Dissertations / Theses on the topic 'Networked Control with delays'
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1
Deng, Yang. "Delay estimation and predictor-based control of time-delay systems with a class of various delays." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0014.
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Le retard est un phénomène largement présent dans les systèmes de commande(i.e.retard physique, latence de communication, temps de calcul) et peut en dégrader les performances ou même les déstabiliser. Si le retard est faible, la stabilité en boucle fermée peut être garantie par des lois de commande conventionnelles mais ces techniques ne sont plus efficaces si le retard est long. Cette thèse est dédiée à la commande des systèmes à retard avec retards longs inconnus ou avec des retards incertains. Pour compenser les retards longs, la commande prédictive est adoptée et des techniques d’estimation de retard sont développées. Selon les différents types de systèmes et de retards, trois objectifs sont visés dans la thèse. Le premier objectif considère la commande des systèmes linéaires avec retards constants inconnus pour lesquels un nouvel estimateur de retard est proposé pour estimer les retards inconnus. Le retard estimé est ensuite utilisé dans la commande prédictive pour stabiliser le système. Le deuxième objectif se concentre sur la stabilisation pratique des systèmes commandés à distance avec des retards inconnus variants. Dans ce cas, les retards sont estimés de manière pratique : une boucle de communication spécifique est utilisée pour estimer le retard en temps fini puis le système est stabilisé par une commande prédictive. Les tests expérimentaux réalisés sur un réseau WiFi ont montré que l’algorithme permet d’estimer de manière robuste les retards variants. Le dernier objectif est consacré à la commande des systèmes commandés en réseau avec retards variants. La commande prédictive discrète est utilisée pour compenser les retards longs et variants et les ré-ordonnancements de paquets dans le canal capteur-contrôleur sont également considérés. De plus, cette méthode est validée par l’asservissement visuel d’un pendule inverse commandé en réseau. Les performances obtenues sont meilleures que les méthodes de commande non-prédictives classiquesTime-delay is a widely-found phenomenon (i.e. physical dead time, communication latency, computation time) in real control systems, which can degrade the performances of the system or destabilize the system. If the time-delay is small, then the closed-loop stability can be guaranteed with conventional control techniques; but these techniques are no longer effective if the time-delay is long. This thesis is dedicated to the control of time-delaysystemswithunknown or uncertain long time-delays. In order to compensate long time-delays, the predictor-based control technique is adopted, and the delay estimation techniques are developed to assist the predictor-based controller. According to the different types of the systems and the time-delays, three objectives are analyzed in the thesis. The first objective considers the control of LTI systems with unknown constant delays, a new type of delay estimator is proposed to estimate the unknown time-delays, then it is plugged into apredictor-based controller to stabilize the system. The second objective focuses on the practical stabilization of remote control systems with unknown time-varying delays, at this time, the time-delays are estimated by a practical way: a specific communication loop is used to estimate the round-trip delay in finite time, and the system is stabilized with a predictor-based controller. This practical delay estimation algorithm is implemented on a real WiFi network, it can estimate the time-varying delays with good performances and robustness. The last objective is devoted to the control of networked control systems with time-varying delays, the discrete predictor-based control techniques are used to compensate long time-varyingdelays,and the packet reordering in the sensor-to-controller channel is also considered. Moreover, this control solution is validated on a networked visual servo inverted pendulum system, and the control performances are fairly better than the non-predictive control methods
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Demirel, Burak. "Architectures and Performance Analysis of Wireless Control Systems." Doctoral thesis, KTH, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-165767.
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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.QC 20150504
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Seuret, Alexandre, Dimos V. Dimarogonas, and Karl Henrik Johansson. "Consensus under communication delays." KTH, Reglerteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-28520.
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This paper deals with the consensus problem under communication network inducing delays. It is well-known that introducing a delay leads in general to a reduction of the performance or to instability due to the fact that timedelay systems are infinite dimensional. For instance, the set of initial conditions of a time-delay system is not a vector but a function taken in an interval. Therefore, investigating the effect of time-delays in the consensus problem is an important issue. In the present paper, we assume that each agent receives instantaneously its own state information but receives the state information from its neighbors after a constant delay. Two stability criteria are provided based on the frequency approach and on Lyapunov-Krasovskii techniques given in terms of LMI. An analytic expression of the consensus equilibrium which depends on the delay and on the initial conditions taken in an interval is derived. The efficiency of the method is tested for different network communication schemes.QC 20110120
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Sargolzaei, Arman. "Time-Delay Switch Attack on Networked Control Systems, Effects and Countermeasures." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2175.
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In recent years, the security of networked control systems (NCSs) has been an important challenge for many researchers. Although the security schemes for networked control systems have advanced in the past several years, there have been many acknowledged cyber attacks. As a result, this dissertation proposes the use of a novel time-delay switch (TDS) attack by introducing time delays into the dynamics of NCSs. Such an attack has devastating effects on NCSs if prevention techniques and countermeasures are not considered in the design of these systems. To overcome the stability issue caused by TDS attacks, this dissertation proposes a new detector to track TDS attacks in real time. This method relies on an estimator that will estimate and track time delays introduced by a hacker. Once a detector obtains the maximum tolerable time delay of a plant’s optimal controller (for which the plant remains secure and stable), it issues an alarm signal and directs the system to its alarm state. In the alarm state, the plant operates under the control of an emergency controller that can be local or networked to the plant and remains in this stable mode until the networked control system state is restored.
In another effort, this dissertation evaluates different control methods to find out which one is more stable when under a TDS attack than others. Also, a novel, simple and effective controller is proposed to thwart TDS attacks on the sensing loop (SL). The modified controller controls the system under a TDS attack. Also, the time-delay estimator will track time delays introduced by a hacker using a modified model reference-based control with an indirect supervisor and a modified least mean square (LMS) minimization technique.
Furthermore, here, the demonstration proves that the cryptographic solutions are ineffective in the recovery from TDS attacks. A cryptography-free TDS recovery (CF-TDSR) communication protocol enhancement is introduced to leverage the adaptive channel redundancy techniques, along with a novel state estimator to detect and assist in the recovery of the destabilizing effects of TDS attacks. The conclusion shows how the CF-TDSR ensures the control stability of linear time invariant systems.
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Nygren, Johannes. "Input-Output Stability Analysis of Networked Control Systems." Doctoral thesis, Uppsala universitet, Reglerteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272344.
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The main focus of the thesis is to derive stability criteria for networked control system (NCS) models featuring imperfections such as time-varying and constant delays, quantization, packet dropouts, and non-uniform sampling intervals. The main method of proof is based on matrix algebra, as opposed to methods using Lyapunov functions or integral quadratic constraints (IQC). This work puts a particular focus on handling systems with a single integrator. This framework is elaborated in different specific directions as motivated by practical realizations of NCSs, as well as through numerical examples. A novel proof of the discrete time multivariate circle criterion and the Tsypkin criterion for systems including a single integrator is presented, as well as a stability criterion for linear systems with a single integrator subject to variable sampling periods and sector-bounded nonlinear feedback. Four stability criteria for different classes of systems subject to packet loss and time-varying delay are given. Stability criteria for a closed loop system switching between a set of linear time-invariant systems (LTIs) are proved. This result is applied to a single-link NCS with feedback subject to packet loss. Finally, necessary and sufficient conditions for delay-independent stability of an LTI system subject to nonlinear feedback are derived.
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Mkondweni, Ncedo Sandiso. "Design and implementation of linear robust networked control systems." Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1195.
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Thesis submitted in fulfilment of the requirements for the degree
Doctor of Technology: Electrical Engineering
in the Faculty of Engineering
at the Cape Peninsula University of Technology, 2013Networked Control Systems is a control system where the plant and the controller exchange information via a shared communication network and the network is considered as part of the closed loop control system. Unfortunately the network introduces network induced random varying time delays and data packet loss amongst the communication network imperfections. The network delays are considered to be between the controller and the actuator and between the sensor and the controller. These network imperfections degrade the performance of the closed loop control system and result in closed loop system instability. The complexity of measuring the communication network imperfection in networked control systems makes it difficult for the control engineers to develop methods for design of controllers that can incorporate and compensate these imperfections in order to improve the performance of the networked control systems. In this thesis a co-simulation toolset called LabNS2 is developed to address the first problem of measuring the communication network imperfections by providing an ideal environment that can be used to investigate the influence of network time delays or packet loss. The software environment of the toolset is based on LabVIEWTM and Network Simulator Version 2 (NS2). A new robust predictive optimal controller design method is developed to address the problem of the destabilising effect of the network induced time delay between the controller and the actuator. The design approach is based on time shifting of the optimisation horizon and a state predictor. The design of the controller is based on a model of the plant with delay in the control vector equal to the delay between the controller and the actuator or to the sum of the delays between the controller and the actuator and between the sensor and the controller. The time shifting approach allows the design of the controller to be performed for a model without time delay. Then the control action is based on the future values of the state space vector estimates. The state predictor is developed to predict these future values of the state using the present and past values of the state estimates and control actions. This technique is made possible by the use of the plant model Transition Matrix. A Discrete Kalman Filter is modified to address the problem of the destabilising effect of the network induced time delay between the sensor and the controller. An additional state estimation vector is added to the filter estimate at every current moment of time. iv The developed methods are implemented for networked control of a dish antenna driven by two stepper motors. The outcomes of the thesis can be used for the education and fundamental research purposes, but the developed control strategies have significant sense towards the Square Kilometer Array projects and satellite systems industry.
