Distributed Control with Low-Rank Coordination

A common approach to distributed control design is to impose sparsity constraints on the controller structure. Such constraints, however, may greatly complicate the control design procedure. This paper puts forward an alternative structure, which is not sparse yet might nevertheless be well suited for distributed control purposes. The structure appears as the optimal solution to a class of coordination problems arising in multi-agent applications. The controller comprises a diagonal (decentralized) part, complemented by a rank-one coordination term. Although this term relies on information about all subsystems, its implementation only requires a simple averaging operation

H2 Optimal Coordination of Homogeneous Agents Subject to Limited Information Exchange

Controllers with a diagonal-plus-low-rank structure constitute a scalable class of controllers for multi-agent systems. Previous research has shown that diagonal-plus-low-rank control laws appear as the optimal solution to a class of multi-agent H2 coordination problems, which arise in the control of wind farms. In this paper we show that this result extends to the case where the information exchange between agents is subject to limitations. We also show that the computational effort required to obtain the optimal controller is independent of the number of agents and provide analytical expressions that quantify the usefulness of information exchange

Battery Capacity of Deferrable Energy Demand

We investigate the ability of a homogeneous collection of deferrable energy loads to behave as a battery; that is, to absorb and release energy in a controllable fashion up to fixed and predetermined limits on volume, charge rate and discharge rate. We derive bounds on the battery capacity that can be realized and show that there are fundamental trade-offs between battery parameters. By characterizing the state trajectories under scheduling policies that emulate two illustrative batteries, we show that the trade-offs occur because the states that allow the loads to absorb and release energy at high aggregate rates are conflicting

A Decomposition Result in Linear-Quadratic Coordinated Control

Scalability is a fundamental requirement in control design for large-scale systems. Typically, it needs to be considered explicitly at the expense of performance degradation and more complicated design procedures. In this paper, we present a class of large scale systems where scalability is an inherent property of the optimal centralized solution. More specifically, we study a coordination problem where a group of identical subsystems are required to satisfy an equality constraint on the sum of their inputs. We show that the problem can be completely decomposed in terms of the unconstrained problems associated with each subsystem. In particular, the computational effort required to obtain the optimal solution is independent of the number of subsystems and the only global information processing required to execute the optimal control law is a simple summation, which scales well when the number of subsystems grows large

Risk assessments for new bioinvasions for the North Sea Region

This deliverable is a compilation of summaries of four scientific papers that cover different aspects of risks connected to marine bioinvasions in the North Sea Region. One of the papers looks deeper into global shipping and adds several factors to shipping density to describe hotspots for potential invasions and invasion routes. Two of the papers dig into concerns of regional perspective (the Wadden Sea), one developing a model of a specific kind of water body’s vulnerability to non-native, the other dealing with questions related to when a species should be stated as a non-native and when it has become part of the native “natural” ecosystem. Finally, one paper is on risk assessment for exemptions of ballast water treatment (also see David, M. and Gollasch, S, 2010, for risk assessment focussing on intra North Sea shipping). All these articles contribute to the understanding of how the risks of bioinvasions must be tackled on a larger geographic scale. Other important risk reduction measures are modelling approaches considering biology and geology of the oceans and monitoring approaches, for example the building of databases on marine invasive species. Here, knowledge about the biology and ecology of the species is important, as well as the abiotic and biotic circumstances of the area of origin, as such information may for example be used to assess whether or not water bodies comply with the ecological demands of the non-natives or to predict scenarios in various kinds of models (e.g. Leewis and Gittenberger, 2011).https://commons.wmu.se/nsbwo/1004/thumbnail.jp

Biofouling : a means of aquatic species transfer

Ships carry seawater in their ballast tanks when they are not fully loaded with cargo, in order to maintain adequate trim, draught and stability, adjust list and limit stresses on the hull. It is now well documented that the water pumped into the ship contains aquatic organisms – which can also sink to the sediments at the bottom of tanks – and that these organisms are thereby transferred from the port of origin to the destination. But it is seldom mentioned that aquatic organisms are also found on the outside of ships, attached on their hulls and appendages, as a result of a very dynamic process called ‘biofouling’.https://commons.wmu.se/nsbwo/1002/thumbnail.jp