This thesis studies two types of medium-voltage (MV) vector controlled PWM induction motor drives for long motor feeder applications, namely voltage source and current source based drives. As rectifiers and inverters are the main elements in any drive system, both are investigated, but with more emphasis on the inverter side. MV PWM current source rectifiers (CSR) usually use selective harmonic elimination as a modulating strategy which provides good harmonic reduction at a low switching frequency. The rectifier performance does not meet the IEEE 519 regulation concerning harmonics injected into the supply current. Two solutions are presented. First, line side passive filters for harmonic mitigation and power factor improvement. Second, shunt active power filters based on p-q theory, with a step-down high-frequency transformer. The presented solutions are compared to highlight their features and limitations. Several topologies can be used for PWM CSRs. A detailed study of the selection criteria for PWM CSR semiconductors is presented based on losses, physical size, and number of series devices. Utilization of a PWM voltage source inverter (VSI) drive system in long motor feeder applications leads to motor terminal over-voltage problems. Surge filters are used to mitigate this phenomenon. Among the various types of filters, the motor terminal RC filter and the inverter output RLC filter are common. A detailed investigation is presented of the effects of these filters on the VSI drive system. PWM current source inverter (CSI) drive systems are characterised by their motor friendly voltage behaviour and controlled short circuit capabilities. Therefore, a proposed indirect vector controlled PWM CSI drive is presented for long motor feeder applications. Performance comparison between PWM VSI and CSI drive systems for long motor feeder applications is performed to clarify features and limitations of each system. Motor voltage is needed for speed estimation but measurement of voltage/speed is impractical for long motor feeder drives. A model reference adaptive system speed estimator is proposed with a novel remote motor voltage calculator that depends on the inverter voltage and feeder parameters. Offset and drift problems that occur during the flux estimation process are solved by a proposed DC-offset eliminator.

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The work presented in this thesis is aimed at improving single phase permanent magnet brushless DC motors; including their operation, design, efficiency and smoothness. Three main areas were identified and researched for further improvement. As a precursor to this work, a detailed literature study related to each area is also presented. The first of these areas concentrates on the improvement of the open circuit torque for a single phase BLDC motor. The open circuit torque is not only due to the slot openings, but is also contributed by the uneven airgap which is conventionally used to solve starting problem. The aim is to enhance the starting torque at alignment positions and attenuate the torque ripple between null points where the back EMF is non-zero. The improvement of the open circuit torque was investigated in two stages. In the first stage the open circuit torque due to the slot openings was reduced, and in the second stage the focus was on enhancing the open circuit torque contributed from the uneven air gap topology with minimum ripple. The second area of investigation was to devise a new encoderless control method for a single phase BLDC motor. A detailed analysis on the derivation of the method is presented. The method has been validated both analytically and numerically. The third area of investigation was the creation of a new non-complex phase advance control method. The details of the analytical simulation and practical implementation are presented. The method has been validated experimentally and it was shown that the experimental results agree well with the analytical predictions.

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Domestic appliances represent very cost conscious applications for drives where the emphasis is on achieving the optimum compromise between cost and performance. The requirements placed on a domestic appliance drive are so radically different from those demanded of an industrial drive, that a detailed re-evaluation of all the constituent sub-units of the drive must be undertaken. Domestic appliances are produced in large volumes so the use of a special arrangement or custom components can be justified if an overall benefit can be demonstrated. The work presented in this dissertation is concerned with small drives which are suitable for domestic appliances. A study of the optimal number of phases for current and possible future power electronic construction methods is presented and their suitability of domestic appliance drives considered. Comparisons based on material utilisation and the quality of the air gap flux waveform are presented. With the power electronic technology available two and three phase drives were found to be the best compromise between cost and complexity, and several drives of each type were built to provide experimental evidence on the performance of each alternative drive topology proposed. The experimental results obtained from the different drives built are related to the conclusions of work on inverter topology and phases number.

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The design of electrical power systems on offshore platforms involves ensuring the safe and reliable operation of the systems. These criteria prompted the need for performing short-circuit studies and fault level calculations. Using the results obtained from these studies together with the load data, the switchgear rating and fault rating of the switchboard can be determined. This study will aid the designer in determining both transient and substransient reactances of the generators, whereby the transient reactance is used in studying the effect of starting a large motor such as a compressor or a pump and the substransient reactance is used in short circuit studies. The generators parameters are therefore essential in the determination of circuit breaker setting, switchboard ratings and the starting capability of motors. These factors have prompted research into methods for determining the parameters of synchronous generators. The tests approved by the British Standards which are usually employed by manufacturers, however suffer from a number of disadvantages such as the possibility of damage to the generator windings as a result of the sudden three phase short circuit test. On the other hand some of these tests such as the d.c. standstill decay test are quoted as 'unconfirmed testing methods'. This study is therefore aimed at developing a method whereby the parameters of synchronous machines can be estimated directly from the on-line voltage and current waveforms. The study starts by determining the parameters of two salient pole generators using the conventional methods. This is used later to establish the accuracy of the proposed method. The effect of varying the generators parameters on voltage and current waveforms is then analysed, leading to the introduction of a method using only three simple tests. The accuracy and reliability of the method is demonstrated using the software simulator SABER. Finally the new parameter estimating technique is used to determine saturated parameters of the two laboratory generators for different field excitations.

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