In this thesis, advanced control methods are presented for torque ripple reduction and performance improvement in switched reluctance motor (SRM) drives. Firstly, a comparative evaluation of power electronic converters including asymmetric, N+1, C dump, split AC, and split DC converters is presented for three-phase SRMs in terms of cost, efficiency and control performance. Secondly, two methods are proposed using torque sharing function (TSF) concepts for torque ripple reduction of SRM over a wide speed range. An offline TSF is proposed to minimize the copper loss and the absolute rate of change of flux linkage (ARCFL) with a Tikhonov factor. Then an online TSF is proposed by adding a proportional and integral compensator with torque error to torque reference of the phase with lower ARCFL. Therefore, the total torque of online TSF is determined by the phase with lower ARCFL rather than the phase with higher ARCFL as in conventional TSFs. The maximum torque-ripple-free speed (TRFS) of the offline TSF and online TSF is validated to be 7 times and 10 times as high as the best case in these conventional TSFs, respectively. Thirdly, two methods are proposed to eliminate mutual flux effect on rotor position estimation of SRM drives without a prior knowledge of mutual flux, one is the variable-hysteresis-band current control for the incoming-phase self-inductance estimation and the other is variable-sampling outgoing-phase self-inductance estimation. Compared with the conventional method which neglects the mutual flux effect, the proposed position estimation method demonstrates an improvement in position estimation accuracy by 2º. Fourthly, a fixed-switching-frequency integral sliding mode current controller for SRM drives is presented, which demonstrates high dynamics, strong robustness and none steady-state error. All the proposed control methods are verified by both simulations and experiments with a 2.3 kW, 6000 rpm, three-phase 12/8 SRM operating in both linear magnetic and saturated magnetic regions. / Thesis / Doctor of Philosophy (PhD)

In an increasingly urgent climate crisis, the use of electric powertrains in smaller, purpose-built vehicles can expedite the global adoption of electrification. This thesis discusses the detailed design of an axial-flux switched reluctance motor for application in a light electric vehicle, such as an E-motorcycle. A vehicle application is studied based on typical driving conditions in an urban environment. The requirements of the propulsion motor are extracted, and a baseline machine topology is analyzed for its performance and manufacturability, towards the goal of a functional prototype. The prototype design includes a self-supporting foil winding, designed to maximize the use of axial space and allow for good conductive heat transfer to the machine casing. The rotor structure is found to be a limiting factor, where maximum speed is limited by the mechanical stresses. The performance of the motor is analyzed in detail, beginning with a numerical iron loss model that is implemented to provide faster simulation time of the machine efficiency than FEA. The efficiency is found to peak at 90%, comparable with other traction motors of similar size on the market. The switching angles are studied, and the trade-offs between torque quality and efficiency are quantified over the drive cycle. It was determined that the vehicle could save 19.6 Wh/km by accepting poor torque quality and operating with the most efficient control parameters. Thermal analysis is performed to determine the realistic performance limitations. The machine was found to have power ratings of 7.12 kW instantaneous and 4.76 kW continuous. The final temperature of the winding during the drive cycle was predicted not to exceed the temperature ratings of the insulation system. Finally, the prototype is assembled, and a test plan is outlined for qualification of the motor. / Thesis / Master of Applied Science (MASc) / This thesis documents the design of a new type of electric motor that is intended to be used in a small electric vehicle. The electric motor is different from the majority of motors used in this application for two reasons: firstly, the motor is a switched reluctance motor, which means that it does not contain any permanent magnets, offering cost savings and additional robustness. Secondly, the machine takes the form of a disk, where the magnetic interface between rotating and stationary components is on the face perpendicular to the axis of rotation. Normally, electric motors have the magnetic interface on the cylindrical surface which is parallel to the axis of rotation. The disk form factor presents multiple design challenges, which when coupled with the switched reluctance motor type, are addressed. A series of mathematical models are built to predict the performance of the motor in the vehicular application. Finally, a prototype of the motor is constructed.

