Composite Nonlinear Feedback Control Research Articles

U-control – a universal platform for control system design with inversion/cancellation of nonlinearity, dynamic and coupling through model-based to model-free procedures

This paper presents the key components in the Universal(U)-control framework for designing dynamic control systems from model-based to model-free paradigms, in which the pillars include U-control system configuration, open-loop dynamic inversion, closed-loop dynamic inversion, general model-free cancellation of nonlinear-dynamic-coupling effect, model-free-sliding-mode control (MFSMC) and model-free composite nonlinear feedback (CNF) control. This paper is devoted to delivering intuitive and easy-to-understand explanations for the involved approaches with a series of schematic diagrams. Readers can refer to the corresponding publications for more details on the theoretical analyses. In addition, some showcase examples are provided in this paper to facilitate the understanding of certain important concepts.

Tracking control for a class of fractional order uncertain systems with time-delay based on composite nonlinear feedback control

<abstract><p>In this paper, we dealt with the tracking control problem of a class of fractional-order uncertain systems with time delays. In order to handle the effects brought by the uncertainties, external disturbances, time-delay terms, and to overcome the obstacles caused by inputs saturation, the tracking controller, which consisted of linear control law, nonlinear law, and robust control law proposed in this paper, was designed by combining the composite nonlinear feedback control method and the properties of fractional order operators. Furthermore, the validation of this tracking controller was proved.</p></abstract>

Composite nonlinear feedback control of a DC-DC boost converter under input voltage and load variation

Voltage boost converters are one of the most important components of DC microgrids, since they are used to enhance the voltage of naturally intermittent energy sources such as solar panels in order to feed unknown demands. In this work, a novel tuning algorithm for Composite Nonlinear Feedback (CNF) is studied in depth to improve transient performance and address output voltage regulation for a DC-DC boost converter in the presence of DC input uncertainty. The proposed CNF controller comprises both linear and nonlinear feedback terms. The linear part contributes to the stability and output tracking with a small damping ratio and a quick response. The nonlinear part, i.e., damping term, reduces the overshoot stemming from the linear feedback law and increases the damping ratio of the overall closed-loop system. The nonlinear part is automatically tuned whereby the transient performance of the DC-DC boost converter improves significantly. To assess the performance of the proposed technique, a boost converter is simulated in MATLAB Simulink considering different scenarios such as changing load, DC input, and voltage reference. The numerical results demonstrate that the tuned CNF controller outperforms the linear controller in the DC boost converter. Additionally, several experiments are conducted to validate the efficacy of the suggested technique.

Robust integral controller design based on composite nonlinear feedback in uncertain systems with constrained inputs and external disturbances

AbstractIn this article, to enhance the transient performances in constrained uncertain systems, a control technique based on linear matrix inequality (LMI) is characterized to the robust integral composite nonlinear feedback (CNF) controller design. To achieve this aim, considering the inputs limitations and the uncertainties, the regulation is transformed into a minimization subjected to several LMIs. Solving an optimization in real‐time, the gains of the controller are calculated. So, the regulation and the disturbance rejection are effectively handled employing the presented control law. Compared with the existing integral methodology, the provided simulations validate the applicability of the robust integral CNF control law in uncertain systems.

Composite nonlinear feedback control for cooperative output regulation of linear multi-agent systems by a distributed dynamic compensator

Composite nonlinear feedback control for cooperative output regulation of linear multi-agent systems by a distributed dynamic compensator

A Novel Two-Phase Mode Switching Control Strategy for PMSM Position Servo Systems With Fast-Response and High-Precision

In this article, a novel mode switching control (MSC) strategy is proposed containing a fast-response phase and a high-precision settling phase to meet the requirement of high-quality point-to-point permanent magnet synchronous motor servo systems. In the fast-response stage, an adaptive trajectory planning method is developed to program the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current profile online based on the reference for the motor to reach the neighborhood of the reference position in minimum time. The chattering in the conventional time-optimal control is overcome and the idea that skipping speed and position loop with preplanned <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current trajectory is first attempted. After switching, the high-precision settling stage that is responsible for improving the transient performance in terms of reducing the overshoot and settling time is built with the proposed robust composite nonlinear feedback (RCNF) control law. This RCNF method cancels the overall disturbance through an extended state observer. The switching condition for the proposed MSC controller is clarified. Afterward, the whole closed-loop system's stability is strictly proved. Experiments are then conducted based on different scenarios to prove the effectiveness and robustness of the proposed MSC method.

