Composite Nonlinear Feedback Research Articles

Composite Disturbance Rejection Attitude Control for Quadrotor With Unknown Disturbance

In this article, a composite disturbance rejection control method is proposed for attitude control of quadrotor using an inner–outer loop control framework, which can effectively improve the angular tracking performance of the quadrotor and achieve the active disturbance rejection. In the inner loop, a novel nonlinear extended state observer (NESO) is designed to estimate the disturbance and nonlinear part of the system model, then a robust control law is embedded in inner-loop controller to attenuate the effect of the estimation error. In the outer loop, a composite nonlinear feedback (CNF) controller is designed to improve the transient performance. Moreover, the stability of two loops are also analyzed, respectively. Numerical simulation and platform experiment are carried out to verify the efficiency of the proposed method.

MME-EKF-Based Path-Tracking Control of Autonomous Vehicles Considering Input Saturation

This paper investigates the path-tracking control issue for autonomous ground vehicles with the integral sliding mode control (ISMC) considering the transient performance improvement. The path-tracking control is converted into the yaw stabilization problem, where the sideslip-angle compensation is adopted to reduce the steady-state errors, and then the yaw-rate reference is generated for the path-tracking purpose. The lateral velocity and roll angle are estimated with the measurement of the yaw rate and roll rate. Three contributions have been made in this paper: first, to enhance the estimation accuracy for the vehicle states in the presence of the parametric uncertainties caused by the lateral and roll dynamics, a robust extended Kalman filter is proposed based on the minimum model error algorithm; second, an improved adaptive radial basis function neural network (RBFNN) considering the approximation error adaptation is developed to compensate for the uncertainties caused by the vertical motion; third, the RBFNN and composite nonlinear feedback (CNF) based ISMC is developed to achieve the yaw stabilization and enhance the transient tracking performance considering the input saturation of the front steering angle. The overall stability is proved with Lyapunov function. Finally, the superiority of the developed control strategy is verified by comparing with the traditional CNF with high-fidelity CarSim-MATLAB simulations.

Event-triggered composite nonlinear control for saturated systems with measurement feedback

The composite nonlinear feedback (CNF) control problem with event-triggered strategy for saturated systems with measurement feedback is considered in this paper. Both the full-order measurement and the reduced-order one are investigated to ensure the satisfactory performance of the closed-loop saturated systems under the proposed event-triggered mechanism. Generally speaking, the CNF control is divided into the linear control part and the nonlinear control part, which are designed separately. The purpose of the former is to shorten the rise time, while the latter aims at reducing the overshoot caused by the former. In this paper, a co-design method of linear and nonlinear control parts is proposed such that the control output tracks the reference input asymptotically with a good transient performance. Moreover, the parameter of CNF is applied to the construction of event-triggered mechanism which can efficiently reduce the communication burden. In order to avoid Zeno behavior, the minimum event-triggering time interval is explicitly formulated. Finally, an example of fighter aircraft is given for illustration.

Robust Output Regulation in Discrete-Time Singular Systems With Actuator Saturation and Uncertainties

This brief studies robust output regulation in discrete-time singular systems with actuator saturation and matched uncertainties. The singularity of dynamical equations makes the design procedure more complex due to the appearance of both algebraic and difference equations in such systems. In addition to this, the actuator saturation constraint along with uncertain terms complicates the design problem. The idea for robust output regulation is to add an additional control term to the composite nonlinear feedback (CNF) controller which guarantees the output regulation of the uncertain closed-loop singular system with an ultimately bounded tracking error. In this regard, a theorem is given which guarantees the output regulation even if the saturation takes place. The accuracy of the theoretical results is tested through simulations for a practical example.

Incremental SMC-based CNF control strategy considering magnetic ball suspension and inverted pendulum systems through cuckoo search-genetic optimization algorithm

A kind of incremental sliding mode control (SMC) approach in connection with the well-known composite nonlinear feedback (CNF) control strategy is newly considered in this research to deal with the nonlinear magnetic ball suspension and inverted pendulum systems, as well. The incremental SMC approach is in fact proposed to handle the aforementioned underactuated systems under control, which have a lower number of actuators than degrees of freedom. Based on the outcomes of the investigation presented here, the small overshoot and short settling time of the system response are fulfilled. In fact, the proposed CNF control strategy comprises two parts: the first term assures the stability of the closed-loop nonlinear system and provides a fast convergence response. The second term reduces its overshoot. The genetic-cuckoo hybrid algorithm is designed to minimize tracking errors for the purpose of finding the most suitable sliding surface coefficients. Finally, the finite time stability for the closed-loop system is proved, theoretically.

