes two different techniques for efficient control of slip energy in a slip-ring induction machine. The static Kramer system merely recovers slip power and returns it to the a.c. supply. As a result only sub-synchronous motoring or super-synchronous generating is possible. In the static Scherbius system, however, the slip power can be controlled both into and out of the secondary circuit. This allows the machine to operate as a motor and generator at both sub- and super-synchronous speeds. For wide speed range operation a current source inverter was used as this can inherently provide reversal of power flow. The operating requirements for the current source inverter operating in the secondary circuit of an induction machine have been determined. These considerations show that the current source inverter control signal must be synchronised to the secondary e.m.f. of the machine. The machine can then operate in a stable manner over a very wide speed range. The conventional analysis of the current source inverter has been developed to include the effect of the secondary slip e.m.f. which is shown to have a major effect on the commutation behaviour of the inverter. The action of the commutation circuit is affected by the phase angle between the secondary current and the slip e.m.f. This angle can be controlled electronically and the effect of this has been predicted and observed. A detailed study of the Kramer system has included analysis of the d.c. link current waveform including Fourier harmonic prediction in terms of the circuit parameters and the operating slip. The operation of the Kramer and Scherbius systems has been studied for both motoring and generating modes of the induction machine and their relative merits have been compared. In particular the novel idea of using the Scherbius system for variable speed wind energy recovery has been considered and reported in a published paper. Finally suggestions have been made for further work particularly for application to wind energy recovery.