National Research Foundation
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Wang, Bo. "Analysis and implementation of time-delay systems and networked control systems." Thesis, University of South Wales, 2008. https://pure.southwales.ac.uk/en/studentthesis/analysis-and-implementation-of-timedelay-systems-and-networked-control-systems(f54e4378-db9b-443d-b505-88b4af5bb72a).html.
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Systems with delays frequently appear in engineering. The presence of delays makes system analysis and control design much more complicated. Networked control systems where the delays are often random are typical cases of such systems. For one particular category of time-delays systems, integral processes with dead time (IPDTs), the control limits that a PI controller can achieve are discussed in this thesis. These limits include the region of the control parameters to guarantee the system stability, the control parameters to achieve the given gain and/or phase margins (GPMs), the constraint on achievable gain and phase margins, the performance of set point tracking and disturbance rejection. Three types of PI controllers, namely typical PI controller, single tuning-parameter PI controller and PI controller under two-degree-of-freedom (2-DOF) structure, are studied. In control schemes of the modified Smith predictor (MSP) where the controller usually includes a distributed delay, the system implementation is not trivial because of the inherent hidden unstable poles. This thesis provides an estimation of the minimal number of implementation steps for the distributed delay in linear control laws. This is obtained by solving an inequality with respect to the number of implementation steps. A coarse estimation is given as the initial value to solve the inequality using bisection algorithms. A minimization process as well as some other techniques are also introduced to further improve the estimation. In networked control systems, the network-transmission delay and data dropout are combinedly represented by a network-induced delay. By designing a data pre processing mechanism, the network-induced delay can be assigned. Such delay as signment is applied to networked predictive control schemes, which alleviates systemstability limits on the network-induced delay. Two stability criteria are given for the closed-loop system with random network-induced delay, and a resulting implementation algorithm is also provided. The control and implementation of a magnetic levitation system over the network is studied in this thesis. Firstly, a test-rig which is suitable to implement control over a network is set up. Feedback linearization and direct local linearization methods for the nonlinear MagLev system are presented. In order to improve the control performance, a networked predictive method is employed, where the system model is identified in real-time. Local control and networked control are implemented on this test-rig, including networked predictive control. Model predictive control demonstrates a clear performance advantage over the networked control strategies which does not incorporate compensation for the network-induced delay. In order to quickly implement networked control systems (NCSs) by simulation or practical application, a MATLAB/Simulink based NCS toolbox is developed. This toolbox incorporates basic parts of a general NCS, that is, network simulation, network interface, plant interface and typical control schemes. With the NCS toolbox, users can focus on the study of new control schemes.
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Shi, Xiaohan. "A reliable real-time transport protocol for networked control systems over wireless networks." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/60160/1/Xiaohan_Shi_Thesis.pdf.
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Deploying wireless networks in networked control systems (NCSs) has become more and more popular during the last few years. As a typical type of real-time control systems, an NCS is sensitive to long and nondeterministic time delay and packet losses. However, the nature of the wireless channel has the potential to degrade the performance of NCS networks in many aspects, particularly in time delay and packet losses. Transport layer protocols could play an important role in providing both reliable and fast transmission service to fulfill NCS’s real-time transmission requirements. Unfortunately, none of the existing transport protocols, including the Transport Control Protocol (TCP) and the User Datagram Protocol (UDP), was designed for real-time control applications. Moreover, periodic data and sporadic data are two types of real-time data traffic with different priorities in an NCS. Due to the lack of support for prioritized transmission service, the real-time performance for periodic and sporadic data in an NCS network is often degraded significantly, particularly under congested network conditions.
To address these problems, a new transport layer protocol called Reliable Real-Time Transport Protocol (RRTTP) is proposed in this thesis. As a UDP-based protocol, RRTTP inherits UDP’s simplicity and fast transmission features. To improve the reliability, a retransmission and an acknowledgement mechanism are designed in RRTTP to compensate for packet losses. They are able to avoid unnecessary retransmission of the out-of-date packets in NCSs, and collisions are unlikely to happen, and small transmission delay can be achieved. Moreover, a prioritized transmission mechanism is also designed in RRTTP to improve the real-time performance of NCS networks under congested traffic conditions. Furthermore, the proposed RRTTP is implemented in the Network Simulator 2 for comprehensive simulations. The simulation results demonstrate that RRTTP outperforms TCP and UDP in terms of real-time transmissions in an NCS over wireless networks.
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Gui, Li. "A transport protocol for real-time applications in wireless networked control systems." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/45460/1/Li_Gui_Thesis.pdf.
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A Networked Control System (NCS) is a feedback-driven control system wherein the control loops are closed through a real-time network. Control and feedback signals in an NCS are exchanged among the system’s components in the form of information packets via the network. Nowadays, wireless technologies such as IEEE802.11 are being introduced to modern NCSs as they offer better scalability, larger bandwidth and lower costs. However, this type of network is not designed for NCSs because it introduces a large amount of dropped data, and unpredictable and long transmission latencies due to the characteristics of wireless channels, which are not acceptable for real-time control systems. Real-time control is a class of time-critical application which requires lossless data transmission, small and deterministic delays and jitter. For a real-time control system, network-introduced problems may degrade the system’s performance significantly or even cause system instability. It is therefore important to develop solutions to satisfy real-time requirements in terms of delays, jitter and data losses, and guarantee high levels of performance for time-critical communications in Wireless Networked Control Systems (WNCSs). To improve or even guarantee real-time performance in wireless control systems, this thesis presents several network layout strategies and a new transport layer protocol. Firstly, real-time performances in regard to data transmission delays and reliability of IEEE 802.11b-based UDP/IP NCSs are evaluated through simulations. After analysis of the simulation results, some network layout strategies are presented to achieve relatively small and deterministic network-introduced latencies and reduce data loss rates. These are effective in providing better network performance without performance degradation of other services. After the investigation into the layout strategies, the thesis presents a new transport protocol which is more effcient than UDP and TCP for guaranteeing reliable and time-critical communications in WNCSs. From the networking perspective, introducing appropriate communication schemes, modifying existing network protocols and devising new protocols, have been the most effective and popular ways to improve or even guarantee real-time performance to a certain extent. Most previously proposed schemes and protocols were designed for real-time multimedia communication and they are not suitable for real-time control systems. Therefore, devising a new network protocol that is able to satisfy real-time requirements in WNCSs is the main objective of this research project. The Conditional Retransmission Enabled Transport Protocol (CRETP) is a new network protocol presented in this thesis. Retransmitting unacknowledged data packets is effective in compensating for data losses. However, every data packet in realtime control systems has a deadline and data is assumed invalid or even harmful when its deadline expires. CRETP performs data retransmission only in the case that data is still valid, which guarantees data timeliness and saves memory and network resources. A trade-off between delivery reliability, transmission latency and network resources can be achieved by the conditional retransmission mechanism. Evaluation of protocol performance was conducted through extensive simulations. Comparative studies between CRETP, UDP and TCP were also performed. These results showed that CRETP significantly: 1). improved reliability of communication, 2). guaranteed validity of received data, 3). reduced transmission latency to an acceptable value, and 4). made delays relatively deterministic and predictable. Furthermore, CRETP achieved the best overall performance in comparative studies which makes it the most suitable transport protocol among the three for real-time communications in a WNCS.
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Moraes, Vitor Mateus. "Delay-dependent output feedback compensators for a class of networked control systems." reponame:Repositório Institucional da UFSC, 2014. https://repositorio.ufsc.br/xmlui/handle/123456789/128874.
