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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 3, Issue 3, March 2009

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Volume 3, Issue 3

March 2009

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    • Implementation of predictive controllers as outer-loop controllers
      • Author(s): F. Tadeo  and  T. Alvarez
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 261 –269
      • DOI:  10.1049/iet-cta:20070374
      • Type: Article
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      • p. 261 –269 (9)
        The implementation of predictive controllers as supervisory control systems is discussed. In this configuration, common in practice, the manipulated variables calculated by the predictive controller do not directly drive the actuators; instead, it is the command signals from the local PID controllers that drive the actuators that act on the physical system. This structure is known to perform less efficiently when the local controllers are re-tuned, because the model used in the predictive controller differs from the real one. Thus, performance decreases and might even lead to oscillations and instabilities of the overall control system. This paper presents a solution to this problem based on the use of an adequate two-degrees-of-freedom structure as an interface between the predictive controller and the local controllers, which makes the predictive controller robust against variations in the local controller. The application of this technique on a simulated industrial boiler achieves the following advantage: the performance of the predictive control system is maintained despite re-tuning of the inner-loop controller.
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      Robust stability bounds for networked controlled systems with unknown, bounded and varying delays
      • Author(s): L. Dritsas  and  A. Tzes
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 270 –280
      • DOI:  10.1049/iet-cta:20070384
      • Type: Article
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      • p. 270 –280 (11)
        A robust control-oriented modelling approach for networked controlled systems (NCS) with uncertain, varying, bounded transmission delays and asynchronous discrete-time control laws is presented. The resulting model is then used for the derivation of sufficient conditions for the robust stability of NCSs and the computation of the maximum allowable delay (constrained within one sampling period) that the closed-loop system can tolerate given a pre-selected set of stabilising gains for the nominally delayed system. The derived stability conditions can be used for both open-loop stable and unstable systems and are numerically simple to use because they rely on singular-value calculations and the solution of a standard discrete Lyapunov equation. The impact of certain designer choices (such as sampling period, nominal delay and tuning parameters appearing in the stability conditions) on the delay range is also investigated. Simulation studies are used to investigate the efficiency of the derived robust stability bound.
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      Design and CPG-based control of biomimetic robotic fish
      • Author(s): W. Zhao ; Y. Hu ; L. Zhang ; L. Wang
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 281 –293
      • DOI:  10.1049/iet-cta:20070204
      • Type: Article
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      • p. 281 –293 (13)
        The authors propose the design and control of a biologically-inspired biomimetic robotic fish capable of three-dimensional locomotion. The mechanical configuration and the hardware system of the robotic fish are described. The control architecture of the robotic fish is constructed based on central pattern generator (CPG). A model for a system of coupled non-linear oscillators is established to construct CPG and has been successfully applied to the four-link robotic fish. The CPGs are modeled as non-linear oscillators for joints and inter-joint coordination is achieved by altering the connection weights between joints. Coordinated gait patterns of rhythmic movements for swimming can be produced by modulating simple control parameters in the CPG model. The CPG-based method shows elegant and smooth transitions between swimming gaits, and enhanced ability to cope with transient perturbations because of non-linear characteristic. A series of swimming tests are designed to give speed evaluation and turning maneuver analysis. The effectiveness of the proposed method is confirmed via simulation and some experimental results.
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      Evaluation and tuning of robust PID controllers
      • Author(s): B. Lennartson  and  B. Kristiansson
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 294 –302
      • DOI:  10.1049/iet-cta:20060450
      • Type: Article
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      • p. 294 –302 (9)
        Based on a general controller evaluation method, taking both performance and robustness in different frequency regions into account, an analytical PID design method is presented. It is related to the well known and often used lambda tuning approach, which is based on internal model control (IMC) for a specific second-order non-minimum phase plant model. The analytical method introduced in this paper includes two tuning parameters, one that guarantees a specified stability margin for the given model, and one that is also able to adjust the control activity to a desired level. The suggested method, called robust IMC, gives the user the important freedom to control both mid- and high-frequency robustness. An extended evaluation procedure also illustrates how efficiently PI and PID controllers including a Smith predictor (SP) can control time delayed plants. More specifically, it is shown to be more profitable to provide a PI controller with derivative action than with a SP for plants with long time delays.
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      Dynamic inversion with zero-dynamics stabilisation for quadrotor control
      • Author(s): A. Das ; K. Subbarao ; F. Lewis
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 303 –314
      • DOI:  10.1049/iet-cta:20080002
      • Type: Article
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      • p. 303 –314 (12)