Robust composite nonlinear feedback for nonlinear Steer-by-Wire vehicle’s Yaw control

Yaw control is a part of an Active Front Steering (AFS) system, which is used to improve vehicle manoeuvrability. Previously, it has been reported that the yaw rate tracking performance of a linear Steer-by-Wire (SBW) vehicle equipped with a Composite Nonlinear Feedback (CNF) controller and a Disturbance Observer (DOB) is robust with respect to side wind disturbance effects. This paper presents further investigation regarding the robustness of the combination between a CNF and a DOB in a nonlinear environment through a developed 7-DOF nonlinear SBW vehicle. Moreover, in contrast to previous studies, this paper also contributes in presenting the validation works of the proposed control system in a real-time situation using a Hardware-in-Loop (HIL) platform. Simulation and validation results show that the CNF and DOB managed to reduce the influence of the side wind disturbance in nonlinearities.

Robust composite nonlinear feedback for nonlinear Steer-by-Wire vehicle’s Yaw control

Yaw control is a part of an Active Front Steering (AFS) system, which is used to improve vehicle manoeuvrability. Previously, it has been reported that the yaw rate tracking performance of a linear Steer-by-Wire (SBW) vehicle equipped with a Composite Nonlinear Feedback (CNF) controller and a Disturbance Observer (DOB) is robust with respect to side wind disturbance effects. This paper presents further investigation regarding the robustness of the combination between a CNF and a DOB in a nonlinear environment through a developed 7-DOF nonlinear SBW vehicle. Moreover, in contrast to previous studies, this paper also contributes in presenting the validation works of the proposed control system in a real-time situation using a Hardware-in-Loop (HIL) platform. Simulation and validation results show that the CNF and DOB managed to reduce the influence of the side wind disturbance in nonlinearities.

Observer-based improved Composite Nonlinear Feedback control for output tracking of time-varying references in descriptor systems with actuator saturation

In this paper, an observer-based improved Composite Nonlinear Feedback (CNF) controller is proposed for output tracking of general time-varying reference signals in descriptor systems subject to actuator saturation. Different parts of the proposed control law are designed based on the reconstructed states by a full-order descriptor observer. Algebraic constraints in descriptor systems can significantly complicate design procedures of the observer and the controller. Moreover, considering the actuator saturation constraint, adds additional complexity to the tracking problem. On the other hand, the proposed improved CNF controller’s performance is also challenged in presence of external disturbances. The effect of external disturbances, along with the previous mentioned constraints, needs extremely intricate calculations for investigating the solvability of the tracking problem. Furthermore, due to the nonlinearity of the closed-loop system, steady-state analysis is also needed to show the uniformly ultimately boundedness of the tracking error in presence of external disturbances. In this regard, precise mathematical operations are performed through a theorem, which investigates the tracking goal for three different cases of the saturation function. Finally, the theoretical achievements are verified by computer simulations through numerical and practical examples.

Composite non-linear feedback control using Mittag-Leffler function

Transient performance of any physical system is very important concern for the controller design of that system. Composite non-linear feedback control (CNF) is one of such controls with which optimum transient performance can be achieved. It has a combination of linear feedback law and non-linear feedback law. In the conventional CNF control, non-linear feedback law uses a decaying exponential function as a non-linear function. In the proposed modified CNF, this exponential function is replaced with Mittag-Leffler function (MLF) for the non-linear control law. Mittag-Leffler function which is one of the special functions from fractional calculus and it is the generalization of exponential function. By fine tuning the parameters in MLF, better control over damping ratio can be achieved. This improves the performance of the system further, giving lesser rise time, settling time and the percentage overshoot. The modern flight control application is used to demonstrate the effectiveness of CNF controller using MLF.

