1,702 research outputs found
Robust control tools for traffic monitoring in TCP/AQM networks
Several studies have considered control theory tools for traffic control in
communication networks, as for example the congestion control issue in IP
(Internet Protocol) routers. In this paper, we propose to design a linear
observer for time-delay systems to address the traffic monitoring issue in
TCP/AQM (Transmission Control Protocol/Active Queue Management) networks. Due
to several propagation delays and the queueing delay, the set TCP/AQM is
modeled as a multiple delayed system of a particular form. Hence, appropriate
robust control tools as quadratic separation are adopted to construct a delay
dependent observer for TCP flows estimation. Note that, the developed mechanism
enables also the anomaly detection issue for a class of DoS (Denial of Service)
attacks. At last, simulations via the network simulator NS-2 and an emulation
experiment validate the proposed methodology
Robust Output Regulation: Optimization-Based Synthesis and Event-Triggered Implementation
We investigate the problem of practical output regulation: Design a controller that brings the system output in the vicinity of a desired target value while keeping the other variables bounded. We consider uncertain systems that are possibly nonlinear and the uncertainty of the linear part is modeled element-wise through a parametric family of matrix boxes. An optimization-based design procedures is proposed that delivers a continuous-time control and estimates the maximal regulation error. We also analyze an event-triggered emulation of this controller, which can be implemented on a digital platform, along with an explicit estimates of the regulation error
Efficient Control Approaches for Guaranteed Frequency Performance in Power Systems
Due to high penetration of renewable energy, converter-interfaced sources are increasing in power systems and degrading the grid frequency response. Synthetic inertia emulation and guaranteed primary frequency response is a challenging task. Still, there is high potential for application of highly controllable converter-interfaced devices to help performance. Renewable energy sources and demand side smart devices also need to be equipped with innovative frequency control approaches that contribute to frequency regulation operations.
First, the wind turbine generator is chosen to represent an example of a converter- interfaced source. An augmented system frequency response model is derived, including the system frequency response model and a reduced-order model of the wind turbine generator representing the supportive active power due to supplementary inputs. An output feedback observer-based control is designed to provide guaranteed frequency performance. System performance is analyzed for different short circuit ratio scenarios where a lower bound to guarantee the performance is obtained.
Second, the load side control for frequency regulation with its challenges is introduced. 5G technology and its potential application in smart grids are analyzed. The effect of communication delays and packet losses on inertia emulation are investigated to show the need of using improved communication infrastructure.
Third, a robust delay compensation for primary frequency control using fast demand response is proposed. Possible system structured uncertainties and communication delays are considered to limit frequency variations using the proposed control approach. An uncertain governor dead-band model is introduced to capture frequency response characteristics. Guaranteed inertial response is achieved and compared with a PI-based Smith predictor controller to show the effectiveness of the proposed method.
Fourth, set theoretic methods for safety verification to provide guaranteed frequency response are introduced. The Barrier certificate approach using a linear programming relaxation by Handelman’s representation is proposed with its application to power systems.
Finally, the Handelman’s based barrier certificate approach for adequate frequency performance is studied. The computational algorithm is provided for the proposed method and validated using power system benchmark case studies with a discussion on a safety supervisory control (SSC)
3 sampled-data control of nonlinear systems
This chapter provides some of the main ideas resulting from recent developments in sampled-data control of nonlinear systems. We have tried to bring the basic parts of the new developments within the comfortable grasp of graduate students. Instead of presenting the more general results that are available in the literature, we opted to present their less general versions that are easier to understand and whose proofs are easier to follow. We note that some of the proofs we present have not appeared in the literature in this simplified form. Hence, we believe that this chapter will serve as an important reference for students and researchers that are willing to learn about this area of research
Robust Output Regulation: Optimization-Based Synthesis and Event-Triggered Implementation
We investigate the problem of practical output regulation, i.e., to design a
controller that brings the system output in the vicinity of a desired target
value while keeping the other variables bounded. We consider uncertain systems
that are possibly nonlinear and the uncertainty of their linear parts is
modeled element-wise through a parametric family of matrix boxes. An
optimization-based design procedure is proposed that delivers a continuous-time
control and estimates the maximal regulation error. We also analyze an
event-triggered emulation of this controller, which can be implemented on a
digital platform, along with an explicit estimates of the regulation error
Event-triggered control for rational and Lur’e type nonlinear systems