        For a quadrotor, one can identify the two well-known inherent rotorcraft characteristics: underactuation and strong coupling in pitch-yaw-roll. To confront these problems and design a station-keeping and tracking controller, dynamic inversion is used. Typical applications of dynamic inversion require the selection of the output control variables to render the internal dynamics stable. This means that in many cases, perfect tracking cannot be guaranteed for the actual desired outputs. Instead, the internal dynamics of the feedback linearised system is stabilised using a robust control term. Unlike standard dynamic inversion, the linear controller gains are chosen uniquely to satisfy the tracking performance. Stability and tracking performance are guaranteed using a Lyapunov-type proof. Simulation with a typical nonlinear quadrotor dynamic model is performed to show the effectiveness of the designed control law in the presence of input disturbances.
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      Improved robust H∞ filtering for uncertain discrete-time switched systems
      • Author(s): K. Hu  and  J. Yuan
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 315 –324
      • DOI:  10.1049/iet-cta:20070253
      • Type: Article
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      • p. 315 –324 (10)
        This paper is concerned with the robust H∞ filtering problem for uncertain switched linear discrete-time systems. Combining the mode-switching idea with the well-known Finsler's lemma, and further utilising the parameter-dependent result, a new characterisation of the asymptotic stability with an H∞ noise-attenuation level bound for the filtering error system has been addressed. The existence condition of such a filter is formulated in terms of dilated linear matrix inequalities. This directly leads to performance improvement and reduction of conservativeness in the filtering solution. Performance of the presented approach in comparison with that of the existing results is illustrated by a numerical example.
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      Robust attitude synchronisation controllers design for spacecraft formation
      • Author(s): J. Erdong  and  S. Zhaowei
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 325 –339
      • DOI:  10.1049/iet-cta:20070240
      • Type: Article
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      • p. 325 –339 (15)
        The attitude synchronisation control problem for spacecraft formation with switching communication topologies and information transmission delays is addressed. Common Lyapunov functions are employed to tackle such a problem. To compensate the adverse effect on an individual spacecraft arising from model uncertainties and external disturbances, parameter estimation variables and nonlinear integral terms are incorporated into the Lyapunov functions. The main result of this research is that one of the presented controllers can render a spacecraft formation consistent to a given trajectory globally with dynamic information exchange graph and non-uniform time-varying delays while coping with the parameter uncertainties and unexpected disturbances. In addition, several corollaries of the main results are provided. By virtue of a corollary of Barbalat's lemma, attractiveness of the proposed controllers for the corresponding closed-loop systems is proven. Numerical simulations are also included to demonstrate the theoretical results.
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      Modelling and analysis of traffic light control systems
      • Author(s): Y.-S. Huang  and  P.-J. Su
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 340 –350
      • DOI:  10.1049/iet-cta:20070368
      • Type: Article
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      • p. 340 –350 (11)
        An urban traffic network of signalised intersections can be suitably modelled as a discrete event system, in which the traffic light alternations are described by means of timed coloured Petri nets (TCPNs). A module of basic traffic TCPN model with a signal timing plan for a day is successfully constructed. The traffic operations are ruled by the control logic of TCPN and an analysis method using place invariant is verified. From the basic TCPN model, some of the complicated traffic signal models will be easily obtained. Moreover, a real-world supervisor of the urban traffic light system is implemented by the new methodology. Finally, an urban traffic light control system with five intersections is realised. Also, the performance of the supervisor of the urban traffic light system can be confirmed by the simulation results.
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      Robust H∞ filtering for uncertain discrete Markov jump singular systems with mode-dependent time delay
      • Author(s): S. Ma  and  E.K. Boukas
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 351 –361
      • DOI:  10.1049/iet-cta:20080091
      • Type: Article
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      • p. 351 –361 (11)
        The robust H∞ filtering problem for mode-dependent time-delay discrete Markov jump singular systems with parameter uncertainties is discussed. Based on delay-dependent linear matrix inequalities, a Markov jump filter is designed, which guarantees that the filtering error system is regular, causal, stochastically stable and satisfies H∞ performance for all admissible uncertainties. The H∞ filter can be of full or of a reduced order. A numerical example is given to illustrate the effectiveness of the proposed method.
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      Smart deadlock prevention policy for flexible manufacturing systems using Petri nets
      • Author(s): Z. Li  and  M. Shpitalni
      • Source: IET Control Theory & Applications, Volume 3, Issue 3, p. 362 –374
      • DOI:  10.1049/iet-cta:20070399
      • Type: Article
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      • p. 362 –374 (13)
        Deadlocks are a highly undesired situation in automated production systems including flexible manufacturing systems. Based on a Petri net formalism, a novel deadlock prevention policy is proposed for a class of Petri nets, S3PR, by using an MIP-based deadlock detection method and elementary siphons of Petri nets. Deadlock prevention is achieved by synthesising a set of monitors that are added to the plant net model. The concept of dominated transitions is proposed, to which the output arcs of the monitors are led. The monitors are computed according to a set of elementary siphons in a plant net model, which is found by using an established algorithm in the literature. When compared with the existing policies, the proposed method leads to a liveness-enforcing Petri net supervisor with a small number of monitors but more permissive behaviour. Examples are used to demonstrate the proposed method.
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