Robust composite nonlinear feedback control based on integral sliding-mode control of uncertain time-delay systems under input saturation

In this research, based on the integral sliding-mode scheme, a robust composite nonlinear feedback (CNF) control is addressed for time-delayed uncertain systems. Such an uncertain system may contain some complexities like time-varying delays, actuators saturation, and exterior disturbances. Hence, the tracking problem would be solved under the mentioned constraints. Thus, for achieving these goals, the tracking problem is firstly formulated by considering system’s limitations. The controller parameters may be determined via a solution for linear matrix inequality. As a result, the CNF tracker law is numerically simulated in some control cases. The simulation outcomes are compared with a similar technique in terms of the transient response, boundedness of the error, and the disturbance rejections. Thus, the findings illustrate the efficiency of the advised CNF control method comparing to the recent technique.

Composite Nonlinear Path-Following Control for Unmanned Ground Vehicles With Anti-Windup ESO

In this article, a composite nonlinear feedback (CNF) controller with anti-windup extended state observer (ESO) is proposed for path-following control of unmanned ground vehicles (UGVs). To describe steering dynamics accurately, a saturation model with bounded disturbances is developed subject to path-following, lateral dynamic, and steering capability. The anti-windup ESO is investigated for real-time disturbance estimation under saturated input. The CNF controller is designed for path-following. In terms of asymptotically null controllability, a practical semiglobal stabilization result is derived for the closed-loop system with saturated input and bounded disturbances. Experimental results show that the proposed strategy is effective for UGVs.

An innovative algorithm for tuning of composite nonlinear feedback control in continuous‐time systems

AbstractThe transient response improvement is the most crucial feature of the composite nonlinear feedback (CNF) controllers. This study proposes a novel CNF tuning method for systems subject to saturation. To achieve the goals, the linear part is optimally obtained via a performance index and the linear matrix inequality (LMI). Then, employing the passivity property, a heuristic way is suggested to adjust the nonlinear term. Thus, the automatic and online features would be the key novelties of this algorithm compared with the offline, trial and error, or nonautomatic ones. Some systems are simulated to evaluate the technique and compare with the existing methods. The outcomes confirm that the proposed tuning yields outstanding improvement concerning the aforementioned systems.

Design of a Novel Integral Sliding Mode-Based Composite Nonlinear Feedback Controller for Electrostatic MEMS Micromirror

In this study, the precise tracking problem for electrostatic micromirror systems with disturbances and input saturation is investigated. Inspired by the composite nonlinear feedback (CNF)’s improvement of the transient performance and the sliding mode control’s enhancement of the robustness, a novel integral sliding mode with reaching law (ISMRL)-based composite nonlinear feedback (CNF) controller is proposed. Then, the stability of the closed-loop system is proved based on Lyapunov theorem. Finally, numerical simulations are investigated to evaluate the effectiveness of the proposed scheme. It is shown that the closed-loop system with the proposed scheme has precise positioning and improved transient performance in presence of time-varying disturbances.

Output tracking of time-delay Hamiltonian descriptor systems under saturation constraints

In this paper, the output tracking problem of Hamiltonian descriptor systems under the influence of saturation and time delay is investigated. In order to achieve fast output tracking and reduce tracking overshoot, an extended composite nonlinear feedback (ECNF) control method is proposed for Hamiltonian descriptor systems. Considering the special form of Hamiltonian descriptor system, based on the method of model transformation, the closed-loop Hamiltonian descriptor system obtained by introducing ECNF controller is replaced by two subsystems without singularity, so as to facilitate the later processing. For two different types of time delays, the criteria of asymptotic output tracking for closed-loop Hamiltonian descriptor systems are obtained respectively. Finally, the control effect of the ECNF method is tested by selecting a practical example and a numerical example.

