| 1. |
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| 2. |
- Ahlen, Anders, et al.
(författare)
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Toward Wireless Control in Industrial Process Automation : A Case Study at a Paper Mill
- 2019
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Ingår i: IEEE Control Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 1066-033X .- 1941-000X. ; 39:5, s. 36-57
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Tidskriftsartikel (refereegranskat)abstract
- Wireless sensors and networks are used only occasionally in current control loops in the process industry. With rapid developments in embedded and highperformance computing, wireless communication, and cloud technology, drastic changes in the architecture and operation of industrial automation systems seem more likely than ever. These changes are driven by ever-growing demands on production quality and flexibility. However, as discussed in "Summary," there are several research obstacles to overcome. The radio communication environment in the process industry is often troublesome, as the environment is frequently cluttered with large metal objects, moving machines and vehicles, and processes emitting radio disturbances [1], [2]. The successful deployment of a wireless control system in such an environment requires careful design of communication links and network protocols as well as robust and reconfigurable control algorithms.
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| 3. |
- Ahlén, Anders, et al.
(författare)
-
Towards Wireless Control in Industrial Process Automation : A Case Study at a Paper Mill
- 2019
-
Ingår i: IEEE CONTROL SYSTEMS MAGAZINE. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1066-033X .- 1941-000X. ; 39:5, s. 36-57
-
Tidskriftsartikel (refereegranskat)abstract
- Wireless sensors and networks are used only occasionally in current control loops in the process industry. With rapid developments in embedded and highperformance computing, wireless communication, and cloud technology, drastic changes in the architecture and operation of industrial automation systems seem more likely than ever. These changes are driven by ever-growing demands on production quality and flexibility. However, as discussed in "Summary," there are several research obstacles to overcome. The radio communication environment in the process industry is often troublesome, as the environment is frequently cluttered with large metal objects, moving machines and vehicles, and processes emitting radio disturbances [1], [2]. The successful deployment of a wireless control system in such an environment requires careful design of communication links and network protocols as well as robust and reconfigurable control algorithms.
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| 4. |
- Ahmadi, Seyed Alireza, et al.
(författare)
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Towards more efficient building energy management systems
- 2012
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Ingår i: Proceedings - 2012 7th International Conference on Knowledge, Information and Creativity Support Systems, KICSS 2012. - : IEEE. - 9780769548616 ; , s. 118-125
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Konferensbidrag (refereegranskat)abstract
- As a first step towards developing efficient building energy management techniques, in this paper, we first study the energy consumption patterns of heating, ventilation and cooling (HVAC) systems across the KTH Royal Institute of Technology campus and we identify some possible areas where energy consumption can be made less wasteful. Later, we describe a test-bed where wireless sensor networks are used to collect data and eventually control the HVAC system in a distributed way. We present some of the data, temperature, humidity, and CO2 measurements, that are collected by the aforementioned network and compare them with the measurements collected by the legacy sensors already in place. In the end we present a preliminary result on modelling the dynamics of the temperature, humidity, and CO2 using the data gather by the sensor network. We check the validity of the model via comparing the out put of the system with measured data. As a future work we identify the possibility of using the models obtained here for model based control, and fault detection and isolation techniques.
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| 5. |
- Altaf, Faisal, et al.
(författare)
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Wireless event-triggered controller for a 3D tower crane lab process
- 2011
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Ingår i: 2011 19th Mediterranean Conference on Control and Automation, MED 2011. - 9781457701252 - 9781457701245 ; , s. 994-1001
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Konferensbidrag (refereegranskat)abstract
- This paper studies the design and real-time implementation of an event-triggered controller for a nonlinear 3D tower crane where the communication between the controller and the actuators is performed over a low-power wireless network. A flexible Event-Generation Circuit (EGC) is proposed in order to implement event-driven controllers for Networked Control Systems. Furthermore, a detailed experimental analysis on the performance of the event-triggered controller and the influence of packet losses on the transmitted actuation messages are presented. The results show that the event-triggered controllers in networked control systems are able to maintain the same level of performance as compared to periodic controllers, while increasing the sensors/actuators lifetime by reducing network bandwidth utilization.
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| 6. |
- Andersson, G., et al.
(författare)
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Cyber-security of SCADA systems
- 2012
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Ingår i: 2012 IEEE PES Innovative Smart Grid Technologies, ISGT 2012. - : IEEE. - 9781457721588 ; , s. 6175543-
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Konferensbidrag (refereegranskat)abstract
- After a general introduction of the VIKING EU FP7 project two specific cyber-attack mechanisms, which have been analyzed in the VIKING project, will be discussed in more detail. Firstly an attack and its consequences on the Automatic Generation Control (AGC) in a power system are investigated, and secondly the cyber security of State Estimators in SCADA systems is scrutinized.
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| 7. |
- Andreasson, Martin, et al.
(författare)
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Correlated Failures of Power Systems : Analysis of the Nordic Grid
- 2011
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Ingår i: Preprints of Workshop on Foundations of Dependable and Secure Cyber-Physical Systems.
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Konferensbidrag (refereegranskat)abstract
- In this work we have analyzed the effectsof correlated failures of power lines on the total systemload shed. The total system load shed is determined bysolving the optimal load shedding problem, which is thesystem operator’s best response to a system failure.We haveintroduced a Monte Carlo based simulation framework forestimating the statistics of the system load shed as a functionof stochastic network parameters, and provide explicitguarantees on the sampling accuracy. This framework hasbeen applied to a 470 bus model of the Nordic power systemand a correlated Bernoulli failure model. It has been foundthat increased correlations between Bernoulli failures ofpower lines can dramatically increase the expected valueas well as the variance of the system load shed.
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| 8. |
- Andreasson, Martin, et al.
(författare)
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Distributed Control of Networked Dynamical Systems : Static Feedback, Integral Action and Consensus
- 2014
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:7, s. 1750-1764
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control.
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| 9. |
- Andreasson, Martin, et al.
