• Energy Research

Made available in DSpace on 2014-10-09T12:37:50Z (GMT). No. of bitstreams: 0 Made available in DSpace on 2014-10-09T14:08:31Z (GMT). No. of bitstreams: 1 05380.pdf: 5707781 bytes, checksum: f7a7b65bad72a837f9123ca6deee3226 (MD5) Dissertacao (Mestrado) IPEN/D Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

In low speed applications such as wind energy conversion systems, the use of direct driven generators, instead of geared machines, reduces the number of drive components, which offers the opportunity to reduce costs and increases system reliability and efficiency. The Axial Flux Permanent Magnet (AFPM) generator is particularly suited for such application, since it can be designed with a large pole number and a high torque density. This paper presents the design, construction and experimental validation of a double-sided AFPM synchronous generator prototype, with internal rotor and slotted stators. Design objectives embrace achieving a good compromise between performance characteristics and feasibility of construction, which results in a cost competitive machine.

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Present plasma direct energy conversion (DEC) system has been developed since proposal of ARTEMIS. The system for D-3He reactor is composed of cusp-type DEC (CuspDEC) for particle discrimination, traveling wave DEC (TWDEC) for recovery of high energy protons, and secondary electron DEC (SEDEC) for recovery of extremely accelerated protons. Studies on each device are in the third stage, where higher capability of each device will be derived. Various proposals and examinations were reported and the present paper treats the researches comprehensively and shows explanation and discussion for some researches: separation of high density plasma and ion-ion separation in CuspDEC, studies on modulation in TWDEC, and improvement of electron collection in SEDEC.

Porous media combustion (PMC) is characterised by intense heat exchange from the combustion gases to the solid media, enabling higher temperatures at the outer surface of the solid matrix, which makes it suitable for coupling with thermophotovoltaic (TPV) systems. This research, for the first time, experimentally and numerically investigates how to regulate combustion and the radiative emission of a porous media matrix to achieve stable spectral control for an active TPV system. As such, this thesis provides a series of systematic steps towards developing a fundamental understanding of a PMC-TPV system, including: a flame stability analysis, combustor design optimisation, radiative control, PV cell characterisation, and system-level optimisation. A radiant reflector was found to shift the stable flame regime and increase the radiant efficiency to 63% at an operating temperature of 1356 C. Additionally, a 24-cell gallium antimonide (GaSb) array, which was attached to a heat sink to prevent overheating, was used to harvest the radiant emission from a hot (>1200 C), yttria-stabilised zirconia/alumina composite (YZA) ceramic foam (both erbia-coated and uncoated). A low-cost erbia (Er2O3) coating on a novel porous media combustion-based thermophotovoltaic (PMC-TPV) reactor was shown to achieve continuous combined heat and power generation. The results indicate that the erbia coating on the YZA foam increased performance, achieving a maximum in-band emission fraction of 25.4% at a firing rate of 1300 kW/m2 (i.e. a 10% of increase compared to the non-coated configuration), which provides a temperature of 1285 C and a 1 Watt electrical output. An electrical model of GaSb cells shows that an undamaged cell array could reach an output power 2.28 W for this configuration. A system-level simulation confirmed that the GaSb-based PMC-TPV system is the most cost-effective option relative to other cell types. Overall, this work has identified promising new directions for how the fields of PMC and PV can be brought together with respect to choosing porous materials, the optical properties of the components (i.e. emitter coatings and filters), and the PV cell type. It is expected that these insights and contributions will form the basis for a new generation of high-performance TPV systems.

A mathematical modeling of a system consisting of Thermionic Energy Converter (TIEC) and an Alkali Metal Thermal to Electrical Converter (AMTEC) is performed to optimize the efficiency of the cascade. The TIEC is heated by electron bombardment, which converts heat partially into electrichy and rejects the remaining. The AMTEC utilizes the rejected heat. A thermal model of the cascade converter has been developed to analyze the key parameters such as power level, heat fluxes, and temperatures. The efficiency of the cascaded cell is improved and h is greater than any of the individual efficiencies of the cells and smaller than the sum of the individual efficiencies. The problem is divided into two smaller segments and then MATHCAD was used to solve 12 non-linear system of equations. Algorithms for solving the system of non-linear equations are also analyzed. The order of two of the algorithms are calculated and recommendation is made for a custom made program which can be used for solving the whole 16 node system of non linear equations.

Power degradation in the PX-3 A Alkali Metal Thermal-to-Electric Converter cell refers to the problem of decrease in power output with time. This problem has been observed for 12000 hours of operation of the cell in experiments. Since the cell has applications in deep-space exploration, it is necessary that the power output does not fall to levels below the minimum requirements of the spacecraft. It is therefore important to investigate the reasons for this power loss. The cell uses â-alumina as a solid electrolyte. The material degrades with time as a result of the chemical and thermal conditions within the cell during operation, â- alumina degradation manifests itself as an increase in its ionic resistance which reduces power output. The â-alumina is responsible for almost all of the power degradation in the first 7000 hours of operation. Thereafter, though â-alumina degradation continues to cause power loss, other factors, components and materials in the cell also contribute to power loss. The role of the P"-alumina in power loss is investigated and quantitatively established and it is shown that other components also are responsible for power degradation. Finally, some suggestions are made that will help reduce the rate of power degradation and extend the useful and functional time of the cell.

D.Ing. (Electrical and Electronic Engineering) The non-linear resonant pole (NLRP) inverter is part of the family of soft switching topologies based on resonant phenomena. The sequence of commutation that occurs between the semiconductors of a conventional voltage source inverter is modified through the mechanisms of energy exchange between added passive energy storage components. The NLRP inverter, through its psuedo resonant behaviour (resonant transition), gives rise to zero voltage and zero current turn-on of the switching devices as well as soft turn-off. The switching device voltage stresses are around 1 p.u, while the current stresses are reduced to around 1.3 p.u, by feeding back a portion of the load current. The rms current flowing through the inductor and switches is greatly reduced by driving the inductor into saturation (non-linear mode of operation). The advantages of soft switching, such as high switching frequency which allows greater dynamic response and higher power densities, along with reduced EMI, are achieved with this topology. Detailed analysis at multi- and sub-cycle levels is carried out, resulting in circuit equations and the criteria for commutation success. The commutation boundaries of the inverter are defined and methods discussed on how to extend them. The modulation of the NLRP inverter and some aspects regarding its use as part of both low and high performance induction motor drives are presented.