Robust Output Feedback Control Research Articles

Adaptive robust output-feedback boundary control of an unstable parabolic PDE subjected to unknown input disturbance

In this paper, an adaptive robust boundary controller is designed for an unstable heat equation with external disturbance flowing into the control end. The disturbance and uncertainty effect is cancelled out in the closed-loop system by using on-line approximation of disturbance upper-bound provided as an output of adaptive robust update law. The asymptotic stability of the controlled system in the presence of unknown disturbance and/or parametric uncertainties is proved utilising the Lyapunov theorem. Unlike previous researches, the control implementation does not require prior knowledge of unknown disturbance. Moreover, the controller does not require measuring the system states or estimating the system states by an observer. The adaptive robust controller can be regarded as a combination of the best qualities of the adaptive controller and the robust controller with no prior knowledge of system uncertainty, and asymptotic tracking error performance. Numerical simulations and comparisons are provided to illustrate the effectiveness of the proposed method.

Fuzzy adaptive output feedback control for uncertain nonlinear systems with unknown control gain functions and unmodeled dynamics

In this work, the fuzzy adaptive robust output feedback control issues are investigated for single-input single-output (SISO) strict-feedback nonlinear systems. The controlled systems under consideration of this paper contain the unknown control gain functions, unmodeled dynamics and immeasurable states. The unknown nonlinear functions are be approximated by utilizing the fuzzy logic systems, and the immeasurable states are estimated by constructing a new fuzzy state observer. In order to handle the unknown control gain functions and the unmodeled dynamics problems, the Logarithm Lyapunov functions are constructed, under which a new fuzzy adaptive robust output feedback control scheme is proposed by using the adaptive backstepping control design technique and a dynamical signal function. The designed fuzzy adaptive control algorithm can ensure that the closed-loop system is semi-globally uniformly ultimately boundedness (SGUUB) and has the robustness to the unmodeled dynamics. Finally, a simulation example is considered to illustrate the availability of the designed controller.

Hysteresis compensation-based robust output feedback control for long-stroke piezoelectric actuators at high frequency

Piezoelectric actuators (PEAs) are the key element for many vital applications and they play a big role in modern industries due to their operational characteristics. However, parametric uncertainties along with nonlinearities due to hysteresis and creep effects certainly impact severely the high precision tracking control of PEAs. This paper presents a robust output feedback controller for PEAs with hysterical dynamics compensated. In addition, a high gain observer is utilized to estimate the PEA’s tip velocity in order to facilitate the operation of the control algorithm. The proposed controller is designed to handle the unknown parameters and uncertainties associated with the nonlinear behavior of the PEAs. It is also tested on a commercial long-stroke PEA using different high frequency profiles. Experimental results show the effectiveness and robustness of the proposed controller compared to existing controllers.

Multi-Objective Non-Fragile Robust Attitude Control for Flexible Microsatellite Close-Proximity Inspection

In this paper, the non-fragile robust attitude control problem is investigated for flexible microsatellite close-proximity inspection, with external disturbances, parameter uncertainties and input constraints. Firstly, the attitude motion model of microsatellite with flexible appendages is established. Secondly, a non-fragile robust dynamic output feedback controller (RDOFC) with multiplicative gain variations (MGV) is designed to satisfy the multi-objective requirements, including pole assignment, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> disturbances attenuation and input constraints. Based on the Lyapunov stability theory, the design of the non-fragile robust H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> attitude control is formulated as the linear matrix inequality (LMI) condition. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed controller.

Global output feedback tracking control for switched nonlinear systems with deferred prescribed performance

In this paper, the global output feedback tracking control is investigated for a class of switched nonlinear systems with time-varying system fault and deferred prescribed performance. The shifting function is introduced to improve the traditional prescribed performance control technique, remove the constraint condition on the initial value, and make the constraint bounds have more alternative forms. To estimate the unmeasured state variables and compensate the system fault, the switched dynamic gain extended state observer is constructed, which relaxes the traditional Lipschitz conditions on the nonlinear functions. Based on the proposed observer, by constructing the new Lyapunov function and using the backstepping method, the global robust output feedback controller is designed to make the output track the reference signal successfully, and after the adjustment time, the tracking error enters into the prescribed set. The stability of the system is analyzed by the average dwell time method. Finally, simulation results are given to illustrate the effectiveness of the proposed method.

