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Demirel, B. (2015). Architectures and Performance Analysis of Wireless Control Systems. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Architectures and Performance Analysis of Wireless Control Systems
2015 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

Modern industrial control systems use a multitude of spatially distributed sensors and actuators to continuously monitor and control physical processes. Information exchange among control system components is traditionally done through physical wires. The need to physically wire sensors and actuators limits flexibility, scalability and reliability, since the cabling cost is high, cable connectors are prone to wear and tear, and connector failures can be hard to isolate. By replacing some of the cables with wireless communication networks, costs and risks of connector failures can be decreased, resulting in a more cost-efficient and reliable system.

Integrating wireless communication into industrial control systems is challenging, since wireless communication channels introduce imperfections such as stochastic delays and information losses. These imperfections deteriorate the closed-loop control performance, and may even cause instability. In this thesis, we aim at developing design frameworks that take these imperfections into account and improve the performance of closed-loop control systems.

The thesis first considers the joint design of packet forwarding policies and controllers for wireless control loops where sensor measurements are sent to the controller over an unreliable and energy-constrained multi-hop wireless network. For a fixed sampling rate of the sensor, the co-design problem separates into two well-defined and independent subproblems: transmission scheduling for maximizing the deadline-constrained reliability and optimal control under packet losses. We develop optimal and implementable solutions for these subproblems and show that the optimally co-designed system can be obtained efficiently.

The thesis continues by examining event-triggered control systems that can help to reduce the energy consumption of the network by transmitting data less frequently. To this end, we consider a stochastic system where the communication between the controller and the actuator is triggered by a threshold-based rule. The communication is performed across an unreliable link that stochastically erases transmitted packets. As a partial protection against dropped packets, the controller sends a sequence of control commands to the actuator in each packet. These commands are stored in a buffer and applied sequentially until the next control packet arrives. We derive analytical expressions that quantify the trade-off between the communication cost and the control performance for this class of event-triggered control systems.

The thesis finally proposes a supervisory control structure for wireless control systems with time-varying delays. The supervisor has access to a crude indicator of the overall network state, and we assume that individual upper and lower bounds on network time-delays can be associated to each value of the indicator. Based on this information, the supervisor triggers the most appropriate controller from a multi-controller unit. The performance of such a supervisory controller allows for improving the performance over a single robust controller. As the granularity of the network state measurements increases, the performance of the supervisory controller improves at the expense of increased computational complexity.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. xix, 157
Series
TRITA-EE, ISSN 1653-5146 ; 2015:016
Keywords
Networked control systems, wireless networks, optimal control, time-delays, packet losses, linear-quadratic control, supervisory control
National Category
Control Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-165767 (URN)978-91-7595-528-5 (ISBN)
Public defence
2015-05-21, F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20150504

Available from: 2015-05-04 Created: 2015-04-29 Last updated: 2015-05-04Bibliographically approved
Demirel, B., Feyzmahdavian, H. R., Ghadimi, E. & Johansson, M. (2015). Stability Analysis of Discrete-Time Linear Systems with Unbounded Stochastic Delays. In: 5th IFAC Workshop on Distributed Estimation and Control of Networked Systems (NECSYS): . Paper presented at 5th IFAC Workshop on Distributed Estimation and Control in Networked Systems NecSys 2015 — Philadelphia, 10-11 September 2015. Elsevier, 48
Open this publication in new window or tab >>Stability Analysis of Discrete-Time Linear Systems with Unbounded Stochastic Delays
2015 (English)In: 5th IFAC Workshop on Distributed Estimation and Control of Networked Systems (NECSYS), Elsevier, 2015, Vol. 48Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates the stability of discrete-time linear systems with stochastic delays. We assume that delays are modeled as random variables, which take values in integers with a certain probability. For the scalar case, we provide an analytical bound on the probability to guarantee the stability of linear systems. In the vector case, we derive a linear matrix inequality condition to compute the probability for ensuring the stability of closed-loop systems. As a special case, we also determine the step size of gradient algorithms with stochastic delays in the unconstrained quadratic programming to guarantee convergence to the optimal solution. Numerical examples are provided to show the effectiveness of the proposed analysis techniques.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Delay, Ranodom delay, Stochastic system
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-183459 (URN)2-s2.0-84992490272 (Scopus ID)
Conference
5th IFAC Workshop on Distributed Estimation and Control in Networked Systems NecSys 2015 — Philadelphia, 10-11 September 2015
Note