Robust tracking composite nonlinear feedback controller design for time-delay uncertain systems in the presence of input saturation

In this study, a robust control technique is investigated for the reference tracking of uncertain time-delayed systems in the existence of the actuator saturation. Due to emerging of some control complexities, as well as the input limitations, time-varying delay, uncertainty, and external disturbance, such a tracking goal would be realized through suitable design of the composite nonlinear feedback (CNF) controller. Thus, considering the mentioned limitations, a Lyapunov-based procedure is used to determine the control law. Then, the parameters of the CNF input are derived by using the solution of a linear matrix inequality (LMI) problem. The planned tracking idea is numerically implemented in two uncertain control systems. Some performance characteristics (i.e., the tracking error, boundedness, and transient responses) are compared with similar ones. Accordingly, the simulations illustrate the efficiency of the suggested control procedure over the existing CNF approaches.

A new configuration of composite nonlinear feedback control for nonlinear systems with input saturation

This study proposes a U-control–based Composite Nonlinear Feedback (U-CNF) design procedure. This U-CNF control establishes a double feedback loop framework for generalisation and simplification in designing the CNF control systems. Two controllers, in terms of double dynamic inversion, are designed separately, (1) to stabilise and cancel the nonlinearities and dynamics (convert the plant into an identity matrix) in the inner closed-loop, and then (2) to improve the system transient response by specifying a second-order linear system with a monotonic nonlinear function to smoothly tune the damping ratio. Accordingly, the conventional CNF characteristics in a concise pathway are achieved. The properties show, under proper conditions, the U-CNF control is plant model-free control, applicable to nonaffine nonlinear dynamic systems, and robust against model uncertainty and external disturbance. For the initial bench tests of the first-time proposed U-CNF configuration, the simulated case studies are provided with a transparent procedure to demonstrate the consistency with the analytical results in the numerical computations and to present guidance for applications.

An Observer-Based Composite Nonlinear Feedback Controller for Robust Tracking of Uncertain Nonlinear Singular Systems With Input Saturation

This study proposes an observer-based Composite Nonlinear Feedback (CNF) controller for the robust tracking of uncertain singular systems with input saturation, nonlinear function, time-delay, and disturbances. The suggested control law is designed based states reconstructed using a singular observer so as to increase steady-state accuracy and improve robustness. The CNF controller is developed based on Generalized Riccati Equations (GRE) and Lyapunov&#x2013;Krasovskii functional. Additionally, the proposed theorem verifies the stability conditions of the system in the presence of uncertainties and disturbances. Among the advantages of this method, are its fewer restrictive assumptions, transient and high-speed performance improvement and steady-state precision. The uniform boundedness of the tracking error in the presence of the input saturation and external disturbances is also a prominent feature of this method. The performance of the proposed approach is assessed using a simulation study.

Anti-disturbance sliding mode control for uncertain nonlinear systems

In this paper, the problem of disturbance-based nonlinear sliding mode observer design is investigated for uncertain time-delay repeated scalar nonlinear systems subject to quantisation output measurement. State and disturbance observers are constructed by using the quantised measured output. Then, an improved nonlinear sliding surface is developed, and sufficient conditions are obtained for the sliding mode dynamics to be asymptotically stable with the desired performance level. In addition, a composite nonlinear feedback control law is synthesised to guarantee the reachability of the nonlinear surface. Finally, examples and simulations are presented to demonstrate the effectiveness of the proposed new design techniques.

On transient behavior improvement of constrained nonlinear time-delay descriptor systems

This article addresses the control of nonlinear time-delay descriptor systems via Composite Nonlinear Feedback (CNF) control technique to attain both improved transient response and asymptotic output regulation. The suggested CNF controller not only prevails for improving the closed-loop system’s transient response, but it is also efficient in overcoming the input saturation constraint and time-delay effects (both constant and time-varying delays). Moreover, the suggested controller is designed under the delay-range dependent condition which causes it to be less conservative than other CNF controllers discussed so far in the literature. The CNF controller’s parameters are obtained by solving LMI problems through the given theorems based on the Lyapunov approach to stability analysis. The theoretical achievements are admitted by computer simulation of some illustrative examples.

