Finite-time Disturbance Observers Research Articles

Composite finite-time control for PMSM with prescribed performance using disturbance compensation technique

Permanent-magnet synchronous motors have attracted great attention and have been widely used in high performance industrial autonomous systems. In order to improve its control performance in the presence of external disturbances, the composite prescribed performance control (PPC) technique has been introduced. It can explicitly regulate the tracking performances like overshoot, convergence rate and steady-state-tracking error. But the current work only promises bounded or asymptotic behavior of the tracking error instead of finite-time convergence. To this end, a composite finite-time control scheme with prescribed performance is investigated for the speed regulation of permanent-magnet synchronous motor. The prescribed transient and steady performance constraints are considered beforehand by using the PPC technique. The external disturbances like load torque, adversely influencing the tracking performance, are estimated by finite-time disturbance observers. Then, based on the adding a power integrator technique, a composite finite-time speed regulation controller is designed by compensating the disturbance estimate via a feedforward manner. The finite-time stability of the closed-loop system is also analyzed rigorously. Finally, both comparative numerical simulations and experiments are conducted to verify the effectiveness of the proposed control scheme.

Finite-time disturbance observers based reliable control for a constrained autonomous flexible manipulator system with mismatched and matched disturbances

This study focuses on a control approach for a constrained autonomous flexible manipulator system (AFMS) with multiple disturbances comprising both matched and mismatched disturbances. First, we propose two disturbance observers to compensate for multiple unknown disturbances in finite time using the finite-time stability theory. Meanwhile, we design the auxiliary systems and barrier Lyapunov functions to tackle input saturations and output constraints. Then based on the proposed disturbance observers, the auxiliary systems, and barrier Lyapunov functions, we propose two reliable control laws to achieve deflection suppression and hub angular displacement tracking. Additionally, the deflection and hub angle tracking error of the AFMS are constrained to a small compact set through controller design. Finally, the deflection suppress control performance of the constrained AFMS with mismatched and matched disturbances is evaluated.

Barrier function-based prescribed-performance adaptive attitude tracking control for spacecraft with uncertainties

This paper addresses the problem of robust adaptive attitude tracking control for spacecraft with mismatched and matched uncertainties. The idea of disturbance estimation and compensation is introduced into the control design. First, finite-time disturbance observers are developed for different channels of spacecraft based on barrier functions for achieving finite-time asymptotic estimates of unknown bounded uncertainties in the system. Second, a class of prescribed performance functions is considered in the design of the barrier function. The spacecraft attitude adaptive tracking control strategy with finite-time convergence capability and prescribed performance is proposed based on the designed finite-time disturbance observers and barrier function. Finally, the theoretical findings are verified by numerical simulations and compared with the simulation results of existing methods.

Multivariable Disturbance Observer-Based Finite-Time Sliding Mode Attitude Control for Fixed-Wing UAVs Under Matched and Mismatched Disturbances

In this letter, we propose a multivariable disturbance observer-based finite-time sliding mode attitude control (MDOB-FT-SM-AC) for fixed-wing UAVs in the presence of both matched and mismatched disturbances. Compared with existing sliding mode attitude controllers, the significant improvements of the proposed MDOB-FT-SM-AC are the multivariable control structure, strong robustness, and high precision performance with continuous control input signal. In the proposed MDOB-FT-SM-AC, we first develop multivariable finite-time disturbance observers such that the precise estimation of both matched and mismatched disturbances is ensured. Next, a nonsingular terminal sliding manifold is designed such that the fixed-wing UAV is driven to track its desired attitude command in finite time. We finally present a multivariable super-twisting reaching law such that the finite-time convergence of the sliding variable and its derivative to zero is guaranteed. Attentive finite-time convergence analysis is derived based on the Lyapunov and homogeneity theories. Simulation results are given to illustrate the superiority of the proposed MDOB-FT-SM-AC.