Super-twisting algorithm-based integral sliding mode control with composite nonlinear feedback control for magnetic levitation system

The paper aims to discuss the issues of actuator saturation and external disturbance in the magnetic levitation (maglev) system. The proposed technique is composed of composite nonlinear feedback (CNF) and super-twisting algorithm (STA)-based integral sliding mode (ISM) control to tackle the problem of actuator saturation and external disturbances simultaneously. The composite nonlinear feedback scheme comprises of linear feedback law which provides stability and fast response whereas the nonlinear feedback law takes care of input saturation and reduces the overshoot. The super-twisting algorithm (STA)-based integral sliding mode (ISM) controller is designed for disturbance rejection. A super-twisting algorithm-based approach is applied on ISM scheme to eliminate the chattering effect and make it continuous in nature for its direct implementation to the physical maglev system. The designed scheme is successfully tested on real-time feedback instruments model of the maglev system.

Nonlinear Trajectory Controller with Improved Performances for Waveriders

This paper presents a nonlinear trajectory controller with improved performances for a general model of the waverider based on feedback linearization theory and composite nonlinear feedback (CNF) technique. First, a nonlinear controller is presented using the dynamic inversion and CNF technique for the MIMO Model, and the robust stability of the proposed controller is proved. Then, the nonlinear model is established on the basis of hypersonic aerodynamic principle, and the dynamic characteristics are analyzed accordingly, and the periodic trajectory is designed and optimized in combination with a fuel optimization problem. Furthermore, the nonlinear controller is applied to the trajectory tracking of the waverider model, and the general design steps are provided the flight controller using this nonlinear control method. Finally, an illustrative example is given to verify the effectiveness of the nonlinear controller of the waverider, and the flight performances are improved accordingly, including system stability, robustness, and tracking ability.

Application of composite nonlinear feedback control approach to linear and nonlinear systems

The objective of this research is to realize a composite nonlinear feedback control approach for a class of linear and nonlinear systems with parallel-distributed compensation along with sliding mode control technique. The proposed composite nonlinear feedback control approach consists of two parts. In a word, the first part provides the stability of the closed-loop system and the fast convergence response, as long as the second one improves transient response. In this research, the genetic algorithm in line with the fuzzy logic is designed to calculate constant controller coefficients and optimize the control effort. The effectiveness of the proposed design is demonstrated by servo position control system and inverted pendulum system with DC motor simulation results.

Super-twisting algorithm-based integral sliding mode control with composite nonlinear feedback control for magnetic levitation system

Super-twisting algorithm-based integral sliding mode control with composite nonlinear feedback control for magnetic levitation system

On Stability Analysis of a Class of Nonlinear Systems with a Focus on Composite Nonlinear Feedback Approach

Obtaining a desired transient performance of closed-loop system is the most important issues in impractical and industrial applications, in general. It is to note that the small overshoot and acceptable settling time of the system response are almost two typical characteristics in the transient performance. There are a number of contradictions between these performances; and therefore, a tradeoff between these ones should deeply be considered. In a word, a so-called composite nonlinear feedback (CNF) method is an efficient and simple technique which is employed to overcome the contradiction of simultaneous achievement of the mentioned transient performances. CNF based sliding mode control (SMC) for nonlinear systems with known upper bound uncertainty are considered in this paper. Unlike the existing results for the linear systems, the proposed CNF based SMC comprises two nonlinear parts. The first term assures the stability of the closed-loop nonlinear system and provides a fast convergence response. The second term reduces the overshoot of the response. Finally, to show the merits of the proposed approach, it is applied to two nonlinear Genesio’s chaotic system and a nonlinear helicopter system. The investigated results verify the effectiveness of the proposed approach.

