Energy Transformations in a Self-Excited Switched Reluctance Generator

Wind generation systems require mechanisms that allow optimal adaptation of the generator to varying wind speed and to extract maximum energy from the wind. Robust and affordable high-performance methods are also needed for isolated sites. This paper takes this approach, in which an AC switched reluctance generator is used as a generator with a variable rotor speed. Although the voltage obtained is of insufficient quality to connect the generator directly to the power grid, this kind of generator can be used in isolated sites to charge a battery bank with a simple bridge rectifier. Due to the nonlinear behavior of the machine with the position and current, along with the alternating nature of the current that circulates through its phases, the machine experiences cyclical energy transformations of a mechanical, electrical and magnetic nature. This paper analyzes these transformations for the purpose of providing guidelines for machine design and optimization as a wind turbine in isolated sites

C-Core switched reluctance generator : constructive and operational aspects

Orientadores: Ernesto Ruppert Filho, Tárcio André dos Santos BarrosTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O gerador de relutância variável (GRV) é considerado uma alternativa competitiva às máquinas elétricas convencionais utilizadas para a produção de energia elétrica a partir da energia eólica em aplicações de pequeno e médio portes. Entre os tipos construtivos dessa máquina elétrica, destaca-se a de fluxo magnético axial com núcleo do tipo C (GRV-C) que é abordada nesta pesquisa. Esta tese apresenta uma proposta de metodologia para o projeto eletromagnético de geradores de relutância variável de fluxo magnético axial com núcleo do tipo C e realiza análises estáticas e dinâmicas da sua operação em modo autoexcitado. O GRV-C é um tipo de gerador de relutância variável não convencional sendo que a maioria das pesquisas realizadas com o GRV focam nas estruturas tradicionais (estruturas regulares e de fluxo radial). Desta forma, este trabalho complementa a literatura, apresentando considerações sobre os dimensionamentos elétrico e magnético do GRV-C de pequeno e médio portes. A metodologia proposta foca diferentes aspectos. Primeiramente, as dimensões de um projeto inicial do núcleo eletromagnético são calculadas por meio de equações analíticas e de considerações baseadas em projetos de máquinas de relutância convencionais. Na sequência, um modelo usando o método dos elementos finitos em duas dimensões (MEF-2D) é utilizado no processo de otimização dos projetos elétrico e magnético. Optou-se pelo MEF-2D no processo de otimização dos parâmetros construtivos a fim de reduzir o tempo de processamento, quando comparado ao método dos elementos finitos em três dimensões (MEF-3D). Foi necessário inserir fatores de correção no modelo em duas dimensões. A análise da operação do GRV-C realizada nesta pesquisa é distinta das encontradas na literatura. Ela apresenta estudos comparativos entre três projetos de geradores obtidos a partir da metodologia proposta. Simulações estáticas e dinâmicas foram realizadas por meio de dois modelos diferentes: um usando o método dos elementos finitos e o outro baseado nas curvas de magnetização do gerador que representam bem as não linearidades magnéticas do gerador elétrico. Seguindo a metodologia de projeto proposta, foram obtidas as dimensões de um quarto gerador (utilizando o material magnético o disponível na empresa responsável pela fabricação) e o protótipo de um dos núcleos C foi construído a fim determinar os resultados estáticos experimentais. Os resultados de simulação e experimentais obtidos atestam a viabilidade e eficiência da metodologia proposta para o projeto de um GRV-CAbstract: The switched reluctance generator (SRG) is considered a competitive alternative to traditional electric machines used in wind energy systems for electric power generation for small and medium power applications. Prominent among the topologies of these electric machines is the Axial-Flux Switched Reluctance Generator with C Core (C-SRG) that is addressed in this research. This thesis presents a methodology proposal for the electromagnetic design of the Axial-Flux Switched Reluctance Generator with C Core and performs statics and dynamics analysis in self-exciting operation mode. The C-SRG is a non-conventional type of the switched reluctance generator and most research focuses on traditional structures of SRG (regular with the radial flux). So, this research supplements the literature, addressing a comprehensive framework of the electric and magnetic design of the C-SRG for small and medium power requirement. The proposed methodology focuses on different aspects. First, the dimensions of one initial design are obtained from analytic equations and design considerations based on traditional switched reluctance machines. After, a two-dimensional finite element method (FEM-2D) model is used to optimize the constructive parameters. The FEM-2D was chosen due to the high processing time during the optimization process when compared to three-dimensional finite element method (FEM-3D) model. However, it was necessary to include correction factors to calculate the inductances of the C-SRG model. The thesis C-SRG operations analysis is distinct from similar studies. It presents the comparative of three C-SRGs designs that were obtained from the proposed methodology. The static and dynamic simulations use two different models: one based on finite element method and the other on the generator¿s magnetization curves that well represents the magnetic nonlinearities of the electric generator. From the proposed design methodology, the final dimensions of a fourth generator are obtained (using the magnetic material available in the company responsible of the manufacturing) and an C-core prototype of the generator was built in order to obtain its experimental static results. The simulated and experimental results attested the viability and efficiency of the proposed methodology on the C-SRG designDoutoradoEnergia EletricaDoutora em Engenharia Elétric

