This thesis is concerned with the development of an a.c. drive suitable for directly driving the rollers of a glass conveyor at low speeds. A variable frequency three phase current source inverter has been developed, which operates on the slitwidth technique and uses power transistors as the switching elements. Open loop control of the machines was investigated initially but was rejected, due to the inadequate speed regulation obtained. Consequently, a digital speed and position measuring transducer was developed using an inexpensive, commercially available slotted disc. Strategies for controlling a.c. machines were then considered. This resulted in the development of a system which allowed a synchronous machine to be controlled with constant torque angle and an induction machine to be controlled with constant slip frequency. These control strategies allow maximum torque to be obtained from the machines over their full speed range. The synchronous machine becomes self starting and cannot lose synchronism even when large loads are applied. The control strategies developed also allow both the synchronous and induction machines' output speeds to be frequency locked to a demand input. A microprocessor interface and appropriate software was then developed to apply ramp demand speed profiles to the machine, simulating the speed profiles required by the conveyor drive. This was followed by an investigation into the speed matching of drives of similar and different types. The frequency locking nature of the control strategies allowed excellent speed matching between drives to be achieved. The same machine was used as both the synchronous and induction machine, enabling a comparison between the two different machine types to be drawn. Both machine types produced similar maximum torque outputs and speed responses. Consequently, the inexpensive and easier to control induction machine is suggested for use as the conveyor drive.

The work presented in this thesis is concerned with some aspects of power electronics largely related to the analysis and design of inverter-fed induction machines. Chapter 1 introduces the problems associated with the operation and analysis of inverter-fed induction machines, and state-of-the-art developments as highlighted in some recent publications. Chapter 2 is concerned with the development of induction machine frequency- and time-domain models and their solution methods. Methods of calculating model parameters are described. Simple and extended versions of the coupled circuit concept are developed for cage-rotor induction machines, and skin-effect is incorporated in these time domain mode is. Chapter 3 provides experimental verification for induction machine parameters and models described in Chapter 2. It also provides comparisons of measured and predicted results of dynamic tests for sinusoidal, quasi-square and sinusoidal PWM wave supply conditions. The measured and predicted results are shown to correlate reasonably well. Some specialised aspects of induction machines operation with non-sinu-soidal supplies such as peak transistor currents are also considered. Chapter 4 presents some design studies for the improvements of induction machine efficiency. Two machines are proposed; an improved 2-pole machine and an alternative 4-pole machine running at twice inverter frequency. For the same rotational speed and equal airgap magnetic and current loadings, the 4-pole version appears to have some advantage. Chapter 5 illustrates development of the time-domain induction machine models for use with the circuit analysis program ASTAP. Theoretical results of induction machine performance using ASTAP are shown to be the same as those obtained using the numerical step-by-step method, and correlate very well with experimental results. A special use of ASTAP was to model, as an equivalent circuit, the complete power-transistor inverter-induction machine system. Some examples of the interaction of the machine and inverter under fault conditions are presented.

Wearable robotics for assistance and rehabilitation are not yet considered commercially mainstream products, and as a result have not yet seen advanced controls systems and interfaces. Consequently, the available technology is mostly adapted from systems used in parallel technologies, rather than custom applications intended for human use. This study concerns itself with the design and development of a custom control system for a 2-degree of freedom powered upper extremity orthosis capable of driving elbow flexion/extension 135º and humeral rotation 95º . The orthosis has been evaluated for use as both a long-term assistive technology device for persons with disabilities, and as a short-term rehabilitative tool for persons recovering injury. The target demographics for such a device vary in age, cognitive ability and physical function, thus requiring several input parameters requiring consideration. This study includes a full evaluation of the potential users of the device, as well as parameter considerations that are required during the design phase. The final control system is capable of driving each DOF independently or simultaneously, for a more realistic and natural coupled-motion, with proportional control by pulse-width modulation. The dual-axis joystick interface wirelessly transmits to the 1.21 pound control pack which houses a custom microcontroller-driven PCB and 1800 milliamp-hour lithium-ion rechargeable battery capable of delivering 4 hours of running time. Upon integration with the 2 DOF orthosis device, a user may complete full range of motion with up to 5 pounds in their hand in less than 7 seconds, providing full functionality to complete acts of daily living, thus improving quality of life.