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Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Automação e Sistemas, Florianópolis, 2014Made available in DSpace on 2015-02-05T20:26:24Z (GMT). No. of bitstreams: 1 330228.pdf: 1707908 bytes, checksum: e9e7656943afa359919bcdb455b78423 (MD5) Previous issue date: 2014
Sistemas de controle via rede (NCS, do inglês Networked Control Systems) são uma classe especial de sistemas amostrados digitalmente, nos quais os dispositivos do sistema de controle se comunicam através de uma rede de comunicação (como mostrado na Fig. I). Significantes avanços tecnológicos tem levado a um maior interesse tanto na utilização de NCS em ambiente industrial (MOYNE; TILBURY, 2007), quanto em pesquisas relacionadas ao assunto (HESPANHA; NAGHSHTABRIZI; XU,2007; HEEMELS; WOUW, 2010; ZHANG; GAO; KAYNAK, 2013). Algumas das vantagens oferecidas por tais sistemas, com relação a sistemas de controle tradicionais, compreendem menor custo de implementação, flexibilidade e facilidade de manutenção. Apesar disso, inerentemente alguns efeitos indesejados também podem ocorrer, tais como atrasos na comunicação e intervalos de amostragem variantes, ocasionando degradação no desempenho do sistema em malha fechada. Devido a esses efeitos, a análise de estabilidade e também o projeto de controladores para NCS tornam-se mais desafiadores (TANG; YU, 2007). De modo geral, os estudos sobre NCS podem ser divididos em duas grandes áreas: controle da rede e controle via rede (GUPTA; CHOW, 2010). A primeira está mais interessada em proporcionar uma melhor qualidade no serviço de transmissão de dados realizado pela rede de comunicação, enquanto a segunda objetiva uma melhor qualidade do desempenho dos sistemas de controle sob determinadas condições induzidas pelos efeitos da utilização da rede. Embora tipicamente tratadas de forma separada, recentemente alguns esforços têm sido empreendidos de modo a integrar algumas características de ambas as áreas em fase de projeto, as chamadas estratégias de co-design (TORNGREN et al., 2006). Uma abordagem integrada é necessária de modo a se obter uma maior compreensão do funcionamento de um NCS, podendo assim obter um melhor desempenho geral do sistema. Neste contexto, especialmente levando em consideração que o uso rede de comunicação é limitado, tal recurso deve ser corretamente distribuído entre os sistemas de controle de modo a garantir um funcionamento adequado. Além disso, requisitos de desempenho individuais de cada planta também devem ser cumpridos, mesmo sujeitos a tais restrições de limites de recursos.
Abstract: Networked control system (NCS) is a special class of sampled-data system where control systems devices are interconnected through a communication network. Despite the advantages, such as lower cost, flexibility and easy of maintenance compared to a more traditional implementation, some undesired effects may be induced by the use of a shared medium in the feedback loop, for instance, time-varying sampling intervals and delays. Due to the multidisciplinary nature of an NCS, the analysis and design of such systems also demand a more comprehensive approach. Thus, the main objective of this thesis is to propose some strategies for the synthesis of dynamic output feedback compensators, assuming an industrial network control system environment with temporal behavior features and requirements. Throughout this document, the NCS is modeled considering unknown time-varying delays, which leads to an uncertain system representation, later overapproximated by a convex polytope with additional norm-bounded uncertainty. Based on parameter dependent Lyapunov functions, closed-loop stability conditions are provided, which can be verified in terms of feasibility of a set of linear matrix inequalities (LMIs). The control designs are then promptly derived from the stability conditions, leading to delay-dependent compensators. Furthermore, an integrated control design and resource management strategy is proposed, taking into account the controller design while also addressing the shared nature of the communication network. This co-design strategy assumes that a supervisor task has the knowledge of all devices that access the network, as well as their allocated bandwidths. Numerical examples and simulations are provided to illustrate the effectiveness of the proposed design methodologies.
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Ji, Kun. "Real-time control over networks." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5834.
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A control system in which sensors, actuators, and controllers are interconnected over a
communication network is called a networked control system (NCS). Enhanced computational
capabilities and bandwidths in the networking technology enabled researchers to develop NCSs
to implement distributed control schemes. This dissertation presents a framework for the
modeling, design, stability analysis, control, and bandwidth allocation of real-time control over
networks. This framework covers key research issues regarding control over networks and can
be the guidelines of NCS design. A single actuator ball magnetic-levitation (maglev) system is
implemented as a test bed for the real-time control over networks to illustrate and verify the
theoretical results of this dissertation. Experimentally verifying the feasibility of Internet-based
real-time control is another main objective of this dissertation.
First, this dissertation proposes a novel NCS model in which the effects of the networkinduced
time delay, data-packet loss, and out-of-order data transmission are all considered.
Second, two simple algorithms based on model-estimator and predictor- and timeout-scheme are
proposed to compensate for the network-induced time delay and packet loss simultaneously.
These algorithms are verified experimentally by the ball maglev test bed. System stability analyses of original and compensated systems are presented. Then, a novel co-design
consideration related to real-time control and network communication is also proposed. The
working range of the sampling frequency is determined by the analysis of the system stability
and network parameters such as time delay, data rate, and data-packet size. The NCS design
chart developed in this dissertation can be a useful guideline for choosing the network and
control parameters in the design of an NCS. Using a real-time operating system for real-time
control over networks is also proposed as one of the main contributions of this dissertation.
After a real-time NCS is successfully implemented, advanced control theories such as
robust control, optimal control, and adaptive control are applied and formulated to improve the
quality of control (QoC) of NCSs. Finally, an optimal dynamic bandwidth management method
is proposed to solve the optimal network scheduling and bandwidth allocation problem when
NCSs are connected to the same network and are sharing the network resource.
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Snickars, Carlo. "Design of a wirelessHART simulator for studying delay compensation in networked control systems." Thesis, KTH, Reglerteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105893.
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Al-Hammouri, Ahmad Tawfiq. "INTERNET CONGESTION CONTROL: COMPLETE STABILITY REGION FOR PI AQM AND BANDWIDTH ALLOCATION IN NETWORKED CONTROL." online version, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1189088621.
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Chen, Yen-Lin. "Cross-layer design and optimization for wireless networked control systems." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61089/1/Yen-Lin_Chen_Thesis.pdf.
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Wireless networked control systems (WNCSs) have been widely used in the areas of manufacturing and industrial processing over the last few years. They provide real-time control with a unique characteristic: periodic traffic. These systems have a time-critical requirement. Due to current wireless mechanisms, the WNCS performance suffers from long time-varying delays, packet dropout, and inefficient channel utilization. Current wirelessly networked applications like WNCSs are designed upon the layered architecture basis. The features of this layered architecture constrain the performance of these demanding applications. Numerous efforts have attempted to use cross-layer design (CLD) approaches to improve the performance of various networked applications. However, the existing research rarely considers large-scale networks and congestion network conditions in WNCSs. In addition, there is a lack of discussions on how to apply CLD approaches in WNCSs. This thesis proposes a cross-layer design methodology to address the issues of periodic traffic timeliness, as well as to promote the efficiency of channel utilization in WNCSs. The design of the proposed CLD is highlighted by the measurement of the underlying network condition, the classification of the network state, and the adjustment of sampling period between sensors and controllers. This period adjustment is able to maintain the minimally allowable sampling period, and also maximize the control performance. Extensive simulations are conducted using the network simulator NS-2 to evaluate the performance of the proposed CLD. The comparative studies involve two aspects of communications, with and without using the proposed CLD, respectively. The results show that the proposed CLD is capable of fulfilling the timeliness requirement under congested network conditions, and is also able to improve the channel utilization efficiency and the proportion of effective data in WNCSs.
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Filippo, Marco. "Stabilizing nonlinear model predictive control in presence of disturbances and off - line approximations of the control law." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4519.
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2009/2010One of the more recent and promising approaches to control is the Receding Horizon one. Due to its intrinsic characteristics, this methodology, also know as Model Predictive Control, allows to easily face disturbances and model uncertainties: indeed at each sampling instant the control action is recalculated on the basis of the reached state (closed loop). More in detail, the procedure consists in the minimization of an adequate cost function with respect to a control input sequence; then the first element of the optimal sequence is applied. The whole procedure is then continuously reiterated. In this thesis, we will focus in particular on robust control of constrained systems. This is motivated by the fact that, in practice, every real system is subjected to uncertainties, disturbances and constraints, in particular on state and input (for instance, plants can work without being damaged only in a limited set of configurations and, on the other side, control actions must be compatible with actuators' physical limits). With regard to the first aspect, maintaining the closed loop stability even in presence of disturbances or model mismatches can result in an essential strategy: moreover it can be exploited in order to design an approximate stabilizing controller, as it will be shown. The control input values are obtained recurring to a Nearest Neighbour technique or, in more favourable cases, to a Neural Network based approach to the exact RH law, which can be then calculated off line: this implies a strong improvement related to the applicability of MPC policy in particular in terms of on line computational burden. The proposed scheme is capable to guarantee stability even for systems that are not stabilizable by means of a continuous feedback control law. Another interesting framework in which the study of the influence of uncertainties on stability can lead to significant contributions is the networked MPC one. In this case, due to the absence of physical interconnections between the controller and the systems to be controlled, stability can be obtained only taking into account of the presence of disturbances, delays and data losses: indeed this kind of uncertainties are anything but infrequent in a communication network. The analysis carried out in this thesis regards interconnected systems and leads to two distinct procedures, respectively stabilizing the linear systems with TCP protocol and nonlinear systems with non-acknowledged protocol. The core of both the schemes resides in the online solution of an adequate reduced horizon optimal control problem.