In recent years, the product life cycle has decreased and demands for new products have emerged due to competition, modern industrial needs and rapidly changing technology. This has necessitated changes in design, development and manufacturing processes to improve the quality and efficiency and to reduce the cost. Computer Aided Design (CAD) helps to meet this challenge both in the design evaluation and product design stages. This thesis contains the development of an interactive software for the optimal design of a motor intended for variable speed applications. The use of finite element analysis methods is proposed as an indispensable part of the CAD system for electrical machine design. An illustration of the method is presented for the design of a switched reluctance motor. / Master of Science

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This thesis deals with the design and optimisation of medium power traction switched reluctance machines with tapered and straight stator poles. Only the prototype of the tapered stator pole machine is constructed and evaluated in this study. A non-commercial finite element package is used in the design and optimisation of the machines. The finite element method is applied directly in the optimisation procedure to optimise the design of the machines in multi-dimensions. The lumped circuit analysis method is used only for the purpose of verifying some of the finite element calculated. It is not used in the optimisation procedure. The performance characteristics of the tapered and straight stator pole machines are compared and discussed and the tapered stator pole machine is found to have better torque performance. Also the calculated and measured static torque versus rotor position characteristics of the tapered stator pole machine are compared and discussed. / AFRIKAANSE OPSOMMING: Die tesis beskryf die ontwerp en optimering van medium drywing trekkrag geskakelde reluktansie masjiene met tapse en reguit stator pole. Slegs 'n prototipe van die tapse stator pool masjien is gebou en geëvalueer. Die masjiene is ontwerp en geoptimeer met behulp van 'n nie-kommersiële eindige element metode pakket. Die eindige element metode is direk in die optimerings algoritme gebruik vir die optimering van die masjiene in multi-dimensies. Die gekonsentreede parameter stroombaananalise is slegs gebruik om sommige van die eindige element berekenings te verifeer. Die vermoës van die tapse en reguit stator pool masjiene is vergelyk en bespreek. Die resultate toon dat die tapse stator pool masjien se draaimoment vermoë beter is as die van die reguit stator pool masjien. Die berekende en gemete statiese draaimoment teenoor rotorposisie van die tapse stator pool masjien is ook vergelyk en bespreek.

L’enjeu de la thèse concerne la modélisation électromagnétique des machines synchrones à réluctance, avec comme objectif final : obtenir un modèle suffisamment précis et rapide pour, d’une part, être capable de calculer les ondulations de couple et d’autre part servir pour de l’optimisation dimensionnelle et pouvoir être couplé à un logiciel de type circuit pour tester une loi de commande. Un modèle du type schéma réluctant a été mis en place petit à petit avec validations à chaque étape. La modélisation des échanges dans l’entrefer utilise en final une fonction originale (intégrale de Fermi-Dirac) qui a entièrement été paramétrée avec les dimensions caractéristiques de la machine.Ce modèle de la machine, piloté par les courant, a ensuite été couplé avec un circuit électrique grâce à une interface de transformation tension-courant. Les optimisations réalisées avec ce modèle ont permis de mettre en évidence certains manques dans les contraintes dimensionnelles initiales et, celles-ci corrigées, de montrer que ce modèle était parfaitement utilisable pour cette démarche d’optimisation. / This thesis aims the electromagnetic modeling of synchronous reluctance machines, with a final goal: to obtain a fast and sufficiently accurate model, able to calculate the torque ripple and to be used for optimal machine design and also capable to be coupled to circuit software to test control techniques.A MEC (magnetic equivalent circuit) model was created step-by-step and validated at each step. Final model of the air-gap is based on a function (Fermi-Dirac integral), which has been completely parameterized by machine dimensions. This model of the machine is driven by current; afterwards it was coupled with an electric circuit thanks to a voltage-current transformation interface. The optimizations made with the model allowed to highlight some deficiencies in the initial dimensional constraints. After corrections the model could be efficiently used in an optimization process.

