Simple Output Feedback Controller Research Articles

Continuous stirred tank reactors: easy to stabilise?

The objective of this work is to make use of methodologies and tools from Lyapunov theory in the design of bounded control laws for the temperature stabilisation of a class of continuous stirred tank reactors with exothermic or endothermic reactions. Simple output feedback control laws, i.e. control laws that feed back only the available measurements, are designed. It is shown that these controllers yield global asymptotic stability and do not require precise knowledge of the system parameters. The capabilities of the proposed method to handle control input constraints and model uncertainties are also discussed. The work is completed with the analysis of a case study: the van der Vusse reaction mechanism.

Adaptive NN control for a class of strict-feedback discrete-time nonlinear systems

In this paper, both full state and output feedback adaptive neural network (NN) controllers are presented for a class of strict-feedback discrete-time nonlinear systems. Firstly, Lyapunov-based full-state adaptive NN control is presented via backstepping, which avoids the possible controller singularity problem in adaptive nonlinear control and solves the noncausal problem in the discrete-time backstepping design procedure. After the strict-feedback form is transformed into a cascade form, another relatively simple Lyapunov-based direct output feedback control is developed. The closed-loop systems for both control schemes are proven to be semi-globally uniformly ultimately bounded.

Oscillation control in non-linear systems using a first-order filter

In this paper we shall address the oscillation control problems in certain classes of non-linear systems whose outputs are required to follow their inputs. It is assumed that the non-linear systems can be well represented by a set of state-space equations and undergo Hopf bifurcation at some particular value of their parameters or their inputs. A simple first-order output feedback controller is proposed for oscillation control in these non-linear systems. First it is shown that in most cases the first-order controller is effective in locally stabilizing a second-order non-linear system which is undergoing Hopf bifurcation. Then a state separation method based on the solution of the associated Riccati equation is applied to the oscillation control of higher-order non-linear systems and a second-order approximated model is developed for the purpose of designing an oscillation controller. The closed-loop stability of the reduced-order model based design is analysed and some sufficient stability conditions are provided. Finally, a detailed application example of a stepper motor is given to show how the controller design method developed in this paper is applied to practical oscillation control problems.

Making a continuous-time minimum-phase system chaotic by using time-delay feedback

A time-delay feedback control approach is developed for making a continuous-time minimum-phase system chaotic. The approach is based on the geometric control theory and a suitable approximate relationship between a time-delay differential equation and a discrete map. If the original system has an exponentially stable equilibrium point, then a simple time-delay output-feedback controller with arbitrarily small amplitude can drive the system chaotic. Two different types of simulation examples are included for demonstration.

A simple adaptive PI controller for linear systems with constant disturbances

It is known that an adaptive controller via high-gain output feedback can globally stabilize a class of minimum phase systems with relative degree one. However, exact output regulation is difficult for systems with disturbances. In this paper, we consider linear single-input/single-output (SISO) systems with unknown constant disturbances. We present a simple adaptive output feedback controller with an integral action and show that it can asymptotically stabilize those disturbed systems. The proposed PI type adaptive controller can also deal with the output tracking problem of a step reference.

Shear force feedback control of flexible robot arms

For flexible robots with rotational joints it has been shown previously by Luo (1993), that direct strain feedback can damp out vibrations very satisfactorily. In this paper, a simple sensor-based output feedback control law, called shear force feedback, is newly proposed to control vibrations arising from structural flexibility of robots of Cartesian or SCARA types. Closed-loop exponential stability of such shear force feedback system is proved. Experimental results on set point control and trajectory tracking control are reported. It is found that the simple PI+shear force feedback can yield good performance for both robot motion and vibration suppression.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Minimax guaranteed cost control for linear continuous-time systems with large parameter uncertainty

This paper presents a method for designing a robust controller for linear systems with structured time-varying uncertainty. The proposed robustness design method results in a simple linear output feedback control law which not only guarantees the asymptotic stability of the closed-loop system, but also minimizes the maximal performance bound over all possible parameter perturbations. The problem is solved by employing a constrained optimization method using analytical gradients. A comparative study of an example shows the improvements and advantages of the proposed method over previous ones.

Model Following Robust Control of Systems with Large Size Uncertain Parameters

In this paper, we develop a robust controller design technique for linear and nonlinear single-input single-output minimum-phase systems with known and constant relative degree and bounded parametric uncertainties. Under some conditions, we show that a simple structure output feedback controller can be designed for the given system such that the closed-loop system is robustly stable and achieves specified model following performance.

Analytical and experimental investigation of output feedback vs linear quadratic regulator

This paper presents analytical and experimental comparison of three control laws for a laboratory structure designed to simulate large space structures. The first control law is the standard time invariant linear quadratic regulator with state estimation, which requires model reduction for practical implementation. This model reduction is associated with the so-called spillover instability. Two new simple direct output feedback control laws guaranteeing stability are proposed. One minimizes the maximum control force, and the other minimizes the same quadratic performance index as the linear quadratic regulator. The three control laws are found to give comparable performance for the modes retained in the reduced model. However, the standard linear quadratic regulator with state estimation provides almost no margin of stability for the unmodeled modes, while the simpler direct feedback laws provide significant stability margins to all modes. The analytical results were verified experimentally using a digital implementation of the control laws. Good agreement between the analytical predictions and experimental measurements was observed.