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Facing the system uncertainties caused by unmodeled dynamics and unpredictable external disturbances, the robot position control for meeting the high-performance control requirements on higher accuracy and faster beat is vital for many industrial applications, such as welding and laser cutting tasks. This work aims to cope with the problem of precise and fast position tracking for robot manipulators with an effective and safe control scheme. Specifically, a discrete-time super-twisting observer (STO) is integrated into the scheme to estimate the uncertain dynamics (e.g. unmodeled dynamics and external disturbances) in the feedforward compensation part of the dynamics. Subsequently, a discrete-time fast terminal sliding mode controller (FTSMC) dominates the robot control to guarantee fast convergence of the position tracking error. The significant improvement of the proposed method with respect to other discrete-time sliding mode control approaches lies in that it is capable of alleviating the chattering-like problem, achieving a fast convergence and improving the robustness of sliding mode control against uncertain dynamics. To illustrate the effectiveness of the presented control scheme, several experiments on a six degrees of freedom (6DoF) robot manipulator are provided. [ABSTRACT FROM AUTHOR]

The ideal fuel rail pressure is a significant component to keep the high-pressure common rail (HPCR) system work stably. The influence of time-varying fuel injection disturbance of the HPCR system is neither fully considered nor well dealt with in traditional rail pressure control approaches. To this end, the rail pressure tracking problem of an HPCR system is investigated in this paper using a generalized proportional integral observer (GPIO)-based composite control algorithm. A nonlinear model of the HPCR system is first established based on fluid dynamics and mechanics laws. Then, a GPIO is utilized to observe the time-varying fuel injection disturbance. Based on the design of a nonlinear sliding surface using the disturbance estimation, a GPIO-based nonsingular terminal sliding mode control (NTSMC) method is proposed to achieve a better rail pressure tracking control performance and a stronger robustness. Finally, a group of simulations in the MATLAB/Simulink environment and experiments in a more realistic Advanced Modeling Environment for performing Simulation of engineering systems (AMESim) environment are conducted, the results of which demonstrate the advantage and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The combination of DC-DC buck power converters with DC motors for generating the so-called smooth start of drives has many advantages in engineering practice. Achieving high performance of such systems is, however, limited by the influence of disturbances/uncertainties of multiple sources. Some of the disturbances are mismatched, which makes them even more difficult to handle. Furthermore, the relatively high order of system dynamics makes the control design challenging. In this paper, a control structure with continuous dynamic sliding mode controller with a finite-time disturbance observer is proposed to address these practical issues. First, a special state transformation is applied, aggregating the acting disturbances/uncertainties in a sole perturbing term of the system expressed in new coordinates. Then, the observer estimates in real time the information about the lumped disturbances based on already available input/output signals and the obtained estimated signals (and their high order time-derivatives) are used to construct a sliding surface. Finally, the sliding mode controller is applied to achieve high performance of the resultant plant dynamics and to robustify the governing scheme against modelling discrepancies. The stability of the closed-loop system is proved here using Lyapunov stability theory and the efficiency of the proposed control method is validated through a multi-criteria numerical simulation. [ABSTRACT FROM AUTHOR]

A composite three-dimensional (3D) missile guidance law is proposed for manoeuvering targets with the consideration of the first-order autopilot dynamics without any linearization. This guidance law consists of a backstepping controller and a feedforward compensation based on disturbance observers. In this control scheme, the unknown target acceleration is regarded as part of the lumped disturbance, estimated by a disturbance observer, and then feedforward compensated. The backstepping controller is introduced to deal with unmatched disturbances. Moreover, both the nonlinear disturbance observer (NDOB) and the generalized proportional integral observer (GPIO) are employed in the derivation. Simulation studies demonstrate the effectiveness of the proposed guidance law, and compare the guidance performance of the two composite guidance laws with different disturbance observers. [ABSTRACT FROM AUTHOR]

This paper develops a systematic iterative learning control (ILC) strategy for systems with mismatched disturbances. The systems with mismatched disturbances are more general and widely exist in practical engineering, where the standard disturbance observer based ILC method is no longer available. To this end, this note proposes a novel ILC scheme based on the disturbance observer, which consists of two parts: a baseline ILC term for stabilizing the nominal system and a disturbance compensation term for attenuating mismatched disturbances by choosing an appropriate compensation gain. It is proven that the performance of the closed-loop system is effectively improved. Finally, the simulation analysis for a permanent-magnet synchronous motor servo system demonstrates the feasibility and efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents an optimal integral sliding mode control method based on a pseudospectral method for a class of affine systems with state and control constraints. First, a general form of an integral sliding mode is presented. Integral sliding mode control cannot deal with the problem of states and control constraints, nor can it satisfy the minimization of the cost function. The pseudospectral method has a high convergence speed and performs well in solving optimal control problems with general performance index, endpoint conditions and path constraints. In consideration of these advantages, an optimal integral sliding mode controller is determined by the pseudospectral method. Then, the stability analysis of optimal pseudospectral sliding mode method is discussed. Finally, numerical simulations show the effectiveness of the proposed method. An application example, consisting of an overhead crane system, is investigated to demonstrate the effectiveness and robustness of the proposed technique. [ABSTRACT FROM AUTHOR]