Una delle strategie di controllo emerse più recentemente, più promettenti e di conseguenza più studiate negli ultimi anni è quella basata sull'approccio Receding Horizon. Grazie alle caratteristiche che contraddistinguono questa tecnica, cui si fa spesso riferimento anche col nome di Model Predictive Control, risulta piuttosto agevole trattare eventuali disturbi e incertezze di modellazione; tale metodo prevede infatti il calcolo di un nuovo ingresso di controllo per ciascun istante di campionamento, in seguito alla minimizzazione ad ogni passo di un'opportuna funzione di costo rispetto ad una sequenza di possibili futuri ingressi, inizializzata sulla base del valore dello stato del sistema all'istante considerato. Il controllo è dato dal primo elemento di tale sequenza ottima; tutto questo viene continuamente ripetuto, il che comporta un aggiornamento costante del segnale di controllo. Gli inconvenienti di questa tecnica risiedono nelle elevate risorse computazionali e nei tempi di calcolo richiesti, così da ridurne drasticamente l'applicabilità specie nel caso di sistemi con elevata dinamica. In questa tesi ci si concentrerà sulle caratteristiche di robustezza del controllore: l'importanza di quest'analisi risiede nel fatto che ogni sistema reale è soggetto a incertezze e disturbi di varia origine cui bisogna far fronte durante le normali condizioni di funzionamento. Inoltre, la capacità di gestire errori di modellazione, come si vedrà, può essere sfruttata per ottenere un notevole incremento delle prestazioni nella stima del valore da fornire in ingresso all'impianto: si tratta di ripartire l'errore complessivo in modo da garantirsi dei margini che consentano di lavorare con un'approssimazione della legge di controllo, come specificato più avanti. In tutto il lavoro si considereranno sistemi vincolati: l'interesse per questa caratteristica dipende dal fatto che nella pratica vanno sempre tenuti in considerazione eventuali vincoli su stato e ingressi: basti pensare al fatto che ogni impianto è progettato per lavorare solo all'interno un determinato insieme di configurazioni, determinato ad esempio da vincoli fisici su attuatori, sensori e così via: non riporre sufficiente attenzione in tali restrizioni può risultare nel danneggiamento del sistema di controllo o dell'impianto stesso. Le caratteristiche di stabilità di un sistema controllato mediante MPC dipendono in modo determinante dalla scelta dei parametri e degli attributi della funzione di costo da minimizzare; nel seguito, con riferimento al caso dei sistemi non lineari, saranno forniti suggerimenti e strumenti utili in tal senso, al fine di ottenere la stabilità anche in presenza di disturbi (che si assumeranno opportunamente limitati). Successivamente tale robustezza verrà sfruttata per la progettazione di controllori stabilizzanti approssimati: si dimostrerà infatti che, una volta progettato adeguatamente il sistema di controllo “esatto” basato su approccio RH e conseguentemente calcolati off-line i valori ottimi degli ingressi su una griglia opportunamente costruita sul dominio dello stato, il ricorso a una conveniente approssimazione di tali valori non compromette le proprietà di stabilità del sistema complessivo, che continua per di più a mantenere una certa robustezza. Da notare che ciò vale anche per sistemi non stabilizzabili mediante legge di controllo feedback continua: la funzione approssimante può essere ottenuta in questo caso con tecniche di tipo Nearest Neighbour; qualora invece la legge di controllo sia sufficientemente regolare si potrà far ricorso ad approssimatori smooth, quali ad esempio le reti neurali. Tutto ciò comporta un notevole miglioramento delle prestazioni del controllore RH sia dal punto di vista del tempo di calcolo richiesto che (nel secondo caso) della memoria necessaria ad immagazzinare i parametri del controllore, risultando nell'applicabilità dell'approccio basato su MPC anche al caso di sistemi con elevata dinamica. Un altro ambito in cui lo studio dell'influenza delle incertezze e dei disturbi sulla stabilità richiede una notevole attenzione è quello dei sistemi networked; anche in questo caso il ricorso all'MPC può portare a ottimi risultati di stabilità robusta, a patto di individuare un' opportuna struttura per il sistema complessivo ed effettuare scelte adeguate per il problema di ottimizzazione. In particolare, si considererà il caso di trasmissione di dati tra un controllore centralizzato e le varie parti dell'impianto in assenza di collegamento fisico diretto. Lo studio della stabilità dovrà allora tenere in considerazione la presenza di perdite di pacchetti o ritardi di trasmissione, condizioni tutt'altro che infrequenti per le reti. Saranno quindi proposte due distinte procedure, che si dimostreranno essere in grado di garantire robustezza a sistemi rispettivamente lineari comunicanti con protocolli di tipo TCP e non lineari in presenza di protocolli UDP. Questo secondo caso è senz'altro il più complesso ma allo stesso tempo il più concreto tra i due. Il nucleo del controllo è ancora basato su una tecnica MPC, ma stavolta il controllore è chiamato a risolvere il problema di ottimizzazione su un orizzonte “ridotto”, che consente la gestione dei ritardi e di eventuali perdite di pacchetto su determinati canali. La lunghezza dell'orizzonte dipenderà dalla presenza o meno dei segnali di ricezione del pacchetto (acknowledgement).
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Kuri, Joy. "Optimal Control Problems In Communication Networks With Information Delays And Quality Of Service Constraints." Thesis, Indian Institute of Science, 1995. http://hdl.handle.net/2005/162.
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In this thesis, we consider optimal control problems arising in high-speed integrated communication networks with Quality of Service (QOS) constraints. Integrated networks are expected to carry a large variety of traffic sources with widely varying traffic characteristics and performance requirements. Broadly, the traffic sources fall into two categories: (a) real-time sources with specified performance criteria, like small end to end delay and loss probability (sources of this type are referred to as Type 1 sources below), and (b) sources that do not have stringent performance criteria and do not demand performance guarantees from the network - the so-called Best Effort Type sources (these are referred to as Type 2 sources below). From the network's point of view, Type 2 sources are much more "controllable" than Type 1 sources, in the sense that the Type 2 sources can be dynamically slowed down, stopped or speeded up depending on traffic congestion in the network, while for Type 1 sources, the only control action available in case of congestion is packet dropping. Carrying sources of both types in the same network concurrently while meeting the performance objectives of Type 1 sources is a challenge and raises the question of equitable sharing of resources. The objective is to carry as much Type 2 traffic as possible without sacrificing the performance requirements of Type 1 traffic.
We consider simple models that capture this situation. Consider a network node through which two connections pass, one each of Types 1 and 2. One would like to maximize the throughput of the Type 2 connection while ensuring that the Type 1 connection's performance objectives are met. This can be set up as a constrained optimization problem that, however, is very hard to solve. We introduce a parameter b that represents the "cost" of buffer occupancy by Type 2 traffic. Since buffer space is limited and shared, a queued Type 2 packet means that a buffer position is not available for storing a Type 1 packet; to discourage the Type 2 connection from hogging the buffer, the cost parameter b is introduced, while a reward for each Type 2 packet coming into the buffer encourages the Type 2 connection to transmit at a high rate.
Using standard on-off models for the Type 1 sources, we show how values can be assigned to the parameter b; the value depends on the characteristics of the Type 1 connection passing through the node, i.e., whether it is a Variable Bit Rate (VBR) video connection or a Continuous Bit Rate (CBR) connection etc. Our approach gives concrete networking significance to the parameter b, which has long been considered as an abstract parameter in reward-penalty formulations of flow control problems (for example, [Stidham '85]).
Having seen how to assign values to b, we focus on the Type 2 connection next. Since Type 2 connections do not have strict performance requirements, it is possible to defer transmitting a Type 2 packet, if the conditions downstream so warrant. This leads to the question: what is the "best" transmission policy for Type 2 packets? Decisions to transmit or not must be based on congestion conditions downstream; however, the network state that is available at any instant gives information that is old, since feedback latency is an inherent feature of high speed networks. Thus the problem is to identify the best transmission policy under delayed feedback information.