QC 20160315

Available from: 2016-03-12 Created: 2016-03-12 Last updated: 2017-06-07Bibliographically approved
Demirel, B., Aytekin, A., Quevedo, D. E. & Johansson, M. (2015). To wait or to drop: On the optimal number of retransmissions in wireless control. In: 2015 European Control Conference, ECC 2015: . Paper presented at European Control Conference, ECC 2015, 15 July 2015 through 17 July 2015 (pp. 962-968). IEEE
Open this publication in new window or tab >>To wait or to drop: On the optimal number of retransmissions in wireless control
2015 (English)In: 2015 European Control Conference, ECC 2015, IEEE , 2015, p. 962-968Conference paper, Published paper (Refereed)
Abstract [en]

The dimensioning of wireless communication protocols for networked control involves a non-trivial trade-off between reliability and delay. Due to the lossy nature of wireless communications, there is a risk that sensor messages will be dropped. The end-to-end reliability can be improved by retransmitting dropped messages, but this comes at the expense of additional delays. In this work, we determine the number of retransmissions that strikes the optimal balance between communication reliability and delay, in the sense that it achieves the minimal expected linear-quadratic loss of the closed-loop system. An important feature of our setup is that it accounts for the random delays and possible losses that occur when unreliable communication is combatted with retransmissions. The resulting controller dynamically switches among a set of infinite-horizon linear-quadratic regulators, and is simple to implement. Numerical simulations are carried out to highlight the trade-off between reliability and delay. © 2015 EUCA.

Place, publisher, year, edition, pages
IEEE, 2015
Keywords
Closed loop systems, Economic and social effects, Wireless telecommunication systems, Communication reliabilities, End-to-end reliabilities, Important features, Infinite horizons, Linear quadratic regulator, Networked controls, Wireless communication protocols, Wireless communications, Reliability
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-186823 (URN)10.1109/ECC.2015.7330666 (DOI)2-s2.0-84963904003 (Scopus ID)9783952426937 (ISBN)
Conference
European Control Conference, ECC 2015, 15 July 2015 through 17 July 2015
Note

QC 20160517

Available from: 2016-05-17 Created: 2016-05-13 Last updated: 2016-05-17Bibliographically approved
Demirel, B., Aytekin, A., Quevedo, D. E. & Johansson, M. (2015). To wait or to drop: on the optimal number of retransmissions in wireless control. In: 2015 EUROPEAN CONTROL CONFERENCE (ECC): . Paper presented at 2015 EUROPEAN CONTROL CONFERENCE (ECC) (pp. 962-968). IEEE
Open this publication in new window or tab >>To wait or to drop: on the optimal number of retransmissions in wireless control
2015 (English)In: 2015 EUROPEAN CONTROL CONFERENCE (ECC), IEEE , 2015, p. 962-968Conference paper, Published paper (Refereed)
Abstract [en]

The dimensioning of wireless communication protocols for networked control involves a non-trivial trade-off between reliability and delay. Due to the lossy nature of wireless communications, there is a risk that sensor messages will be dropped. The end-to-end reliability can be improved by retransmitting dropped messages, but this comes at the expense of additional delays. In this work, we determine the number of retransmissions that strikes the optimal balance between communication reliability and delay, in the sense that it achieves the minimal expected linear-quadratic loss of the closed-loop system. An important feature of our setup is that it accounts for the random delays and possible losses that occur when unreliable communication is combatted with retransmissions. The resulting controller dynamically switches among a set of infinite-horizon linear-quadratic regulators, and is simple to implement. Numerical simulations are carried out to highlight the trade-off between reliability and delay.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-243725 (URN)000380485400150 ()
Conference
2015 EUROPEAN CONTROL CONFERENCE (ECC)
Note