Path planning and robust fuzzy output-feedback control for unmanned ground vehicles with obstacle avoidance

Obstacle avoidance strategy is important to ensure the driving safety of unmanned ground vehicles. In the presence of static and moving obstacles, it is challenging for the unmanned ground vehicles to plan and track the collision-free paths. This paper proposes an obstacle avoidance strategy consists of the path planning and the robust fuzzy output-feedback control. A path planner is formed to generate the collision-free paths that avoid static and moving obstacles. The quintic polynomial curves are employed for path generation considering computational efficiency and ride comfort. Then, a robust fuzzy output-feedback controller is designed to track the planned paths. The Takagi–Sugeno (T–S) fuzzy modeling technique is utilized to handle the system variables when forming the vehicle dynamic model. The robust output-feedback control approach is used to track the planned paths without using the lateral velocity signal. The proposed obstacle avoidance strategy is validated in CarSim® simulations. The simulation results show the unmanned ground vehicle can avoid the static and moving obstacles by applying the designed path planning and robust fuzzy output-feedback control approaches.

Robust Output Feedback Tracking Control for Flexible-Joint Robots Based on CTSMC Technique

This brief considers a robust finite-time output feedback control scheme for the tracking problem of flexible-joint (FJ) robotic systems subject to unknown matched and mismatched time-varying disturbances. For this purpose, a novel dynamic terminal sliding mode surface is firstly constructed base on a sliding mode observer. Then, a continuous finite-time control scheme is developed to cope with these disturbances. Besides, the proposed controller guarantees the finite-time convergence of the closed-loop system and requires only the measurements of link positions. Finally, a two-link FJ robot as an example is provided to illustrate the effectiveness of the proposed control scheme.

Robust Output Feedback Control for Input-Saturated Systems Based on a Sliding Mode Observer

This paper designs a robust output feedback controller for input-saturated systems with parametric uncertainties and external disturbances based on the parametric Riccati equation and the sliding mode observer. The stability of the closed-loop system is ensured by the designed controller. The main advantages of the approach proposed in this paper are as follows: (a) the designed sliding mode observer can estimate unknown external disturbances and parametric uncertainties; (b) the designed output feedback controller can increase the state convergence speed; and (c) the control gain can be obtained from the solution of the parametric Riccati equation. The simulation results for a spacecraft rendezvous system illustrate the feasibility of the designed controller.

Robust prescribed performance-based control of autonomous tractor-trailers convoy with limited communication range

This paper investigates the problem of a nonlinear platoon controller design for a group of autonomous tractor-trailers with limited communication ranges in order to increase the load transportation capacity. The main control objective is to force each consecutive pair of tractor-trailers to follow each other in a convoy-like formation based on their posture and velocity measurements in the presence of unmodelled dynamics and external disturbances. The prescribed performance strategy is effectively applied to the relative range and angle between each successive pair in the group to preserve their connectivity without any possible collision by defining some preassigned performance characteristics on the transient and steady-state responses. A high-gain observer, an adaptive robust controller and a three-layer neural network are heuristically utilised to develop an efficient robust output-feedback platoon controller as well. The stability of the entire state-feedback and output-feedback control system is investigated by the Lyapunov stability method and some numerical simulations are presented to validate the controller efficiency in an autonomous transportation application.

Iterative LMI approach to robust static output feedback control of uncertain polynomial systems with bounded actuators

This paper presents a novel static output feedback stabilization of polynomial systems with bounded actuators. We propose a new sufficient condition for static output feedback design for nominal polynomial systems with constraints on input magnitudes. In the proposed stabilization condition, the system matrices and the Lyapunov matrices are separated, and hence parameterization of the controller is independent of the Lyapunov matrices. The main result is the novel parameter-dependent Lyapunov functions that are readily applied to robust static output feedback design of polynomial systems subject to parametric uncertainty. The proposed design conditions are bilinear in the decision variables. Hence, we provide iterative algorithms to solve the design problems. At each iteration, the design condition is cast as parameter-dependent linear matrix inequalities using the sum-of-squares technique and can be efficiently solved. The proposed approach leads to enhanced static output feedback design with computationally tractable formulation. Effectiveness of the proposed approach is demonstrated by numerical examples.

