Global Adaptive Output-feedback Control Research Articles

Adaptive output feedback control for [formula omitted]-normal nonlinear time-varying delay systems with unknown output function

This paper tackles the global adaptive output feedback control issue for a family of p-normal nonlinear time-delay systems with output function unknown. Firstly, an output feedback controller (OFC) is designed through adding a power integrator technique to stabilize the nominal system (without nonlinear terms) globally. Based on the above OFC, two novelly-designed dynamic gains and a Lyapunov-Krasovskii functional are constructed to deal with the uncertainties and time-varying delays, respectively. It can be proved that the p-normal nonlinear lower-triangular time-delay system is globally asymptotically stable (GAS) with bounded dynamic gains. Finally, a numerical example demonstrates the feasibility of the control strategy.

Global adaptive output feedback control for a class of stochastic nonlinear systems with unknown homogeneous growth rates

AbstractThis article focuses on the adaptive output feedback stabilization for a class of stochastic nonlinear systems whose drift and diffusion terms satisfy homogeneous growth conditions. Since the homogeneous growth rates are unknown, two dynamic gains are coupled into the full‐order homogeneous observer. By virtue of adding a power integrator technique and the homogeneity theory, two adaptive laws and a homogeneous output feedback controller are designed. Based on the celebrated nonnegative semimartingale convergence theorem and the general stochastic Barbˇlat's lemma, it is indicated that all the signals of the closed‐loop system are bounded almost surely, and all the system states of the closed‐loop system converge to origin almost surely. Finally, the effectiveness of the proposed control scheme is verified by means of both numerical and practical examples.

Adaptive event‐triggered output feedback control for a class of p‐normal nonlinear systems with sensor failure

SummaryThis article investigates the problem of global adaptive output feedback control for a class of p‐normal nonlinear systems with time‐varying sensor failure and unknown growth rate via an event‐triggered strategy. Due to the existence of time‐varying sensor failure, only the system output with sensor failure is available for feedback control design. To overcome this obstacle, an adaptive reduced‐dimensional observer using only failure output is constructed. Subsequently, a novel adaptive event‐triggered controller is designed by virtual of a dynamic gain technique, under which all the states of the considered closed‐loop systems are bounded as well as the proposed event‐triggered mechanism is Zeno‐free. Finally, two examples are provided to demonstrate the validity of the presented control method.

Global adaptive output-feedback control for switched uncertain nonlinear systems

In this paper, we investigate the problem of global output-feedback regulation for a class of switched nonlinear systems with unknown linear growth condition and uncertain output function. Based on the backstepping method, an adaptive output-feedback controller is designed to guarantee that the state of the switched nonlinear system can be globally regulated to the origin while maintaining global boundedness of the resulting closed-loop switched system under arbitrary switchings. A numerical example is given to demonstrate the effectiveness of the proposed control scheme.

A Singular Perturbation Based Global Dynamic High Gain Scaling Control Design for Systems With Nonlinear Input Uncertainties

A general class of uncertain nonlinear systems with input nonlinearities is considered. The system structure includes a core nominal system of triangular structure with additive uncertain nonlinear functions. The control input is allowed to enter non-affinely into the system dynamics as well as to have uncertainties coupled with it in terms of an uncertain nonlinear function of the input and output. The control design is based on dual controller/observer dynamic high-gain scaling with an additional dynamic scaling based on a singular-perturbation-like redesign to address the non-affine and uncertain nature of the input appearance into the system dynamics. The proposed approach yields a global robust adaptive output-feedback control design.

Global adaptive output feedback control for a class of nonlinear time-delay systems

This paper addresses the problem of global output feedback control for a class of nonlinear time-delay systems. The nonlinearities are dominated by a triangular form satisfying linear growth condition in the unmeasurable states with an unknown growth rate. With a change of coordinates, a linear-like controller is constructed, which avoids the repeated derivatives of the nonlinearities depending on the observer states and the dynamic gain in backstepping approach and therefore, simplifies the design procedure. Using the idea of universal control, we explicitly construct a universal-type adaptive output feedback controller which globally regulates all the states of the nonlinear time-delay systems.

Adaptive output feedback asymptotic stabilization of nonholonomic systems with uncertainties

A global adaptive output feedback control strategy is presented for a class of nonholonomic systems in generalized chained form with drift nonlinearity and unknown virtual control parameters. The purpose is to design a nonlinear output feedback switching controller such that the closed-loop system is globally asymptotically stable. By using the input-state scaling technique and an integrator back-stepping approach, an output feedback controller is given. A filter of observer gain is introduced for state and parameter estimates. Meanwhile, in order to avoid the over-parameters, a tuning function technique is utilized. A novel switching control strategy based on the output measurement of the first subsystem rather than time is used to overcome the uncontrollability of the x 0 -subsystem in the origin. The proposed controller can guarantee that all the system states globally converge to the origin, while other signals maintain bounded. The numerical simulation testifies the effectiveness.