In this paper, the position tracking control problem of pneumatic servo systems is investigated. These systems usually have high nonlinearities and unmeasurable piston velocities. Firstly, by using adding a power integrator technique, a global finite-time state feedback controller is proposed. Secondly, based on homogeneous theory, a nonlinear observer is developed to estimate the piston velocity. Finally, the corresponding output feedback controller is derived, which local finite-time stabilizes the position tracking error system. Compared with the conventional backstepping output feedback control scheme, the developed nonsmooth output feedback control scheme offers a faster convergence rate and a better disturbance rejection property. Numerical simulations illustrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Binary distillation columns are essentially multi-variable systems with couplings, non-minimum phase characteristics, model mismatches and various external disturbances. To get the desired top (distillate) and bottom product composition, a composite disturbance rejection control strategy using a radial basis function network (RBFN) is proposed in this paper. The composite controller includes neural network inverse controller (NNIC) and neural network disturbance observer (NNDOB) both using the inverse model of system which is identified by the RBFN. The stability of the identified inverse model is proved, and a rigorous analysis is also given to show why the NNDOB can effectively suppress the disturbances. Performances of the proposed scheme are compared with PID and NNIC without disturbance compensation in three cases by simulation studies. The simulations demonstrate the feasibility, effectiveness and disturbance rejection property of the proposed method in controlling the product composition of the binary distillation columns. [ABSTRACT FROM AUTHOR]

This paper focuses on the global stabilization problem of controlling direct current–direct current switched power converters in the presence of coil magnetic saturation. A finite-time controller is investigated for the modified nonlinear system model by utilizing an adding a power integrator technique. With the finite-time control scheme, not only a faster convergence rate is obtained, but also better suppression ability to the inevitable disturbances is achieved for the closed-loop system. Simulation comparison results show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

The continuous finite-time anti-disturbance control problem for a class of nonlinear system under external disturbances and parameter uncertainties is investigated in this article. First, a continuous terminal sliding mode control (CTSMC) is introduced to stabilize the nominal system dynamics. Concerning the unsatisfying performance of the CTSMC in the presence of severe external disturbances and parameter uncertainties, a finite-time disturbance observer (FTDO) is employed to estimate the uncertainties to its nominal dynamics. By integrating the CTSMC method with the FTDO technique, a composite controller is presented for such kind of nonlinear system under external disturbances and parameter uncertainties. The composite controller obtains finite-time convergence property in the presence of disturbances and also nominal control performance recovery in the absence of disturbances. Moreover, compared with conventional sliding mode control, the proposed control law is continuous and no chattering phenomenon exists. The property of stability and the finite-time convergence of the closed-loop system under the proposed controller is guaranteed by means of Lyapunov stability criteria. The proposed control method is finally applied for the tracking control problem of robotic manipulators. Simulation results show that the proposed method exhibits promising control performance in the presence of severe external disturbances and parameter uncertainties. [ABSTRACT FROM AUTHOR]

Successful future asteroid landing missions require that the control method provides advanced disturbance rejection performance and strong robustness against parameter uncertainties to give higher accuracy and reliability in the complex space environment. Motivated by the requirement for safe and precise soft landing on asteroids, the finite-time soft-landing problem of an asteroid probe is addressed in this paper via a nonsingular terminal sliding mode (NTSM) control technique. The problem is formulated as a two-point boundary-value constraints control problem, where the initial and terminal requirements of the soft-landing problem are all included in the problem formulations. Then, according to the specific characteristics of the problem, an NTSM control law for soft landing on an asteroid is proposed. Simulation results demonstrate that, compared to the widely used traditional sling mode control method, the proposed method provides a much faster convergence rate, higher accuracies, better disturbance rejection properties and stronger robustness against parameter uncertainties. [ABSTRACT FROM PUBLISHER]

The practical ozone dosing process of drinking water treatment is essentially a complicated nonlinear process with time delay. It is difficult to establish an exact mathematical model and implement a satisfying real-time control for the frequent changes of water quality, water flow rate and process operational conditions. In this paper, the control strategy of keeping a constant ozone exposure is attempted instead of conventional keeping a constant ozone dosage or dissolved ozone residual. To this end, an adaptive model predictive control (MPC) scheme based on the radial basis function (RBF) neural network model is proposed to maintain a constant ozone exposure by adjusting ozone dosage. With the proposed control scheme, a RBF neural network model is established as the prediction model of practical ozone dosing process. Then an adaptive model predictive controller is designed. Owing to the online updating of RBF neural-network weights, the proposed MPC scheme can cope with the frequent changes of water quality, water flow rate and process operational conditions. Both simulation and experimental results demonstrate the effectiveness and practicality of this real-time control method. [ABSTRACT FROM PUBLISHER]