(författare)
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Distributed integral action : stability analysis and frequency control of power systems
- 2012
-
Ingår i: 2012 IEEE 51st Annual Conference on Decision and Control (CDC). - : IEEE. - 9781467320665 ; , s. 2077-2083
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Konferensbidrag (refereegranskat)abstract
- This paper analyzes distributed proportional-integral controllers. We prove that integral action can be successfully applied to consensus algorithms, where attenuation of static disturbances is achieved. These control algorithms are applied to decentralized frequency control of electrical power systems. We show that the proposed algorithm can attenuate step disturbances of power loads. We provide simulations of the proposed control algorithm on the IEEE 30 bus test system that demonstrate its efficiency.
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| 10. |
- Andreasson, Martin, et al.
(författare)
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Performance and scalability of voltage controllers in multi-terminal HVDC networks
- 2017
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Ingår i: Proceedings of the American Control Conference. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509059928 ; , s. 3029-3034
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Konferensbidrag (refereegranskat)abstract
- In this paper, we compare the transient performance of a multi-terminal high-voltage DC (MTDC) grid equipped with a slack bus for voltage control to that of two distributed control schemes: A standard droop controller and a distributed averaging proportional-integral (DAPI) controller. We evaluate performance in terms of an ℋ2 metric that quantifies expected deviations from nominal voltages, and show that the transient performance of a droop or DAPI controlled MTDC grid is always superior to that of an MTDC grid with a slack bus. In particular, by studying systems built up over lattice networks, we show that the ℋ2 norm of a slack bus controlled system may scale unboundedly with network size, while the norm remains uniformly bounded with droop or DAPI control. We simulate the control strategies on radial MTDC networks to demonstrate that the transient performance for the slack bus controlled system deteriorates significantly as the network grows, which is not the case with the distributed control strategies.
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| 11. |
- Araujo, Jose, et al.
(författare)
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Control over a Hybrid MAC Wireless Network
- 2010
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Ingår i: 2010 IEEE 1ST INTERNATIONAL CONFERENCE ON SMART GRID COMMUNICATIONS. ; , s. 197-202
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Konferensbidrag (refereegranskat)abstract
- Wireless Sensor Networks and Control Systems are an essential part of the Smart Grid. We consider the problem of performing control over large complex networked systems with packet drops. More specifically, we are interested in improving the performance of the regulation of control loops when the communication is made over low-cost wireless networks. In control over wireless networks it is common to use Contention-Free (CF) schemes where no losses occur with the price of low scalability and complicated scheduling policies. In this work we propose a hybrid MAC and control architecture, where a small number of control loops with high demand of attention are scheduled in a CF scheme and well regulated loops are scheduled in a lossy, asynchronous and highly scalable, Contention-Access (CA) scheme. We model and analyze the performance of such system with Markov Jump Linear System (MJLS) tools and compare it with other architecture types. Performance is evaluated using a quadratic cost function of the state.
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| 12. |
- Araujo, Jose, et al.
(författare)
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Experimental Validation of a Localization System Based on a Heterogeneous Sensor Network
- 2009
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Ingår i: ASCC. - NEW YORK : IEEE. - 9781424454402 ; , s. 465-470
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Konferensbidrag (refereegranskat)abstract
- The experimental implementation and validation of a localization system based on a heterogeneous sensor network is described. The sensor network consists of ultrasound ranging sensors and web cameras. They are used to localize a mobile robot under sensor communication constraints. Applying a recently proposed sensor fusion algorithm that explicitly takes communication delay and cost into account, it is shown that one can accurately trade off the estimation performance by using low-quality ultrasound sensors with low processing time and low communication cost versus the use of the high-quality cameras with longer processing time and higher communication cost. It is shown that a periodic schedule of the sensors is suitable in many cases. The experimental setup is discussed in detail and experimental results are presented.
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| 13. |
- Besselink, Bart, et al.
(författare)
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Controllability of a class of networked passive linear systems
- 2013
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Ingår i: Proceedings of the 52nd IEEE Conference on Decision and Control, Florence, Italy. - : IEEE conference proceedings. ; , s. 4901-4906
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Konferensbidrag (refereegranskat)abstract
- In this paper, controllability properties of networks of diffusively coupled linear systems are considered through the controllability Gramian. For a class of passive linear systems, it is shown that the controllability Gramian can be decomposed into two parts. The first part is related to the dynamics of the individual systems whereas the second part is dependent only on the interconnection topology, allowing for a clear interpretation and efficient computation of controllability properties for a class of networked systems. Moreover, a relation between symmetries in the interconnection topology and controllability is given. The results are illustrated by an example.
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| 14. |
- Besselink, Bart, et al.
(författare)
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Model reduction of networked passive systems through clustering
- 2014
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Ingår i: 2014 European Control Conference, ECC 2014. - : IEEE. - 9783952426913 ; , s. 1069-1074
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Konferensbidrag (refereegranskat)abstract
- In this paper, a model reduction procedure for a network of interconnected identical passive subsystems is presented. Here, rather than performing model reduction on the subsystems, adjacent subsystems are clustered, leading to a reduced-order networked system that allows for a convenient physical interpretation. The identification of the subsystems to be clustered is performed through controllability and observability analysis of an associated edge system and it is shown that the property of synchronization (i.e., the convergence of trajectories of the subsystems to each other) is preserved during reduction. The results are illustrated by means of an example.
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| 15. |
- Briat, C., et al.
(författare)
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The Conservation of Information, Towards an Axiomatized Modular Modeling Approach to Congestion Control
- 2015
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Ingår i: IEEE/ACM Transactions on Networking. - 1063-6692 .- 1558-2566. ; 23:3, s. 851-865
-
Tidskriftsartikel (refereegranskat)abstract
- We derive a modular fluid-flow network congestion control model based on a law of fundamental nature in networks: the conservation of information. Network elements such as queues, users, and transmission channels and network performance indicators like sending/acknowledgment rates and delays are mathematically modeled by applying this law locally. Our contributions are twofold. First, we introduce a modular metamodel that is sufficiently generic to represent any network topology. The proposed model is composed of building blocks that implement mechanisms ignored by the existing ones, which can be recovered from exact reduction or approximation of this new model. Second, we provide a novel classification of previously proposed models in the literature and show that they are often not capable of capturing the transient behavior of the network precisely. Numerical results obtained from packet-level simulations demonstrate the accuracy of the proposed model.
