Showing papers by "Richard H. Middleton published in 2001"

Optimal tracking performance for SIMO systems

Abstract: This paper studies the optimal tracking performance for linear time-invariant single-input multi-output (SIMO) systems responding to a step reference signal. An integral square error criterion is used as the measure of the tracking performance. First, a formula of the tracking error is derived for stable multivariable systems, which is applicable to both right-invertible and non-right-invertible cases. Then, explicit expressions of the tracking error for SIMO systems are developed. The results show that, together with the nonminimum phase zeros and unstable poles of the plant, the variation of the plant direction with frequency also contributes to the tracking difficulty in SIMO systems.

Sensitivity and robustness properties in the preview control of linear non-minimum phase plants

Abstract: Non-minimum phase zeros emit the achievable performance and robustness of a feedback control loop. These limitations can be expressed as an upper limit on the bandwidth that may be achieved without necessarily incurring a large peak in closed loop sensitivity. In the case of preview control, it is known that advance (or anti-causal) knowledge of the reference to be tracked permits accurate, rapid tracking over bandwidths which exceed the normal performance limits. The first aim of this paper is to explain this apparent paradox. In addition, we briefly discuss sensitivity and robustness issues for preview control systems.

Adaptive Servo Control of Large Antenna Structures

Abstract: This contribution considers the design of servo tracking loops for large antennae structures which exhibit lightly damped flexible modes. A cascaded loop control structure employing performance oriented adaptive feedforward in the outer loop is developed. The procedures for designing the inner current (motor drive), rate loop and position loop as well as the adaptive feedforward compensator are presented. It is demonstrated that this constitutes a practical and robust solution to the problem of controlling servo tracking systems in the presence of non trivial resonances. The control structure provides excellent tracking of parabolic trajectories as well as disturbance rejection. The conclusions are supported by analysis, simulation, and experimental results on 22m, 26m and 64m radio-astronomy and telecommunication antennae across Australia.

Achievable performance and sensitivity integral constraints in preview control

Abstract: Preview control refers to a tracking control scheme whereby a reference trajectory, and a finite 'preview' of future values of the reference trajectory are used in the controller. Such controllers have been explored in the context of linear and nonlinear inverse tracking controllers, where particularly for non stably invertible plants, preview of the reference trajectory gives significant performance advantages. Without the presence of preview, it has been known that lack of a stable inverse imposes inherent limitations on the achievable performance of a feedback control loop. In this paper, we explore the extension of these performance limitations to the preview control case. In particular, we consider the infimal achievable H/sub /spl infin// performance, and Poisson sensitivity integral results for the finite preview case.

Brief Paper Further results on localization-based switching adaptive control q

Abstract: We investigate a switching adaptive control scheme based on falsi"cation which is conceptually di!erent from existing switching adaptive control schemes A feature of the proposed localization method is its fast model falsi"cation capability In the LTI case this is manifested as the rapid convergence of the switching controller By analysing the geometry of localization we give a complete solution to the problem of optimal localization ( 2000 Elsevier Science Ltd All rights reserved

A method for switching controller design for discrete time hybrid systems

Abstract: We propose a systematic switching control design method applicable to a class of piecewise linear hybrid systems. We consider a class of systems controlled by a finite state actuator (i.e. switching controller). For the class of systems considered, precise conditions for stabilizability are unknown. However, by considering the same systems with unknown but bounded exogenous disturbances, we are able to give finitely computable conditions, sufficient for stabilizability without disturbances, yet necessary for stabilizability with disturbances.

Performance for SIMO Systems

Abstract: This paper studies the optimal tracking performance for linear timeinvariant SIMO systems responding to a step reference signal. An integral square error criterion is used as the measure of the tracking performance. First, a formula of the tracking error is derived for stable multivariable systems, which is applicable to both right-invertible and non-right-invertible cases. Then, explicit expressions of the tracking error for SIMO systems are developed. The results show that together with the nonminimum phase zeros and unstable poles of the plant, the variation of the plant direction with frequency also contributes to the tracking difficulty in SIMO systems.

Time domain integrals for linear sampled data control systems

Abstract: It is well known that linear time invariant control of plants with unstable poles results in time domain integral constraints on the closed loop system. This leads to the question of whether nonlinear or time varying control can be used to ameliorate these constraints. In this paper a particular class of time varying controllers, namely sampled data feedback controllers, is studied. An integral constraint, analogous to one for continuous time systems, is derived for sampled data systems with an unstable plant pole and an output disturbance. Analysis of this constraint in several examples shows that the performance limitation is often worse than in the continuous time case.