António Roque

Control of a power supply with cycling current using different controllers

Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) relaxometers require controlled current sources in order to get accurate flux density with respect to its magnet. The main elements of the proposed solution are a power semiconductor, a DC voltage source and the magnet. The power semiconductor is commanded in order to get a linear control of the flux density. To implement the flux density control, a Hall Effect sensor is used. Furthermore, the dynamic behavior of the current source is analyzed and compared when using a PI controller and a PD2I controller.

Current source of a FFC NMR relaxometer linearly controlled

A Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) relaxometer combines optimized magnets (low volume and power losses) and power apparatus that integrate power supplies and control methods. The magnet of a FFC NMR relaxometer determines the requirements of the main power supply. As main requirement, the magnet current should be controlled linearly in order to control the magnet flux density. In addition, the current control should be accurate and having an adequate thermal stability. In this paper, framed by the main blocks that integrate a FFC NMR relaxometer, the topology of the magnet current source is presented. The operating modes and the control methodology are also described. Experimental results are presented validating the proposed solution according to the application requirements. A power losses analysis supported by experimental results is performed for the generalized operating modes.

Charging electric vehicles from photovoltaic generation with intermediate energy storage

The consumption of fossil fuels on a large scale and the environmental problems resulting from the emission of polluting gases into the atmosphere, created the need for change in mobility habits in todays daily life. Responding to these new challenges, strong investments have been made by companies and governments in the automotive sector being the development of electric vehicles and the technologies associated with them an assumed priority by all the stakeholders. Fast charging of batteries is one of the technical issues that have been addressed. In addition, fast charging of electric vehicles in remote locations can be implemented taking advantage of renewable energy systems and avoiding power demand from conventional power grids. In this paper, the power can be supplied by a photovoltaic generation system and is managed taking advantage of an intermediate energy storage system based on a battery bank and supercapacitors. The operation of the proposed system is observed performing simulations conditions, which allow checking the correct operation of the system and its response to possible failures of the subsystems that constitute it.

Comparing two power supplies for Fast-Field Cycling Nuclear Magnetic Resonance relaxometers power losses and performance

The 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.

Electromagnetic and thermal aspects of a Fast Field Cycling NMR equipment

The Fast Field Cycling Nuclear Magnetic Resonance (FFC-NMR) technique has been spreading its application to new areas such as oil and food industry. Consequently, new features and improvements concerning the equipment available has been investigated and exploited. Under this context, this paper describes the main aspects concerning the electromagnetic and thermal behavior of the main power supply and the magnet, respectively. The proposed power supply and the magnet were developed under the specifications of the FFC-NMR equipment and in order to match the requirements of the most recent areas of application. The dynamic behavior of the power supply is analyzed based on simulation results, being the thermal study of the magnet performed using finite element method software.

FFC NMR relaxometers on education: Topologies, control techniques and electromagnetic devices

The Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) equipment has been mainly developed by engineers with a strong background in power electronics, control and physics. This technique has been widely used by physicists, chemists, biologists, pharmacists and food analysts. During the last decades, the development of this type of apparatus has been taking advantage of the power semiconductors, topologies of the power electronic converters, control techniques, computational tools and materials, among other aspects. In this paper, teaching aspects of using this type of equipment and technique in courses of physics and electrical engineering is described.