This thesis describes the design, construction and testing of an axial field permanent magnet machine for an aero-engine variable guide vane actuation system. The electrical machine is used in combination with a leadscrew unit that results in a minimum torque specification of 50Nm up to a maximum speed of 500rpm. The combination of the geometry of the space envelope available and the modest maximum speed lends itself to the consideration of an axial field permanent magnet machines. The relative merits of three topologies of double-sided permanent magnet axial field machines are discussed, viz. a slotless toroidal wound machine, a slotted toroidal machine and a yokeless axial field machine with separate tooth modules. Representative designs are established and analysed with three-dimensional finite element method, each of these 3 topologies are established on the basis of a transient winding current density of 30A/mm2. Having established three designs and compared their performance at the rated 50Nm point, further overload capability is compared in which the merits of the slotless machine is illustrated. Specifically, this type of axial field machine retains a linear torque versus current characteristic up to higher torques than the other two topologies, which are increasingly affected by magnetic saturation. Having selected a slotless machine as the preferred design, further design optimization was performed, including detailed assessment of transient performance. A key feature of this design is the use of a solid (i.e. non-laminated) toroidal stator core. This provides a stator with increased mechanical robustness, improved heat transfer and a ready means of incorporating fixing points into the core. However, these advantages are gained at the expense of a significant eddy currents in the stator core. A series of three-dimensional, magneto-dynamic finite element simulations were performed. Although the resulting eddy current losses are excessive for continuous operation, the reduction in transient performance which results from the eddy currents is shown to be manageable. The loss analysis is supplemented by transient three-dimensional finite element thermal modelling. Three-dimensional mechanical analysis is performed in combination with analytical equation to analyse the stator and rotor plate deflection subject to axial attractive force. The construction of a prototype double-sided axial field machine is described in this thesis which contains several interesting design features including a profiled rotor core to reduce mass, radially magnetised rotor magnets to produce torque from the axially oriented conductors on the inner edge of the toroidal winding. The testing of the machine is performed under a series of load points up to 75Nm to validate the predicted torque versus current density characteristics.

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This thesis presents two different non-permanent magnet machine designs for belt-driven integrated starter-generator (B-ISG) applications. The goal of this project is to improve the machine performance over a benchmark classical switched reluctance machine (SRM) in terms of efficiency, control complexity, torque ripple level and power factor. The cost penalty due to the necessity of a specially designed H-bridge machine inverter is also taken into consideration by implementation of a conventional AC inverter. The first design changes the classical SRM winding configuration to utilise both self-inductance and mutual-inductance in torque production. This allows the use of AC sinusoidal current with lower cost and comparable or even increased torque density. Torque density can be further increased by using a bipolar square current drive with optimum conduction angle. A reduction in control difficulty is also achieved by adoption of standard AC machine control theory. Despite these merits, the inherently low power factor and poor field weakening capability makes these machines unfavourable in B-ISG applications. The second design is a wound rotor synchronous machine (WRSM). From FE analysis, a six pole geometry presents a lower loss level over four pole geometry. Torque ripple and iron loss are effectively reduced by the use of an eccentric rotor pole. To determine the minimum copper loss criteria, a novel algorithm is proposed over the conventional Lagrange method, where the deviation is lowered from ± 10% to ± 1%, and the simulation time is reduced from hours to minutes on standard desktop PC hardware. With the proposed design and control strategies, the WRSM delivers a comparable field weakening capability and a higher efficiency compared with the benchmark SRM under the New European Driving Cycle, where a reduction in machine losses of 40% is possible. Nevertheless, the wound rotor structure brings mechanical and thermal challenges. A speed limit of 11,000 rpm is imposed by centrifugal forces. A maximum continuous motoring power of 3.8 kW is imposed by rotor coil temperature performance, which is extended to 5 kW by a proposed temperature balancing method. A prototype machine is then constructed, where the minimum copper loss criteria is experimentally validated. A discrepancy of no more than 10% is shown in back-EMF, phase voltage, average torque and loss from FE simulation.

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Fault tolerant machine drives are key enabling technologies for safety critical applications such as electric vehicle traction, and aerospace power generation, actuation and propulsion. High performance in healthy conditions and excellent fault tolerance against various faults are required for a fault tolerant drive, however, these two aspects usually conflict with each other. Thus, this PhD study aims to develop a fault tolerant machine drive which exhibits high performance and good fault tolerance, and can be realised in a simple and cost-effective manner. First, a novel triple redundant 3x3-phase permanent magnet assisted synchronous reluctance machine (PMA SynRM) with segregated windings is proposed. Its performance under healthy conditions and its ability to tolerate various faults with appropriate mitigation measures are investigated and assessed. Based on outcomes of the investigation, a 40kW machine is designed to tolerate all key electrical faults, including the worst single turn short circuit, and is optimised to maximise the efficiency in healthy conditions whilst satisfying the electrical, thermal and mechanical constraints. To analyse and realise a fault tolerant machine drive, fault modelling and fault detection techniques are essential. Thus, a general model is proposed based on the magneto-motive force (MMF) decomposition. The model is capable of predicting the machine behaviour in various operation modes, including the healthy condition, open circuit, short circuit and inter-turn short circuit fault with different number of turns and different coil locations. With the aid of the fault modelling technique, a turn fault detection technique is developed using the 2nd harmonics in the instantaneous reactive and active powers as fault indicators for motoring and generating modes, respectively. By cross-reference of the fault indicators of the three 3-phase sets, the technique can detect the turn fault during transient without false alarm. The optimised machine drive is constructed and the developed fault detection technique together with fault mitigation strategies is implemented in a DSP based controller. The performance of the drive under healthy conditions and its fault tolerant capability are validated by extensive tests. The accuracy of the fault modelling and the effectiveness of the detection technique are also experimentally evaluated. The test results demonstrate that the developed fault tolerant machine drive can be a competitive candidate for safety critical applications.

With the increasing concerns about the price of rare-earth material, machines with less or no permanent magnet material have been extensively analyzed for application in electrical vehicles (EVs). As one typical magnetless machine, the variable flux reluctance machine (VFRM) is comprehensively investigated in this thesis in terms of operation principle, stator/rotor pole combination, winding configuration, power factor, current profiling technique, rotor shaping technique and design method.