On LMI conditions to design robust static output feedback controller for continuous-time linear systems subject to norm-bounded uncertainties

This paper addresses the problem of Static Output Feedback (SOF) stabilisation for continuous-time linear systems subject to norm-bounded parameter uncertainties using the Linear Matrix Inequality (LMI) approach. Usually, this issue leads to the feasibility of a Bilinear Matrix Inequality (BMI), which is difficult to linearise to get non-conservative LMI conditions. We present first, in this paper, some background results on the SOF controller design and that are found to be extended to the case of norm-bounded uncertainties. We show that some restrictions on the feasibility of these results should be guaranteed. Moreover, by means of some technical Lemmas, we transform the BMI into a new LMI with a line search over a scalar variable. An enhanced and less conservative LMI condition with a line search over two scalar variables is also developed. Furthermore, a simplified version of each LMI condition without a priori fixed parameters is also presented. An extensive portfolio of numerical examples is presented in order to evaluate the conservativeness and to show the superiority of the proposed design method to the background results.

Rejecting the effects of both input disturbance and measurement noise: A second‐order control system example

SummaryThis article originates from the well‐accepted observations in practice: rejection of both input disturbance and measurement noise is practically important for high‐precision tracking control, and the classic estimators, such as the uncertainty and disturbance estimator (UDE) and disturbance observer, are proven to be inherently sensitive to measurement noises. Motivated by these observations, we develop a robust control solution and demonstrate the possibility of unifying the design of noise estimator (NE) and UDE for a class of second‐order systems. Interestingly, the NE and UDE have three important features in common: (i) the designs are based on system model and reliable state measurement; (ii) a first‐order filter is used to ensure that the design is physical realizable, rather than to filter out undesired signals; (iii) the filter parameters are readily determined by an introduced singular perturbation parameter. The performance of UDE is improved when augmented with NE to reject measurement noises. Then, a simple mapping for parameter tuning is presented, by which the estimation performance can be explicitly analyzed using the singular perturbation theory. Comparative simulation and experimental studies show that the proposed NE+UDE‐based solution is not only less sensitive to measurement noise than the classic UDE‐based control, but also able to deliver superior trajectory‐tracking performance over other robust output feedback control approaches.

Adaptive Super-Twisting Sliding Mode Control for Mobile Robots Based on High-Gain Observers

In this paper, a robust adaptive output feedback control strategy based on a sliding mode super-twisting algorithm is designed for the trajectory tracking control of a wheeled mobile robot. First, a robust adaptive law is designed to eliminate the influence of parameter uncertainties. Second, a double-power sliding mode surface is designed to improve the response speed of the robot system. Finally, a high-gain observer is employed to estimate the speed information. The stability of the closed-loop system is proved using the Lyapunov stability theorem. The effectiveness of the proposed control strategy is verified by simulation.

Robust output-feedback VFO-ADR control of underactuated spatial vehicles in the task of following non-parametrized paths

This article concerns the development of the Vector Field Orientation – Active Disturbance Rejection (VFO-ADR) cascaded path-following controller for underactuated vehicles moving in a 3-dimensional space. The proposed concept of a cascaded control structure decouples system kinematics from system dynamics, resembling the approach utilized for nonholonomic systems. Thanks to the use of an ADR control approach in the dynamic-level controller, the proposed control structure is robust to even significant model uncertainties and external disturbances. Application of an error-based form of the Extended State Observer (ESO), implemented within the ADR inner-loop controller, implies the output-feedback characteristic of the control structure, i.e., only position and attitude of the vehicle body are expected to be measured. The kinematic-level controller is designed according to the VFO method utilizing the non-parametrized path representation to calculate the commanded velocities. The description of the proposed control structure is followed by the theoretical analysis utilizing the Input-to-State Stability (ISS) theorem and the simulation verification of the proposed solution.

Optimal robust model predictive reset control design for performance improvement of uncertain linear system

This study aims to design a robust reset dynamic output feedback control (DOFC) for a class of uncertain linear systems. This procedure is performed as following. First, the elements of the robust DOFC are designed via the linear matrix inequality (LMI) technique such that closed-loop exponential stability is achieved. Second, reset law which contains value of after reset and a constraint for the reset action is determined. Genetic algorithm (GA) is applied to minimize the proposed objective function to find the reset times by using the specified after reset value for individual reset instances. To do this, a model-predictive-based optimization is adopted by using output information. The proposed robust controller is applied to two uncertain systems; distillation column, and B747-100/200 aircraft model. The merits of the proposed robust reset controller in improving transient performance are demonstrated by comparing its results with state-of-the-art methods.