Three-dimensional cooperative guidance law for intercepting hypersonic targets

This paper proposes a three-dimensional adaptive sliding mode cooperative guidance law using multiple low-speed interceptors with time-varying speeds for effectively intercepting hypersonic targets. The guidance commands are divided into commands along and normal to the line-of-sight (LOS). First, based on the algebraic graph and consensus theories, the guidance command along the LOS is designed to ensure that multiple interceptors achieve finite-time convergence to simultaneously intercept a hypersonic target. Second, to address the external disturbance caused by the manoeuvring of the hypersonic target in the direction normal to the LOS, finite-time disturbance observers are designed to accurately estimate the acceleration information of the hypersonic target with rapid convergence. Next, the guidance command normal to the LOS is formulated based on the sliding mode control method, which can nullify the LOS angular rate, ensuring progressive convergence to zero at interception. Moreover, thrust and drag models are incorporated to ensure that the guidance model is reasonably realistic. Numerical simulations are performed for different manoeuvring modes of the hypersonic target, and comparative simulations are conducted using the proportional navigation and sliding mode cooperative guidance laws. The simulation results demonstrate the superiority and effectiveness of the proposed guidance law.

Enhanced fractional order sliding mode control for a class of fractional order uncertain systems with multiple mismatched disturbances

To improve the control performance of the fractional order uncertain systems with multiple mismatched disturbances, an enhanced fractional order sliding mode control (FOSMC) method is developed in this paper. The multiple disturbances and uncertainties are estimated by the finite-time disturbance observers (FTDO) and a fractional order extended state observer (FOESO), respectively. A fractional order switching law is designed to provide a fast convergence mode for the system states. Then a novel FOSMC law is developed by incorporating the feedforward compensation, the fractional order switching law, and the auxiliary state for input saturation. The proposed method is applied to numerical examples and to a motor speed control problem. The effectiveness of the proposed method is demonstrated by the performance comparisons with some existing control methods.

Dual-disturbance-observer-based robust finite-time trajectory tracking control for robotic surface vehicle under measurement uncertainties

In this paper, the finite-time trajectory tracking control of a fully actuated robotic surface vehicle (RSV) with multiple uncertainties is investigated. Particularly, besides model uncertainties, environmental disturbances, and actuator saturation, the measurement uncertainties are also taken into account. When considering the measurement uncertainties, the RSV becomes a mismatching system, which brings a great difficulty to the control design. To resolve this problem, a novel robust finite-time control approach is proposed based on a dual-disturbance-observer-based architecture. First, two finite-time disturbance observers are developed to estimate the mismatched and matched lumped disturbances in the kinematics and dynamics of the RSV, respectively. Then, the robust finite-time controller is synthesized by incorporating the two finite-time disturbance observers into the adding a power integrator technique. It is strictly proved that the robust finite-time controller can ensure the actual position and velocity tracking errors stabilize to the small neighborhoods around the origin in finite time. Benefiting from the feedforward disturbance compensation, the proposed controller is not only robust against model uncertainties and environmental disturbances, but also insensitive to measurement uncertainties. At last, the effectiveness and advantages of the proposed control approach are verified through numerical simulations on a benchmark RSV model called CyberShip Ⅱ.

Robust finite-time control design for attitude stabilization of spacecraft under measurement uncertainties

This paper investigates the finite-time attitude stabilization of spacecraft under multiple uncertainties. Besides inertia uncertainties, external disturbances, and actuator faults, the measurement uncertainties are particularly considered. When including the measurement uncertainties, the spacecraft attitude control system becomes a mismatching system, which brings a great challenge to the control design. To resolve this problem, a novel robust finite-time attitude control approach is proposed by using a dual-disturbance-observer-based structure. First, two finite-time disturbance observers are developed to estimate the mismatched and matched lumped disturbances in the spacecraft attitude kinematics and dynamics, respectively. Then, the robust finite-time attitude controller is synthesized by incorporating the two finite-time disturbance observers into the adding a power integrator technique. It is strictly proved that the proposed robust finite-time attitude controller can ensure the actual attitude and angular velocity stabilize to the small neighborhoods around the origin in finite time even subject to multiple uncertainties. Benefiting from the feedforward disturbance compensation, the proposed controller is not only robust against inertia uncertainties, external disturbances, and actuator faults, but also insensitive to measurement uncertainties. Lastly, the effectiveness and advantages of the proposed control approach are validated through simulations and comparisons.