For the terminal phase of tactical missiles intercepting maneuvering targets, the terminal guidance problem is studied. Based on an integral sliding mode (ISM) control method and nonlinear disturbance observer technique, a novel composite guidance law is designed in the case of constrained impact angle and a first-order-lag autopilot. Regarding the target acceleration and the external disturbance of autopilot as unknown bounded disturbance, a nonlinear ISM guidance law is designed. The obtained guidance law guarantees the line-of-sight (LOS) angular rate and LOS angle a finite-time convergence characteristics. Then, to alleviate the chattering problem and guarantee the disturbance rejection performance, the composite guidance law combining the ISM guidance law with feedforward compensation terms based on nonlinear disturbance observers is obtained. Finally, simulation comparison results are provided to demonstrate the effectiveness of the presented methods. [ABSTRACT FROM AUTHOR]

In this paper, an output feedback finite-time controller based on a finite-time stable observer is developed for a bioreactor system. The observer is proposed to estimate the biomass concentration in finite time. Based on the estimation of the biomass concentration, an output feedback controller is designed to track the reference signal in finite time. A Lyapunov function is constructed to prove that the observer is a finite-time stable observer. The finite-time stability results for cascaded systems are employed to prove that the closed-loop system satisfies the finite-time stability. Thus, the observer and the controller can be designed separately, both with finite-time convergence. Numerical simulation results demonstrate the effectiveness of the method. [ABSTRACT FROM PUBLISHER]

This paper presents a new control strategy for overhead crane systems. First, by utilizing a coordinate change, the underactuated overhead crane dynamical model can be transformed into an upper-triangular form. Second, a finite-time controller is designed based on the nonlinear nested saturation and adding a power integrator technique. Rigorous proof shows that the controller can guarantee finite-time stability of the closed-loop system. Simulations show the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

In order to improve the disturbance rejection property of Permanent-Magnet Synchronous Motor servo systems, a novel adaptive composite control method for the speed regulation problem is proposed in this paper. The composite controller is composed of a proportional feedback controller and a feedforward compensation based on a Radial Basis Function Network Disturbance Observer (P+RBFNDOB). The RBFNDOB is designed to estimate the lumped disturbances, including external disturbances and internal disturbances caused by parameter variations, and the estimation value is used for feedforward compensation design. Different from traditional Linear DOB (LDOB), an RBFN is used to approximate the inverse model of the system instead of selecting the inverse of the nominal model as in LDOB. By using an on-line learning algorithm, the identified inverse model can track the variations of the real plant. Thus, the RBFNDOB can still observe the disturbances when the parameters of the system vary in a wide range, while conventional DOB may not be suitable in such situations. So the composite controller obtained is inherently robust against parameter variations and external disturbances. A nearest neighbour clustering algorithm combining crude regulation and fine regulation is introduced as the on-line learning method to simplify the network structure and accelerate the learning speed. Rigorous analysis is also given to show why the RBFNDOB can effectively suppress the lumped disturbances of a closed-loop system. Simulation comparisons with two other methods, the composite control method with proportional feedback plus feedforward compensation based on LDOB (P+LDOB) and the conventional PI control method, verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

This research delves into the development of a composite model predictive controller designed for the current loop in a permanent magnet synchronous motor (PMSM) servo system. In order to enhance the performance of a system, the proposed controller integrates an extended state observer (ESO) and actuating delay compensation. The ESO is employed for the estimation of the lumped disturbance affecting the PMSM, while the prediction model incorporates both the estimated lumped disturbance and the delayed actuating output to derive an optimized control law. Simulation and experimental results further validate the effectiveness of the approach, offering an innovative solution to the actuating delay challenge and a considerable increase in the bandwidth of the current loop. [ABSTRACT FROM AUTHOR]

This paper considers the finite-time speed regulation problem of permanent magnet synchronous motor (PMSM) servo system. Based on homogeneous system theory, a finite-time proportional-integral controller is first constructed for the d-axis current loop system, such that the desired current can be tracked in finite time. To overcome the influence of the unmatched load torque disturbance of the second-order model for the speed regulation system, a nonlinear integral dynamic is introduced. Then, based on an appropriate coordination and homogeneous system theory, a new finite-time proportional-integral-derivative controller is constructed. Strict theoretical analysis based on Lyapunov stability theory is provided to verify the finite-time stability of the corresponding closed-loop system. Finally, numerical simulation and experimental results are conducted to validate the effectiveness of the proposed finite-time control method. [ABSTRACT FROM AUTHOR]

This paper develops a predictive observer–based control (PO-BC) scheme to address the output stabilization problem of a class of time-delay systems subject to mismatched complex disturbances. Initially, a novel predictive observer is proposed to anticipate future information related to both disturbances and system states. By integrating these predictions, a composite controller is constructed, comprising feedback and feedforward compensation. A systematic approach for selecting control parameters is presented to facilitate easy implementation. The theoretical analysis demonstrates that as long as appropriate parameters are selected, the predictive observer can accurately predict both disturbances and system states, and the system’s output can asymptotically converge to zero. Finally, the effectiveness of the proposed scheme is validated through sufficient simulations. [ABSTRACT FROM AUTHOR]