Disturbance rejection control for PMSM using integral sliding mode based composite nonlinear feedback control with load observer

The low-speed high-torque permanent magnet synchronous motor (PMSM) drive system is a kind of typical nonlinear, strong-coupling and easy-parameter perturbation electromechanical coupling system. The control system is uncertainties and subject to unknown external interferences as well. In this paper, a disturbance rejection control method combining robust speed controller and load observer is proposed for low-speed high-torque PMSM. The robust speed controller combines the composite nonlinear feedback (CNF) which has advantage in improving the transient responsive performance and the integral sliding mode (ISM) advancing in improving system robustness. Subsequently, the effects of unknown external interferences are avoided by using a sliding mode observer (SMO), in which the chattering is reduced by introducing fuzzy control, and the observation is used for feed-forward compensation. The proposed robust speed controller solves the contradiction between the rapidity and overshoot of the traditional control method, and combines the load observer to compensate the influence of the load mutations and wide range of the load changes on the control system. Finally, the numerical simulation and experiments demonstrate that the proposed speed control method is able to achieve good transient performance in inhibiting system overshoot and reducing stable state error. Additionally, it successfully suppresses the influence of load disturbances and mutations, and shows the proposed method has better robustness.

Low-conservative robust composite nonlinear feedback control for singular time-delay systems

A low-conservative composite nonlinear feedback controller is proposed for singular time-delay systems with time-varying delay. The proposed composite nonlinear feedback controller not only improves the transient responses of the closed-loop system but it also has less conservatism than other composite nonlinear feedback controllers. The gain of the linear part of the composite nonlinear feedback controller is obtained by precise mathematical calculation to depend not only on the upper bound of the delay but also on the delay range and rate of its changes. More advantages of the proposed composite nonlinear feedback controller are its accurate operation in the presence of actuator saturation, model uncertainties, and system singularities. The linear and nonlinear parts of the proposed controller are designed by solving a linear matrix inequality problem confirmed through a theorem using Lyapunov stability analysis. The theoretical achievements are endorsed by computer simulation through numerical and practical examples.

Observer-based tracker design for discrete-time descriptor systems with constrained inputs

In this paper, the problem of time-varying output tracking is studied in discrete-time descriptor systems. The descriptor system is subject to practical constraints such as input saturation and exogenous disturbances and consists of algebraic equations besides the difference equations in system modeling. The control problem is solved by proposing an observer-based composite nonlinear feedback controller to attain a suitable response and desired performance. The proposed control law is designed based on estimated states from a full-order descriptor observer. Considering the nonlinearity behavior and complicated analysis procedure, a theorem is dedicated to studying the closed-loop system that looks into the operation of the proposed observer-based control law upon different cases of the saturation function. It is demonstrated that the proposed control law is capable of working even if the saturation occurs. Furthermore, ultimate boundedness analysis is also done to verify the performance of the proposed control law in the presence of exogenous disturbance. The accuracy of theoretical achievements is endorsed by computer simulations through a numerical example and a practical example (a hydraulic tank system).

Fuzzy Observer-Based Transitional Path-Tracking Control for Autonomous Vehicles

This study addresses the path-tracking control issue of autonomous vehicles (AVs) when the GPS measurement is temporarily unavailable. In such a case, the vehicle states, location or the curvature of the reference path might be unobtainable, while the camera can be potentially used to detect the path-tracking states. To this end, this paper proposes a fuzzy-observer-based composite nonlinear feedback (CNF) controller with a Takagi-Sugeno (T-S) vehicle lateral dynamic model to guarantee the normal path-tracking maneuver and improve the transient performance. A parallel distributed compensation (PDC)-based CNF control method is developed to realize the control objective with the T-S vehicle model considering the transient performance and actuator saturation. The closed-loop stability and ${H} _{ \boldsymbol {\infty }}$ index performance integrating the tracking and estimation errors have been proved with a Lyapunov approach. The observer-based controller design has been implemented based on the formulation of the linear matrix inequalities (LMIs). High-fidelity simulations using CarSim-Matlab/Simulink have demonstrated the validity of the proposed approach in terms of enhancing the tracking performance under the input saturation and disturbances in GPS-denied environments.