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| 16. |
- Chen, J., et al.
(författare)
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Protecting Positive and Second-Order Systems against Undetectable Attacks
- 2017
-
Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 8373-8378
-
Tidskriftsartikel (refereegranskat)abstract
- Undetectable attacks in security studies of cyber-physical systems render the measurements of the system equal to a possible physical response. In this paper, we investigate defense strategies against the undetectable single-attack for positive systems and second-order systems, which both can be reinterpreted in terms of graphs with nodes and edges, while the undetectable attack is added through one of the nodes. We show that an arbitrary placement of a sensor prevents undetectable single-attack for these classes of systems. It is worth emphasising that we do not need to measure at the corrupted node to prevent the undetectable single-attack, but can measure at any node. The defense strategy is of a low complexity and can be readily implemented.
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| 17. |
- Farokhi, Farhad, 1987-, et al.
(författare)
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Complexity Reduction for Parameter-Dependent Linear Systems
- 2013
-
Ingår i: 2013 American Control Conference (ACC). - : American Automatic Control Council. - 9781479901777 ; , s. 2624-2630
-
Konferensbidrag (refereegranskat)abstract
- We present a complexity reduction algorithm for a family of parameter-dependent linear systems when the system parameters belong to a compact semi-algebraic set. This algorithm potentially describes the underlying dynamical system with fewer parameters or state variables. To do so, it minimizes the distance (i.e., $H_\infty$-norm of the difference) between the original system and its reduced version. We present a sub-optimal solution to this problem using sum-of-squares optimization methods. We present the results for both continuous-time and discrete-time systems. Lastly, we illustrate the applicability of our proposed algorithm on numerical examples.
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| 18. |
- Farokhi, Farhad, 1987-, et al.
(författare)
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Optimal H-Infinity Control Design under Model Information Limitations and State Measurement Constraints
- 2013
-
Ingår i: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357166 ; , s. 6218-6225
-
Konferensbidrag (refereegranskat)abstract
- We present a suboptimal control design algorithm for a family of continuous-time parameter-dependent linear systems that are composed of interconnected subsystems. We are interested in designing the controller for each subsystem such that it only utilizes partial state measurements (characterized by a directed graph called the control graph) and limited model parameter information (characterized by the design graph). The algorithm is based on successive local minimizations and maximizations (using the subgradients) of the H∞-norm of the closed-loop transfer function with respect to the controller gains and the system parameters. We use a vehicle platooning example to illustrate the applicability of the results.
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| 19. |
- Giani, A., et al.
(författare)
-
The VIKING project : An initiative on resilient control of power networks
- 2009
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the work on resilient and secure power transmission and distribution developed within the VIKING (vital infrastructure, networks, information and control system management) project. VIKING receives funding from the European Community's Seventh Framework Program. We will present the consortium, the motivation behind this research, the main objective of the project together with the current status.
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| 20. |
- Hendrickx, Julien M., et al.
(författare)
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Efficient Computations of a Security Index for False Data Attacks in Power Networks
- 2014
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:12, s. 3194-3208
-
Tidskriftsartikel (refereegranskat)abstract
- The resilience of Supervisory Control and Data Acquisition (SCADA) systems for electric power networks for certain cyber-attacks is considered. We analyze the vulnerability of the measurement system to false data attack on communicated measurements. The vulnerability analysis problem is shown to be NP-hard, meaning that unless P = NP there is no polynomial time algorithm to analyze the vulnerability of the system. Nevertheless, we identify situations, such as the full measurement case, where the analysis problem can be solved efficiently. In such cases, we show indeed that the problem can be cast as a generalization of the minimum cut problem involving nodes with possibly nonzero costs. We further show that it can be reformulated as a standard minimum cut problem (without node costs) on a modified graph of proportional size. An important consequence of this result is that our approach provides the first exact efficient algorithm for the vulnerability analysis problem under the full measurement assumption. Furthermore, our approach also provides an efficient heuristic algorithm for the general NP-hard problem. Our results are illustrated by numerical studies on benchmark systems including the IEEE 118-bus system.
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| 21. |
- Henriksson, Erik, 1982-
(författare)
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Compensating for Unreliable Communication Links in Networked Control Systems
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Control systems utilizing wireless sensor and actuator networks can be severely affectedby the properties of the communication links. Radio fading and interferencemay cause communication losses and outages in situations when the radio environmentis noisy and low transmission power is desirable. This thesis proposes amethod to compensate for such unpredictable losses of data in the feedback controlloop by introducing a predictive outage compensator (POC). The POC is a filter tobe implemented at the receiver sides of networked control systems where it generatesartificial samples when data are lost. If the receiver node does not receive thedata, the POC suggests a command based on the history of past data. It is shownhow to design, tune and implement a POC. Theoretical bounds and simulationresults show that a POC can improve the closed-loop control performance undercommunication losses considerably. We provide a deterministic and a stochasticmethod to synthesize POCs. Worst-case performance bounds are given that relatethe closed-loop performance with the complexity of the compensator. We also showthat it is possible to achieve good performance with a low-order implementationbased on Hankel norm approximation. Tradeoffs between achievable performance,communication loss length, and POC order are discussed. The results are illustratedon a simulated example of a multiple-tank process. The thesis is concludedby an experimental validation of wireless control of a physical lab process. Herethe controller and the physical system are separated geographically and interfacedthrough a wireless medium. For the remote control we use a hybrid model predictivecontroller. The results reflect the difficulties in wireless control as well as theyhighlight the flexibility and possibilities one obtains by using wireless instead of awired communication medium.