Modified composite nonlinear feedback control for output tracking of nonstep signals in singular systems with actuator saturation

SummaryThis paper considers output tracking of nonstep reference signals for multi‐input multi‐output singular systems subject to actuator saturation and external disturbances. Singularity of the system alongside the actuator saturation constraint and external disturbances adds more complexity to stability analysis and controller design than normal systems. Moreover, the problem of output tracking of nonstep reference signals in singular systems via the composite nonlinear feedback (CNF) control law is not studied so far in the literature, and this article will investigate this problem for the first time by proposing the modified CNF control law. For this purpose, first, a singular reference generator system is constructed to produce the desired nonstep reference signal. Then, the dynamical error system is obtained by defining a new state vector as the tracking error and augmenting it to the main system. Different parts of the modified CNF control law are designed afterwards. Due to complexities caused by the singularity of the system and the saturation constraint, detailed mathematical calculations are done. In this regard, a theorem is given that guarantees the tracking problem for three different cases of the saturation function. Moreover, the given theorem will investigate the uniform ultimate boundedness analysis of the tracking error in the face of external disturbances. Finally, the theoretical results are affirmed by computer simulations through three examples to verify the performance and applicability of the proposed control law.

Robust composite nonlinear feedback control for spacecraft rendezvous systems under parameter uncertainty, external disturbance, and input saturation

This paper presents a new robust composite nonlinear feedback control law for accurate, smooth, and fast regulation in the presence of parameter uncertainties, external disturbances, and input saturation for a class of spacecraft rendezvous systems. The novel proposed method consists of the original composite nonlinear feedback part for good transient performance plus a nonlinear disturbance rejection part for reducing the steady-state error stemming from variable disturbances and simultaneously producing feasible control input. The nonlinear disturbance rejection relies on sliding-mode observer for disturbance estimation. Closed-loop system stability has been proved with the Lyapunov theory. Simulation results show the closed-loop stability and superior control performance.

Adaptive composite non‐linear feedback‐based sliding mode control for non‐linear systems

An adaptive composite non-linear feedback based sliding mode controller is proposed for a class of non-linear systems comprising uncertainty terms. In these cases, it is theoretically proved that the trajectory of the closed-loop system converges to the sliding surface in a finite-time manner. Also, by the means of numerical linear matrix inequality technique, the stability of the non-linear system along the sliding surface is turned to an linear matrix inequality problem. By solving such problem, the unknown matrix of the sliding surface and composite non-linear feedback based sliding mode controller is obtained. Finally, to show the merits of the proposed approach, it is applied to practical non-linear DC servomotor.

Composite nonlinear feedback design for discrete-time switching systems with disturbances and input saturation

ABSTRACTThis paper addresses the problem of robust controller design for a class of discrete-time switching systems with input saturation. To this aim, the composite nonlinear feedback method is extended to design a robust controller with improved performances in terms of the response speed and overshoot in the presence of disturbances and input saturation. The proposed approach is theoretically analysed and its closed-loop stability is proved. Then, the performance of the proposed method is verified using numerical simulations.

Robust finite-time composite nonlinear feedback control for synchronization of uncertain chaotic systems with nonlinearity and time-delay

This paper proposes a combination of finite-time robust-tracking theory and composite nonlinear feedback approach for the finite-time and high performance synchronization of the chaotic systems in the presence of the external disturbances, parametric uncertainties, Lipschitz nonlinearities and time delays. The composite nonlinear feedback control technique develops an accurate and high-performance response for the following of the master chaotic system and the finite time concept provides the convergence of the error signals to zero in the finite time. Therefore, in this work, we will develop a new finite time robust tracking and model following control approach based on the composite nonlinear feedback scheme. Using the Lyapunov stability approach, we have proved that the tracking errors of the uncertain chaotic system converge to the origin in the finite time. Moreover, a sufficient criterion is derived to guarantee the robust asymptotic stability of the synchronization error dynamics. Simulation results on Chua's chaotic system are presented to prove the performance of the suggested controller compared to the other technique.

Composite nonlinear feedback integral sliding mode tracker design for uncertain switched systems with input saturation

In this paper, a composite nonlinear feedback technique is proposed for robust tracking control of switched systems with unmatched uncertainties and input saturation. The proposed self-tuning integral sliding mode tracker presents a time-varying boundary layer width and a variable control gain, which could improve the transient performance and steady-state accuracy simultaneously. This scheme guarantees robustness against uncertainties, removes reaching phase, and avoids chattering problem. To adapt the variation of the tracking targets, a new scaled nonlinear function is employed. Simulation results are included to exhibit the efficiency of the suggested method.