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This work set out to investigate the adaptation, operating modes and integration of the reverse blocking GTO within multi-MW brushless dc machines with the specific intention to maximise torque density and power density of variable speed drives without taking undue risks. A major aspect of this work was to develop an understanding of the roles played by power electronics and machine topology in a novel commutation process that allowed the elapsed time of commutation events to be minimised whilst the timing of commutation events, relative to rotor position, was freely adjustable. This elapsed time had a direct bearing upon the highest order of current harmonics that could be exploited whilst the adjustable timing of commutation events allowed load angle to be optimised. In order to maximise power density it was necessary to fully integrate the static power electronic commutator within the machine. Standard reverse blocking GTO wafers were selected as the preferred switching device because they were expected to provide adequate performance at the low switching frequencies that would be used in such machines, and they presented a relatively low commercial risk. Stacks of unhoused pressure contact GTO devices and heatsinks were immersed in the same force-circulated liquid dielectric coolant that was used by the machine. As such, it was found possible to house the converter within the confines of a normal size motor terminal box and to allow the use of a common cooling system. The GTOs were operated in unity gain turn off mode and a remotely located gate drive was employed so as to permit unimpeded flow of the liquid dielectric coolant. As such it was necessary to understand the commutation implications of gate drive interconnections. The effects of rotor geometry and dampers upon commutation and harmonic exploitation were taken into account and were demonstrated using a small experimental machine. A series of tests on full scale components led to the manufacture of a multi-MW machine that was used to demonstrate the benefits of physical and functional integration under normal running and fault conditions.

A novel approach to the collection of fault related data associated with induction motor drives is presented. The stator to rotor magnetic flux of an induction motor is monitored by a number of strategically positioned search coils, each wound around a single stator pole. The data collected is in the form of time records of the induced voltage in the coils and is subsequently used to form the data base for a fault detection and diagnosis strategy. Voltage waveforms obtained from a single coil and from two coils connected in series are obtained whilst the system is subjected to a range of applied electro-mechanical faults. The applied faults are applied both to the mechanical load and to the induction motor itself. A comparison is made of the efficacy of using two search coils compared to employing a single coil for fault detection. The fault related data is collected under both steady-state and accelerating running conditions. Strictly the acceleration period waveforms are non-stationary, however, since the time dependant frequency changes are relatively slow, the author applied the FFT technique to both steady-state derived data and the acceleration period derived data. Processing is carried out on both the time domain and the corresponding frequency domain data. The non-stationary nature of the acceleration period records is taken into account and the Wigner-Ville technique is employed to establish a time-frequency-distribution. Amplitude-time-frequency 3-D representations are produced, from which the amplitude versus time activity of a typical acceleration period component frequency is presented.

This research is concerned with the evolution of an advanced drive system for use with permanent magnet synchronous motors. The proposed drive system incorporates state-of-the art control strategies with a switching matrix current loop which is a special case of the sliding mode control loop, implemented using field programmable gate array (FPGA) devices. This significantly increases the bandwidth of the current control loop, in comparison with systems using PI current controllers and therefore improves the dynamic performance of the drive system. The hard-wired FPGA implementation of a current control loop greatly reduces the processing and computational burden imposed on the controller. Most importanUy, in contrast to the OSP technology, independent functions may be implemented without the constraint of a shared arithmetic unit. In this research a novel hard-wired algorithm implementation is proposed for advanced control of brushless permanent magnet synchronous motor (PMSM) servo-drives. The PM servomotor control system has been developed as a set of modular subsystems in the form of algorithms, which can be easily interconnected at the top-level. The novel features of the control system have been made possible by the FPGA implementation with the creation of special algorithms and multiple sampling periods. The application under study is the speed and position control of synchronous motor drives. Initially, a conventional proportional and integral (PI) speed controller was implemented to enable comparison of performance to be made with the forced dynamic control (FOC) law emerging during the final stage of the research programme, which takes advantage of the flexibility offered by digital FPGA implementation. This offers high robustness to uncertainties in the dynamics of the driven load and unknown external load torques and yields a prescribed closed-loop dynamic response to reference inputs. The proposed system not only has the prescribed mutual orthogonality between the magnetic flux and stator current vectors, but also the realisation of a chosen form of speed response transient These FOC strategies have not yet been commercially exploited and it is emphasised that the recent advances in FPGA technology render such control methods highly cost effective. It is therefore anticipated that the outcomes of the research work will provide significant benefits in the development of a new generation of high performance and competitive servo drives.

Induction motors are the most widely used motors among electric motors in industries. These are due to their reasonable cost, reasonably small sizes, ruggedness, low maintenance, and operation with an easily available power supply including their high reliability. However, these motors are often exposed to hostile environments during operation. These abnormal situations may lead to early deterioration of motors i.e., development of faults. Without any actions, these faults may increase to severe problems such as secondary damages to downstream equipment, unexpected breakdowns. Condition monitoring is modern technologies generally used to observe the health of electric machines regularly. Several condition monitoring methods for the induction motors have been developed using the MCSA (Motor Current Signature Analysis) and vibration analysis which explore the possibility of the early detection of developing faults in the electric machines so that the rectification can be planned in advance before any catastrophic failure. Vibration based condition monitoring requires the installation of number of vibration sensors and can detect the early fault but the quantification of the electrical faults (either in the stator or rotor or both) is generally impossible. However the other option - the MCSA doesn't require additional sensors. Hence the present research study utilized the use of the MCSA for the early detection and the quantification of faults which would be useful for quick rectification of the identified faults in practice.