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| 22. |
- Henriksson, Erik, et al.
(författare)
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Predictive Compensation for Communication Outages in Networked Control Systems
- 2008
-
Ingår i: Proceedings of the 47<sup>th</sup> IEEE Conference on Decision and Control. - Cancun, Mexico. - 9781424431243 ; , s. 2063-2068
-
Konferensbidrag (refereegranskat)abstract
- A predictive outage compensator co-located with the actuator node in a networked control system can be used to counteract unpredictable losses of data in the feedback control loop. When a new control command is not received at the actuator node at an appropriate time instance, the predictive outage compensator suggests a replacement command based on the history of past control commands. It is shown that a simple tuning phase together with the monitoring of the control history can lead to a compensator that can improve the closed-loop control performance under communication outages considerably compared to traditional schemes. Worst case performance bounds are given that relate the quality of the tuning phase and the complexity of the compensator with the length of the communication outage period. Zero-order-hold (holding the past control command if the current is lost) and applying an a priori decided constant signal (using a redefined value on the control command if the current is lost) are special cases of the more general compensation scheme presented. The predictive outage compensator is illustrated through computer simulation with communication outages.
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| 23. |
- Henriksson, Erik, et al.
(författare)
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Reduced-Order Predictive Outage Compensators for Networked Systems
- 2009
-
Ingår i: Proceedings of the combined 48<sup>th</sup> IEEE Conference on Decision and Control and 28<sup>th</sup> Chinese Control Conference. - Shanghai, P.R. China. - 9781424438716 ; , s. 3775-3780
-
Konferensbidrag (refereegranskat)abstract
- Control systems utilizing wireless sensor and actuator networks can be severely affected by the properties of the wireless links. Radio fading and interference may cause communication outage of several samples in situations when the radio environment is noisy and low transmission power is desirable. We propose a method to compensate for outages by introducing a predictive outage compensator (POC), which is a filter to be implemented at the receiver sides of networked control systems and that generates artificial samples during the outage. The main contribution of the paper is to show that a POC can be derived based on a Kalman filter formulation and that it is possible to achieve good performance with a low-order implementation based on Hankel norm approximation. Tradeoffs between achievable closed-loop performance, outage length, and POC order are discussed. The results are illustrated on a simulated example of a multiple-tank process.
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| 24. |
- Herdeiro Teixeira, André, et al.
(författare)
-
Strategic stealthy attacks : The output-to-output ℓ2-gain
- 2016
-
Ingår i: Proceedings of the IEEE Conference on Decision and Control. - : IEEE conference proceedings. - 9781479978861 ; , s. 2582-2587, s. 2582-2587
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we characterize and analyze the set of strategic stealthy false-data injection attacks on discrete-time linear systems. In particular, the threat scenarios tackled in the paper consider adversaries that aim at deteriorating the system's performance by maximizing the corresponding quadratic cost function, while remaining stealthy with respect to anomaly detectors. As opposed to other work in the literature, the effect of the adversary's actions on the anomaly detector's output is not constrained to be zero at all times. Moreover, scenarios where the adversary has uncertain model knowledge are also addressed. The set of strategic attack policies is formulated as a non-convex constrained optimization problem, leading to a sensitivity metric denoted as the output-to-output ℓ2-gain. Using the framework of dissipative systems, the output-to-output gain is computed through an equivalent convex optimization problem. Additionally, we derive necessary and sufficient conditions for the output-to-output gain to be unbounded, with and without model uncertainties, which are tightly related to the invariant zeros of the system.
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| 25. |
- Ishizaki, T., et al.
(författare)
-
Structured model reduction of interconnected linear systems based on singular perturbation
- 2013
-
Ingår i: Proceedings of the American Control Conference 2013. - : American Automatic Control Council. - 9781479901777 ; , s. 5524-5529
-
Konferensbidrag (refereegranskat)abstract
- This paper proposes a singular perturbation approximation that preserves system passivity and an interconnection topology among subsystems. In the first half of this paper, we develop a singular perturbation approximation valid for stable linear systems. Using the relation between the singular perturbation and the reciprocal transformation, we derive a tractable expression of the error system in the Laplace domain, which provides a novel insight to regulate the approximating quality of reduced models. Then in the second half, we develop a structured singular perturbation approximation that focuses on a class of interconnected systems. This structured approximation provides a reduced model that not only possesses fine approximating quality, but also preserves the original interconnection topology and system passivity.
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| 26. |
- Ishizakiy, T., et al.
(författare)
-
Singular perturbation approximation of semistable linear systems
- 2013
-
Ingår i: 2013 European Control Conference, ECC 2013. - : IEEE. - 9783033039629 ; , s. 4508-4513
-
Konferensbidrag (refereegranskat)abstract
- This paper proposes a singular perturbation approximation for semistable linear systems. In particular, we derive a novel expression of error systems in the Laplace domain. As a result, we obtain an h2-error bound in terms of the sum of eigenvalues of an index matrix, which coincides with a controllability gramian of the state-derivative. Furthermore, we show that the singular perturbation model appropriately preserves the semistability of the original system and also guarantees the stability of the error system. The efficiency of the proposed method is shown through a numerical example of a Markov chain model approximation.
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| 27. |
- Iwaki, Takuya, et al.
(författare)
-
Wireless Sensor Network Scheduling for Remote Estimation under Energy Constraints
- 2017
-
Ingår i: 2017 IEEE 56TH ANNUAL CONFERENCE ON DECISION AND CONTROL (CDC). - : IEEE. - 9781509028733 ; , s. 3362-3367
-
Konferensbidrag (refereegranskat)abstract
- This paper studies a design problem of how a group of wireless sensors are selected and scheduled to transmit data efficiently over a multi-hop network subject to energy-saving consideration, when they are observing multiple independent discrete-time linear systems. Each time instant, some sensors are selected to transmit their measurements to a remote estimator. We formulate an optimization problem, minimizing a linear combination of the averaged estimation error and the averaged transmission energy consumption to obtain suitable network scheduling and estimation algorithms. Necessary conditions for optimality are derived and these conditions help trim the feasible solution space so that the optimal solution can be computed efficiently. A numerical example is provided to demonstrate the theoretical results.