Fault-tolerant control for the multi-quadrotors cooperative transportation under suspension failures

This paper focuses on the fault-tolerant control of the multi-quadrotors cooperative payload transportation under suspension failures. A dynamic load reassignment and control strategy is proposed for the cooperative quadrotors by incorporating the high-order sliding mode disturbance observer into a dynamic surface control-based backstepping design. The dynamics of the cable-suspended payload transportation with multiple quadrotors are formulated. The unmeasurable suspension cable tensions, which will greatly impact the quadrotors' dynamics and stability, are respectively viewed as one part of the lumped disturbance and estimated by the super-twisting sliding mode-based finite-time disturbance observers. With the estimated disturbance compensation, the dynamic surface control laws are established for the cooperative quadrotors. Moreover, to guarantee the fault-tolerant control under suspension cable broken, a dynamic load assignment strategy is proposed to stably recover the cooperative load transportation. Finally, the stability of tethered quadrotors' flight control systems is analyzed. The simulation results show the effectiveness of the proposed algorithm under suspension failures.

Finite-Time Path Following Control of an Underactuated Marine Surface Vessel with Input and Output Constraints

This paper develops a finite-time path following control scheme for an underactuated marine surface vessel (MSV) with external disturbances, model parametric uncertainties, position constraint and input saturation. Initially, based on the time-varying barrier Lyapunov function (BLF), the finite-time line-of-sight (FT-LOS) guidance law is proposed to obtain the desired yaw angle and simultaneously constrain the position error of the underactuated MSV. Furthermore, the finite-time path following constraint controllers are designed to achieve tracking control in finite time. Additionally, considering the model parametric uncertainties and external disturbances, the finite-time disturbance observers are proposed to estimate the compound disturbance. For the sake of avoiding the input saturation and satisfying the requirements of finite-time convergence, the finite-time input saturation compensators were designed. The stability analysis shows that the proposed finite-time path following control scheme can strictly guarantee the constraint requirements of the position, and all error signals of the whole control system can converge into a small neighborhood around zero in finite time. Finally, comparative simulation results show the effectiveness and superiority of the proposed finite-time path following control scheme.

Fast finite-time backstepping for helicopters under input constraints and perturbations

This work addresses the issue of trajectory tracking of helicopters under disturbances and input constraints via the proposed fast finite-time backstepping framework. Backstepping with the property of fast finite-time convergence exhibits fast transient convergence both at a distance from and at a close range of the equilibrium. Moreover, finite-time disturbance observers based on multivariable super-twisting are employed to counteract the effect of perturbations. Aiming at the adverse effect of input saturation, a novel auxiliary system is developed to avoid the singularity by transforming auxiliary variables for three times. In addition, the framework is also applied into helicopter control problem, in which thrust magnitude and thrust direction are used as intermediate control variables, connecting external translational dynamics and internal angular dynamics. A rigorous proof of finite-time stability of the closed-loop system is derived from Lyapunov theory. Finally, the effectiveness and superiority of the proposed framework are verified by comparative simulation.

Finite-time path following control for small-scale fixed-wing UAVs under wind disturbances

By integrating the finite time control technique and finite-time disturbance observers together, the finite-time three-dimensional path following control problem for small-scale fixed-wing UAVs subject to external wind disturbances is investigated in this paper. The external wind disturbances are estimated through finite-time disturbance observers and the estimates are then incorporated into the finite-time feedback controller such that a composite control scheme is proposed. Under the proposed control scheme, the closed-loop system possesses not only faster convergence rate but also stronger disturbance rejection ability and better robustness, which is the main contribution of the paper. The effectiveness and superiorities of the proposed composite control scheme are demonstrated by numerical simulations.

