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Online ISSN 1751-8652 Print ISSN 1751-8644

IET Control Theory & Applications

Volume 4, Issue 4, April 2010

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Volume 4, Issue 4

April 2010

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  • Regular Papers

    • Adaptive formation control in absence of leader's velocity information
      • Author(s): K. Choi ; S.J. Yoo ; J.B. Park ; Y.H. Choi
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 521 –528
      • DOI:  10.1049/iet-cta.2009.0074
      • Type: Article
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      • p. 521 –528 (8)
        In the leader-following approach, it has been commonly assumed that the leader robot's velocity information may be either measured or telecommunicated. However, in some circumstances, it is difficult to satisfy it because the follower robots may not have the sensor or the communication device to obtain accurate enough leader robot's velocity. Therefore this study proposes an adaptive formation control approach for multiple mobile robots in the absence of the velocity information of the leader robot. The proposed control system only requires a knowledge of the leader–follower relative distance and the bearing angle. The smooth projection algorithm is employed to estimate time-invariant or time-varying velocities of the leader robot. Using Lyapunov stability theory, it is shown that the formation errors are uniformly ultimately bounded and converge to an adjustable neighbourhood of the origin. Simulation and experiment results are provided to demonstrate the performance and stability of the proposed formation scheme.
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      Periodic adaptive learning compensation of state-dependent disturbance
      • Author(s): H.-S. Ahn  and  Y.Q. Chen
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 529 –538
      • DOI:  10.1049/iet-cta.2008.0417
      • Type: Article
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      • p. 529 –538 (10)
        This study addresses an improved version of periodic adaptive learning compensation scheme of state-dependent disturbances. The main contribution of this paper is the relaxation of assumptions given by Ahn and Chen and the generalisation of the periodic adaptive learning compensation for a broad class of practical engineering applications. The results of this study are developed on the basis of Lyapunov stability analysis along the state domain, the so-called s-domain. The state-dependent disturbance is a function of position, and the position is repetitive as a unit mass is moving forward continuously and returns to the initial position. For the continuous forward moving in the first repetition, new control schemes are proposed. After the first repetitive trajectory, the authors ensure continuously forward moving, that is v(t)>0), of the system by satisfying a velocity requirement at a specified point along the trajectory.
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      Robust control for a two-axis gimbaled sensor system with multivariable feedback systems
      • Author(s): S.B. Kim ; S.H. Kim ; Y.K. Kwak
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 539 –551
      • DOI:  10.1049/iet-cta.2008.0195
      • Type: Article
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      • p. 539 –551 (13)
        A dynamic model for the stabilisation loop of a two-axis gimbaled sensor system is formulated and system parameters have been identified by practical experiments. The validity of the dynamic model is illustrated by the experimental and simulation result. The Lead-proportional-integral (PI) controller design using a loop-shaping method based on the frequency response for the stabilisation loop of the sensor system is realised. This practical design approach has been proven to be simple and robust in actual application. The robust H∞ controller design approach combining model matching and mixed sensitivity problem to improve the command following and disturbance rejection performance in the presence of external disturbances and model uncertainties is implemented, which is designed within the framework of the standard H∞ optimisation problem by combining a conventional mixed sensitivity and model matching problem with robust stability. The experimental and simulation results show that the both two proposed controllers satisfy all desired requirements for the stabilisation loop associated with the gain crossover frequency, the gain and phase margin and the body-motion decoupling performance. It is shown through performance comparison and analysis that the proposed H∞ controller is preferable to the proposed Lead-PI controller in terms of system stability, the disturbance rejection rate and because of its fast time response characteristics. However, it is clear that the two proposed controller design procedures for the robust control of the stabilisation loop of a two-axis gimbaled sensor system can be very effective in practical applications in terms of both stability and disturbance rejection.
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      Design of an explicit constrained predictive sliding mode controller
      • Author(s): M. Pérez ; E. Jiménez ; E.F. Camacho
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 552 –562
      • DOI:  10.1049/iet-cta.2009.0057
      • Type: Article