QC 20190227

Available from: 2019-02-27 Created: 2019-02-27 Last updated: 2019-08-21Bibliographically approved
Demirel, B., Zou, Z., Soldati, P. & Johansson, M. (2014). Modular Design of Jointly Optimal Controllers and Forwarding Policies for Wireless Control. IEEE Transactions on Automatic Control, 59(12), 3252-3265
Open this publication in new window or tab >>Modular Design of Jointly Optimal Controllers and Forwarding Policies for Wireless Control
2014 (English)In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 12, p. 3252-3265Article in journal (Refereed) Published
Abstract [en]

We consider the joint design of packet forwarding policies and controllers for wireless control loops where sensor measurements are sent to the controller over an unreliable and energy-constrained multi-hop wireless network. For fixed sampling rate of the sensor, the co-design problem separates into two well-defined and independent subproblems: transmission scheduling for maximizing the deadline-constrained reliability and optimal control under packet loss. We develop optimal and implementable solutions for these subproblems and show that the optimally co-designed system can be efficiently found. Numerical examples highlight the many trade-offs involved and demonstrate the power of our approach.

Keywords
Markov decision process, optimal control, wireless sensor networks
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-158389 (URN)10.1109/TAC.2014.2351972 (DOI)000345526200012 ()2-s2.0-84914127442 (Scopus ID)
Note

QC 20150112

Available from: 2015-01-12 Created: 2015-01-07 Last updated: 2017-12-05Bibliographically approved
Demirel, B. (2013). Design and Performance Analysis of Wireless Networked Control Systems. (Licentiate dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Design and Performance Analysis of Wireless Networked Control Systems
2013 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

Networked control systems (NCSs) are distributed systems that use shared communication networks to exchange information between system components such as sensors, controllers and actuators. The networked control system architecture promises advantages in terms of increased flexibility, reduced wiring and lower maintenance costs, and is finding its way into a wide variety of applications, ranging from automobiles and automated highway systems to process control, and power distribution systems. However, NCSs also pose many challenges in their analysis and design, since transmitting signals over wireless networks has several side effects, such as: (i) variable sampling intervals, (ii) variable communication delays, (iii) packet losses caused by the unreliability of the network. In this thesis, we aim at developing three different design frameworks, which take some of these side effects into account for improving the performance of the overall system.

This thesis firstly presents the joint design of packet forwarding policies and controllers for wireless control loops where sensor measurements are sent to the controller over an unreliable and energy--constrained multi--hop wireless network. For fixed sampling rate of the sensor, the co--design problem separates into two well-defined and independent subproblems: transmission scheduling for maximizing the deadline--constrained reliability and optimal control under packet loss. We develop optimal and implementable solutions for these subproblems and show that the optimally co--designed system can be efficiently found. Numerical examples highlight the many trade-offs involved and demonstrate the power of our approach.

Secondly, this thesis proposes a supervisory control structure for networked systems with time-varying delays. The control structure, in which a supervisor triggers the most appropriate controller from a multi-controller unit, aims at improving the closed-loop performance relative to what can be obtained using a single robust controller. Our analysis considers average dwell-time switching and is based on a novel multiple Lyapunov-Krasovskii functional. We develop stability conditions that can be verified by semi-definite programming, and show that the associated state feedback synthesis problem also can be solved using convex optimization tools. Extensions of the analysis and synthesis procedures to the case when the evolution of the delay mode is described by a Markov chain are also developed. Simulations on small- and large-scale networked control systems are used to illustrate the effectiveness of our approach.