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| 28. |
- Milosevic, Jezdimir, et al.
(författare)
-
Analysis and Mitigation of Bias Injection Attacks Against a Kalman Filter
- 2017
-
Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 8393-8398
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider a state estimation problem for stochastic linear dynamical systems in the presence of bias injection attacks. A Kalman filter is used as an estimator, and a chi-squared test is used to detect anomalies. We first show that the impact of the worst-case bias injection attack in a stochastic setting can be analyzed by a deterministic quadratically constrained quadratic program, which has an analytical solution. Based on this result, we propose a criterion for selecting sensors to secure in order to mitigate the attack impact. Furthermore, we derive a condition on the necessary number of sensors to secure in order for the impact to be less than a desired threshold.
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| 29. |
- Milosevic, Jezdimir, et al.
(författare)
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Quantifying the Impact of Cyber-Attack Strategies for Control Systems Equipped with an Anomaly Detector
- 2018
-
Ingår i: 2018 European Control Conference, ECC 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9783952426982 ; , s. 331-337
-
Konferensbidrag (refereegranskat)abstract
- Risk assessment is an inevitable step in the implementation of cost-effective security strategies for control systems. One of the difficulties of risk assessment is to estimate the impact cyber-attacks may have. This paper proposes a framework to estimate the impact of several cyber-attack strategies against a dynamical control system equipped with an anomaly detector. In particular, we consider denial of service, sign alternation, rerouting, replay, false data injection, and bias injection attack strategies. The anomaly detectors we consider are stateless, cumulative sum, and multivariate exponentially weighted moving average detectors. As a measure of the attack impact, we adopt the infinity norm of critical states after a fixed number of time steps. For this measure and the aforementioned anomaly detectors, we prove that the attack impact for all of the attack strategies can be reduced to the problem of solving a set of convex minimization problems. Therefore, the exact value of the attack impact can be obtained easily. We demonstrate how our modeling framework can be used for risk assessment on a numerical example.
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| 30. |
- Moberg, Christina, et al.
(författare)
-
De unga gör helt rätt när de stämmer staten
- 2022
-
Ingår i: Aftonbladet. - 1103-9000.
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 31. |
- Molin, Adam, et al.
(författare)
-
Consistency-preserving event-triggered estimation in sensor networks
- 2015
-
Konferensbidrag (refereegranskat)abstract
- This paper is concerned with linear state estimation in sensor networks with an event-triggered exchange of information. It is assumed that each sensor node transmits its local estimate to a fusion center whenever an appropriately chosen error norm exceeds a threshold. The fusion rule is a modified version of the Covariance Intersection Algorithm. We investigate how to incorporate the event information of not having transmitted at the fusion center such that the filter remains unbiased and consistent with regard to its error covariance. An upper bound on the error covariance matrix is derived by exploiting the structure of the posterior probability distribution. This enables us to replace the event information by the virtual transmission of consistent local estimates. Based on the consistency-preserving property of the proposed scheme, we show stability of the event-triggered state estimator in terms of a bounded mean square error.
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| 32. |
- Paridari, Kaveh, et al.
(författare)
-
Demand response for aggregated residential consumers with energy storage sharing
- 2015
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Konferensbidrag (refereegranskat)abstract
- A novel distributed algorithm is proposed in this paper for a network of consumers coupled by energy resource sharing constraints, which aims at minimizing the aggregated electricity costs. Each consumers is equipped with an energy management system that schedules the shiftable loads accounting for user preferences, while an aggregator entity coordinates the consumers demand and manages the interaction with the grid and the shared energy storage system (ESS) via a distributed strategy. The proposed distributed coordination algorithm requires the computation of Mixed Integer Linear Programs (MILPs) at each iteration. The proposed approach guarantees constraints satisfaction, cooperation among consumers, and fairness in the use of the shared resources among consumers. The strategy requires limited message exchange between each consumer and the aggregator, and no messaging among the consumers, which protects consumers privacy. Performance of the proposed distributed algorithm in comparison with a centralized one is illustrated using numerical experiments.
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| 33. |
- Paridari, Kaveh, et al.
(författare)
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Energy and CO2 efficient scheduling of smart appliances in active houses equipped with batteries
- 2014
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Ingår i: Automation Science and Engineering (CASE), 2014 IEEE International Conference on. - : IEEE conference proceedings. ; , s. 632-639
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a novel method for scheduling smart appliances and batteries, in order to reduce both the electricity bill and the CO2 emissions. Mathematically, the scheduling problem is posed as a multi-objective Mixed Integer Linear Programming (MILP), which can be solved by using standard algorithms. A case study is performed to assess the performance of the proposed scheduling framework. Numerical results show that the new formulation can decrease both the CO2 emissions and the electricity bill. Furthermore, a survey of studies that deal with scheduling of smart appliances is provided. These papers use methods based on MILP, Dynamic Programming (DP), and Minimum Cut Algorithm (MCA) for solving the scheduling problem. We discuss their performance in terms of computation time and optimality versus time discretization and number of appliances.
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| 34. |
- Paridari, Kaveh, et al.
