Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 151-164). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references.

Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This thesis deals with the design and evaluation of a 300 kW double stage axial-flux permanent magnet generator with an ironless stator. The magnetic and electrical design equations are derived for sinewave and quasi-squarewave axial-flux permanent magnet machines. The thermal design approach used is also described. The machine is optimised for maximum torque per current loading. A Matlab program code is developed to do the necessary calculations in the design optimisation and the calculation of the machine parameters. Mechanical finite element simulations are conducted to investigate the severity of the magnetic attraction force between the rotor discs. The results obtained from the simulations suggested an increase in the yoke thickness in order to withstand the attraction force. The construction of the prototype machine's rotor and stator is described. The flux density in the airgap is thoroughly investigated through measurements and analysis. Thermal measurements are also conducted to investigate the effect of eddy currents in the stator winding. Furthermore, no-load measurements conducted on the 300 kW machine showed that the machine has a serious problem of circulating currents in the parallel connected coils. Possible solutions for this are investigated and recommendations are given. Due to the circulating current problem and the relative high eddy current losses, it was not possible to do full-load tests on the machine. / AFRIKAANSE OPSOMMING: Hierdie tesis handeloor die ontwerp en evaluering van 'n multi-stadium Aksiale Vloed Permanente Magneet (AFPM) masjien met 'n ysterlose stator. Die magnetiese - en elektriese ontwerp-vergelykings is afgelei vir sinusgolf en quasi vierkantsgolf AFPM masjiene. Die termiese ontwerp word ook bespreek. Die masjien is geoptimeer vir maksimum draairnoment per stroombelasting. Daar is 'n program-kode in Matlab geskryf om die nodige berekeninge vir die optimering van die masjien uit te voer en vir die bepaling van die masjien-parameters. Meganiese eindige element berekenings is gedoen om die invloed van die magnetiese aantrekkingskrag tussen die rotorskywe te ondersoek. Die resultate het aangedui dat die rotorskyfdikte nie die magnetiese aantrekkingskrag van die magnete kan weerstaan nie en moes in dikte vedubbel word. Die konstruksie van die masjien se rotor en stator is behandel. Die vloeddigtheid in die luggaping is noukeurig ondersoek deur metings en analise. Termiese metings is ook gedoen om die invloed van die werwel strome in die statorwikkelings te ondersoek. Verder het die nullas-toetse wat gedoen is op die masjien, aangedui dat die masjien 'n ernstige probleem het met sirkuierende strome in die parallelle geleiers van die statorspoele. Moontlike oplossings is ondersoek en aanbevelings word gegee. Dit was nie moontlik om vollastoetse op die masjien te doen nie, as gevolg van die probleem met sirkuierende strome en die relatiefhoë werwelstoom-verliese in die statorwikkelings.

The rise in popularity of renewable energy solutions, in particular wind energy systems, has resulted in a greater demand for low-speed direct-drive machines. The Vernier machine has inherent properties such as high torque density, sinusoidal induced voltages and low torque ripple which makes it suitable for low-speed direct-drive wind applications. Additionally, its mechanical structure is as simple as a conventional permanent magnet (PM) machine, whilst eliminating the need for a mechanical gearbox. The research problem addressed by this dissertation relates to the assessment of the Vernier permanent magnet (VPM) machine topology for direct-drive wind applications. It aims to outline a sizing, detailed design and analysis approach for a three-phase VPM wind generator. Furthermore, a comparative study is conducted using two different rotor types and two different stator types, namely; spoke-type and surface-mounted and fractional slot and integral slot respectively. Vernier theory is used to size the designs after which 2D Finite Element Analysis (FEA) simulations are used to analyse and validate the designs. The main outcome of the comparative study is an assessment of the suitability of four topologies for the direct-drive wind application. The design is assessed on parameters which are critical for wind turbine functionality; namely efficiency, torque ripple, torque density and material consumption. The most suitable of the topologies is selected for prototyping. The rotor is made more robust by adding structural features which mechanically secure laminations and PMs to the shaft. The FEA analysis of the prototype showed favourable performance characteristics, albeit with a small cost in power density. The prototype was -thus manufactured with further mechanical reinforcements made to the bearing system. Experimental results reveal the presence of a defect in the windings. Parameters which are dependent on the winding design are much lower than the analytical and FEA values. These parameters include resistance, inductance, and back-EMF. Further work should look into determining the root cause of the prototype defects.