Event-triggered tracking control for nonlinear systems subject to time-varying external disturbances

Event-triggered tracking control for a class of nonlinear systems with disturbances is investigated in this paper. Compared to existing related results, the nonlinearities only need to satisfy a generalized Lipschitz condition, and the time-varying external disturbances are allowed to be unmatched. By using finite-time disturbance observers, the finite-time estimation of the steady states is achieved to reduce the complexity of tracking control design. The event-triggered controller is designed by a new feedback domination approach, which can dynamically compensate for both errors caused by disturbances and the sampled-data implementation of the controller. A new Lyapunov stability analysis is given to show that all the signals of the closed-loop system are globally bounded and the tracking error is ensured to converge to a set, which can be made as small as desired by adjusting control parameters. Finally, a numerical example demonstrates the effectiveness of the designed scheme.

Leader–follower formation control of surface vehicles: A fixed-time control approach

In this paper, a novel fixed-time controller (FTC) strategy based on leader–follower mechanism and finite-time disturbance observer (FDO) is proposed for surface vehicles (SVs) formation suffering from complex unknowns. The excellent features of designed strategy are shown below: (1) A fixed-time tracking control (FTTC) approach combining with integral sliding mode (ISM) technology is devised for a nominal leader SV such that fixed-time stability can be ensured; (2) To achieve formation efficiently, a fixed-time formation controller (FTFC) strategy incorporating with backstepping technology is proposed for coordinating follower SVs; (3) Considering complex disturbances in the entire formation system, finite-time disturbance observers (FDOs) are injected into the FTFC framework which in turn contributes to accurate formation control with fixed-time convergence. Finally, simulation results demonstrate remarkable performance of the proposed FDO-FTFC scheme.

Continuous Integral Terminal Sliding Mode Control for Double-Layer Peltier System Based on Finite-Time Observer

This paper addresses the finite-time tracking problem for the double-layer Peltier system. Peltier is a semiconductor thermoelectrical transform device. It is widely used in the thermal tactile reappearance area. To expand temperature differences, Peltier is usually used in the form of double layers. There are some uncertain factors such as state coupling, external disturbance, and parameter perturbation in double-layer Peltier. Therefore, it is of great theoretical and practical significance to design a controller with superior performance. To this end, a compound continuous integral terminal sliding mode control strategy is proposed here. Firstly, finite-time disturbance observers are designed for feedforward compensation and evaluating the external disturbances. Secondly, the strong robustness of the sliding mode control enhances the disturbance rejection of the system. The continuous integral sliding mode makes the input continuous and weakens the chattering. Also, the terminal sliding mode improves the convergence speed of the system on the sliding surface significantly. The performance of the proposed method is analyzed through Lyapunov stability analysis, simulations, and experiments. Compared to nonsmooth finite-time control, the continuous integral terminal sliding mode control achieves rapid temperature stability and better disturbance rejection under the same condition of finite-time convergence.

Backstepping Control for Large Signal Stability of High Boost Ratio Interleaved Converter Interfaced DC Microgrids With Constant Power Loads

With the penetration of renewable generation and tightly regulated power electronic loads, the power quality and stability of modern dc microgrids are greatly challenged. To solve this problem, energy storage systems (ESSs) are widely proposed. Unfortunately, most of the existing control methods for ESSs can only ensure the stability of dc microgrids with small signal disturbances, which may not be satisfying for real-time applications where large signal disturbances exist. Moreover, they are usually designed for low boost ratio and low power converters, negating their suitability for grid-scale applications. To ensure the large signal stability of dc microgrids using high boost ratio interleaved converter interfaced ESSs, this article proposes a new backstepping control strategy with finite-time disturbance observers. Its effectiveness is verified by simulation and experiments carried out on an interleaved double dual boost converter.