(författare)
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Robust Scheduling of Smart Appliances in Active Apartments With User Behavior Uncertainty
- 2015
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Ingår i: IEEE Transactions on Automation Science and Engineering. - : IEEE Press. - 1545-5955 .- 1558-3783. ; 13:1, s. 247-259
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a robust approach for scheduling of smart appliances and electrical energy storages (EESs) in active apartments with the aim of reducing both the electricity bill and the CO2 emissions. The proposed robust formulation takes the user behavior uncertainty into account so that the optimal appliances schedule is less sensitive to unpredictable changes in user preferences. The user behavior uncertainty is modeled as uncertainty in the cost function coefficients. In order to reduce the level of conservativeness of the robust solution, we introduce a parameter allowing to achieve a trade-off between the price of robustness and the protection against uncertainty. Mathematically, the robust scheduling problem is posed as a multi-objective Mixed Integer Linear Programming (MILP), which is solved by using standard algorithms. The numerical results show effectiveness of the proposed approach to increase both the electricity bill and CO2 emissions savings, in the presence of user behavior uncertainties. Mathematical insights into the robust formulation are illustrated and the sensitivity of the optimum cost in the presence of uncertainties is investigated. Although home appliances and EESs are considered in this work, we point out that the proposed scheduling framework is generally applicable to many use cases, e.g., charging and discharging of electrical vehicles in an effective way. In addition, it is applicable to various scenarios considering different uncertainty sources, different storage technologies and generic programmable electrical loads, as well as different optimization criteria.
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| 35. |
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| 36. |
- Ramesh, Chithrupa, 1982-
(författare)
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Contention-based Multiple Access Architectures for Networked Control Systems
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Networked Control Systems (NCSs) use a wireless network for communication between sensors and controllers, and require a Medium Access Controller (MAC) to arbitrate access to the shared medium. Traditionally, a MAC for control systems is chosen primarily based on the delay it introduces in the closed loop. This thesis focuses on the design of a contention-based MAC, in a time-varying, resource-constrained network for closed loop systems. In this thesis, we advocate the use of a state-aware MAC, as opposed to an agnostic MAC, for NCSs. A state-aware MAC uses the state of the plant to influence access to the network. The state-aware policy is realized using two different approaches in the MAC: a regulatory formulation and an adaptive prioritization. Our first approach is a regulatory MAC, which serves to reduce the traffic in the network. We use a local state-based scheduler to select a few critical data packets to send to the MAC. We analyze the impact of such a scheduler on the closed loop system, and show that there is a dual effect for the control signal, which makes determining the optimal controller difficult. We also identify restrictions on the scheduling criterion that result in a separation of the scheduler, observer and controller designs. Our second approach is a prioritized MAC that uses state-based priorities called Attentions, to determine access to the network. We use a dominance protocol called tournaments, to evaluate priorities in a contention-based setting, and analyze the resulting performance of the MAC. We also consider a NCS that uses a wireless multihop mesh network for communication between the controller and actuator. We design an optimal controller, which uses packet delivery predictions from a recursive Bayesian network estimator.
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| 37. |
- Ramesh, Chithrupa, et al.
(författare)
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LQG and Medium Access Control
- 2009
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Ingår i: Proceedings of the 1st IFAC Workshop on Estimation and Control of Networked Systems (NecSys2009). ; , s. 328-333
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Konferensbidrag (refereegranskat)abstract
- The communication channel is a shared resource in networked control systems, and channel access at every instant cannot be guaranteed. In this paper, we propose a novel architecture for control over wireless networks with integrated medium access control (MAC).We evaluate the impact of constrained channel access on the cost of controlling a single plant over a network and establish that the separation principle holds under certain conditions on the MAC. We arrive at a classification of random access methods for networked control systems and identify a structure for each method. Then, by evaluating the increase in cost compared to a conventional setup, we identify an adaptive random access method which uses a threshold-based decision criteria on the current data to determine channel access. Finally, we give stability criteria for control applications using these medium access methods.
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| 38. |
- Ramesh, Chithrupa, et al.
(författare)
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Multiple access with attention-based tournaments for monitoring over wireless networks
- 2009
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Ingår i: Proceedings of the European Control Conference 2009. - : EUCA. - 9789633113691 - 9783952417393 ; , s. 4302-4307
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Konferensbidrag (refereegranskat)abstract
- Wireless sensor networks for control and moni- toring applications introduce critical constraints on the design of multiple access schemes. Controlling dynamic processes requires that priority must be given to critical systems for the use of the wireless medium. Tournaments in the medium access control (MAC) layer are presented as a way to evaluate priorities and assign channel resources in a distributed manner. The priorities are dynamically assigned based on the attention that each data packet requires. A mathematical formulation of attention is presented together with the corresponding performance analysis of the multiple access scheme. Priorities based on the attention emphasize the information content in the data to be transmitted and the related process dynamics. It is shown that under certain conditions, the performance of this distributed scheme converges to a scheduling policy based on minimizing the per-sample variance of the error in the estimates obtained with limited communication resources. Sustainable data rates for a cluster of linear processes are also derived.
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| 39. |
- Ramesh, Chithrupa, et al.
(författare)
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On the Dual Effect in State-based Scheduling of Networked Control Systems
- 2011
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Ingår i: Proceedings of the 2011 American Control Conference. - : IEEE. - 9781457700804 ; , s. 2216-2221
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Konferensbidrag (refereegranskat)abstract
- In this paper, we show that there is a dual effect with state-based scheduling. In general, this makes the optimal scheduler and controller hard to find. However, by removing past controls from the scheduling criterion, we find that certainty equivalence holds. This condition is related to the classical result of Bar-Shalom and Tse, and it leads to the design of a sub-optimal scheduler with a certainty equivalent controller. Furthermore, we show that a mapping of the state-based scheduler into one which fulfills this condition, and consequently has an optimal certainty equivalent controller, does not result in an equivalent class of design in the sense of Witsenhausen. Computing the estimate remains hard, but can be simplified by introducing a symmetry constraint on the scheduler.
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| 40. |
- Ramesh, Chithrupa, et al.
(författare)
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Stability analysis of multiple state-based schedulers with CSMA
- 2012
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Ingår i: 2012 IEEE 51st Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467320641 ; , s. 7205-7211
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Konferensbidrag (refereegranskat)abstract
- In this paper, we identify sufficient conditions for Lyapunov Mean Square Stability (LMSS) of a contention-based network of first-order systems, with state-based schedulers. The stability analysis helps us to choose policies for adapting the scheduler threshold to the delay from the network and scheduler. We show that three scheduling laws can result in LMSS: constant-probability laws and additively increasing or decreasing probability laws. Our results counter the notions that increasing probability scheduling laws alone can guarantee stability of the closed-loop system, or that decreasing probability scheduling laws are required to mitigate congestion in the network.