Robust output feedback control of fixed-wing aircraft

PurposeThis paper aims to devise a robust controller for the non-linear aircraft model using output feedback control topology in the presence of uncertain aerodynamic parameters.Design/methodology/approachFeedback linearization-based state feedback (SFB) controller is considered along with a robust outer loop control which is designed using Lyapunov’s second method. A high-gain observer (HGO) in accordance with the separation principle is used to implement the output feedback (OFB) control scheme. The robustness of the controller and observer is assessed by introducing uncertain aerodynamics coefficients in the dynamic model. The proposed scheme is validated using MATLAB/SIMULINK.FindingsThe efficacy of the proposed scheme is authenticated with the simulation results which show that HGO-based OFB control achieves the SFB control performance for a small value of the high-gain parameter in the presence of uncertain aerodynamic parameters.Originality/valueA HGO for the non-linear model of aircraft with uncertain parameters is a novel contribution which could be further used for the unmanned aerial vehicles autopilot, flight trajectory tracking and path following.

A Robust Control Strategy for Landing an Unmanned Aerial Vehicle on a Vertically Moving Platform

In this work, we solve the uncertain unmanned aerial vehicle smooth landing problem over a moving platform, assuming that the aircraft position relative to the platform and its acceleration is always measurable. The landing task is carried out by an output-feedback robust controller, together with a repulsive force. The robust controller controls the nominal model, accomplishes the needed tracking trajectory, and counteracts the unknown uncertainties. To assure that the aircraft is always above the platform, we include a repulsive force that only works in a small vicinity of the platform. To estimate the relative aircraft velocity and platform acceleration, we use a supertwisting-based observer, assuring finite-time convergence of these signals. This fact allowed us to design the feedback state stabilizer independently of the observer design (in accordance with the separation principle). We confirmed the effectiveness of our control approach by convincing numerical simulations.

Robust Adaptive Contact Force Control of Pantograph–Catenary System: An Accelerated Output Feedback Approach

The pantograph-catenary system plays the crucial role in high-speed electric trains for electrical power collection, where continuity and smoothness of the contact between the pantograph and the catenary is one of the key factors ensuring high-quality power collection essential for safe and reliable train operation. In this article, a nonlinear and highly coupled model for the pantograph-catenary system is established, and an accelerated robust adaptive output feedback control method based on a high-gain observer is proposed to solve the contact force tracking control problem of the pantograph-catenary system using output information only. It is shown that, with the proposed method, the tracking error of the contact force is ensured to be ultimately uniformly bounded with an accelerated preassignable decay rate, resulting in smooth contact force and good-quality current collection. Both theoretical analysis and numerical simulation confirm the effectiveness and benefits of the method.

An Alternative Algorithm to the D-K Iterations for Robust Control Design

This letter presents a new algorithm for designing robust output-feedback controllers in the presence of structured uncertainty. The proposed approach is an alternative to the popular D-K Iterations, consisting of a pair of LMIs (Linear Matrix Inequalities) and an associated iterative algorithm. The new algorithm is illustrated by examples and its performance is compared with the D-K iterations by solving instances of the COMPleib benchmark library.

Robust l2−l∞ dynamic output feedback control design for uncertain discrete‐time switched systems with random time‐varying delay

SummaryThis article deals with the problem of robust output feedback control design for a class of switched systems with uncertainties and random time‐varying delay. Our purpose is focused on designing a full order dynamic output feedback controller and an appropriate switching rule to ensure the exponential mean square stability of the resulting closed‐loop switching system with an l2−l∞ performance level. The appealing aspects of the proposed control scheme include: (a) the development of LMI based delay‐dependent sufficient conditions for the exponential stability analysis of the stochastic hybrid systems using the appropriate choice of the augmented Lyapunov–Krasovskii functional, the partitioning technique and the average dwell time, (b) conservatism reduction of the unified design conditions, and (c) the controller designed exhibiting robustness with l2−l∞ performance against uncertainties and external disturbance. Finally, representative examples are given to demonstrate the validity and the merit of the proposed design technique.