Approximate Dynamic Inversion for Nonaffine Nonlinear Systems With High-Order Mismatched Disturbances and Actuator Saturation

In this paper, a novel disturbance-observer-based approximate dynamic inversion (ADI) approach is developed for pure-feedback nonaffine-in-control nonlinear systems (PFNNSs) in the presence of both high-order mismatched disturbances and actuator saturation. Finite-time disturbance observers (FTDOs) are utilized to estimate the disturbances and their derivatives. Then, we rebuild the system with the outputs of FTDOs. Thereafter, ADI is employed to derive the desired virtual and actual control of the nominal system, where no disturbances and saturation are presented. Furthermore, an augmented intermediate subsystem is constructed for the reduced slow subsystem to compensate for the difference between inputs with and without saturation by approximating its inversion. The stability of the closed-loop system is studied using Tikhonov's theorem. The proposed method is applied to a numerical example and a one-link robotic system with a brush DC motor. The simulation results demonstrate the validity of the presented approach.

Finite-time Backstepping for Attitude Tracking with Disturbances and Input Constraints

Backstepping (BS) is an important framework to stabilize the high-order nonlinear system. This work develops a finite-time convergence property for the BS framework combined with an auxiliary input saturation compensator and applies it to address attitude tracking problem of a rigid body subjected to disturbances and input constraints. The finite-time convergence of the tracking error is guaranteed by introducing the fractional power of tracing errors. Meanwhile, the finite-time filters of the target commands and the finite-time disturbance observers inspired by multivariable super-twisting algorithm are employed to construct the finite-time BS framework. Another novelty is to propose a novel auxiliary system to handle the adverse effect of input saturation. The singularity of auxiliary dynamics is avoided by the cubic representation of auxiliary variables. Attitude tracking errors are demonstrated to converge to zeros in finite time despite the presence of input saturation and disturbances through Lyapunov theory. Comparative simulations are conducted to demonstrate the effectiveness and superiority of the proposed control system.

Design of Head-Pursuit Guidance Law Based on Backstepping Sliding Mode Control

In order to meet the needs of high-precision guidance for intercepting hypersonic targets, a novel head-pursuit guidance law considering the dynamic characteristics of a missile control system and the target mobility is presented via combining a fast power reaching law with backstepping sliding mode control in this paper. Initially, a three-dimensional head-pursuit system model of the missile and target is established. Subsequently, the system model is decomposed into a pitch plane system and lateral plane system, the control system dynamics are equivalent to second-order systems, and finite-time disturbance observers are introduced to estimate the target accelerations. On the basis of the previous work, the head-pursuit guidance laws of the vertical system and the lateral system which can stabilize the closed-loop system are designed separately and strict proofs of the methods are given. Finally, simulations are carried out to verify the effectiveness of this head-pursuit guidance law.

Distributed prescribed performance control for consensus output tracking of nonlinear semi-strict feedback systems using finite-time disturbance observers

ABSTRACTThe distributed consensus output tracking problem is dealt with for a class of nonlinear semi-strict feedback systems in the presence of mismatched nonlinear uncertainties, external disturbances and uncertain nonlinear virtual control coefficients of the subsystems. The systems are under a directed communication graph, where the leader node is the root. The controller is designed in a backstepping manner, and the dynamic surface technique is adopted to avoid direct differentiation. At each step of virtual controller design, a prescribed performance controller is constructed to achieve prescribed transient performance so that the system states remain in the feasible domain. Then each virtual controller is enhanced by a finite-time disturbance observer which estimates the disturbance term in a finite-time. The properties of the control system are analysed theoretically. It is clarified that the prescribed performance control technique ensures that the system signals stay in the feasible domain, whereas sufficiently small ultimate control errors can be achieved by the finite-time disturbance observers. Finally, the performance of the proposed methods is confirmed by numerical studies.