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| 41. |
- Ramesh, Chithrupa, 1982-
(författare)
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State-based Channel Access for a Network of Control Systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless networked control systems use shared wireless links to communicate between sensors and controllers, and require a channel access policy to arbitrate access to the links. Existing multiple access protocols perform this role in an agnostic manner, by remaining insular to the applications that run over the network. This approach does not give satisfactory control performance guarantees. To enable the use of wireless networks in emerging industrial applications, we must be able to systematically design wireless networked control systems that provide guaranteed performances in resource-constrained networks.In this thesis, we advocate the use of state-based channel access policies. A state-based policy uses the state of the controlled plant to influence access to the network. The state contains information about not only the plant, but also the network, due to the feedback in the system. Thus, by using the state to decide when and how frequently to transmit, a control system can adapt its contribution to the network traffic, and enable the network to adapt access to the plant state. We show that such an approach can provide better performance than existing methods. We examine two different state-based approaches that are distributed and easy to implement on wireless devices: event-based scheduling and adaptive prioritization.Our first approach uses events to reduce the traffic in the network. We use a state-based scheduler in every plant sensor to generate non-coordinated channel access requests by selecting a few critical data packets, or events, for transmission. The network uses a contention resolution mechanism to deal with simultaneous channel access requests. We present three main contributions for this formulation. The first contribution is a structural analysis of stochastic event-based systems, where we identify a dual predictor architecture that results in separation in design of the state-based scheduler, observer and controller. The second contribution is a Markov model that describes the interactions in a network of event-based systems. The third contribution is an analysis of the stability of event-based systems, leading to a stabilizing design of event-based policies.Our second approach uses state-based priorities to determine access to the network. We use a dominance protocol to evaluate priorities in a contention-based setting, and characterize the resulting control performance. An implementation and evaluation of this channel access mechanism on sensor nodes is also presented.The thesis finally examines the general networked control problem of jointly optimizing measurement and control policies, when a nonlinear measurement policy is used to perform quantization, event-triggering or companding. This contribution focuses on some of the fundamental aspects of analyzing and synthesizing control systems with state-based measurement policies in a more generalized setting. We comment on the dual effect, certainty equivalence and separation properties for this problem. In particular, we show that it is optimal to apply separation and certainty equivalence to a design problem that permits a dynamic choice of the measurement and control policies.
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| 42. |
- Ramesh, Chithrupa, et al.
(författare)
-
State-based Priorities for Tournaments in Wireless Networked Control Systems
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We introduce a state-based distributed prioritization mechanism for a sensor associated with a dynamical system to access a wireless network, when multiple such systems share the same network link. The priorities, designated Attention Factors, are assigned by each sensor to its data packets, based on measurements of the system state. The Attention Factor represents a quantized value of the minimum risk in not transmitting a given measurement. The Attention Factors from different sensors are evaluated and allotted slots, in a distributed manner, using a dominance-based protocol called tournaments. Packets with the same Attention Factor in a tournament collide, and are lost. We analytically evaluate the probability of a successful transmission using this access mechanism. We also find an upper bound for the estimation and control performance of a system using tournament access, which shows the benefits of using state-based priorities. The proposed tournament mechanism is implemented on the IEEE 802.15.4 standard protocol stack, and evaluated in a hardware-in-the-loop experimental setup.
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| 43. |
- Ramesh, Chithrupa, et al.
(författare)
-
Steady State Performance Analysis of Multiple State-based Schedulers with CSMA
- 2011
-
Ingår i: Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference. ; , s. 4729-4734
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Konferensbidrag (refereegranskat)abstract
- In this paper, we analyze the performance ofmultiple event-based systems that share access to the samenetwork. Transmissions are attempted only when a local statebasedscheduler generates an event, and access to the networkis determined using a Carrier Sensing Multiple Access (CSMA)protocol. In general, the interactions in such a multiple accessnetwork introduce correlations between the system variablesof the various loops, and the respective traffic contributionsas well. Hence, analyzing the performance of this network isdifficult. However, a class of state-based schedulers, introducedin the paper, permits a joint analysis of the scheduler andthe Contention Resolution Mechanism (CRM). The analysisis based on a Markov model, which is validated throughsimulations. The resulting steady-state model makes it possibleto characterize the statistics of packet arrivals in this network.
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| 44. |
- Sadamoto, Tomonori, et al.
(författare)
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Distributed Design of Locally Stabilizing Controllers for Large-Scale Networked Linear Systems
- 2015
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Ingår i: 2015 IEEE CONFERENCE ON CONTROL AND APPLICATIONS (CCA 2015). - : IEEE conference proceedings. - 9781479977871 ; , s. 1835-1840
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider designing locally stabilizing controllers, each of which stabilizes each disconnected subsystem, in a distributed manner for large-scale networked linear systems. To this end, we design a low-dimensional hierarchical distributed compensator such that the L-2-performance of the closed-loop system improves as long as that of the locally stabilizing controllers improves. We solve a controller reduction problem where the approximation error of the low-dimensional compensator gets better as long as the performance of the locally stabilizing controllers improves, while preserving the hierarchical distributed structure of the original compensator. Finally, we demonstrate the efficiency of the proposed method through a numerical example of a power network.
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| 45. |
- Sadamoto, Tomonori, et al.
(författare)
-
Retrofitting State Feedback Control of Networked Nonlinear Systems Based on Hierarchical Expansion
- 2016
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Ingår i: 2016 IEEE 55th Conference on Decision and Control, CDC 2016. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509018376 ; , s. 3432-3437
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a systematic method to design retrofit controllers for networked nonlinear systems. The retrofit controller, which consists of a linear state feedback controller and a dynamical compensator, can improve the control performance for a subsystem of interest, while guaranteeing the stability of the whole closed-loop system. Towards the retrofit controller design, we introduce a type of state-space expansion, called hierarchical expansion. The cascade structure of the hierarchical expansion realization enables the systematic design of a stabilizing controller for a low-dimensional linear model extracted from the subsystem of interest. As a result, we can design a retrofit controller without explicit consideration of the dynamics of subsystems other than the subsystem of interest. The effectiveness of the proposed method is demonstrated through a power network example.