Ferrofluids are stable colloidal homogeneous mixtures of nano-size single-domain ferromag¬netic particles covered by surfactant layer, and suspended in a carrier fluid compatible with the surfactant. Physical properties of ferrofluid allows one to control it externally using magnetic field without being in direct contact with it. The thesis presents a novel mechanism to pump ferrofluid based on the principle of variable reluctance, in an external magnetic field. The static and dynamic pressure behavior of ferrofluid in a switched DC magnetic field gives an insight into the variable reluctance behavior of ferrofluid. A ferrofluid pump based on the prin¬ciple of variable reluctance of ferrofluid subjected to an external magnetic field, is developed and hence the pump is named as Variable Reluctance Ferrofluid Pump (VRFP). Three configurations of VRFP are developed: • Single stage one-phase VRFP • Single stage two phase VRFP • Multi-stage VRFP A one-phase VRFP consisting of a check valve along with an electromagnet is designed. The valve is modeled and its transfer function is estimated using System Identification method. This model is then used in the simulation model of the pump. The pump is modeled based on the hydraulic-electric analogies. An electric circuit which represents the gross level equivalent of the pump is simulated and the results are compared with that of the experimental measurements. A two phase VRFP is implemented with two electromagnets on either side of the valve around the tube. Two types of magnetic actuation methods are introduced based on the switching sequences of the two electromagnets, namely Full Step Sequencing and Half Step Sequencing. Simulations and experiments were conducted for different pumping conditions. The one phase and two phase VRFPs are single stage structures. A multi-stage VRFP concept, in which the ferrofluid flow channel (tube) is looped through the electromagnets multiple times, is introduced. For the implementation purpose, a two-stage VRFP is discussed in this thesis. Simulations and experiments resulted in significant improvement in case of two-stage VRFP in the pump performance compared to that of single-stage VRFPs. The work presents a simple and novel design of a ferrofluid pump, which is capable of higher flow rates and pumping against higher back pressure compared to the ferrofluid pumps reported in literature. Keywords: Ferrofluid Pump, VRFP, Variable Reluctance, Multi Stage, Magnetic Fluid,

This dissertation contains a comprehensive analysis of both non-coupled and mutually coupled switched reluctance motors with concentrated windings for an electric bicycle traction application. Multiple pole configurations are analyzed and compared for each motor type. Includes magnetic design, thermal analysis, and structural analysis. A prototype is designed, manufactured, and validated. / This thesis discusses the design of both a conventional non-coupled switched reluctance motor (CSRM) and a mutually-coupled SRM (MCSRM) for an exterior rotor e-bike application. Several novel pole configurations were analyzed for each machine type, and the performance of the final CSRM and MCSRM designs were compared for this application. A commercially available e-bike permanent magnet synchronous motor (PMSM) was purchased, reverse engineered, and validated to define the geometry constraints and performance targets for the designs. Since switched reluctance motors do not use rare-earth permanent magnets, they are often seen as a potential low-cost alternative to permanent magnet machines. The goal of this research is to explain the relative advantages of CSRMs and MCSRMs when compared to PMSM machines for a direct-drive e-bike application. The final CSRM and MCSRM designs are analyzed in detail; electromagnetic, controls, thermal, and structural considerations are all studied. A prototype of the final CSRM design was manufactured and validated experimentally, using a dynamometer setup. The finalized CSRM design is shown to be competitive with the PMSM machine when considering torque output, and is superior in terms of peak efficiency, and high speed torque performance. However, the CSRM noise output and torque ripple were not compared to the PMSM, and a less-common asymmetric-bridge converter is required for the CSRM, which may hinder the ability for the machine to be implemented into existing e-bike packages. The high speed torque performance of the MCSRM is shown to be inferior to both the CSRM and PMSM, as is the torque quality and efficiency. The MCSRM is shown to be highly resistant to saturation which gives it the potential for high torque output at low speed (if thermal limits are not breached), though low saturation levels also contribute to low machine power factor. The MCSRM may be better suited to lower speed, high torque applications, for this reason. / Thesis / Doctor of Philosophy (PhD) / This thesis studies the design process and analysis of two different motor types, for an electric bicycle application. They are designed to replace a commercially available permanent magnet synchronous motor (PMSM). This type of motor is typically expensive due to the rare-earth magnet material it requires. The two motors discussed in this thesis are switched reluctance motors (SRMs), which do not require magnet material, and thus have the potential to save cost (in addition to other benefits). One of the SRMs has magnetic fields that are independently controlled (CSRM), and one has fields that are controlled together to produce torque (MCSRM). The magnetics, control, thermal, and structural aspects of the CSRM and MCSRM are studied in detail. Novel geometry considerations (i.e. novel pole configurations) which impact the magnetics of each machine are compared to find the best-performing configuration for each machine type.

