Switched Reluctance Motors (SRMs) are gaining recognition due to their robust design, cost-effectiveness, fault tolerance, and reliable high-speed performance, positioning them as promising alternatives to traditional electric motors. However, SRMs face high torque ripples, vibration, acoustic noise, and nonlinear modeling complexities. Through careful geometry design optimization, these drawbacks can be mitigated. Design optimization for SRMs is a multi-objective and nonlinear problem that requires an accurate finite element analysis (FEA) model to relate designable parameters to output objectives. The geometric design process follows a multi-stage and iterative approach, leading to prohibitive computational time until the optimal design is reached. Machine learning algorithms (MLAs) have recently acquired attention in electric machine design. This study introduces an extensive analysis of various MLAs applied to SRM modeling and design. Additionally, it presents a robust framework for a comprehensive evaluation of these MLAs, facilitating the selection of the optimal machine learning topology for SRM design. Existing research on the geometry optimization of SRMs using MLAs has focused only on the machine’s static characteristics. This thesis introduces an advanced optimization method utilizing an MLA to act as a surrogate model for both static and dynamic characteristics of the SRM. The dynamic model incorporates conduction angles optimization to enhance the torque profile. The proposed MLA is applied to map out the SRM geometrical parameters, stator and rotor pole arc angles and their dynamic performance metrics, such as average torque and torque ripples. The optimal design improves the average torque and significantly reduces the torque ripples. Radial forces constitute a critical objective that should be considered alongside average torque, efficiency, and torque ripple in the design optimization of SRMs. Accurate modeling of radial forces is a prerequisite for optimizing motor geometry to mitigate their adverse effects on vibrations and acoustic noise. This work presents an MLA-based surrogate model for the most influential radial force harmonic components, facilitating the integration of radial force reduction into a multi-objective optimization framework. The proposed optimization framework employs two MLA-based surrogate models: the first correlates SRM pole arc angles with average torque and torque ripples, while the second models the most significant radial force harmonics. A genetic algorithm leverages these surrogate models to predict new geometrical parameters that enhance the SRM's torque profile and reduce radial forces. The optimization framework significantly reduced torque ripples and radial forces while slightly increasing average torque. The optimal design candidates were verified using FEA and MATLAB simulations, confirming the effectiveness of the proposed method, which offers significant computational time savings compared to traditional FEA techniques. / Thesis / Doctor of Philosophy (PhD)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Power transformers are essential and a large part of the asset cost structure of the electrical power system. When they present any defect or failure, it will be required high costs to repair or replace them, due their commercial costs and by the capability loss to transmit power during a period of time. Generally, transformer failure can occur as a result of the weakness insulation caused by the electrochemical processes involving the cooling liquid (oil), by vibrations due the electromagnetic forces in normal operation, i.e., steady state, and also by winding deformation as the result of short-circuits. It is expected that a transformer will experience and survive a number of short circuits during its service life. But one such event will cause some slight winding movement, which can gradually increasing and the ability of the transformer to withstand further electromechanical forces will be then reduced. It is therefore very important to check the mechanical condition of transformers periodically, particularly for older units, to provide an early warning of an impending catastrophic failure. Thus a specialist technique is required for the monitoring and assessment of mechanical condition of winding transformer. Despite designers and manufacturers, as well as the operation and maintenance technicians of power supply companies worry about this subject, new methodologies and tools to assess the strength effects as the result of short circuits in transformers are still necessaries. So, this work proposes to know the strength characteristics caused by the radial and axial forces in winding transformers. In this context, it will be presented different strengths that can occur in winding transformer, identifying the principal failures as the result of these stresses. Besides, it will be developed an analytical method to evaluate the forces and stresses in winding three phase transformer under a three phase short circuit. Finally, the analytical method results will be compared with a computer simulation based in time domain using the software FEMM, which applies the finite element method. / Transformadores de potência são equipamentos essenciais aos sistemas elétricos e também um de seus componentes de maior preço. Quando estes equipamentos se danificam ou apresentam algum tipo de falha, o seu reparo ou até mesmo sua substituição demanda altíssimos custos financeiros, tanto pelo alto valor comercial destes equipamentos como pela perda temporária da capacidade de transmissão de energia elétrica. Muitas falhas destes equipamentos devem-se à redução da suportabilidade da isolação dos seus condutores/enrolamentos causado pelos fenômenos eletroquímicos do líquido de resfriamento (óleo), pelas vibrações produzidas pelas forças eletromecânicas durante a sua operação normal, ou seja, em regime permanente, e também pelas deformações dos enrolamentos causadas pelas altas correntes de curto-circuito. Espera-se, no entanto, que um transformador suporte um determinado número de curtos-circuitos durante seu tempo de operação. No entanto, verifica-se que cada evento poderá provocar pequenos deslocamentos relativos nos enrolamentos, os quais podem aumentar cumulativamente, reduzindo desta forma a capacidade do transformador de suportar novos esforços eletromecânicos. Neste contexto, torna-se importante a verificação periódica das suas condições mecânicas, principalmente nas unidades com muito tempo de operação, de forma a se obter subsídios para impedir falhas catastróficas. O emprego de técnicas especiais é requerido para o monitoramento e avaliação das condições mecânicas do enrolamento de um transformador. Apesar de este assunto ser uma preocupação constante dos projetistas e fabricantes de transformadores, bem como dos profissionais de manutenção e operação das empresas de energia elétrica, há certa carência de metodologias e ferramentas consistentes para se avaliar os efeitos dos esforços mecânicos decorrentes das elevadas correntes transitórias sobre estes equipamentos. Nessa perspectiva, este trabalho tem por meta o entendimento das características dos esforços mecânicos causados pelas forças radiais e axiais nos enrolamentos dos transformadores. Para tanto, esta dissertação mostrará os diferentes tipos de esforços eletromecânicos passíveis de ocorrer nos enrolamentos de um transformador, identificando os principais tipos de falhas provocadas por essas solicitações. Em seguida, será desenvolvida uma metodologia analítica para estimar as forças e estresses nos enrolamentos de um transformador trifásico submetidos a um curto-circuito trifásico. Assim, os valores obtidos pela metodologia analítica serão confrontados com resultados de uma simulação computacional no domínio do tempo utilizando-se o programa FEMM baseado na técnica de elementos finitos. / Mestre em Ciências