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| 46. |
- Sadamoto, T., et al.
(författare)
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Weak resilience of networked control systems
- 2017
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Ingår i: 2016 European Control Conference, ECC 2016. - : IEEE. - 9781509025916 ; , s. 977-982
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a method to establish a networked control system that maintains its stability in the presence of certain undesirable incidents on local controllers. We call such networked control systems weakly resilient. We first derive a necessary and sufficient condition for the weak resilience of networked systems. Networked systems do not generally satisfy this condition. Therefore, we provide a method for designing a compensator which ensures the weak resilience of the compensated system. Finally, we illustrate the efficiency of the proposed method by a power system example based on the IEEE 14-bus test system.
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| 47. |
- Sandberg, Henrik, et al.
(författare)
-
Cyberphysical security in networked control systems : An introduction to the issue
- 2015
-
Ingår i: IEEE CONTR SYST MAG. - 1066-033X. ; 35:1, s. 20-23
-
Tidskriftsartikel (refereegranskat)abstract
- This special issue provides an introduction to cyberphysical security of networked control systems (NCSs) and summarizes recent progress in applying fundamentals of systems theory and decision sciences to this new and increasingly promising area. NCS applications range from large-scale industrial applications to critical infrastructures such as water, transportation, and electricity networks. The security of NCSs naturally depends on the integration of cyber and physical dynamics and on different ways in which they are affected by the actions of human decision makers. Thus, problems in this area lie at the intersection of control systems and computer security. The six articles that constitute this special issue approach cyberphysical security from a variety of perspectives, including control theory, optimization, and game theory. They cover a range of topics such as models of attack and defense, risk assessment, his special issue provides an introduction to cyberphysical security of networked control systems (NCSs) and summarizes recent progress in applying fundamentals of systems theory and decision sciences to this new and increasingly promising area. NCS applications range from large-scale industrial applications to critical infrastructures such as water, transportation, and electricity networks. The security of NCSs naturally depends on the integration of cyber and physical dynamics and on different ways in which they are affected by the actions of human decision makers. Thus, problems in this area lie at the intersection of control systems and computer security. The six articles that constitute this special issue approach cyberphysical security from a variety of perspectives, including control theory, optimization, and game theory. They cover a range of topics such as models of attack and defense, risk assessment,attack detection and identification, and secure control design.A common theme among these contributions is an emphasis on the development of a principled approach to cyberphysical security of NCS.
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| 48. |
- Sandberg, Henrik, et al.
(författare)
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Estimation over heterogeneous sensor networks
- 2008
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. ; , s. 4898-4903
-
Konferensbidrag (refereegranskat)abstract
- Design trade-offs between estimation performance, processing delay and communication cost for a sensor scheduling problem is discussed. We consider a heterogeneous sensor network with two types of sensors: the first type has low-quality measurements, small processing delay and a light communication cost, while the second type is of high quality, but imposes a large processing delay and a high communication cost. Such a heterogeneous sensor network is common in applications, where for instance in a localization system the poor sensor can be an ultrasound sensor while the more powerful sensor can be a camera. Using a time-periodic Kalman filter, we show how one can find an optimal schedule of the sensor communication. One can significantly improve estimation quality by only using the expensive sensor rarely. We also demonstrate how simple sensor switching rules based on the Riccati equation drives the filter into a stable time-periodic Kalman filter. ￜ 2008 IEEE.
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| 49. |
- Sasahara, Hampei, et al.
(författare)
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Distributed Design of Glocal Controllers via Hierarchical Model Decomposition
- 2023
-
Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 68:10, s. 6146-6159
-
Tidskriftsartikel (refereegranskat)abstract
- This article proposes a distributed design method of controllers with a glocal (global/local) information structure for large-scale network systems. The glocal controller of interest has a hierarchical structure, wherein a global subcontroller coordinates a set of disjoint local subcontrollers. The global subcontroller regulates interarea oscillations among subsystems, while local subcontrollers individually regulate intraarea oscillations of the respective subsystem. The distributed design of the glocal controller is addressed to enhance the scalability of controller synthesis, where the global subcontroller and all local subcontrollers are designed independently of each other. A design problem is formulated for subcontroller sets such that any combination of subcontrollers each of which belongs to its corresponding set guarantees stability of the closed-loop system. The core idea of the proposed method is to represent the original network system as a hierarchical cascaded system composed of reduced-order models representing the interarea and intraarea dynamics, referred to as hierarchical model decomposition. Distributed design is achieved by virtue of the cascade structure. The primary findings of this study are twofold. First, a tractable solution to the distributed design problem and an existence condition of the hierarchical model decomposition are presented. Second, a clustering method appropriate for the proposed framework and a robust extension are provided. Numerical examples of a power grid highlight the practical relevance of the proposed method.
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| 50. |
- Shames, Iman, et al.
(författare)
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Agents Misbehaving in a Network : a Vice or a Virtue?
- 2012
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Ingår i: IEEE Network. - : IEEE Communications Society. - 0890-8044 .- 1558-156X. ; 26:3, s. 35-40
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Tidskriftsartikel (refereegranskat)abstract
- Misbehaviors among the agents in a network might be intentional or unintentional, they might cause a system-wide failure or they might improve the performance or even enable us to achieve an objective. In this article we consider examples of these possible scenarios. First, we argue the necessity of monitoring the agents in a network to detect if they are misbehaving or not and outline a distributed method in which each agent monitors its neighbors for any sign of misbehavior. Later, we focus on solving the problem of distributed leader selection via forcing the agents to temporarily misbehave, and introduce an algorithm that enables the agents in a network to select their leader without any interference from the outside of the network.
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