Lastly, we consider an event--triggered control framework for a linear time--invariant process. We introduce a range based event--triggering algorithm that is used to transmit information from the controller to the actuator. We also analytically characterize the control performance and communication rate for a given event threshold. Additionally, we provide a systematic way to analyze the trade--off between the communication rate and control performance by appropriately selecting an event threshold. Using numerical examples, we demonstrate the effectiveness of the proposed framework. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. p. xiii, 108
Series
Trita-EE, ISSN 1653-5146 ; 2013:021
Keywords
Networked control; switched systems; optimal control; event-triggered control
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-121203 (URN)978-91-7501-748-8 (ISBN)
Presentation
2013-05-14, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130424

Available from: 2013-04-24 Created: 2013-04-23 Last updated: 2013-04-24Bibliographically approved
Demirel, B., Briat, C. & Johansson, M. (2013). Deterministic and stochastic approaches to supervisory control design for networked systems with time-varying communication delays. Nonlinear Analysis: Hybrid Systems, 10(1), 94-110
Open this publication in new window or tab >>Deterministic and stochastic approaches to supervisory control design for networked systems with time-varying communication delays
2013 (English)In: Nonlinear Analysis: Hybrid Systems, ISSN 1751-570X, E-ISSN 1878-7460, Vol. 10, no 1, p. 94-110Article in journal (Refereed) Published
Abstract [en]

This paper proposes a supervisory control structure for networked systems with time-varying delays. The control structure, in which a supervisor triggers the most appropriate controller from a multi-controller unit, aims at improving the closed-loop performance relative to what can be obtained using a single robust controller. Our analysis considers average dwell-time switching and is based on a novel multiple Lyapunov-Krasovskii functional. We develop stability conditions that can be verified by semi-definite programming, and show that the associated state feedback synthesis problem also can be solved using convex optimization tools. Extensions of the analysis and synthesis procedures to the case when the evolution of the delay mode is described by a Markov chain are also developed. Simulations on small and large-scale networked control systems are used to illustrate the effectiveness of our approach.

Keywords
Linear matrix inequality, Stochastic switched systems, Switched systems, Time-delay systems
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-126033 (URN)10.1016/j.nahs.2013.03.006 (DOI)000323856800008 ()2-s2.0-84881250021 (Scopus ID)
Note

QC 20130819

Available from: 2013-08-19 Created: 2013-08-19 Last updated: 2017-12-06Bibliographically approved
Demirel, B., Gupta, V. & Johansson, M. (2013). On the trade-off between control performance and communication cost for event-triggered control over lossy networks. In: 2013 European Control Conference, ECC 2013: . Paper presented at 2013 12th European Control Conference, ECC 2013; Zurich; Switzerland; 17 July 2013 through 19 July 2013 (pp. 1168-1174). IEEE
Open this publication in new window or tab >>On the trade-off between control performance and communication cost for event-triggered control over lossy networks
2013 (English)In: 2013 European Control Conference, ECC 2013, IEEE , 2013, p. 1168-1174Conference paper, Published paper (Refereed)
Abstract [en]

This paper develops a theoretical framework for quantifying the trade-off between communication cost and control performance in event-triggered control over lossy networks. We consider a system where the communication between the controller and actuator is dictated by a threshold-based event-triggering algorithm, and develop a Markov-chain model that describes the attempted and successful transmissions of control messages over the lossy communication channel. A feature of our model is that it considers retransmissions of unsuccessful messages and that it accounts for the delay associated with such retransmissions. A systematic framework for analyzing the trade-off between the communication rate and control performance and for optimal tuning of the event threshold emanates by combining this model with an analytical model of the closed-loop performance. Numerical examples demonstrate the effectiveness of the proposed framework.