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      • p. 552 –562 (11)
        This article presents a generalised predictive controller with improved performance and robustness by means of a reaching law to force a pseudosliding dynamic behaviour. This work has been motivated first by the existence of many industrial non-linear processes that can be well approximated by first-order plus dead time models. Thus, an explicit control law can be obtained, which overcomes some of the disadvantages of traditional sliding mode control and generalised predictive control strategies. Moreover, the necessity of providing the operators with useful values for a controller first tuning computed from the modelled pole and delay is also satisfied. Some simulation examples show the good characteristics of the proposed controller, coping with modelling errors, constraints on the control variable and on the manipulated variable, and time-varying delays.
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      Stability analysis and output-feedback stabilisation of discrete-time systems with an interval time-varying state delay
      • Author(s): K.F. Chen  and  IK. Fong
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 563 –572
      • DOI:  10.1049/iet-cta.2009.0100
      • Type: Article
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      • p. 563 –572 (10)
        This study focuses on the stability of discrete-time systems with a time-varying state delay and uncertainties in system matrices. New linear matrix inequality conditions are derived for determining bounds of the delay size to ensure the asymptotic stability. There is no need to assume that the system is stable when the delay vanishes. Conservativeness of the conditions is reduced as much as possible by introducing the free-weighting matrices in a novel way, and using the least inequality in the derivation process. Then a new static output-feedback stabilisation method is proposed with the gain matrix as a direct design variable. Compared with the existing results, the proposed methods indeed give larger delay bounds for many cases.
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      Modelling and control scheme of the ball–plate trajectory-tracking pneumatic system with a touch screen and a rotary cylinder
      • Author(s): D. Yuan  and  Z. Zhang
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 573 –589
      • DOI:  10.1049/iet-cta.2008.0540
      • Type: Article
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      • p. 573 –589 (17)
        For the multivariable and complicated ball–plate control system, in this study a touch screen and a rotary pneumatic cylinder are adopted instead of a camera and a step motor, respectively. A touch screen is utilised to collect the ball coordinates, and it is of high precision, rapid response and strong anti-interference ability. Using the rotary-cylinder position pneumatic servo mechanism to actuate the ball–plate system, it has high control precision, large speed variation range and good low-speed characteristics. Models of the rotary-cylinder servo mechanism and the ball–plate system are, respectively, built. For the non-linearity of the system, it is hard to attain good performance by using the traditional control method, so the controller is designed with a state observer and fuzzy control algorithm. Simulation results show that it has good dynamic and static characteristics with the proposed control method. And a hardware-in-the-loop (HIL) model is further built to realise the steady run of the system.
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      Kalman filtering for continuous-time systems with time-varying delay
      • Author(s): W. Wang ; H. Zhang ; L. Xie
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 590 –600
      • DOI:  10.1049/iet-cta.2008.0544
      • Type: Article
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      • p. 590 –600 (11)
        The optimal filtering problem for continuous-time linear systems with time-varying delay is considered. The purpose is to find a Riccati equation-based solution to the linear minimum mean square error filter. The time-varying delayed observation is firstly rewritten as an equivalent observation with multiple constant delays by defining a binary variable to model the arrival process of the observation. Then, by constructing certain multiple channel observations sequence that contains the same amount of information as the original one and applying the re-organised innovation analysis approach, the proposed problem is transformed to performing standard time-varying Kalman filtering.
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      Stabilisation of individual generators with SVC designed via phase plane partitioning
      • Author(s): J. Zhou
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 601 –612
      • DOI:  10.1049/iet-cta.2009.0069
      • Type: Article
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      • p. 601 –612 (12)
        By phase plane partitioning, dynamics of individual generators in multimachine systems are approximately represented by means of a sequence of linear time-invariant (LTI) state-space equations, based on which various static VAR compensators (SVCs) are designed to stabilise the individual generators by exploiting the well-known LTI stabilisation techniques. More precisely, the author works out state-feedback-controlled SVCs through pole assignment (PA) and least quadratic regulation (LQR), respectively. The suggested SVCs can also accommodate transient and steady-state performance specification on the generator's dynamics, besides its stabilisation. Numeric examples clearly illustrate efficacy and convenience of the stabilisation techniques.