Adaptive output-feedback control of nonlinear systems with unknown nonlinearities

In this paper, we consider global adaptive output-feedback control of nonlinear systems in output-feedback form, without a priori knowledge of system nonlinearities. Our proposed adaptive controller is a high-gain linear controller (since we have no knowledge on system nonlinearities), with the high-gain parameter tuned online via a switching logic. Global stability results of the closed-loop system have been proved.

Switching adaptive output-feedback control of nonlinearly parametrized systems

In this paper, we consider global adaptive output-feedback control of nonlinear systems in output-feedback form, with unknown parameters entering nonlinearly. Such unknown parameters are not required to lie in a known compact set. Our proposed adaptive output-feedback controller is a switching-type controller, in which the controller parameter is tuned in a switching manner via a switching logic. Global stability results of the closed-loop system have been proved.

A NONLINEAR TRANSFORMATION APPROACH TO GLOBAL ADAPTIVE OUTPUT FEEDBACK CONTROL OF 3RD-ORDER UNCERTAIN NONLINEAR SYSTEMS

In this paper, we present a global adaptive output feedback control scheme for a class of 3rd-order uncertain nonlinear systems to which adaptive observer backstepping method may not be applicable directly. In contrast to the existing output feedback form, the allowed extended output feedback structure includes quadratic and multiplicative dependency of unmeasured states. Our novel design technique employs a change of coordinates and adaptive backstepping. With these proposed tools, we can remove linear and quadratic dependence on the unmeasured states in the state equation. Also, the multiplication of the two unmeasured states can be eliminated. From the transformed systems, a state observer can be constructed in a very easy way. The overall scheme achieves globally exponential convergence of the tracking error to zero while maintaining global boundedness of all the signals and states.

Adaptive nonlinear output-feedback control with unknown high-frequency gain sign

A global adaptive output-feedback control scheme, which does not require a priori knowledge of high-frequency gain sign, is proposed for general nonlinear systems in output-feedback form. Unlike in Ding (1998), the removal of a priori knowledge of the high-frequency gain sign is not at the price of making growth restrictions on system nonlinearities, and furthermore, only the minimal number of parameters needs to be updated.

A combined backstepping and small-gain approach to adaptive output feedback control

In this brief article, a novel combined backstepping and small-gain approach is presented to the global adaptive output feedback control of a class of uncertain nonlinear systems with unmodeled dynamics. The use of small-gain techniques permits removal of a common restriction, i.e. that the nonlinearities in the system are only dependent on the measured output. The design procedure is divided into two parts. In the first part, based on a partial-state observer, integrator backstepping is used to design an adaptive output-feedback controller which ensures robustness with respect to unknown parameters and uncertain nonlinearities. In the second part, it is shown that the adaptive controller can be made robust against dynamic uncertainties by means of recent nonlinear small-gain results.

Global adaptive output feedback control of induction motors with uncertain rotor resistance

The authors design a global adaptive output feedback control for a fifth-order model of induction motors, which guarantees asymptotic tracking of smooth speed references on the basis of speed and stator current measurements, for any initial condition and for any unknown constant value of torque load and rotor resistance. The proposed seventh-order nonlinear compensator generates estimates both for the unknown parameters (torque load and rotor resistance) and for the unmeasured state variables (rotor flux); they converge to the corresponding true values under persistency of excitation which actually holds in typical operating conditions. The control algorithm generates references for the magnetizing flux component and for the torque component of stator current which lead to significant simplification for current-fed motors. Simulations show that the proposed controller is suitable for high dynamic performance applications.

Global adaptive output-feedback control of nonlinear systems. I. Linear parameterization

The problem of designing global adaptive output-feedback tracking controls for single-input single-output nonlinear systems which are linear with respect to the input and an unknown constant parameter vector is addressed. A class of systems which can be globally controlled by adaptive observer-based output-feedback compensators is identified by geometric coordinate-free conditions. The nonlinearities depend on the output only: growth conditions are not required. Each system in the class admits observers with linear error dynamics and is minimum phase, i.e., it has linear asymptotically stable zero dynamics. When the parameters are known, new sufficient conditions for global output-feedback tracking control are obtained as a special case. For linear systems the result recovers a well-known fundamental adaptive result. Three examples are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>