Place, publisher, year, edition, pages
IEEE, 2013
Keywords
Closed-loop performance, Communication cost, Communication rate, Control performance, Event-triggered controls, Markov-chain models, Systematic framework, Theoretical framework
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-143328 (URN)000332509701092 ()2-s2.0-84893335740 (Scopus ID)978-303303962-9 (ISBN)
Conference
2013 12th European Control Conference, ECC 2013; Zurich; Switzerland; 17 July 2013 through 19 July 2013
Note

QC 20140319

Available from: 2014-03-19 Created: 2014-03-19 Last updated: 2014-04-24Bibliographically approved
Güvenç, B. A., Necipoǧlu, S., Demirel, B. & Güvenç, L. (2013). Robust control of atomic force microscopy. In: Mechatronics: (pp. 103-132). John Wiley & Sons
Open this publication in new window or tab >>Robust control of atomic force microscopy
2013 (English)In: Mechatronics, John Wiley & Sons, 2013, p. 103-132Chapter in book (Other academic)
Abstract [en]

The atomic force microscope (AFM) is an instrument used for acquiring images at nanometer scale. Obtaining better image quality at higher scan speed is a research area of great interest in the control of an AFM. Improving the dynamic response of the scanning probe in the vertical direction and the dynamic response of the scanning motion in the lateral plane are the two major areas of application of advanced control methods to an AFM. The uncertainties inherent in the models of AFM vertical and lateral direction motion stages dictates the application of robust control methods. In this chapter, robust control methods are applied to AFM, treating first the vertical direction and then the lateral plane.

Place, publisher, year, edition, pages
John Wiley & Sons, 2013
Keywords
AFM imaging, AFM robust control, MIMO disturbance, Tapping mode AFM, Vertical direction
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-140088 (URN)10.1002/9781118614549.ch4 (DOI)2-s2.0-84886973772 (Scopus ID)9781848213081 (ISBN)
Note

QC 20140120

Available from: 2014-01-20 Created: 2014-01-17 Last updated: 2014-01-20Bibliographically approved
Zou, Z., Demirel, B. & Johansson, M. (2012). Minimum-energy packet forwarding policies for guaranteed LQG performance in wireless control systems. In: 2012 IEEE 51st Annual Conference on Decision and Control (CDC): . Paper presented at 51st IEEE Conference on Decision and Control, CDC 2012; Maui, HI; United States; 10 December 2012 through 13 December 2012 (pp. 3341-3346). IEEE
Open this publication in new window or tab >>Minimum-energy packet forwarding policies for guaranteed LQG performance in wireless control systems
2012 (English)In: 2012 IEEE 51st Annual Conference on Decision and Control (CDC), IEEE , 2012, p. 3341-3346Conference paper, Published paper (Refereed)
Abstract [en]

This paper studies minimum-energy packet forwarding policies for communicating sensor measurements from plant to controller over an unreliable multi-hop wireless network so as to guarantee that the optimal controller achieves a prespecified closed-loop performance. For fixed sampling interval, we demonstrate that the minimal linear-quadratic control loss is monotonically decreasing in the reliability of the sensor-to-controller communication. This allows us to decompose the overall design problem into two separate tasks: finding the minimum end-to-end reliability that allows to achieve a prespecified linear-quadratic loss, and developing minimum-energy packet forwarding policies under a deadline-constrained reliability requirement. We develop optimal solutions for both subproblems and show how the co-designed system with minimum forwarding energy cost and guaranteed LQG control performance can be found by a one-dimensional search over admissible sampling periods. The paper ends with a numerical example which demonstrates the effectiveness of the proposed framework.

Place, publisher, year, edition, pages
IEEE, 2012
Series
IEEE Conference on Decision and Control. Proceedings, ISSN 0191-2216
Keywords
Networks, Delay
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-104769 (URN)10.1109/CDC.2012.6426253 (DOI)000327200403112 ()2-s2.0-84874270942 (Scopus ID)978-1-4673-2066-5 (ISBN)
Conference
51st IEEE Conference on Decision and Control, CDC 2012; Maui, HI; United States; 10 December 2012 through 13 December 2012
Funder
ICT - The Next Generation
Note

QC 20121116

Available from: 2012-11-20 Created: 2012-11-12 Last updated: 2013-12-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4733-2240

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