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The thesis reviews methods for the analysis of thyristor bridge circuits using a digital computer. Tensor techniques based on the work of Kron, and which deal efficiently and effectively with the varying topology of the bridge circuits, are then used to analyse both the 6-pulse and the l2-pulse fully-controlled circuits which are the most common convertor configurations in hvdc transmission systems. The work then extends to a more complete representation of such a system, with the transmission line being represented by a series of lumped T-section elements. Harmonic filtering is included in the later stages of the work, with consideration given to the most significant harmonics produced in the A.C. side of the invertors. The elements of a typical hvdc transmission system have been assembled in the laboratory, and the model system has been used as a check on the accuracy of results provided by the computer programs. A study has been made of the most common faults which occur in an hvdc system, including misfiring, backfire, faults in the transmission line, and the effects of a strike by lightning. Close agreement between computed and experimental results has been obtained over a wide range of normal and fault conditions.

The dynamic ship positioning problem using Kalman filtering techniques is considered. The main components of the system are discussed. The ship dynamics, based on a linearised model, are represented by state equations. These equations involve low and high frequency subsystems. A simplified design procedure for the implementation of a Kalman filter is described based on the linearised equations of motion. The Kalman filter involves a model of the system and is therefore particularly appropriate for separating the low and high frequency motions of the vessel. The filtering problem is one of estimating the low-frequency motions of the vessel so that control can be applied. An optimal feedback control system simulation based on optimal stochastic control theory is used. The optimal control performance criterion weighting matrices Q, R were pre-selected and the optimal feedback gain matrix was computed. This control scheme involves the low-frequency part of the ship model. The Kalman filter has been simulated on a digital computer for different modelled operating conditions. The computer simulation results showing the behaviour and responses of the Kalman filter applied to the dynamic ship positioning problem were investigated. The system dynamics vary as the weather conditions vary and can be classified from a calm sea condition (Beaufort number 5) to the worst condition (Beaufort number 9). Different tests involving systems modelling and filter mismatching have been carried out. Another field in which the robustness of a Kalman filter has been assessed involved a test in which the system observation noise covariance was increased keeping the filter with the usual noise information. Saving in both computation and computer storage requirement were achieved using a form of semi-constant filter gain and reduced-order Kalman filter respectively. System non-linearities have been considered and a non-linear control algorithm was proposed and implemented using an extended Kalman filter. These non-linearities involve the thruster dynamics and the associated low-frequency part of the system model. All data that have been used within this work for system implementation were obtained from two different models ("Wimpey Sealab" and "Star Hercules" vessels). Our system has been employed by GEC Electrical Projects Limited, Rugby, for a new vessel ("Star Hercules") and this has been commissioned and is currently operating successfully off Brazil.

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This thesis is concerned with the analysis of reversing shaded pole motors. Chapter two develops a saturable finite-element analysis for induction machines which includes the effects of rotor harmonics and rotor skew. The analysis consists of two iterative schemes. Firstly, the Newton-Raphson algorithm is used to provide the solution of the nonlinear field problem in which the current sources and potentials are complex. A second minimisation process ensures that the terminal conditions are satisfied and provides, therefore, the output characteristics of the motor. Finally, some technical details concerning computer implementation of the method are discussed.In chapter three, the analysis is applied to a shaded-pole motor operating, in the first instance, with reduced rotor end-rings, in the second, with full end-rings. The predicted performance characteristics of the machine are compared with those determined experimentally, to indicate the validity of the method.Chapter four represents a discussion on some practical aspects of the application of the analysis.Chapter five provides some suggestions for further improvement of the technique and also indicates the scope for future work.

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