Browsing by Author "Sousa, Duarte M."
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- Comparing the power losses of power supplies for fast-field cycling nuclear magnetic resonance equipmentPublication . Lima, Marco; Pereira, Bruno; Sousa, Duarte M.; Roque, António; Margato, ElmanoThe main feature of the Fast-Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) power supplies is to drive a controlled current fulfilling the requirements of this technique. This feature allows fast switching the current of the FFC magnet and performing accurate and repetitive current cycles. When designing this equipment the power losses is not a fundamental parameter of the optimization process but are estimated in order to validate the topology of the final solution giving that the efficiency of the power solution influences the power consumption, and therefore the operational costs, which should be minimized. Under this context, from the power efficiency viewpoint, the power losses of two possible solutions are compared and discussed in this paper. Typical FFC current cycles are used as reference in order to balance the pros and cons of both solutions.
- Comparing two power supplies for fast-field cycling nuclear magnetic resonance relaxometers power losses and performancePublication . Lima, Marco; Pereira, Bruno; Sousa, Duarte M.; Roque, António; Margato, ElmanoThe main power supply of a Fast Field-Cycling Nuclear Magnetic Resonance (FFC-NMR) is the key element comparing the performance of different solutions. The power supply is a current source that supplies a magnet being the current controlled in order to perform adjustable and repetitive current cycles. This power supply can be based on different topologies, operating principles and controlled using distinct techniques. If for the final users of this experimental technique the current cycles of the equipment is the core feature, for the developers also the power losses distribution needs to be analyzed in order to develop efficient solutions. In this paper, the power losses and the dynamic behavior of two solutions for the FFC-NMR power supply are compared and discussed.
- Design overview of a toroidal fast-field cycling electromagnetPublication . Cunha, João T.; Sebastião, Pedro J.; Roque, António; Vaz da Silva, V; Sousa, Duarte M.In this paper, the design and development of a novel Fast-Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) relaxometer’s electromagnet is described. This magnet is tailored to increase the relaxometers’s usability, by increasing its portability capacities. It presents a compact toroidal shaped iron core, allowing to operate in a field range of 0 to 0.21 T, with high field homogeneity (less than 800 ppm in a volume of ≈ 0.57 cm3 ), low power consumption and reduced losses (about 40W). The simulation software COMSOL Multiphysics® is used to characterize the induced magnetic field, the heating and the cooling effects. The proposed optimized layout constitutes an innovative solution for FFC magnets.
- FFC-NMR power supply with hybrid controlo of the semiconductor devicesPublication . Roque, Antonio; Sousa, Duarte M.; Oliveira Sebastião, Pedro José; Vaz da Silva, Vitor; Margato, ElmanoThe performance of FFC-NMR power supplies is evaluated not only considering the technique requirements but also comparing efficiencies and power consumption. Since the characteristics of FFC-NMR power supplies depend on the power circuit topology and on the control solutions, the control design is a core aspect for the development of new FFC systems. A new hybrid solution is described that allows controlling the power of semiconductors by switches (ON/OFF mode) or as a linear device. The approach avoids over-design of the power supply and makes it possible to implement new low power solutions constituting a novel design by joining a continuous match between the ON/OFF mode and the linear control of the power semiconductor devices.
- Magnetic flux density distribution in the air gap of a ferromagnetic core with superconducting blocks: three-dimensional analysis and experimental NMR resultsPublication . Roque, António; Sousa, Duarte M.; Margato, Elmano; Machado, Vítor Malo; Sebastião, Pedro J.; Marques, G. D.The design of magnetic cores can be carried out by taking into account the optimization of different parameters in accordance with the application requirements. Considering the specifications of the fast field cycling nuclear magnetic resonance (FFC-NMR) technique, the magnetic flux density distribution, at the sample insertion volume, is one of the core parameters that needs to be evaluated. Recently, it has been shown that the FFC-NMR magnets can be built on the basis of solenoid coils with ferromagnetic cores. Since this type of apparatus requires magnets with high magnetic flux density uniformity, a new type of magnet using a ferromagnetic core, copper coils, and superconducting blocks was designed with improved magnetic flux density distribution. In this paper, the designing aspects of the magnet are described and discussed with emphasis on the improvement of the magnetic flux density homogeneity (Delta B/B-0) in the air gap. The magnetic flux density distribution is analyzed based on 3-D simulations and NMR experimental results.
- Management of an electric vehicle charging system supported by RES and storage systemsPublication . Fernao Pires, Vitor; Roque, António; Sousa, Duarte M.; Margato, ElmanoIt is predicted to the near future that electric vehicle (EV) charging systems will have an important impact on the electric infrastructures. Thus, in order to contribute to a sustainable world, the use of renewable energy sources (RES) will play an important role to generate the required energy to the EVs. However, in order to optimize the global electrical efficiency, the RES should be placed as near as possible to the EVs charging systems. On the other hand, to provide stability to the system, energy storage systems, such as batteries and supercapacitors should also be considered. Under this context, this paper presents an EV charging system supported by RES and a storage system (supercapacitors and batteries). It will be presented the management of the storage systems, as well, an overall controller to stabilize the DC voltage bus. Several modes of the charging system operation will be presented. It also be presented results of the overall system showing the effectiveness of the proposed algorithms.
- Reversible current power supply for fast-field cycling nuclear magnetic resonance equipmentPublication . Lima, Marco; Sousa, Duarte M.; Roque, António; Margato, ElmanoThe Fast Field-Cycling Nuclear Magnetic Resonance (FFC-NMR) is a technique used to study the molecular dynamics of different types of materials. The main elements of this equipment are a magnet and its power supply. The magnet used as reference in this work is basically a ferromagnetic core with two sets of coils and an air-gap where the materials' sample is placed. The power supply should supply the magnet being the magnet current controlled in order to perform cycles. One of the technical issues of this type of solution is the compensation of the non-linearities associated to the magnetic characteristic of the magnet and to parasitic magnetic fields. To overcome this problem, this paper describes and discusses a solution for the FFC-NMR power supply based on a four quadrant DC/DC converter.