Este trabalho se insere num contexto de desenvolvimento da capacitação para aplicações de motores de relutância chaveados, com ênfase aos aspectos eletromagnéticos do acionamento. Inicialmente, são apresentados os principais aspectos construtivos do motor e de funcionamento do seu conversor. São discutidos os fluxos de energia do acionamento e sao apresentadas as suas características operacionais, bem como as possibilidades para o seu controle. Foi desenvolvida uma metodologia de projeto embasada numa formulação empírica e no método dos elementos finitos, implementado através do programa flux2d. Desta forma, foi projetado um protótipo para desenvolver meio newton-metro a três mil rotações por minuto. A formulação empírica baseia-se na adoção de diversas hipóteses simplificadoras do circuito ferromagnético. O método dos elementos finitos foi empregado com a finalidade da obtenção de um refinamento do dimensionamento do motor. O protótipo projetado foi fabricado e testado. Os objetivos dos ensaios foram a confrontação com os diversos valores calculados no projeto e a verificação do seu desempenho em diversas condições de carga. Finalizando o trabalho, os resultados obtidos são analisados, ressaltando-se os aspectos relevantes ocorridos durante o seu desenvolvimento. São também apresentadas, as atividades subsequêntes previstas. / This work is related to the development activities of switched reluctance motors, mainly on their electromagnetic characteristics. The motor\'s basic construction features and the converter\'s operation characteristics are showed, as well as, the energy flows, performance aspects and the effects of the control parameters. The principal elements of motor desigm are discussed. A method of design is developed based on empirical formulas and on finite elements method (using the software FLUX2D). Thus, a prototype was designed with ratings of 0,5 Nm at 3000 rpm. The empirical formulas are developed on a simplified model of the motor and taking into account the referred author\'s experience. The finite elements method was used with the aim of getting a design refinement, as well as, the static torque characteristics, inductances and flux as a function of rotor position and current. The prototype was built and tested. The tests were conducted to compare the actual with the designed parameters and to evaluate the performance characteristics. Finally, the results are analysed and the main facts observed during the development of the work are reported. The next planned activities are also showed.

Este trabalho se insere num contexto de desenvolvimento da capacitação para aplicações de motores de relutância chaveados, com ênfase aos aspectos eletromagnéticos do acionamento. Inicialmente, são apresentados os principais aspectos construtivos do motor e de funcionamento do seu conversor. São discutidos os fluxos de energia do acionamento e sao apresentadas as suas características operacionais, bem como as possibilidades para o seu controle. Foi desenvolvida uma metodologia de projeto embasada numa formulação empírica e no método dos elementos finitos, implementado através do programa flux2d. Desta forma, foi projetado um protótipo para desenvolver meio newton-metro a três mil rotações por minuto. A formulação empírica baseia-se na adoção de diversas hipóteses simplificadoras do circuito ferromagnético. O método dos elementos finitos foi empregado com a finalidade da obtenção de um refinamento do dimensionamento do motor. O protótipo projetado foi fabricado e testado. Os objetivos dos ensaios foram a confrontação com os diversos valores calculados no projeto e a verificação do seu desempenho em diversas condições de carga. Finalizando o trabalho, os resultados obtidos são analisados, ressaltando-se os aspectos relevantes ocorridos durante o seu desenvolvimento. São também apresentadas, as atividades subsequêntes previstas. / This work is related to the development activities of switched reluctance motors, mainly on their electromagnetic characteristics. The motor\'s basic construction features and the converter\'s operation characteristics are showed, as well as, the energy flows, performance aspects and the effects of the control parameters. The principal elements of motor desigm are discussed. A method of design is developed based on empirical formulas and on finite elements method (using the software FLUX2D). Thus, a prototype was designed with ratings of 0,5 Nm at 3000 rpm. The empirical formulas are developed on a simplified model of the motor and taking into account the referred author\'s experience. The finite elements method was used with the aim of getting a design refinement, as well as, the static torque characteristics, inductances and flux as a function of rotor position and current. The prototype was built and tested. The tests were conducted to compare the actual with the designed parameters and to evaluate the performance characteristics. Finally, the results are analysed and the main facts observed during the development of the work are reported. The next planned activities are also showed.

The variable reluctance motor (VRM) is known for its structural simplicity, lower cost and capability of higher specific outputs compared with the AC induction motor. These favourable attributes arise from the way the torque is generated. An asymmetric half bridge would commonly be used as the controller for the VRM. It is also a relatively simple circuit because unlike the requirement with an AC induction motor, the imput current for a VRM would only need to be able to travel in one direction.