We study this problem in the framework of Markov Decision Theory. With appropriate assumptions on the arrivals, service times and scheduling discipline at a network node, we formulate our problem as a Partially Observable Controlled Markov Chain (PO-CMC). We then give an equivalent formulation of the problem in terms of a Completely Observable Controlled Markov Chain (CO-CMC) that is easier to deal with., Using Dynamic Programming and Value Iteration, we identify structural properties of an optimal transmission policy when the delay in obtaining feedback information is one time slot. For both discounted and average cost criteria, we show that the optimal policy has a two-threshold structure, with the threshold on the observed queue length depending, on whether a Type 2 packet was transmitted in the last slot or not.
For an observation delay k > 2, the Value Iteration technique does not yield results. We use the structure of the problem to provide computable upper and lower bounds to the optimal value function. A study of these bounds yields information about the structure of the optimal policy for this problem. We show that for appropriate values of the parameters of the problem, depending on the number of transmissions in the last k steps, there is an "upper cut off" number which is a value such that if the observed queue length is greater than or equal to this number, the optimal action is to not transmit. Since the number of transmissions in the last k steps is between 0 and A: both inclusive, we have a stack of (k+1) upper cut off values. We conjecture that these (k + l) values axe thresholds and the optimal policy for this problem has a (k + l)-threshold structure.
So far it has been assumed that the parameters of the problem are known at the transmission control point. In reality, this is usually not known and changes over time. Thus, one needs an adaptive transmission policy that keeps track of and adjusts to changing network conditions. We show that the information structure in our problem admits a simple adaptive policy that performs reasonably well in a quasi-static traffic environment.
Up to this point, the models we have studied correspond to a single hop in a virtual connection. We consider the multiple hop problem next. A basic matter of interest here is whether one should have end to end or hop by hop controls. We develop a sample path approach to answer this question. It turns out that depending on the relative values of the b parameter in the transmitting node and its downstream neighbour, sometimes end to end controls are preferable while at other times hop by hop controls are preferable.
Finally, we consider a routing problem in a high speed network where feedback information is delayed, as usual. As before, we formulate the problem in the framework of Markov Decision Theory and apply Value Iteration to deduce structural properties of an optimal control policy. We show that for both discounted and average cost criteria, the optimal policy for an observation delay of one slot is Join the Shortest Expected Queue (JSEQ) - a natural and intuitively satisfactory extension of the well-known Join the Shortest Queue (JSQ) policy that is optimal when there is no feedback delay (see, for example, [Weber 78]). However, for an observation delay of more than one slot, we show that the JSEQ policy is not optimal. Determining the structure of the optimal policy for a delay k>2 appears to be very difficult using the Value Iteration approach; we explore some likely policies by simulation.
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Seitz, Timothy M. "Modeling and Robust Stability of Advanced, Distributed Control Systems." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1497201155817062.
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Al-Azzawi, Waleed. "Robust controller for delays and packet dropout avoidance in solar-power wireless network." Thesis, De Montfort University, 2013. http://hdl.handle.net/2086/9026.
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Solar Wireless Networked Control Systems (SWNCS) are a style of distributed control systems where sensors, actuators, and controllers are interconnected via a wireless communication network. This system setup has the benefit of low cost, flexibility, low weight, no wiring and simplicity of system diagnoses and maintenance. However, it also unavoidably calls some wireless network time delays and packet dropout into the design procedure. Solar lighting system offers a clean environment, therefore able to continue for a long period. SWNCS also offers multi Service infrastructure solution for both developed and undeveloped countries. The system provides wireless controller lighting, wireless communications network (WI-FI/WIMAX), CCTV surveillance, and wireless sensor for weather measurement which are all powered by solar energy.
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QUET, Pierre-Francois D. "A ROBUST CONTROL THEORETIC APPROACH TO FLOW CONTROLLER DESIGNS FOR CONGESTION CONTROL IN COMMUNICATION NETWORKS." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1032194223.
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ARGENTO, CLAUDIO. "Complex networks: analysis and control." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/596.
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The introduction provides an overview on complex networks, trying to investigate what apparently different kinds of networks have in common. Some statistical properties are illustrated and a simulation tool for the analysis of complex networks is presented. A weighted directed random graph is used as network model. The graph contains a fixed number N of nodes and a variable number of edges: in particular, each edge is present with probability p. Some statistical properties (such as strong connection, global and local efficiency, cost, etc) are computed and their reliance on probability p is studied. Some probability distributions (such as shortest path, edge/node load) are also drawn and, by using the method of stages, the best fitting curves are computed. The way as parameters characterizing such curves change when p varies is also investigated. The general structure of the proposed fitting technique allows to model several aspects of complex networks and makes possible its use in many different fields. Finally, the tracking control problem of linear time invariant (LTI) systems when the plant and the controller belong to the same network is considered. Time delays can degrade significantly the performance of a networked control system, eventually leading to instability. The problem characterized by constant and known network delays is analytically examined, showing how to construct a plant state predictor in order to compensate the time delays between the plant and the controller, so to allow the tracking of a reference signal. Computer simulations illustrate the effectiveness of the proposed technique, also when time delays slightly vary around a mean value.
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Suess, Sérgio Ricardo. "Redes IP em aplicações de controle em malha fechada : proposta de estratégias para lidar com o indeterminismo temporal." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/15741.
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Este trabalho apresenta uma proposta de solução para compensar o atraso variável, característico de redes IP. O preditor de Smith é tradicionalmente usado para compensar atrasos, mas no caso deste tipo de rede um fator importante que pode degradar o controle do sistema são as grandes variações nos atrasos sofridos pelas mensagens. Para tratar este problema, este trabalho baseia-se na criação de uma estrutura de dados de armazenamento para a saída do preditor de Smith, possibilitando a comparação do valor de saída da planta com o valor adequado guardado na estrutura. Para determinação do valor correspondente, este está associado a um índice calculado com o tempo de roundtrip obtido de informações dos pacotes de dados proveniente da planta. Para se chegar a tal solução, foi analisada nas primeiras seções a influência do atraso em malhas de controle e posteriormente um estudo do estado da arte para tipos de controle sobre redes IP. Ao final é apresentada uma análise experimental, demonstrando resultados promissores da aplicação desta proposta.This work presents a solution to compensate the varying delay, characteristic of IP networks. The Smith predictor is traditionally used to compensate delays but in this type of networks an other important factor that can destabilize the system is the large jitter of the delay. In order to solve this problem, the solution presented here is based on a data structure to save the output from the model of the plant used by the Smith predictor, that make possible to compare the output from the plant with the corresponding value in the structure. In order to take the correspondent value, it is associated to an index which is calculated with the roundtrip obtained from the informations in the packet arrived from the plant. In order to formulate this solution, it was analised in the first sections the influence of the delay in control systems and then a study of the state of art of the control systems over IP networks. At the end, an experimental analise to demonstrate the good result of the application of this solution is presented.
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Araújo, José. "Design, Implementation and Validation of Resource-Aware and Resilient Wireless Networked Control Systems." Doctoral thesis, KTH, Reglerteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-152535.
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Networked control over wireless networks is of growing importance in many application domains such as industrial control, building automation and transportation systems. Wide deployment however, requires systematic design tools to enable efficient resource usage while guaranteeing close-loop control performance. The control system may be greatly affected by the inherent imperfections and limitations of the wireless medium and malfunction of system components. In this thesis, we make five important contributions that address these issues. In the first contribution, we consider event- and self-triggered control and investigate how to efficiently tune and execute these paradigms for appropriate control performance. Communication strategies for aperiodic control are devised, where we jointly address the selection of medium-access control and scheduling policies. Experimental results show that the best trade-off is obtained by a hybrid scheme, combining event- and self-triggered control together with contention-based and contention-free medium access control. The second contribution proposes an event-based method to select between fast and slow periodic sampling rates. The approach is based on linear quadratic control and the event condition is a quadratic function of the system state. Numerical and experimental results show that this hybrid controller is able to reduce the average sampling rate in comparison to a traditional periodic controller, while achieving the same closed-loop control performance. In the third contribution, we develop compensation methods for out-of-order communications and time-varying delays using a game-theoretic minimax control framework. We devise a linear temporal coding strategy where the sensor combines the current and previous measurements into a single packet to be transmitted. An experimental evaluation is performed in a multi-hop networked control scenario with a routing layer vulnerability exploited by a malicious application. The experimental and numerical results show the advantages of the proposed compensation schemes. The fourth contribution proposes a distributed reconfiguration method for sensor and actuator networks. We consider systems where sensors and actuators cooperate to recover from faults. Reconfiguration is performed to achieve model-matching, while minimizing the steady-state estimation error covariance and a linear quadratic control cost. The reconfiguration scheme is implemented in a room heating testbed, and experimental results demonstrate the method's ability to automatically reconfigure the faulty system in a distributed and fast manner. The final contribution is a co-simulator, which combines the control system simulator Simulink with the wireless network simulator COOJA. The co-simulator integrates physical plant dynamics with realistic wireless network models and the actual embedded software running on the networked devices. Hence, it allows for the validation of the complete wireless networked control system, including the study of the interactions between software and hardware components.QC 20140929
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Belapurkar, Rohit K. "Stability and Performance of Propulsion Control Systems with Distributed Control Architectures and Failures." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357309068.