Analysis and control of five-phase induction motor drives are investigated in this thesis. A vector model for five-phase induction motors is derived. Two distinct aspects related to multi-phase induction motor modelling are revealed and determination of the equivalent circuit parameters is explained from theoretical and experimental viewpoints. Modulation techniques for the five-phase voltage source inverter are developed, with both separate and simultaneous space excitation included. The analysis of five-phase induction motor drives is verified using a practical test rig. Indirect vector control applied to the first and third space harmonics, with separate excitation and simultaneous excitation, are experimentally assessed.

This thesis provides an investigation into the online measurement of stator winding resistance and presents a procedure designed to be used and comply with standard polyphase induction motor efficiency tests.

The main objective of this thesis was to investigate the effect of phase parameter asymmetries on the torque of a 3-phase Permanent Magnet (PM) synchronous motor, and to identify an optimal control strategy that minimizes the torque and speed ripple by modifying the standard vector control scheme. The study was carried out in three stages. The first stage involved the development of a mathematical model for simulation of phase parameter asymmetries. In the second stage, the torque and speed ripple were analysed in two ways. Firstly, the analysis was done in an open-loop system, i.e., without position- feedback phase 'commutation and secondly in closed-loop system, i.e., with vector control. The last stage involved the minimization of the ripple through a vector control strategy. F or experimental purposes, the asymmetries were artificially introduced in the available PM synchronous motor by attaching an external impedance between two supply lines. Such a combination emulated an asymmetrical motor and allowed changes in the level of asymmetries.

For high performance drive applications, the accuracy of speed estimation from a digital shaft encoder is reduced in the low speed range. Drive performance can be further impaired at low speed when low cost low-resolution digital encoders are used. This thesis contributes to the development of a quasi-sensorless solution for AC induction motor drives, where instead of a conventional position sensor and MH" or closed loop observer, an artificial intelligence based 64PPR SKF sensor bearing is proposed. Furthermore, the performance of speed-controlled IM drives is sensitive to rotor time constant mismatch. A newly developed closed loop RMLE-GNA observer is proposed as a new adaption mechanism with a Model Reference Adaptive Scheme for rotor flux estimation and on-fine rotor time constant adaptation. For high performance sensorless speed controlled IM drive applications, the IM is required to operate at low speed in all four-quadrants in a stable manner whilst maintaining constant air-gap flux and torque. Such low speed operation fails with conventional open loop observers and MRAS, and closed loop observers such as EKF suffer from a tuning problem and extensive computing time. Parameter uncertainty is a further factor limiting drive performance. A new joint state estimation and parameter adaptation closed loop Recursive Maximum Likelihood Estimator with an iterative Gauss Newton Raphson Algorithm (RMLE-GNA) is developed for the sensorless speed estimation and on-line parameter adaptation of IM drives. Two case studies are presented: correct and stable convergence of the closed loop observer within two iteration local loops utilising a full order IM model, and correct and stable convergence within a single iteration local loop utilising a simplified full order IM model. In both cases it is shown that the closed loop observer can provide satisfactory and stable convergence for 4-quadrant operation. Of particular interest are the correct convergence, robustness against parameter mismatch and the stability of the sensorless speed controlled IM drive at zero speed and zero stator flux frequency. Thus, a small signal transfer function of the closed loop observer with the sensorless speed vector controlled IM drives is derived. The stability analysis shows the robustness and the convergence of the observer for 4-quadrant operation for high and low speed' and up to the rated load torque. The effect of various machine model parameters on the stability and convergence of the RMLE-GNA-based sensorless drive system is investigated, providing an insight into the inherent dynamic characteristics of the proposed closed loop observer-based sensorless speed-controlled IM drives.

This thesis explores aspects of the design, analysis, and experimental test of permanent magnet axial flux machines for use in diesel engine generator sets, vertical axis wind turbines, and wheel motors for solar cars. The characteristic geometry of axial flux machines is naturally more suitable than that of conventional topologies in certain applications. However, convenient and accurate methods of electromagnetic design and analysis are less well established for such machines. The purpose of the research described herein is to benchmark a range of methods of analysis which can be extended to novel designs. There is a particular focus on the use of Finite Element Analysis to facilitate greater understanding of these machines through the illustration and quantification of the electromagnetic aspects of their operation, and the verification of a selection of analytical approaches. Prototype TORUS machines are first considered; the various analyses are then extended to iron-cored axial flux machines having slotted conductors and finally to a selection of novel machines having concentrated coils and an ironless stator. The analyses are successfully extended to a range of machines, and the particular suitability of axial flux permanent magnet machines in certain direct drive applications is demonstrated.