Integrated motor drives: state of the art and future trends

With increased need for high power density, high efficiency and high temperature capabilities in Aerospace and Automotive applications, Integrated Motor Drives (IMD) offers a potential solution. However, close physical integration of the converter and the machine may also lead to an increase in components temperature. This requires careful mechanical, structural and thermal analysis; and design of the IMD system. This paper reviews existing IMD technologies and their thermal effects on the IMD system. The effects of the power electronics (PE) position on the IMD system and its respective thermal management concepts are also investigated. The challenges faced in designing and manufacturing of an IMD along with the mechanical and structural impacts of close physical integration is also discussed and potential solutions are provided. Potential converter topologies for an IMD like the Matrix converter, 2-level Bridge, 3-level NPC and Multiphase full bridge converters are also reviewed. Wide band gap devices like SiC and GaN and their packaging in power modules for IMDs are also discussed. Power modules components and packaging technologies are also presented

Romanian Suburban Housing : Home Improvement through Owner-building

The new suburban housing developments in post-socialist cities have been ubiquitous icons of socioeconomic and physical change. This paper examines suburban owner-built housing as a long-term strategy of home improvement in Romania. It analyses residents’ motivations and financial strategies to move up the housing ladder through owner-building and their responses to key neighbourhood problems, in particular poor public infrastructure and non-existent public facilities. I argue that owner-builders generally benefitted from the economic informality, the relaxed legal culture and the unregulated housing context of the Romanian post-socialist transition; but the absence of public actors has weakened their achievements, which is most apparent at neighbourhood level. The paper draws attention to a context of politico-economic reforms and a set of socio-cultural values of housing privatism in which resident responses may frequently generate consequential (collective) problems localised at the level of streets, neighbourhoods or even the whole society.PostprintPeer reviewe

Overcrowding and ‘under-occupancy’ in Romania : a case study of housing inequality

This paper examines aspects of space consumption in two very different housing types, the communist mid-rise estates and post-communist suburban self-built housing. Examining residents’ perceptions in order to categorize space as overcrowded or under-occupied, the paper engages critically with the issue of the inefficient distribution of Romanian housing, that is a considerable mismatch between dwelling and household size. The analysis documents the continued salience of overcrowding in the communist estates and conversely, self-builders’ satisfaction with the generous size of their new homes. Market forces permit various modes of residential mobility but their likely outcome is growing housing inequality while any redistributive impact will remain insignificant unless policy incentives could facilitate conversion of under-occupied space into (social) renting housing. However, only a sustained delivery of larger and affordable new dwellings could alleviate overcrowding.PostprintPeer reviewe

Effective train routing selection for real-time traffic management: Improved model and ACO parallel computing

The real-time Railway Traffic Management Problem (rtRTMP) is the problem of detecting and solving time overlapping conflicting requests made by multiple trains on the same track resources. This problem consists in retiming, reordering and rerouting trains in such a way that the propagation of disturbances in the railway network is minimized. The rtRTMP is an NP-complete problem and finding good strategies to simplify its solution process is paramount to obtain good quality results in a short computation time. Solving the Train Routing Selection Problem (TRSP) aims to reduce the size of rtRTMP instances by limiting the number of routing variables: during the pre-processing, the most promising routing alternatives among the available ones are selected for each train. Then, the selected alternatives are the only ones used for the rtRTMP. A first version of the TRSP has been recently proposed in the literature. This paper presents an improved TRSP model, where rolling stock re-utilization timing constraints and estimation of train delay propagation are taken into account. Additionally, a parallel Ant Colony Optimization (ACO) algorithm is proposed. We analyze the impact of the TRSP model and algorithm on the rtRTMP through a thorough computational campaign performed on a French case study with timetable disturbances and infrastructure disruptions. The presented model leads to a better correlation between TRSP and rtRTMP solutions, and the proposed ACO algorithm outperforms the state-of-the-art algorithm

Train routing selection problem: Ant colony optimization versus integer linear programming

The real-time Railway Traffic Management Problem (rtRTMP) is the problem of detecting and solving time-overlapping conflicting request done by multiple trains on the same track resources. It typically consists in taking retiming, reordering or rerouting train actions in such a way that the propagation of disturbances in the railway network is minimized. The rtRTMP is an NP-Hard problem and finding good strategy to simplifying its solution process is paramount to obtain good quality solutions in a short computation. Solving the Train Routing Selection Problem (TRSP) aims to do so, by limiting the number of routing variables through a pre-processing that selects the most promising routing alternatives among the available ones for each train in order to reduce the size of rtRTMP instances. This paper studies the performance of an Ant Colony Optimization (ACO) algorithm for the same problem. An integer linear programming formulation for the TRSP is presented and solved using a commercial software, and it is considered as a benchmark. Computational experiments are performed on two practical case studies of the French railway infrastructure: the line near the city of Rouen and the Lille terminal station area. ACO and the commercial solver perform comparably only on small instances and both are able to find optimal solutions. However, on larger instances, the ACO algorithm outperforms the commercial software, both in terms of computation time and solution quality

Performance Evaluation of a Parallel Ant Colony Optimization for the Real-Time Train Routing Selection Problem in Large Instances

The real-time Train Routing Selection Problem (rtTRSP) is the combinatorial optimization problem of selecting, for each train in a rail network, the best routing alternatives. Solving the rtTRSP aims to limit the search space of train rescheduling problems, highly affected by the number of routing variables. The rtTRSP is modelled as the minimum weight clique problem in an undirected k-partite graph. This problem is NP-hard and the problem size strongly affects the time required to compute optimal solutions. A sequential version of the Ant Colony Optimization (ACO) for the rtTRSP has been proposed in the literature. However, in large instances the algorithm struggles to find high-quality solutions. This paper proposes the performance evaluation of a parallel ACO for large rtTRSP instances. Specifically, we analyze the performance of the algorithm by standard parallel metrics. In addition, we test two parallel local search strategies, which consider different solution neighbourhoods. Computational experiments are performed on the practical case study of Lille Flandres station area in France. The results show a significant speed-up of the rtTRSP search space exploration and more promising diversification patterns. Both these improvements enhance the rtTRSP solutions

Preparation and characterization of PbTiO 3-epoxy resin compositionally graded thick films

The preparation and properties of compositionally graded PbTiO3 (PT)-epoxy resin (EPR) composite thick films are reported in this study. Various graded specimens were prepared using gravity casting method by embedding PT powders into the EPR matrix. The existence of a graded structure with two distinct phases, a good intermixing, some air pores, and different morphologies, was confirmed by scanning electron microscopy micrographs. The dielectric constants of these composites have values in the range 5-12 at the frequency of 3c104 Hz and about 3-13 at 3c5 7 108Hz. The composites with permittivity gradient act as a natural impedance match system in the frequency range 2-4 GHz, resulting in very low reflections. Therefore, the compositionally graded PT-EPR composite thick films are suitable as adapting impedance materials for microwave applications