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Wu, Fei. "Ultra-Low Delay in Complex Computing and Networked Systems: Fundamental Limits and Efficient Algorithms." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu155559337777619.
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Michelin, Thiago José. "Análise do impacto da comunicação via rede FlexRay em sistemas de controle." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/103813.
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A importância das redes de comunicação industriais em modernos sistemas de automação e controle industriais tem aumentado significativamente nos últimos anos, devido aos avanços nas áreas de processadores e softwares embarcados, que permitem o desenvolvimento de dispositivos com elevada capacidade de processamento a custos reduzidos. Estas características também são muito importantes em sistemas automotivos, visto que existe uma tendência para a substituição de sistemas mecânicos e hidráulicos em veículos e o espaço disponível para implementação é bastante reduzido. Esta substituição passa pela elaboração de complexos algoritmos de controle, os quais, quando operam sobre uma rede de comunicação, precisam considerar explicitamente os efeitos do canal de comunicação compartilhado na dinâmica do sistema em malha fechada. Este trabalho apresenta uma análise do impacto da comunicação em rede sobre sistemas de controle. Mais especificamente, analisa-se o comportamento do protocolo Flexray, recentemente desenvolvido por um consórcio de importantes empresas e que incorpora interessantes conceitos para escalonamento de mensagens síncronas e assíncronas. No trabalho foram realizados experimentos com três diferentes tipos de controladores aplicados ao estudo de caso de uma suspensão ativa, onde o sistema tem sua malha fechada sobre a rede FlexRay.The importance of communication networks on modern automation systems has increased significantly over the last years, mostly due to advances in embedded microprocessor and software technologies, which enable the development of devices with high processing power at reduced costs. These characteristics are very important for vehicle systems, since there is nowadays a trend to replace mechanical and hydraulic systems, and the space available for implementation is limited. This replacement requires very complex control algorithms, which, when operating on a communication network, have to consider explicitly the effects introduced by the shared communication channel on the closed loop system dynamics. This work presents an analysis of the network communication impact over control systems. More specifically, it is of interest to analyse the behavior of the FlexRay protocol, which has been recently developed by a Consortium of important companies and incorporates interesting concepts of synchronous and asynchronous message scheduling. In this work, some experiments were performed with three controllers, which were developed using different methodologies, applied to the case study of an active suspension system, where the loop is closed over the FlexRay protocol.
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Stankovic, Nikola. "Set-based control methods for systems affected by time-varying delay." Thesis, Supélec, 2013. http://www.theses.fr/2013SUPL0025/document.
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On considère la synthèse de la commande basée sur un asservissement affecté par des retards. L’approche utilisée repose sur des méthodes ensemblistes. Une partie de cette thèse est consacrée à une conception de commande active pour la compensation des retards qui apparaissent dans des canaux de communication entre le capteur et correcteur. Ce problème est considéré dans une perspective générale du cadre de commande tolérante aux défauts où des retards variés sont vus comme un mode particulier de dégradation du capteur. Le cas avec transmission de mesure retardée pour des systèmes avec des capteurs redondants est également examiné. Par conséquent, un cadre unifié est proposé afin de régler le problème de commande basé sur la transmission des mesures avec retard qui peuvent également être fournies par des capteurs qui sont affectés par des défauts soudains.Dans la deuxième partie le concept d’invariance positive pour des systèmes linéaires à retard à temps discret est exposé. En ce qui concerne l’invariance pour cette classe des systèmes dynamiques, il existe deux idées principales. La première approche repose sur la réécriture d’un tel système dans l’espace d’état augmenté et de le considérer comme un système linéaire. D’autre part, la seconde approche considère l’invariance dans l’espace d’état initial. Cependant, la caractérisation d’un tel ensemble invariant est encore une question ouverte, même pour le cas linéaire. Par conséquent, l’objectif de cette thèse est d’introduire une notion générale d’invariance positive pour des systèmes linéaires à retard à temps discret. Également, certains nouveaux éclairages sur l’existence et la construction pour les ensembles invariants positifs robustes sont détaillés. En outre, les nouveaux concepts d’invariance alternatives sont décritsWe considered the process regulation which is based on feedback affected by varying delays. Proposed approach relies on set-based control methods. One part of the thesis examines active control design for compensation of delays in sensor-to controller communication channel. This problem is regarded in a general perspective of the fault tolerant control where delays are considered as a particular degradation mode of the sensor. Obtained results are also adapted to the systems with redundant sensing elements that are prone to abrupt faults. In this sense, an unified framework is proposed in order to address the control design with outdated measurements provided by unreliable sensors.Positive invariance for linear discrete-time systems with delays is outlined in the second part of the thesis. Concerning this class of dynamics, there are two main approaches which define positive invariance. The first one relies on rewriting a delay-difference equation in the augmented state-space and applying standard analysis and control design tools for the linear systems. The second approach considers invariance in the initial state-space. However, the initial state-space characterization is still an open problem even for the linear case and it represents our main subject of interest. As a contribution, we provide new insights on the existence of the positively invariant sets in the initial state-space. Moreover, a construction algorithm for the minimal robust D-invariant set is outlined. Additionally, alternative invariance concepts are discussed
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Wood, Samuel Bennett. "Social network coding rate control in information centric delay tolerant networks." Thesis, University of California, Santa Cruz, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1583279.
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Tactical and emergency-response networks require efficient communication without a managed infrastructure in order to meet the requirements of mission critical applications. In these networks, mobility, disruption, limited network resources, and limited host resources are the norm instead of the exception. Despite these constraints, applications must quickly and reliably share data collected from their environment to allow users to coordinate and make critical decisions. Our previous work demonstrates that applying information-centric paradigms to the tactical edge can provide performance benefits over traditional address centric approaches. We expand on this work and investigate how social relationships can be inferred and exploited to improve network performance in volatile networks.
As a result of our investigation, we propose SOCRATIC (SOCial RATe control for Information Centric networks), a novel approach to dissemination that unifies replication and network coding, which takes advantage of social content and context heuristics to improve network performance. SOCRATIC replicates network encoded blocks according to a popularity index metric that captures social relationships, and is shared during neighbor discovery. The number of encoded blocks that is relayed to a node depends on its interest in the data object and its popularity index, i.e., how often and for how long it meets other nodes. We observe that nodes with similar interests tend to be co-located and we exploit this information through use of a generalization of a data object-to-interest matching function that quantifies this similarity. Encoded blocks are subsequently replicated towards the subscriber if a stable path exists. We evaluate an implementation of SOCRATIC through a detailed network emulation of a tactical scenario and demonstrate that it can achieve better performance than the existing socially agnostic approaches.
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Andersson, Pär, and Farkhan Jamalzadeh. "Wireless networked control systems." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199310.
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Zhao, Yun-Bo. "Packet-Based Control for Networked Control Systems." Thesis, University of South Wales, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490204.
