System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

HVDC Systems in Smart Grids

© 1963-2012 IEEE. The use of direct current (dc) power networks, either at high voltage or at medium voltage, is being increasingly seen in modern smart grids. This is due to the flexible control possible with dc and its ability to transmit and distribute power under circumstances where alternating current (ac) networks are either unable to, or less economic. This paper provides an overview of the evolution of high-voltage dc (HVDC) transmission from early Thury systems, to modern ultrahigh-voltage dc and multiterminal voltage-source converter systems. The operation of both current-source and voltage-source systems is discussed, along with modeling requirements. The paper provides a snapshot of the state of the art of HVDC with copious references to enable in-depth reading. Key developments over the last 20 years are highlighted. Issues surrounding multiterminal operation and dc protection are explained, along with drivers in economics and policy. This will inform HVDC integration into smart grids.status: publishe

Managing emergent changes: ad hoc teams\u27 praxis and practices

Purpose The purpose of this paper is to explore how emergent changes are handled in research and development (R&D) projects. R&D projects\u27 business potential lies in their exploration of the unknown; conversely, this makes them uncertain endeavours, prone to emergent changes. Design/methodology/approach Uses a single-case-study design, based on a projects-as-practice perspective and a soft systems methodology (SSM) analysis, to map how ad hoc R&D teams handle emergent changes, specifically the solution identification and assessment phase and the implementation plan. An R&D project in the power industry, involving over 250 engineers, was analysed. Findings This paper shows how emergent changes are handled differently from initiated changes during the decision-making phase. The system analysis shows that the most critical factors for managing these changes are: collective reflection between project parties; and including experienced engineers in implementation-plan reviews. Practical implications The results are of relevance both to R&D managers aiming to improve team performance and to general project management. Informal notions of emergent changes can be formalised in the change request process. Weaknesses in the project team\u27s organisation are highlighted, and details of how of how to mitigate these are provided. Originality/value Combines engineering-design and project-management research on emergent changes, adding to the former regarding people-organisational and strategic issues. Furthers understanding of the projects-as-practice approach and emergent change (deviations) handling by ad hoc teams in a project environment. SSM has not previously been used to explore aspects of projects-as-practice, and this is a novel way of adding to the body of knowledge on project praxis and practise