Multi-objective torque control of switched reluctance machine

PhD ThesisThe recent growing interest in Switched Reluctance Drives (SRD) is due to the electrification of many products in industries including electric/hybrid electric vehicles, more-electric aircrafts, white-goods, and healthcare, in which the Switched Reluctance Machine (SRM) has potential prospects in satisfying the respective requirements of these applications. Its main merits are robust structure, suitability for harsh environments, fault-tolerance, low cost, and ability to operate over a wide speed range. Nevertheless, the SRM has limitations such as large torque ripple, high acoustic noise, and low torque density. This research focuses on the torque control of the SRD with the objectives of achieving zero torque error, minimal torque ripple, high reliability and robustness, and lower size, weight, and cost of implementation. Direct Torque Control and Direct Instantaneous Torque Control are the most common methods used to obtain desired torque characteristics including optimal torque density and minimized torque ripple in SRD. However, these torque control methods, compared to conventional hysteresis current control, require the use of power devices with a higher rating of about 150% to achieve the desired superior performance. These requirements add extra cost, conduction loss, and stress on the drive’s semiconductors and machine winding. To overcome these drawbacks, a simple and intuitive torque control method based on a novel adaptive quasi sliding mode control is developed in this study. The proposed torque control approach is designed considering the findings of an investigation performed in this thesis of the existing widely used control techniques for SRD based on information flow complexity. A test rig comprising a magnet assisted SRM driven by an asymmetric converter is constructed to validate the proposed torque control method and to compare its performance with that of direct instantaneous torque control, and current hysteresis control methods. The simulation and experimental results show that the proposed torque control reduces the torque ripple over a wide speed range without demanding a high current and/or a high switching frequency. In addition, It has been shown that the proposed method is superior to current hysteresis control method in the sensorless operation of the machine. Furthermore, the sensorless performance of the proposed method is investigated with the lower component count R-Dump converter. The simulation results have also demonstrated the excellent controller response using the standard R-Dump converter and also with its novel version developed in this thesis that needs only one current sensor

Fast track to renewables: Low emission electricity for south west Australia by 2030

Could renewable energy be implemented rapidly and on a large scale to supply the demand of stationary electrical grid systems? This thesis takes a step towards answering this question by simulating 100% renewable energy scenarios for the South-West Interconnected System (SWIS), which supplies electricity to most of the population and industry in the southwest of Western Australia (SWWA). The SWIS is remarkable in that it is both isolated from other grids and currently has little available hydro-power. Solar and wind energy were chosen as the energy sources to be simulated because they are commercially mature technologies, already have a presence in the SWIS, are widely available in many other parts of the world, yet they are geographically and temporally variable. To simulate the operation of rooftop solar PV and large scale solar and wind power plants, heuristic models were built to generate synthetic hourly values of solar and wind energy resources anywhere within the SWWA. An integrated simulation of the SWIS grid was built using simple models of population increase, energy efficiency, distributed battery storage and seasonal power to gas storage. The construction schedules required to build a 100% renewable system for the SWIS by the year 2030 were found to be achievable for scenarios with a mix of solar PV, solar thermal and wind. If solar PV, wind and battery storage capacity could maintain exponential growth, then the required growth rates are less than current global growth rates. Energy efficiency would need to improve at a greater rate, though still moderate, than the current global improvement rate. However, the more that energy efficiency is improved, the lower the total demand, and the easier the task becomes for the other technologies. The findings of this thesis have positive implications for world-wide rapid transformation to low emission electricity generation