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      Robust sliding mode control for uncertain discrete-time systems with time delay
      Design of backstepping particle-swarm-optimisation control for maglev transportation system
      • Author(s): R.J. Wai  and  K.L. Chuang
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 625 –645
      • DOI:  10.1049/iet-cta.2008.0270
      • Type: Article
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      • p. 625 –645 (21)
        This study focuses on the design of a backstepping particle-swarm-optimisation control (BSPSOC) for the on-line levitated balancing and propulsive positioning of a magnetic levitation (maglev) transportation system. The dynamic model of a maglev transportation system including levitated electromagnets and a propulsive linear induction motor (LIM) based on the concepts of mechanical geometry and motion dynamics is first constructed. The aim is to design an on-line particle-swarm-optimisation (PSO) control methodology to cope with the problem of the complicated control transformation and the chattering control effort in backstepping control (BSC) design, and to directly ensure the stability of the controlled system without the requirement of strict constraints, detailed system information and auxiliary compensated controllers despite the existence of uncertainties. In the proposed BSPSOC scheme, a PSO control is utilised to be the major control role, and adaptation laws derived from Lyapunov stability analyses are manipulated to adjust appropriate evolutionary coefficients. The effectiveness of the proposed control strategy for the maglev transportation system is verified by experimental results, and the superiority of the BSPSOC scheme is indicated in comparison with the total sliding-mode control (TSMC) and BSC strategies.
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      Formation controllability of high-order linear time-invariant swarm systems
      Tracking control of a two-axis motion system via a filtering-type sliding-mode control with radial basis function network
      • Author(s): F.-J. Lin ; H.-J. Hsieh ; P.-H. Chou
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 655 –671
      • DOI:  10.1049/iet-cta.2008.0279
      • Type: Article
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      • p. 655 –671 (17)
        In this study, a filtering-type sliding-mode control with a radial basis function network (FSCRBFN) for a two-axis motion control system, which consists of two permanent magnet linear synchronous motors (PMLSMs), is proposed. First, the dynamics of the single-axis motion system with a lumped uncertainty which contains parameter variations, external disturbances, cross-coupled interference and non-linear friction force is derived. Next, a filtering-type sliding-mode control (FSC) is adopted for the two-axis motion control system to confront the lumped uncertainty. Then, to improve the control performance in contour tracking, the FSCRBFN control approach is developed. In the control approach, a radial basis function network (RBFN) is employed mainly to estimate the lumped uncertainty. Moreover, the proposed control approach is performed on a digital signal process (DSP)-based control system using TMS320C32. Finally, some experimental results are illustrated to show the validity of the proposed control approach.
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      Transmission probability condition for stabilisability of networked control systems
      • Author(s): Y.F. Guo  and  S.Y. Li
      • Source: IET Control Theory & Applications, Volume 4, Issue 4, p. 672 –682
      • DOI:  10.1049/iet-cta.2008.0407
      • Type: Article
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      • p. 672 –682 (11)
        In this study, the authors study the stabilisability of networked control systems (NCSs) with random packet dropout, where the network packet loss is modelled as an i.i.d. Bernoulli process. Two commonly used strategies compensating for the lost signal, namely, ‘zero signal’ and the ‘last available signal’ strategy are compared. First, NCSs with the ‘zero signal’ strategy is considered. Several necessary and sufficient conditions for stabilisability are established and further analysis of it is conducted. A critical transmission probability (CTP) is introduced, which is the least required transmission probability for the purpose of stabilising a networked plant. An explicit formula for CTP is derived and it shows that the CTP is merely dependent on the unstable poles of the plant. The authors theoretically validate that the least required information for stabilising a plant has an explicit relationship with the degree of instability of its own. Then a necessary condition for the stabilisability of NCSs with the ‘last available signal’ strategy is proposed. It is theoretically proved that the ‘last available signal’ strategy cannot compensate the effect of loss data better than the ‘zero signal’ does. Two illustrative examples are provided to show the validity of the proposed results.
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