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Publicações

Publicações por Rui Esteves Araujo

2016

Evaluation of a Novel BEV Concept Based on Fixed and Swappable Li-Ion Battery Packs

Autores
Barreras, JV; Pinto, C; de Castro, R; Schaltz, E; Andreasen, SJ; Rasmussen, PO; Araujo, RE;

Publicação
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

Abstract
In this paper, a novel battery electric vehicle (BEV) concept based on a small fixed and a big swappable Li-ion battery pack is proposed in order to achieve longer range, lower initial purchase priceand lower energy consumption at short ranges. For short ranges, the BEV is only powered by the relatively small-fixed battery pack, without the large swappable battery pack. In this way, the mass of the vehicle is reduced and, therefore, the energy consumed per unit distance is improved. For higher ranges, the BEV is powered by both battery packs. This concept allows the introduction of subscription-based ownership models to distribute the cost of the large battery pack over the vehicle lifetime. A methodology is proposed for the analysis and evaluation of the proposed concept in comparison with a direct owned nonswappable single-pack BEV, proving that significant improvements on city fuel economy (up to 14%) and economic benefits are achievable under several scenarios. These results encourage further study of battery swapping service plans energy management strategies.

2016

Evaluation of Advanced Control for Li-ion Battery Balancing Systems Using Convex Optimization

Autores
Pinto, C; Barreras, JV; Schaltz, E; Araujo, RE;

Publicação
IEEE TRANSACTIONS ON SUSTAINABLE ENERGY

Abstract
Typically, the unique objective pursued in either active or passive balancing is equalization of single cell charge. However, a balancing circuit may offer more control features, like virtual equalization of single cell internal resistance or thermal balancing. Such control features for balancing systems are evaluated in this paper by means of convex optimization. More than one hundred cases in a pure EV application are evaluated. Balancing circuits' efficiency models are implemented and realistic cell-to-cell parameter distributions are considered based on experimental data. Different battery sizes and driving cycles are considered. Balancing circuit topology is taken into account by selecting a specific category of energy transfer: cell-to-heat, bypass, cell-to-pack, pack-to-cell, cell-to-cell shared, cell-to-cell distributed or cell-to-pack-to-cell. In general, better results in terms of energy losses, available capacity or temperature are obtained for the last three categories, even for moderate balancing currents. In particular, remarkable improvements are observed under conditions of high power demand with high variability, i.e., smaller battery sizes and more demanding driving cycles.

2016

Indoor localization with audible sound - Towards practical implementation

Autores
Moutinho, JN; Araujo, RE; Freitas, D;

Publicação
PERVASIVE AND MOBILE COMPUTING

Abstract
This paper presents an innovative evaluation and comparison of several methods and techniques necessary to implement an indoor localization system based on audible sound. Experiments were conducted in a room with conditions very close to possible practical application demonstrating that time delay estimation using generalized cross-correlation phase transform provides the best estimate to the distance to fixed anchors, and highlight the benefits of a new localization method entitled circle shrinking based on an optimization methodology. Of the three optimization methods tested, Gauss-Newton proves to be the most adequate, and among the three medium access methods evaluated, code division multiple access acoustic transmission provided the best results. A localization system combining these components and using only off-the-shelf hardware reached an average accuracy of 1.3 cm in the central area of the test room with an excitation signal-to-noise ratio as low as 7.2 dB, an almost unperceivable noise like audio signal. These results represent an advance of the state-of-the-art in indoor localization systems, pointing towards the possibility of widespread practical implementation with everyday use components.

2013

Automatic decomposition and allocation of safety integrity levels using a penalty-based genetic algorithm

Autores
Parker, D; Walker, M; Azevedo, LS; Papadopoulos, Y; Araujo, RE;

Publicação
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Abstract
Automotive Safety Integrity Levels (ASILs) are used in the new automotive functional safety standard, ISO 26262, as a key part of managing safety requirements throughout a top-down design process. The ASIL decomposition concept, outlined in the standard, allows the safety requirements to be divided between multiple components of the system whilst still meeting the ASILs initially allocated to system-level hazards. Existing exhaustive automatic decomposition techniques drastically reduce the effort of performing such tasks manually. However, the combinatorial nature of the problem leaves such exhaustive techniques with a scalability issue. To overcome this problem, we have developed a new technique that uses a penalty-based genetic algorithm to efficiently explore the search space and identify optimum assignments of ASILs to the system components. The technique has been applied to a hybrid braking system to evaluate its effectiveness. © 2013 Springer-Verlag.

2017

Control of an isolated single-phase bidirectional AC-DC matrix converter for V2G applications

Autores
Varajao, D; Araujo, RE; Miranda, LM; Pecas Lopes, JP; Weise, ND;

Publicação
Electric Power Systems Research

Abstract
This paper describes a new current control method that enhances the dynamic performance of a single-phase bidirectional AC-DC battery charger to provide a high-frequency link between the grid and electric vehicle. The single-stage structure and the bidirectional power flow make the matrix converter an attractive solution for electric vehicle (EV) battery charging applications in the context of smart grids. The operating principles and modulation method are analyzed and discussed in detail. Furthermore, a current controller improved with a Smith predictor is proposed to decrease the phase delay in the measurement of the average current in the battery pack. The SP reduces the rise time to around a third and the settling time to half when compared with a PI controller. Simulations and experimental results from a laboratory prototype are shown to verify the feasibility of the proposed control scheme. © 2017 Elsevier B.V.

2013

Indoor Sound Based Localization: Research Questions and First Results

Autores
Moutinho, J; Freitas, D; Araujo, RE;

Publicação
TECHNOLOGICAL INNOVATION FOR THE INTERNET OF THINGS

Abstract
This PhD work has the goal to develop an inexpensive, easily deployable and widely compatible localization system for indoor use, suitable for pre-installed public address sound systems, avoiding costly installations or significant architectural changes in spaces. Using the audible sound range will allow the use of low cost off-the-shelf equipment suitable for keeping a low deployment cost. The state-of-the-art presented in this paper evidences a technological void in low-cost, reliable and precise localization systems and technologies. This necessity was also confirmed by the authors in a previous project (NAVMETRO (R)) where no suitable technological solution was found to exist to overcome the need to automatically localize people in a public space in a reliable and precise way. Although research work is in its first steps, it already provides a thorough view on the problem while discussing some possible approaches and predicting strategies to overcome the key difficulties. Some experiments were already conducted validating some initial premises and demonstrating how to measure the signal's time-of-flight necessary to infer on distance calculations.

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