Contract Composition for Dynamical Control Systems: Definition and Verification using Linear Programming

Designing large-scale control systems to satisfy complex specifications is hard in practice, as most formal methods are limited to systems of modest size. Contract theory has been proposed as a modular alternative to formal methods in control, in which specifications are defined by assumptions on the input to a component and guarantees on its output. However, current contract-based methods for control systems either prescribe guarantees on the state of the system, going against the spirit of contract theory, or can only support rudimentary compositions. In this paper, we present a contract-based modular framework for discrete-time dynamical control systems. We extend the definition of contracts by allowing the assumption on the input at a time $k$ to depend on outputs up to time $k-1$, which is essential when considering the feedback connection of an unregulated dynamical system and a controller. We also define contract composition for arbitrary interconnection topologies, under the pretence of well-posedness, and prove that this notion supports modular design, analysis and verification. This is done using graph theory methods, and specifically using the notions of topological ordering and backward-reachable nodes. Lastly, we use $k$-induction to present an algorithm for verifying vertical contracts, which are claims of the form "the conjugation of given component-level contracts is a stronger specification than a given contract on the integrated system". These algorithms are based on linear programming, and scale linearly with the number of components in the interconnected network. A numerical example is provided to demonstrate the scalability of the presented approach, as well as the modularity achieved by using it.Comment: 17 pages, 6 figure

Formal techniques for the procedural control of industrial processes

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On the Control of Microgrids Against Cyber-Attacks: A Review of Methods and Applications

Nowadays, the use of renewable generations, energy storage systems (ESSs) and microgrids (MGs) has been developed due to better controllability of distributed energy resources (DERs) as well as their cost-effective and emission-aware operation. The development of MGs as well as the use of hierarchical control has led to data transmission in the communication platform. As a result, the expansion of communication infrastructure has made MGs as cyber-physical systems (CPSs) vulnerable to cyber-attacks (CAs). Accordingly, prevention, detection and isolation of CAs during proper control of MGs is essential. In this paper, a comprehensive review on the control strategies of microgrids against CAs and its defense mechanisms has been done. The general structure of the paper is as follows: firstly, MGs operational conditions, i.e., the secure or insecure mode of the physical and cyber layers are investigated and the appropriate control to return to a safer mode are presented. Then, the common MGs communication system is described which is generally used for multi-agent systems (MASs). Also, classification of CAs in MGs has been reviewed. Afterwards, a comprehensive survey of available researches in the field of prevention, detection and isolation of CA and MG control against CA are summarized. Finally, future trends in this context are clarified

Environmental Technology Applications in the Retrofitting of Residential Buildings

The impact of buildings on the environment is nothing short of devastating. In recent years, much attention has been given to creating an environmentally friendly built environment. Nonetheless, it has been levied on new buildings. Residential buildings make up at least 80% of the built environment, most of which were built before any energy efficiency guidelines or regulations were introduced. Retrofitting existing residential buildings is a key yet neglected priority in effecting the transition to an environmentally friendly, sustainable built environment. It is pivotal to reducing a building’s energy consumption while simultaneously improving indoor environmental quality and minimizing harmful emissions. This Special Issue showcases studies investigating applications of environmental technology that is tailored to enhance the sustainable performance of existing residential buildings. It helps to better understand the innovations that have been taking place in retrofitting residential buildings, as well as highlighting many opportunities for future research in this field

Rainwater Harvesting for Drought Mitigation and Flood Management

Rainwater harvesting (RWH) in the UK has seen a low level of uptake relative to similar settings such as Australia and Germany. The relatively low cost of municipal water in the UK limits the financial savings associated with RWH systems, especially in a domestic setting. Although financial benefits can be relatively low (in terms of reduced water bills), academic and practitioner studies have demonstrated the potential for RWH to significantly reduce potable water demands at typical UK houses. Hence, increased uptake of RWH has potential to contribute to mitigating droughts in water scarce regions. Stormwater management in the UK is receiving increasing attention at all levels; from grass-roots sustainable drainage systems (SuDS) such as downpipe disconnections and raingardens; through to implementation of urban realm attenuation schemes and continued development of guidance from UK policy makers. The public realm nature of most SuDS presents a need for partnership approaches to be fostered between infrastructure mangers and the general public. The application of RWH as a technology within the SuDS management train has been limited in the UK as policy makers have taken the view that RWH tanks may be full at the start of a design storm, and thus the potential for attenuation and peak discharge reduction has been largely ignored. However, in the last few years there has been a shift in emphasis; from RWH perceived purely as a water demand management technology to a focus on its wider benefits e.g. mitigating surface water flooding through improved stormwater management. RWH systems examined in this thesis are now available which offer multiple benefits to both end-users and water service providers. The application of RWH in a dual purpose configuration (to displace potable water demands and control stormwater discharges) has seen increasing interest during the development of this thesis. However, the successful design of RWH as a stormwater management tool requires a series of calculations to be completed. To date, practitioners have frequently relied upon low-resolution heuristic methods which lead to a small range of configurations being deployed, with minimal demonstrable stormwater control benefits. In this thesis, full details of novel and traditional RWH technologies were identified and described. Empirical data was collected, both in laboratory conditions and at field sites, to identify the real world operating characteristics of a range of RWH configurations. Additionally a new time series evaluation methodology was developed to enable RWH systems to be designed and analysed. This method quantifies water demand benefits and also focusses on stormwater management metrics (i.e. largest annual discharge and total discharge volume per year). The method was developed to enable a range of RWH configurations to be evaluated at a given site. In addition, a decision support tool (RainWET) was developed and tested which enabled the methods to be deployed in real world settings. The application of the RainWET software allowed a UK-wide, time series analysis of RWH configurations to be completed and the holistic benefits of a range of dual purpose RWH systems to be analysed and described. Evidence from the UK study suggests that a traditional RWH installation (3000l storage, 300l/day demand and 60m2 roof) installed at a house in a water scarce region (London, SAAR 597mm) was able to fully mitigate stormwater overflows over a 20 year analysis whilst providing a mean water saving of 31,255l/annum. An equivalent system located in the wettest region studied (Truro, SAAR 1099mm) saw mean reductions in the largest annual storm of 62% (range 35-86%) whilst satisfying a mean rainwater demand of 50,912l/annum. The study concluded that suitably designed dual purpose RWH systems offered better stormwater management benefits than those designed without a stormwater control device. In addition, the integration of smart RWH controls were shown to maximise stormwater control benefits with little or no reduction in a system’s ability to satisfy non-potable water demands.Severn Trent WaterEPSR

Virtual Power Plant for Smart Grid Ready Buildings and Customers

This report contains a summary of results from the ForskEL project: Virtual Power Plant for Smart Grid Ready Buildings and Customers