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Networked control systems (NCSs) are such control systems where the control loop is closed via some form of communication networks. These control systems are widely applicable in remote and distributed control applications. The inserted network however presents great challenges to conventional control theory as far as the design and analysis of NCSs are concerned. These challenges are caused primarily by the communication constraints in NCSs, e.g., network-induced delay, data packet dropout, data packet disorder, network access constraint, etc., which significantly degrade the system performance or even destabilize the system. When applying conventional control approaches to NCSs, considerable conservativeness is inevitable due to the failure to exploit network characteristics. Therefore, the co-design approach to NCSs in which control approaches and characteristics of NCSs are both fully considered, is believed to be the best way forward for the design of NCSs. In this thesis, we investigate the packet-based transmission of the network being used in NCSs, and propose a packet-based control (PB-control) approach to NCSs. In this approach, the 'packet' structure of data transmission in NCSs which is distinct from conventional control systems, is taken advantage of where, the control signals are first 'packed' and then sent as a sequence instead of one at a time as done in conventional control systems. \Vith the efficient use of the 'packet' structure, we can then actively compensate for the communication constraints in NCSs including the network-induced delay, data packet dropout and data packet disorder simultaneously. After determining the PB-control structure, we then extend its application to several categories of problems as follows. j • The first application is to two types of special nonlinear systems described by a Hammerstein model and a Wiener model respectively. A 'two-step' approach is adopted in this situation to separate the nonlinear process from the whole system which then enables the PB-control approach to be implemented. • It is observed that the communication constraints in NeSs are stochastic in nature, and thus a stochastic analysis of the PB-control approach is presented -----'''-'--'--~-• .:.o'... '-~.::C''c:....'..:..'..;...';';;;'~~.~'----' ......;.''''- ---'- ..-..;.;.~~ / iii under the Markov jump system framework, by modeling the network-induced delay and data packet dropout as a homogeneous ergodic Markov chain. The sufficient and necessary conditions for stochastic stability and stabilization in this situation are also obtained. • Continuous-time plant and continuous network-induced delay are observed to be more difficult to handle when implementing the PB-control approach. For this challenge, a discretization technique is introduced for the continuous network-induced delay and as a result, a novel model for NCSs is derived which is different to that obtained by conventional analysis from time delay system theory. A stabilized controller is also obtained in this situation by using delay-dependent analysis. • The last application is to deal with the situation where a set of NeSs share the network and thus the network access constraint has to be considered. For this situation, a PB-control and scheduling co-design approach is proposed where, PB-control is still applied to each subsystem while scheduling algorithms are applied to schedule the network resources among the subsystems to guarantee the stability of the whole system. We also point out in the thesis that further research on the PB-control approach is still needed as far as nonlinear, continuous-time systems and stochastic analysis are concerned.
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Lim, Lee Booi. "Network delay control through adaptive queue management." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8887.
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Timeliness in delivering packets for delay-sensitive applications is an important QoS (Quality of Service) measure in many systems, notably those that need to provide real-time performance. In such systems, if delay-sensitive traffic is delivered to the destination beyond the deadline, then the packets will be rendered useless and dropped after received at the destination. Bandwidth that is already scarce and shared between network nodes is wasted in relaying these expired packets. This thesis proposes that a deterministic per-hop delay can be achieved by using a dynamic queue threshold concept to bound delay of each node. A deterministic per-hop delay is a key component in guaranteeing a deterministic end-to-end delay. The research aims to develop a generic approach that can constrain network delay of delay-sensitive traffic in a dynamic network. Two adaptive queue management schemes, namely, DTH (Dynamic THreshold) and ADTH (Adaptive DTH) are proposed to realize the claim. Both DTH and ADTH use the dynamic threshold concept to constrain queuing delay so that bounded average queuing delay can be achieved for the former and bounded maximum nodal delay can be achieved for the latter. DTH is an analytical approach, which uses queuing theory with superposition of N MMBP-2 (Markov Modulated Bernoulli Process) arrival processes to obtain a mapping relationship between average queuing delay and an appropriate queuing threshold, for queue management. While ADTH is an measurement-based algorithmic approach that can respond to the time-varying link quality and network dynamics in wireless ad hoc networks to constrain network delay. It manages a queue based on system performance measurements and feedback of error measured against a target delay requirement. Numerical analysis and Matlab simulation have been carried out for DTH for the purposes of validation and performance analysis. While ADTH has been evaluated in NS-2 simulation and implemented in a multi-hop wireless ad hoc network testbed for performance analysis. Results show that DTH and ADTH can constrain network delay based on the specified delay requirements, with higher packet loss as a trade-off.
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Zhong, Qingchang. "Robust control of systems with delays." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405412.
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Wolpert, Daniel Mark. "Overcoming time delays in visuomotor control." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334286.
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Heinrich, Benjamin. "Delay-Stability of Power Control in Wireless Networks." Thesis, KTH, Reglerteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91843.
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In this thesis, we investigate the stability of uplink power control algorithms in wireless networks. We derive an abstract block-diagram model of the power-control loop similar to the model in [6]. The power control loop regulates the energy output of the mobile devices based on measurements of the incoming signal strengths, background noise and interference. The goal of the implemented algorithm is to maintain a certain Signal-to- Interference Ratio (SIR) for all users. Our analysis is done locally by linearizing the system around a steady state. There, we can use a system-specific multivariate Nyquist criterion to analyze stability. In this framework, we also find bounds on the rate of convergence as a performance measure. A focus in this work lies on the influence of time delays and how one can compensate for them. Consequently, we investigate Time-Delay Compensation (TDC, see [6]) and find an extended version of it. We also extend our model to incorporate binary control feedback to match the realworld system. The emerging oscillatory behavior is then predicted and investigated by multivariate describing-function methods. The work is concluded by evaluating our findings with simulations using a Matlab/ Simulink model.
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Ji, Meng. "Graph-Based Control of Networked Systems." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16313.
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Networked systems have attracted great interests from the control society during the last decade. Several issues rising from the recent research are addressed in this dissertation. Connectedness is one of the important conditions that enable distributed coordination in a networked system. Nonetheless, it has been assumed in most implementations, especially in continuous-time applications, until recently. A nonlinear weighting strategy is proposed in this dissertation to solve the connectedness preserving problem. Both rendezvous and formation problem are addressed in the context of homogeneous network. Controllability of heterogeneous networks is another issue which has been long omitted. This dissertation contributes a graph theoretical interpretation of controllability. Distributed sensor networks make up another important class of networked systems. A novel estimation strategy is proposed in this dissertation. The observability problem is raised in the context of our proposed distributed estimation strategy, and a graph theoretical interpretation is derived as well.
The contributions of this dissertation are as follows:
It solves the connectedness preserving problem for networked systems. Based on that, a formation process is proposed.
For heterogeneous networks, the leader-follower structure is studied and sufficient and necessary conditions are presented for the system to be controllable.
A novel estimation strategy is proposed for distributed sensor networks, which could improve the performance. The observability problem is studied for this estimation strategy and a necessary condition is obtained.
This work is among the first ones that provide graph theoretical interpretations of the controllability and observability issues.
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Tipsuwan, Yodyium. "Gain Scheduling for Networked Control System." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-08282003-105850/.
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Performances of closed-loop control systems operated over a data network are typically degraded by network-induced delays. Furthermore, the closed-loop control systems can become unstable. The purpose of this research has been to develop a control methodology to handle network-induced delay effects using optimal gain scheduling on existing controllers. The proposed gain scheduling technique adapts controller gains externally by modifying a controller output to enable the controller for uses over a data network. Since existing controllers can still be utilized, the proposed methodology can reduce control system reinstallation and replacement costs. First, the effectiveness of the proposed gain scheduling technique on networked DC motor speed control using a PI (Proportional-Integral) controller is investigated. Also, the concept of network traffic condition measurement to select optimal controller gains is presented. Then, a middleware framework to measure network traffic conditions on an IP network based on delays and delay variations and to modify controller gains is described. Suggestion of using neural network in the gain scheduling scheme is also given. Finally, the gain scheduling technique with the middleware framework is then extended to mobile robot path-tracking control.
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Risberg, Daniel, and Peter Henningsson. "Networked Control of Unmanned Air Vehicles." Thesis, KTH, Fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-125912.
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It is not just our phones that are getting smarter, it is the buildings as well. Connecting multiple sensors in a house to a main control unit allows this smart building to control things that a human normally would have to. Unmanned Air Vehicles (UAVs) are aircrafts that are capable of piloting without a human on board and is a great addition to the smart building environment. The main goal of this project is to investigate the possibility of integrating UAVs to smart buildings by implementing a PID steering controller and an obstacle avoidance algorithm. In order to make the smart building more autonomous new applications for UAVs are discussed. As a conclusion we are able to show that the UAV used in this project successfully avoided a wall and then managed to navigate through a window in order to reach a reference point located at the other side of the wall.
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Colandairaj, J. "An approach to wireless networked control." Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479280.
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Chacón, Vásquez Mercedes. "Strategies for wireless networked control systems." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28771.