In the present work, the design of event-triggered controllers for two classes of nonlinear systems is addressed: rational systems and Lur’e type systems. Lyapunov theory techniques are used in both cases to derive asymptotic stability conditions in the form of linear matrix inequalities that are then used in convex optimization problems as means of computing the control system parameters aiming at a reduction of the number of events generated. In the context of rational systems, state-feedback control is considered and differentialalgebraic representations are used as means to obtain tractable stability conditions. An event-triggering strategy which uses weighting matrices to strive for less events is proposed and then it is proven that this strategy does not lead to Zeno behavior. In the case of Lur’e systems, observer-based state-feedback is addressed with event generators that have access only to the system output and observed state, but it imposes the need of a dwell-time, i.e. a time interval after each event where the trigger condition is not evaluated, to cope with Zeno behavior. Two distinct approaches, exact time-discretization and looped-functional techniques, are considered to ensure asymptotic stability in the presence of the dwell-time. For both system classes, emulation design and co-design are addressed. In the emulation design context, the control law (and the observer gains, when appropriate) are given and the task is to compute the event generator parameters. In the co-design context, the event generator and the control law or the observer can be simultaneously designed. Numerical examples are presented to illustrate the application of the proposed methods.Neste trabalho Ă© abordado o projeto de controladores baseados em eventos para duas classes de sistemas nĂŁo lineares: sistemas racionais e sistemas tipo Lur’e. TĂ©cnicas da teoria de Lyapunov sĂŁo usadas em ambos os casos para derivar condições de estabilidade assintĂłtica na forma de inequações matriciais lineares. Tais condições sĂŁo entĂŁo utilizadas em problemas de otimização convexa como meio de calcular os parâmetros do sistema de controle, visando uma redução no nĂşmero de eventos gerados. No contexto de sistemas racionais, realimentação de estados Ă© considerada e representações algĂ©brico-diferenciais sĂŁo usadas como meio de obter condições de estabilidade tratáveis computacionalmente. Uma estratĂ©gia de disparo de eventos que usa uma medida de erro ponderado atravĂ©s de matrizes definidas positivas Ă© proposta e Ă© demonstrado que tal estratĂ©gia nĂŁo gera comportamento de ZenĂŁo. No caso de sistemas tipo Lur’e, considera-se o caso de controladores com restrições de informações, a saber, com acesso apenas Ă s saĂdas do sistema. Um observador de estados Ă© entĂŁo utilizado para recuperar a informação faltante. Neste contexto, Ă© necessária a introdução de um tempo de espera (dwell time, em inglĂŞs) para garantir a inexistĂŞncia de comportamento de ZenĂŁo. Todavia, a introdução do tempo de espera apresenta um desafio adicional na garantia de estabilidade que Ă© tratado neste trabalho considerando duas tĂ©cnicas possĂveis: a discretização exata do sistema e o uso de looped-functionals (funcionais em laço, em uma tradução livre). Para ambas classes de sistemas, sĂŁo tratados os problemas de projeto por emulação e co-design (projeto simultâneo, em uma tradução livre). No projeto por emulação, a lei de controle (e os ganhos do observador, quando apropriado) sĂŁo dados a priori e a tarefa Ă© projetar os parâmetros do gerador de eventos. No caso do co-design, o gerador de eventos e a lei de controle ou o observador sĂŁo projetados simultaneamente. Exemplos numĂ©ricos sĂŁo usados para ilustrar a aplicação dos mĂ©todos propostos
Nonlinear and sampled data control with application to power systems
Sampled data systems have come into practical importance for a variety of reasons.
The earliest of these had primarily to do with economy of design. A more recent surge of interest
was due to increase utilization of digital computers as controllers in feedback systems. This thesis
contributes some control design for a class of nonlinear system exhibition linear output. The
solution of several nonlinear control problems required the cancellation of some intrinsic dynamics
(so-called zero dynamics) of the plant under feedback. It results that the so-dened control will
ensure stability in closed-loop if and only if the dynamics to cancel are stable. What if those
dynamics are unstable? Classical control strategies through inversion might solve the problem while
making the closed loop system unstable. This thesis aims to introduce a solution for such a problem.
The main idea behind our work is to stabilize the nonminimum phase system in continuous- time
and undersampling using zero dynamics concept. The overall work in this thesis is divided into
two parts. In Part I, we introduce a feedback control designs for the input-output stabilization
and the Disturbance Decoupling problems of Single Input Single Output nonlinear systems. A
case study is presented, to illustrate an engineering application of results. Part II illustrates the
results obtained based on the Articial Intelligent Systems in power system machines. We note
that even though the use of some of the AI techniques such as Fuzzy Logic and Neural Network
does not require the computation of the model of the application, but it will still suer from some
drawbacks especially regarding the implementation in practical applications. An alternative used
approach is to use control techniques such as PID in the approximated linear model. This design
is very well known to be used, but it does not take into account the non-linearity of the model. In
fact, it seems that control design that is based on nonlinear control provide better performances
PI and LQR controllers for Frequency Regulation including Wind Generation
The increasing use of renewable technologies such as wind turbines in power systems may require the contribution of these new sources into grid ancillary services, such as Load Frequency Control. Hence, this work dealt with the performance comparison of two traditional control structures, PI and LQR, for secondary regulation of Load Frequency Control with the participation of variable-speed wind turbines. For this purpose, the doubly-fed induction generator wind turbine was modeled with additional control loops for emulation of the inertial response of conventional machines for frequency regulation tasks. Performance of proposed strategies was verified through simulation in a benchmark adapted from the WSCC 3 machines 9-bus test system. Results showed overall superior performance for LQR controller, although requiring more strenuous control effort from conventional units than PI control
Sampled-Data Sliding Mode Control Design of Single- Link Flexible Joint Robotic Manipulator
International audienceIn this paper, we have designed a sampled data control law for the single-link flexible joint robotic manipulator using two different approaches. First, we have designed the sampled-data sliding mode control (SMC) based on the continuous time system. In the second approach, we have obtained the approximate discrete model of the system and then designed discrete sliding mode control based on this approximate system. Simulation results have been obtained and a performance comparison has been presented for both techniques
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