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Control Theory & Applications, IET

Issue 4 • Date April 2008

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Displaying Results 1 - 10 of 10
  • Linear matrix inequality-based robust h control of sampled-data systems with parametric uncertainties

    Page(s): 253 - 260
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    The problem of robust Hinfin controller design for sampled-data systems with time-varying norm-bounded parameter uncertainties in the state matrices is investigated. Attention is focused on the design of a causal sampled-data controller which guarantees the asymptotical stability of the closed-loop system and reduces the effect of the disturbance input on the controlled output to a prescribed Hinfin performance bound for all admissible uncertainties. Sufficient condition for the solvability of the problem is in terms of linear matrix inequalities (LMIs) technique. It is shown that the desired Hinfin controller can be constructed by solving certain LMIs. An illustrative example is given to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Frequency domain stability observer and active damping control for stable haptic interaction

    Page(s): 261 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (445 KB)  

    Stable haptic interaction has been studied extensively using an energy-based approach, because energy is an indirect index reflecting unstable haptic behaviour. When a haptic system generates energy, the system becomes unstable. Therefore the energy-based approach should provide a point of reference for defining generated energy. However, in some practical cases, such as a multi-layered virtual wall, it is difficult to determine the point of reference. As a result, unstable behaviour cannot be detected promptly. To resolve this problem, a new observer, working in the frequency domain, was tested in this research. The observer directly examined unstable behaviour vibration, rather than analysing the indirect index reflecting the behaviour. The observer quantified the degree of instability of a haptic system, and a newly developed controller generated variable damping in proportion to this quantitative instability. In the case of a multi-layered virtual wall, the proposed methods were much faster in detecting haptic instability than other schemes, and successfully eliminated unstable behaviour. View full abstract»

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  • Asymptotic rejection of unmatched general periodic disturbances in a class of nonlinear systems

    Page(s): 269 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (221 KB)  

    The study deals with asymptotic rejection of unmatched general periodic disturbances in nonlinear systems in the output feedback form. The class of disturbances covers asymmetric wave forms in the half period such as alternating sawtooth wave form, as well as disturbances with symmetric half-period wave forms such as sinusoidal disturbances and triangular disturbances etc. The amplitude and phase of the disturbances are unknown. An equivalent input disturbance is introduced based on the periodic steady-state solutions of the system state variables. Conditions are identified for the existence of such an equivalent input disturbance. The half-period alternating feature is ensured for the equivalent input disturbance based on the fact that the steady state solutions of stable linear systems are shown to be half-period alternating if the inputs are. As the half-period alternating property is persevered in the equivalent input disturbances, recently proposed asymptotic rejection, based on the half-period integration and delay operations, of general periodic disturbances with asymmetric half-period wave forms can be applied, with a careful consideration of the phase offsets in the equivalent input disturbances. The proposed control design with the disturbance estimation asymptotically rejects the unknown disturbance and ensures the overall stability of the system. View full abstract»

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  • Robust pole assignment in high-order descriptor linear systems via proportional plus derivative state feedback

    Page(s): 277 - 287
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (221 KB)  

    The problem of robust pole assignment (RPA) in high-order descriptor linear system is considered. By using the result of eigenstructure assignment via proportional plus derivative state feedback and the perturbation theory of generalised pole problem proposed by Stewart, the RPA problem in high-order descriptor linear system is converted into a minimisation problem, and a simple algorithm is derived for solution to this RPA problem. An example of third-order is worked out with multiple solutions, both the indices and the numerical robustness test demonstrate the effect of the proposed approach. View full abstract»

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  • Flatness-based estimated state feedback control for a rotating flexible beam: experimental results

    Page(s): 288 - 302
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (603 KB)  

    A novel flatness-based estimated state feedback control design for a rotating flexible beam is introduced. The horizontally rotating beam is modelled as a boundary controlled Euler-Bernoulli partial differential equation. A so-called flat output is introduced in order to parameterise the system's variables in power series. These series lead to open- and closed-loop controls which can solve finite-time motion planning problems. The performance of the proposed control is experimentally compared with existing control methods for certain rest-to-rest motion planning problems. View full abstract»

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  • Parametric eigenstructure assignment by state feedback in descriptor systems

    Page(s): 303 - 309
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (149 KB)  

    A new complete parametric approach for eigenstructure assignment in the descriptor linear system Ex = Ax + Bu via state feedback control u = Kx is presented. Based on a proposed complete parametric solution to the generalised Sylvester matrix equation, explicit parametric forms of the closed-loop eigenvectors and the feedback gain matrix are given. The approach involves mainly a series of singular value decompositions, and is thus numerically simple and reliable. The approach assigns arbitrary rank(f) finite relative eigenvalues to the closed-loop system and guarantees the closed-loop regularity. A numerical example is worked out to demonstrate the effect of the proposed approach. View full abstract»

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  • Modified energy-balancing-based control for the tracking problem

    Page(s): 310 - 312
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    The authors extend energy-balancing-based control for set-point regulation to the problem of trajectory tracking for Euler-Lagrange (EL) systems. In addition to producing a new tracking control, this method also provides a re-interpretation of established results, such as computed torque control, PD+ control and Slotine-Li control. The authors also consider port-controlled Hamiltonian (PCH) systems, which are more general than EL systems. They develop a new matching equation for PCH systems so that interconnection damping assignment passivity-based control (IDA-PBC) can be applied to the control of a larger class of under-actuated PCH systems and the tracking control of some non-passive systems. View full abstract»

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  • Non-smooth progress function algorithm for frequency-shaping control design

    Page(s): 323 - 336
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (978 KB)  

    In classical controller design, closed-loop performance specifications arise naturally as constraints on restricted frequency bands. This leads to a difficult design problem, which is currently circumvented by heuristic techniques. The authors develop a non-smooth progress function algorithm which enjoys features similar to exact penalisation strategies to solve the problem. This allows one to compute locally optimal solutions to the frequency-shaping control design problem. The new technique is highly efficient, as demonstrated by the method of two case studies, a large dimension power system and a flexible telescope. View full abstract»

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  • Digital control of nonlinear systems: optimal linearisation-based digital redesign approach

    Page(s): 337 - 351
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (582 KB)  

    A new digital redesign technique for nonlinear systems based on the new stabilisable optimal linear model of the nonlinear system is proposed. The term digital redesign herein involves the process of converting a pre-designed analogue state-feedback controller into an equivalent digital one, in the state-matching sense. A constructive digital redesign algorithm is formulated in terms of bilinear and linear matrix inequalities. It is shown that the proposed methodology achieves Lagrange stability of the nonlinear system controlled by the digitally redesigned controller. An illustrative example is presented to demonstrate the effectiveness of the proposed method. View full abstract»

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  • Sliding mode control of two-dimensional systems in Roesser model

    Page(s): 352 - 364
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (265 KB)  

    The study is concerned with the problem of sliding mode control of two-dimensional (2D) discrete systems. Given a 2D system in Roesser model, attention is focused on the design of sliding mode controllers, which guarantee the resultant closed-loop systems to be asymptotically stable. This problem is solved by using two different methods: model transformation method and Choi's 1997 method. In terms of linear matrix inequality, sufficient conditions are formulated for the existence of linear switching surfaces guaranteeing asymptotic stability of the reduced-order equivalent sliding mode dynamics. Based on this, the problem of controller synthesis is investigated, with two different controller design procedures proposed, which can be easily implemented by using standard numerical software. A numerical example is provided to illustrate the effectiveness of the proposed controller design methods. View full abstract»

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IET Control Theory & Applications is devoted to control systems in the broadest sense, covering new theoretical results and the applications of new and established control methods.

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