High speed photographic and time and space resolved spectroscopic investigations have been undertaken to quantify the processes governing arc thermal reignition phenomena. A fixed nozzle and electrode geometry was used with SF6 as the host gas. A sonic flow of gas at the nozzle throat was sustained using an upstream vessel pressure of 7.8 psig. A 35.5mF capacitor bank was used to supply electrical energy for reduced and full power arcing tests using different circuit configurations. Sophisticated optical diagnostic instrumentation has enabled photographic and spectroscopic investigations with high time and space resolution to be made during the current zero period of both the full and reduced power arcing cases. The results of above experimental investigations are of value in determining the thermal structure and the processes governing thermal reignition of the circuit breaker arc of the present investigation. In particular, temperature profiles derived from the above investigations have been used to quantify the important terms of the dynamic current zero energy balance. Experimental investigations have thus been performed during the critical current zero period of a full power circuit breaker arc. The significance of these results has been realised in evaluating the current zero temperature profiles and subsequently the energy conservation equation terms for severe circuit breaking conditions

Bipedal locomotion is a challenging control engineering problem due to the non-linear dynamics and postural instability of the bipedal form. In addition to these challenges, some dynamical effects such as the ground reaction force are difficult to model accurately in simulation. To this end, it is essential to develop physical hardware to validate walking control strategies and gait generation methods. This thesis develops an on-line walking control strategy for humanoid robots and the electromechanical design of a physical platform for experimental validation. The first part of the thesis presents the development of a 14 degrees-of-freedom (DOF) lower body humanoid robot. The initial electromechanical design of the proposed system is derived from dynamic modeling of a general multibody system. Kinematic trajectories for the lower body joints are extracted from motion captured human gait data to form the preliminary design specifications. The drivetrain components are selected by analyzing the mechanical power requirements, torque-speed profiles, efficiency and thermal characteristics of actuators. The supporting mechanical chassis and power transmission system are designed to raise the center-of-mass (to reduce the swinging inertia of each leg) while minimizing the overall weight of the system. Refining the design of a complex multibody robotic system like the biped is an iterative process. The mechanical model of the system is transferred from Computer-Aided-Design (CAD) software to a dynamic simulator for analysis and the design is revised to improve performance. This iterative approach is necessary as small changes in the mechanical model can have significant impact on the overall dynamics of the system as well as implications for control design. A streamlined prototyping toolchain is developed in this thesis to extract the relevant kinematic/dynamic parameters of a mechanical system in CAD and automatically generate the equivalent system in a dynamic simulator. This toolchain is used to revise the electromechanical design and generate forward dynamics simulations. The second portion of this thesis develops a novel walking control strategy for on-line gait synthesis for 3D bipedal robots based on Wight's Foot Placement Estimator (FPE) algorithm. This algorithm is used to determine the desired swing foot position on the ground to \emph{restore} balance for a 2D bipedal robot. The FPE algorithm is extended to the general 3D case by selecting a suitable plane in the desired direction of motion. Complete gait cycles are formed by combining a finite state machine with the 2D FPE solution along the selected plane. Gait initiation is accomplished by computing state-dependent task space trajectories on-line to produce a forward momentum along the selected plane. A whole-body motion control framework (Jacobian-based prioritized task space control scheme) tracks the task space trajectories and generates the appropriate joint level command for each state. The joint level commands are tracked by local high gain PD controllers. This framework produces the desired whole-body motion during each state while satisfying higher priority constraints. Gait termination is accomplished by controlling the swing foot position to track the FPE point on the ground along the selected plane. The proposed control strategy is verified in simulation and experiments. A parallel hardware-in-the-loop (HIL) testing environment is developed for the physical lower body humanoid robot. The motion control framework and joint dynamics used in the proposed walking control strategy are verified through HIL experiments.

This paper aims to design and simulate the surface-micromachining micro tunable capacitor for parameters optimization. This work also creates an equivalent circuit model of micro tunable capacitor and proceeds relative electromechanical analysis, including the distribution of field and charge, resonant frequency and pull-in voltage analysis. This micro tunable capacitor is constructed by one suspended top metal plate and two stationary bottom metal plates (one is signal electrode and the other one is bias electrode). By driving electrostatic force, the gap between top and bottom electrodes will be changed and results in a variation of capacitance. To increase the tuning range, the micro tunable capacitor with two different gap space will be presented in this research. High frequency analysis, equivalent circuit analysis and electromechanical dynamic analysis are using Ansoft HFSS, Agilent ADS and the IntelliSuite software respectively. Through these simulation and analysis, it is possible to obtain the optimized specification of micro tunable capacitor. The quality factor (Q) and the pull-in voltage extracted by simulation software well match to the measured results; thus, the function of the analysis method and equivalent model adopted in this thesis can be demonstrated.

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