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No description available.

No description available.

Recent developments in power electronics switching devices have led to significant improvements in AC drives which, coupled with the obvious advantages of squirrel-cage induction motors, have generated a customerled demand for an increase in AC drive performance. This thesis describes the design and construction of a 3-phase pulsewidth modulated inverter using gate turn-off (GTO) thyristor switching devices, which drives a 0.75 kW 3-phase squirrel-cage induction motor. The inverter control circuit comprises a purpose-built large-scale integrated circuit, which generates the 3-phase pwm drive signals and allows the output voltge and frequency to be varied independently. When operating in open-loop, the drive system is capable of reverse operation, and the maximum rate of acceleration and deceleration of the motor may be controlled. Compensation for resistive voltage drop is provided when the motor is running at low speed. An analogue closed-loop proportional-integral-derivative speed controller is described, and for efficient operation under both no-load and on-load conditions torque feedback is also included. This provision both reduces the no-load losses in the motor and improves the torque-speed characteristic under load conditions. The improved closed-loop performance also includes power factor correction when the motor is lightly loaded,.together with an automatic boost to the motor voltage when loads are applied at low speed. A comparison is made between the performance of the analogue system and a digital real-time control implemented using a microcomputer. A series of computer programs are presented which simulate the performance of the drive system and which are suitable for running on the University mainframe computer. The programs enable the effects of the modulation technique and the inverter frequency on the pwm inverter steady-state output to be studied, and the performance of the induction motor to be investigated. Throughout the work, the theoretical predictions are supported by considerable experimental results.

Flux switching machines (FSM) employing a segmental rotor have field and armature systems on the stator and a presentation of an unexcited rotor with isolated segments. The single-tooth winding arrangement on the stator provides a potential for material and energy savings. The principle for producing bipolar flux in the armature stator teeth relies on the natural switching of the armature tooth flux, accomplished by the moving segments of the rotor. Three phase configurations have been studied, from conception and design to construction and testing, with field excitation provided by either a field winding or permanent magnets (PM). Flux switching machines have shown characteristics that are peculiar when employing a segmental rotor, significantly affecting the symmetry of the induced armature EMF waveform and parity of magnitudes of the positive and negative torques. For three phase operation, six topologies are feasible when employing a 12-tooth stator and two other topologies may be produced on a 24-tooth stator. An optimum topology on the 12/8-configuration and another proof-of-principle topology on the 12/5-configuration, using field-windings and permanent-magnets, have been designed and constructed, while applying modern practices and considerations for manufacture. The characteristics of FSMs employing a segmental rotor, initially predicted by finiteelement (FE) modelling, have been verified by measurements. The FSM employing a field-winding is found to have a specific torque output which is similar to the conventional switched reluctance motor and still substantially higher than that of the synchronous reluctance motor. Although the PM adaptation of the FSM produces specific torque output which is nearly twice that of the wound-field FSM and about 64% that of an equivalent permanent-magnet synchronous motor (PMSM) with surface or insert magnets, accounting for the usage of the magnets reflects its specific torque output to be about 1.48 times higher than the PMSM. Although the FSM is operated as an AC machine with sinusoidal three-phase currents, its dq-equivalent representation shows significant differences from that of the conventional AC machine. In the prediction of the performance, it is found, in both the wound-field and PM configurations, that the dq model is more dependable if the coupling dq inductance is taken into account.

This thesis presents two designs for modulated pole machines from concept through to validating prototypes, each comparing favourably with other modulated pole machines. The key feature to these designs is that they employ novel fabrication techniques which are realisable in low cost manufacture without compromise in performance. This is achieved by reviewing the specific properties of soft magnetic composite and laminated steel. Each material was then utilised in such a way as to take best advantage of its distinguishing properties leading to the development of novel fabrication and construction techniques. The designs are each presented in three stages. Firstly the development of the concept is presented and the use of finite element simulation to reach a design worthy of construction is documented. The development of fabrication techniques for the various parts is then presented along with the assembly into a working single phase prototype. Finally testing and comparison of results with simulated and other existing published designs is presented.

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A generalised analysis method for N-phase induction machines is presented. The Nphase system is analysed using 2N degrees of freedom. A new conceptual view of a multi-phase system using an N-dimensional vector space has been developed. It is shown that such an N-dimensional vector space can be decoupled into 'h(N+PJ independent two dimensional vector planes, where if N is odd, p=l, otherwise P=O. Each vector plane is shown to be the combination oftwo positive and negative sequence components ofthe same phase order. Each vector space is shown to be independent and can be controlled separately by an N-phase inverter. Each inverter state is shown to have a location in every vector space. A vector control strategy has been realised for developing independent vectors in decoupled vector spaces, resulting in the desired voltage waveforms at the inverter outputs. A five-phase induction motor is designed, and constructed as an integral part of five-phase drive system. A five-phase decoupled vector space controller is implemented in a fixed-point digital signal processor and the practical five-phase inverter based drive system validates the proposed decoupled vector space theory. The analysis of multi-phase machines during imbalanced. electrical operation is considered using decoupled vector space theory. It is shown that each independent vector in the decoupled vector spaces produces unique flux distributions in an N-phase AC machine, but only one vector space develops fundamental rotor linked flux and thus fundamental torque. The interaction of decoupled vector spaces with winding harmonics is developed in order to analyse the effects of unbalanced currents in a i' practical induction motor. It is shown that torque is produced only by the primary vector space currents in a sinusoidally wound machine. The additional freedom available from auxiliary vector spaces can be used to compensate for imbalance caused by faulty machine phases. It is shown that there exists 2N-3 degrees of freedom for an N-phase system of fluxes of an N-phase machine with a floating neutral. These degrees of freedom can be used to compensate for the phase imbalance created by opencircuited inverter legs. The machine can still be fluxed to produce rotational power. At the pre-fault to post-fault transition, the current vectors of the operational phases are reoriented to produce a rotating fundamental flux. A five-phase induction motor drive system demonstrates the performance for the loss of one and two phases. Harmonic winding function generated flux interaction is analysed and interpreted in terms of a five-phase motor with single and two phase loss.

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