No description available.

Energy resources are under tremendous pressure with society’s ever increasing need for electricity. However, resources are becoming scarce and the effect of our power generation on the environment is cause for concern. The cost of electricity is also increasing and thus the need to reduce energy consumption is apparent. Most electrical energy generated is consumed by electric motors. Most of these motors are induction motors because they are reliable, efficient and durable. Though these motors are highly efficient, there is still room for improvement when the strain on electrical energy is taken into account. Constructing motors with better efficiency can result in a reduction in energy consumption and cost savings to the consumer. One method of increasing a motor’s efficiency is to use permanent magnets in the construction of the motor’s core. Permanent magnets eliminate the excitation losses experienced by induction machines, thereby increasing the motor’s efficiency. A retrofit design is considered because of the ease of manufacturing for motor suppliers and the ability to apply the solution to existing operating induction machines. The prototype will lay the foundation for future optimisation strategies. The optimised design should provide improved efficiency with a minimum effect on the motors already operating in industry. The design process followed uses the design principles for inductions machines and for sizing permanent magnets. The design is then verified through the use of finite element method software packages, FEMM and ANSYS Maxwell®, and validated by performance testing. A comparison is drawn between the calculated results and the results determined from the performance analysis. The retrofit design performed as expected during the testing with some discrepancies in final values attributed to the manufacturing process. However, the efficiency is lower than designed and requires the implementation of machine optimisation strategies. / MSc (Electrical and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

Energy resources are under tremendous pressure with society’s ever increasing need for electricity. However, resources are becoming scarce and the effect of our power generation on the environment is cause for concern. The cost of electricity is also increasing and thus the need to reduce energy consumption is apparent. Most electrical energy generated is consumed by electric motors. Most of these motors are induction motors because they are reliable, efficient and durable. Though these motors are highly efficient, there is still room for improvement when the strain on electrical energy is taken into account. Constructing motors with better efficiency can result in a reduction in energy consumption and cost savings to the consumer. One method of increasing a motor’s efficiency is to use permanent magnets in the construction of the motor’s core. Permanent magnets eliminate the excitation losses experienced by induction machines, thereby increasing the motor’s efficiency. A retrofit design is considered because of the ease of manufacturing for motor suppliers and the ability to apply the solution to existing operating induction machines. The prototype will lay the foundation for future optimisation strategies. The optimised design should provide improved efficiency with a minimum effect on the motors already operating in industry. The design process followed uses the design principles for inductions machines and for sizing permanent magnets. The design is then verified through the use of finite element method software packages, FEMM and ANSYS Maxwell®, and validated by performance testing. A comparison is drawn between the calculated results and the results determined from the performance analysis. The retrofit design performed as expected during the testing with some discrepancies in final values attributed to the manufacturing process. However, the efficiency is lower than designed and requires the implementation of machine optimisation strategies. / MSc (Electrical and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

The Norwegian Network Code FIKS from the Norwegian Transmission System Operator (TSO) Statnett, states that synchronous generators ≥ 25 MVA must have a static excitation system. It also includes requirements on the step time response and the available field winding ceiling voltage of the excitation system. An improved brushless excitation system is in operation in some pilot power plants. A rotating thyristor bridge is controlled via Bluetooth. The step time response is as fast as conventional static excitation systems. However, a ceiling voltage factor of 2 requires the thyristor bridge to operate at firing angles about 60 degrees. High torque pulsations, low power factor and low utilization of the exciter is the end result. New power electronic interfaces on the shaft results in a betterutilization of the designed exciter and improves the mechanical performance as well as the controllability of the generator field winding. Permanent magnet rotating exciters increase the field forcing strength of the synchronous generator, yielding improved transient stability (Fault Ride-Through req.). Brushless exciters also reduces regular maintenance of the generator. The thesis includes experiments on a state of the art synchronous generator test setup including constructed PM exciter and different power electronic solutions. Some investigations has been done on industrial power plants as well.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy