Power System Stability With a High Penetration of Inverter-Based Resources

Inverter-based resources (IBRs) possess dynamics that are significantly different from those of synchronous-generator-based sources and as IBR penetrations grow the dynamics of power systems are changing. This article discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorizations of power system stability in terms of angle, frequency, and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency, and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronization, inertia, and voltage control. The concept of duality is used to unify the synchronization principles of GFM and GFL inverters and, thus, established the generalized angle dynamics. This enables the analytical study of GFM-GFL interaction, which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fall back to the GFL mode during faults to avoid oversizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified, including: 1) extensions of nonlinear stability analysis to accommodate new inverter behaviors with cross-coupled time frames; 2) establishment of spatial–temporal indices of system strength and stability margin to guide the provision of new stability services; and 3) data-driven approaches to combat increased system complexity and confidentiality of inverter models

Disrupting technologies:can the planetary technosphere be steered politically toward a post-capitalist metabolism?

The dominant approach in (trans/sub)national governance of ecological crises, mostnotably climate change, is ecological modernisation. As a framing of collectiveaction, ecological modernisation assumes that the structure of economic growth canbe made sustainable by deploying market instruments to drive the sociotechnicaltransition away from the present fossil-fueled technological base. However, scientistsare warning that such a market-driven technology-frst approach, ensconced inthe UNFCCC since at least the Kyoto Protocol, might not be comprehensive andrapid enough to prevent global warming beyond 2°C above the pre-industrial levelsand thus a signifcant breakdown of ecosystems, rendering vulnerable indigenous,low-income, and working-class communities across the world.This thesis analyses how organisations that are operating in the “middle ground,”between the policymaking arena and their social constituencies, are seeking todisrupt the hegemony of technology-frst policies, while at the same time proposingalternative pathways to transition away from the extractivist and capitalist socialmetabolism to a plurality of environmentally livable and socially just futures for all.Taking an iterative theory-building approach, the thesis frst conceptualises thestrategic agency of these social actors: against the historical trajectory of industrialcapitalist social metabolism; within the power-diferentiated social structures of thecapitalist state; and through the framing and distributive struggles sited betweenthe climate action arena and the social feld. By drawing on a set of complementarytheories — ecological Marxism, environmental humanities, science and technology studies, the critical theory of technology, strategic-relational approach, andinstitutional logics theory — it proposes two analytical frameworks to indicatestrategic openings for “middle-ground” organisations to impact sociotechnical andsociometabolic transitions.In a second step, the thesis provides two case studies contrasting two organisations and two environmentalisms: a degrowth-oriented Institute for Political Ecology,hailing from the periphery of European capitalism; and a green new deal-orientedindustrial trade union Unite the Union, hailing from one of the centres of Europeancapitalism. Drawing on interviews, analysis of documents, and joint research withthe two organisations, it argues that they engage the governance terrain as epistemicactors and work with diferent social constituencies to instil distributive justice into climate action. These actors are disrupting the dominant market-driven technologyfrst approach and are thereby re-politicising and re-democratising the environmentalgovernance. In a fnal step, the thesis analyses and speculates on the prospects oftheir counter-proposals in the present political and environmental conjuncture.<br/

Structural engineering of evolving complex dynamical networks

Networks are ubiquitous in nature and many natural and man-made systems can be modelled as networked systems. Complex networks, systems comprising a number of nodes that are connected through edges, have been frequently used to model large-scale systems from various disciplines such as biology, ecology, and engineering. Dynamical systems interacting through a network may exhibit collective behaviours such as synchronisation, consensus, opinion formation, flocking and unusual phase transitions. Evolution of such collective behaviours is highly dependent on the structure of the interaction network. Optimisation of network topology to improve collective behaviours and network robustness can be achieved by intelligently modifying the network structure. Here, it is referred to as &amp;quot;Engineering of the Network&amp;quot;. Although coupled dynamical systems can develop spontaneous synchronous patterns if their coupling strength lies in an appropriate range, in some applications one needs to control a fraction of nodes, known as driver nodes, in order to facilitate the synchrony. This thesis addresses the problem of identifying the set of best drivers, leading to the best pinning control performance. The eigen-ratio of the augmented Laplacian matrix, that is the largest eigenvalue divided by the second smallest one, is chosen as the controllability metric. The approach introduced in this thesis is to obtain the set of optimal drivers based on sensitivity analysis of the eigen-ratio, which requires only a single computation of the eigenvector associated with the largest eigenvalue, and thus is applicable for large-scale networks. This leads to a new &amp;quot;controllability centrality&amp;quot; metric for each subset of nodes. Simulation results reveal the effectiveness of the proposed metric in predicting the most important driver(s) correctly. &amp;nbsp;&amp;nbsp;&amp;nbsp; Interactions in complex networks might also facilitate the propagation of undesired effects, such as node/edge failure, which may crucially affect the performance of collective behaviours. In order to study the effect of node failure on network synchronisation, an analytical metric is proposed that measures the effect of a node removal on any desired eigenvalue of the Laplacian matrix. Using this metric, which is based on the local multiplicity of each eigenvalue at each node, one can approximate the impact of any node removal on the spectrum of a graph. The metric is computationally efficient as it only needs a single eigen-decomposition of the Laplacian matrix. It also provides a reliable approximation for the &amp;quot;Laplacian energy&amp;quot; of a network. Simulation results verify the accuracy of this metric in networks with different topologies. This thesis also considers formation control as an application of network synchronisation and studies the &amp;quot;rigidity maintenance&amp;quot; problem, which is one of the major challenges in this field. This problem is to preserve the rigidity of the sensing graph in a formation during motion, taking into consideration constraints such as line-of-sight requirements, sensing ranges and power limitations. By introducing a &amp;quot;Lattice of Configurations&amp;quot; for each node, a distributed rigidity maintenance algorithm is proposed to preserve the rigidity of the sensing network when failure in a sensing link would result in loss of rigidity. The proposed algorithm recovers rigidity by activating, almost always, the minimum number of new sensing links and considers real-time constraints of practical formations. A sufficient condition for this problem is proved and tested via numerical simulations. Based on the above results, a number of other areas and applications of network dynamics are studied and expounded upon in this thesis

KC 1.1: Cultural Heritage and Climate Change: Exploring the Impacts and Issues

As noted at the 2017 ICOMOS Assembly in Delhi, cultural heritage is both under threat from climate change, and an asset in our attempts to adapt to and mitigate its impacts. The Paris Agreement emphasizes the need for urgency about climate change; cultural heritage can play a central role in this effort. For example, iconic sites at risk from storms, coastal erosion, wildfires or permafrost thaw can alert public to the very real impacts and costs of climate change. World Heritage Sites (WHS) around the world play a key role in alerting the public to the impacts of local climate change because they are highly visible, and are acknowledged as being important to national, regional and local heritage. As such, broad publicity about impacts and continuing losses such as the news coverage of the sea-level rise at Rapa Nui and Skara Brae and the degradation of the Cedars of Lebanon illustrate the value of both the iconic sites, their resources, and the wide media coverage they can project. Loss and damage due to climate change also includes the impacts on large landscapes and their associated communities. The loss of cultural heritage in these landscapes runs the gamut from intangible heritage such as folk tales, to immoveable cultural heritage, to the lifeways of cultures that have developed over centuries and millennia. Placing those impacts into a broader context is the role, and the goal, of the CCHWG Working Group. This session will address ongoing work by the Climate Change and Heritage Working Group (CCHWG) of ICOMOS that explores the nexus between climate change and heritage. Heritage interacts with climate change through a spectrum of impacts from the physical degradation of standing structures and site ecosystems, to the role that cultural heritage plays in the resilience of communities and their ontological security. Although the focus of the session will be on the impacts of climate change on rural landscapes, the discussion will cover the broad range of the work of the committee. Attached to this abstract is the full report of the Working Group, delivered to the UNESCO World Heritage Committee (WHC) on June 3, 2019 at the 43rd Meeting of the WHC in Baku, Azerbaijan. The audience will be asked to engage with the report to identify publications and case study examples that should be incorporated into the next steps of the work of the CCHWG

12th EASN International Conference on "Innovation in Aviation & Space for opening New Horizons"

Epoxy resins show a combination of thermal stability, good mechanical performance, and durability, which make these materials suitable for many applications in the Aerospace industry. Different types of curing agents can be utilized for curing epoxy systems. The use of aliphatic amines as curing agent is preferable over the toxic aromatic ones, though their incorporation increases the flammability of the resin. Recently, we have developed different hybrid strategies, where the sol-gel technique has been exploited in combination with two DOPO-based flame retardants and other synergists or the use of humic acid and ammonium polyphosphate to achieve non-dripping V-0 classification in UL 94 vertical flame spread tests, with low phosphorous loadings (e.g., 1-2 wt%). These strategies improved the flame retardancy of the epoxy matrix, without any detrimental impact on the mechanical and thermal properties of the composites. Finally, the formation of a hybrid silica-epoxy network accounted for the establishment of tailored interphases, due to a better dispersion of more polar additives in the hydrophobic resin