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Networked Control Systems (NCS) and Wireless Networked Control Systems (WNCS) are control systems where controllers, sensors and final elements of control are connected to a mutual communication network. The inclusion of the network introduces delays and dropouts, which greatly influence the stability and robustness of the controller. While there is wealth in theoretical contributions to NCS, it is still imperative to study more applications and investigate the effects of networks in a real-time operation. There are also open problems that require further study of the impact of disturbances, constraints and strong interactions in complex NCS. This thesis is concerned with the design of control strategies for WNCS mainly focused on Model-Based Predictive Control (MBPC), Proportional Integral Derivative (PID) and decentralised schemes with the aim of creating control laws suitable for compensating time-varying delays and dropouts. These strategies rely on optimisation problems which incorporate robustness and performance restrictions to compute the optimum controller. The performance and robustness of the controllers are evaluated through extensive experiments in a network simulator. A new adaptive Internal Model Control (IMC) controller has been developed to adapt to the network requirements and compute the IMC model parameters online. A new robust PID for NCS under random delays has been created by solving a new constrained optimisation problem that included constraints of maximum sensitivity to guarantee robustness. A novel optimal immune PID is developed to improve the performance of NCS under time-varying delays and dropouts. Simulation results show that the controller offers greater flexibility and improves the performance and robustness with respect to the other methods studied. Four more controllers have been tested and extensive tests have indicated stability for a limited percentage of process model variations and dropouts. Predictive PID controllers, with similar properties to MBPC, are developed to compensate dropouts in WNCS. A quadratic programming problem optimises a new MBPC cost function to find the optimal PID gains. The approach successfully maximises the performance by changing the controller gains at every sampling time and allowing maximum variations of system parameters and dropouts. Also, a new constrained predictive PID controller is presented to deal with input saturation. Simulation results show the superiority of the design in comparison with the control schemes studied earlier. Furthermore, a decentralised wireless networked model predictive control design for complex industrial systems has been developed. Also, the method has been applied to wind farm control. The proposed decentralised control offers an effective and innovative solution to improve the performance of large industrial applications.
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Khalil, Ashraf F. "Networked control of distributed energy systems." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3380/.
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This thesis reports a new method for stability analysis and maximum time delay estimation in networked control systems with applications to distributed energy systems. The proposed new method is based on using finite difference approximation for the delay term and then the Lyapunov system stability theorem is applied to derive the time delay boundary allowed to the system. The proposed method has been applied to networked control systems with state feedback controllers, with dynamic controllers, and to multi-units interconnected networked control systems. The proposed method is then extended to a class of networked control system with bounded nonlinearity and uncertainties. It is found that increasing the nonlinearity in the system will result in decreasing the maximum allowable time delay. Compared with most of the methods reported in the published literature, the new method is simple to use while the results are comparable. When the time delay is modelled using Markov Chain the stability of the networked control system is formulated as finding the solutions for Bilinear Matrix Inequalities. An improved V-K iteration algorithm is used to solve the Bilinear Matrix Inequalities in order to derive a controller to stabilize the systems.
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O'Brien, Kevin M. (Kevin Michael). "Task-level control for networked telerobotics." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39764.
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Juhlin-Henricson, Teddy, and Ludvig Aarflot. "Networked control of unmanned air vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199314.
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Hallqvist, Erik, and Sebastian Håkansson. "Networked control of autonomous ground vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199347.
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Ehrlin, E., and M. Törnqvist. "Networked control of autonomous ground vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199313.
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Athari, Kayvan. "Networked control of autonomous ground vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199389.
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Li, Vladimir, and Zacharias Zafirakis. "Networked control of unmanned air vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199397.
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Bakutis, Vladas, and Qiao Jin. "Networked Control of Autonomous Ground Vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200572.
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Chamoun, Christian, and Alan Goran. "Networked Control of Unmanned Air Vehicles." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200575.
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Costello, Zachary Kohl. "Distributed computation in networked systems." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54924.
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The objective of this thesis is to develop a theoretical understanding of computation in networked dynamical systems and demonstrate practical applications supported by the theory. We are interested in understanding how networks of locally interacting agents can be controlled to compute arbitrary functions of the initial node states. In other words, can a dynamical networked system be made to behave like a computer? In this thesis, we take steps towards answering this question with a particular model class for distributed, networked systems which can be made to compute linear transformations.
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Ouyang, Hua. "Networked predictive control systems : control scheme and robust stability." Thesis, University of South Wales, 2007. https://pure.southwales.ac.uk/en/studentthesis/networked-predictive-control-systems(9c6178d7-e6a4-420b-b35f-2d62d35ff5b0).html.
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Networked predictive control is a new research method for Networked Control Systems (NCS), which is able to handle network-induced problems such as time-delay, data dropouts, packets disorders, etc. while stabilizing the closed-loop system. This work is an extension and complement of networked predictive control methodology. There is always present model uncertainties or physical nonlinearity in the process of NCS. Therefore, it makes the study of the robust control of NCS and that of networked nonlinear control system (NNCS) considerably important. This work studied the following three problems: the robust control of networked predictive linear control systems, the control scheme for networked nonlinear control systems (NNCS) and the robust control of NNCS. The emphasis is on stability analysis and the design of robust control. This work adapted the two control schemes, namely, the time-driven and the event driven predictive controller for the implementation of NCS. It studied networked linear control systems and networked nonlinear control systems. Firstly, time-driven predictive controller is used to compensate for the networked-induced problems of a class of networked linear control systems while robustly stabilizing the closed-loop system. Secondly, event-driven predictive controller is applied to networked linear control system and NNCS and the work goes on to solve the robust control problem. The event-driven predictive controller brings great benefits to NCS implementation: it makes the synchronization of the clocks of the process and the controller unnecessary and it avoids measuring the exact values of the individual components of the network induced time-delay. This work developed the theory of stability analysis and robust synthesis of NCS and NNCS. The robust stability analysis and robust synthesis of a range of different system configurations have been thoroughly studied. A series of methods have been developed to handle the stability analysis and controller design for NCS and NNCS. The stability of the closed-loop of NCS has been studied by transforming it into that of a corresponding augmented system. It has been proved that if some equality conditions are satisfied then the closed-loop of NCS is stable for an upper-bounded random time delay and data dropouts. The equality conditions can be incorporated into a sub-optimal problem. Solving the sub-optimal problem gives the controller parameters and thus enables the synthesis of NCS. To simplify the calculation of solving the controller parameters, this thesis developed the relationship between networked nonlinear control system and a class of uncertain linear feedback control system. It proves that the controller parameters of some types of networked control system can be equivalently derived from the robust control of a class of uncertain linear feedback control system. The methods developed in this thesis for control design and robustness analysis have been validated by simulations or experiments.
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Chai, Senchun. "Design of the networked predictive control method for wired and wireless networked systems." Thesis, University of South Wales, 2007. https://pure.southwales.ac.uk/en/studentthesis/design-of-the-networked-predictive-control-method-for-wired-and-wireless-networked-systems(1c68e3c4-bc45-4823-95ae-66f9f51ea5f8).html.
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The closed-loop control of processes over networks has in recent years become an increasingly popular research topic. This is a very viable solution for a wide variety of applications due to the rapid developments in communication network technologies and the widespread expansion of network devices and users. The convergence of communication networks technologies and advanced control methods do have a great potential to replace traditional control systems. The research programme presented in this thesis led to a development of networked predictive control algorithms over wired local area networks, general packet radio service wireless networks and wireless local area networks. Since the network is taken as a part of a control system, the network-induced time delay and data dropout are unavoidable. How to compensate for these issues is the main challenge in designing control methodologies for networked control systems. Five solutions were presented in this thesis to address these problems and were termed as recursive predictive control method I, inner loop predictive control method, outer loop predictive control method, modified generalised predictive control method and recursive predictive control method II. Irrespective of the different implementations of the networked control methods used, there is a common structure for each method which consists of a predictive control generator, a network delay compensator, a buffer and a plant output predictor. The predictive control generator and network delay compensator were used to compensate for the network delay and data dropout in the forward channel. The network delay and data dropout in the feedback channel was compensated for by using the plant output predictor, buffer and network delay compensator. The relationship between the sampling rate, packet size, network delay and data dropout were examined by using a round trip time delay method. Two network delay measurement methods were also presented and analysed in this thesis. The results of the real-time measurement of the network delay were used in an offline simulation. A networked servo system was built to test the system performance for an approximately linear, open-loop stable system and a networked inverted pendulum system was used to illustrate the system performance for an open-loop unstable system. The stability of each method was also considered. In order to simplify the software development, the Matlab/Simulink/Real-time workshop integrated development suit was used in the practical control system. The simulation block diagram in the Simulink environment was translated to the standard C language by using the real-time workshop. The ARMLINUX-GCC 3.4.4 was used to compile the generated C language file into the executable file running on an embedded board. In order to monitor the status of the control system and change the parameters of the controller, a network-based supervisory program was also developed using Microsoft Visual C++ 6.0.