Stabilization of networked control systems via dynamic output-feedback controllers

This paper investigates the problem of stabilization of networked control systems via dynamic output-feedback controllers. The physical plant and the dynamic controller are in continuous time, and a communication channel exists between the output of the physical plant and the input of the dynamic controller. Three important communication features are considered: measurement quantization, signal transmission delay, and data packet dropout, which appear typically in a networked environment. Attention is focused on the design of dynamic output-feedback controllers which ensure asymptotic stability of the closed-loop systems. Linear matrix inequality (LMI)-based conditions are formulated for the existence of admissible controllers. If these conditions are satisfied, a desired controller can be readily constructed. A satellite system is used to illustrate the applicability and effectiveness of the proposed controller design method.published_or_final_versio

New summation inequalities and their applications to discrete-time delay systems

This paper provides new summation inequalities in both single and double forms to be used in stability analysis of discrete-time systems with time-varying delays. The potential capability of the newly derived inequalities is demonstrated by establishing less conservative stability conditions for a class of linear discrete-time systems with an interval time-varying delay in the framework of linear matrix inequalities. The effectiveness and least conservativeness of the derived stability conditions are shown by academic and practical examples.Comment: 15 pages, 01 figur

Networked control systems in the presence of scheduling protocols and communication delays

This paper develops the time-delay approach to Networked Control Systems (NCSs) in the presence of variable transmission delays, sampling intervals and communication constraints. The system sensor nodes are supposed to be distributed over a network. Due to communication constraints only one node output is transmitted through the communication channel at once. The scheduling of sensor information towards the controller is ruled by a weighted Try-Once-Discard (TOD) or by Round-Robin (RR) protocols. Differently from the existing results on NCSs in the presence of scheduling protocols (in the frameworks of hybrid and discrete-time systems), we allow the communication delays to be greater than the sampling intervals. A novel hybrid system model for the closed-loop system is presented that contains {\it time-varying delays in the continuous dynamics and in the reset conditions}. A new Lyapunov-Krasovskii method, which is based on discontinuous in time Lyapunov functionals is introduced for the stability analysis of the delayed hybrid systems. Polytopic type uncertainties in the system model can be easily included in the analysis. The efficiency of the time-delay approach is illustrated on the examples of uncertain cart-pendulum and of batch reactor

Dissipative Stabilization of Linear Systems with Time-Varying General Distributed Delays (Complete Version)

New methods are developed for the stabilization of a linear system with general time-varying distributed delays existing at the system's states, inputs and outputs. In contrast to most existing literature where the function of time-varying delay is continuous and bounded, we assume it to be bounded and measurable. Furthermore, the distributed delay kernels can be any square-integrable function over a bounded interval, where the kernels are handled directly by using a decomposition scenario without using approximations. By constructing a Krasovski\u{i} functional via the application of a novel integral inequality, sufficient conditions for the existence of a dissipative state feedback controller are derived in terms of matrix inequalities without utilizing the existing reciprocally convex combination lemmas. The proposed synthesis (stability) conditions, which take dissipativity into account, can be either solved directly by a standard numerical solver of semidefinite programming if they are convex, or reshaped into linear matrix inequalities, or solved via a proposed iterative algorithm. To the best of our knowledge, no existing methods can handle the synthesis problem investigated in this paper. Finally, numerical examples are presented to demonstrate the effectiveness of the proposed methodologies.Comment: Accepted by Automatic

Delay-dependent output feedback compensators for a class of networked control systems

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia de Automação e Sistemas, Florianópolis, 2014Sistemas 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