Disturbance Observer Technique Research Articles

Neuroadaptive high-order fully-actuated system approach for roll autopilot with unknown uncertainties

In this paper, a neuroadaptive high-order fully-actuated system approach control scheme incorporating the disturbance observer technique is proposed for the missile roll autopilot, subject to model uncertainties generated by the induced roll moment, along with actuator control efficiency deterioration and external disturbance. To address model uncertainties, the radial basis function neural network is implemented. The external disturbance and approximation error are treated as compound disturbances and estimated by a nonlinear disturbance. To avoid the “differential explosion” inherent in the backstepping technique, the high-order fully-actuated system approach is invoked to track the desired roll angle command. The semi-globally uniformly bounded of the closed-loop system is demonstrated via the Lyapunov method. Numerous simulations under various conditions have been conducted to verify the effectiveness of the proposed roll autopilot.

Disturbance Observer and Adaptive Control for Disturbance Rejection of Quadrotor: A Survey

Quadrotors are widely applied in many fields, but they often face various external disturbances in actual operation. This makes it necessary to design a controller that can handle disturbances. Disturbance observer and adaptive control techniques are commonly used disturbance rejection techniques, the core idea of which is to estimate the disturbances in real time and incorporate the estimated values into the controller to suppress the disturbances. In this paper, various disturbance observers and adaptive control techniques, including nonlinear disturbance observers, extended state observers, neural networks, and fuzzy logic systems, are introduced, along with their variants or different structures. These techniques improve the adaptability and robustness of quadrotors to complex environments. Finally, future research directions for the disturbance rejection of quadrotors are also presented.

Fractional Order T–S Fuzzy Chaotic Models for Secure EEG Signal via a Wireless Communication Protocol Using a Disturbance Observer and Sliding Mode Control Technique

Fractional Order T–S Fuzzy Chaotic Models for Secure EEG Signal via a Wireless Communication Protocol Using a Disturbance Observer and Sliding Mode Control Technique

Autonomous Finite-Time Backstepping Control for Decentralized Economic Power Dispatch in DC Microgrids Toward Large-Signal Stability

The power electronic loads usually behave as constant power loads (CPLs) in DC microgrids (MGs), which degrades the system stability due to their high-order non-linearity and negative impedance characteristics. Furthermore, the stability concern will be more complicated for the distributed generators (DGs) in DC MGs considering both economic efficiency and plug-and-play performance. In this paper, an autonomous finite-time backstepping controller (FTBC) for decentralized economic power dispatch and precise DC bus voltage regulation of a DC MG is proposed. The high-order nonlinear disturbance observer (HONDO) technique is adopted to estimate the power exchanges between the DGs and loads. So that the decentralized economic power dispatch and rapid voltage regulation can be achieved without any extra output current sensors. In addition, the use of HONDO improves the system's dynamic performance by estimating the disturbances and system uncertainties, and the FTBC guarantees the bus voltage tightly tracking within a finite-time convergence. A rigorous stability analysis is performed to prove the large-signal stability of the regulated system, and some simulations and experiments are carried out.

Discrete-time integral terminal sliding mode load following controller coupled with disturbance observer for a modular high-temperature gas-cooled reactor

With the appearance of digital computers and microprocessor technologies, the control systems used in nuclear reactors continue to transform from analog devices to digital ones in recent years. A heavy challenge is that applying the pre-existing intelligent load following control algorithms developed in the continuous-time domain to the current digital devices of the nuclear reactors may yield the so-called digital chattering effects, and even trigger system instability. To this end, this paper presents a discrete-time integral terminal sliding mode controller (DTITSMC) coupled with a discrete-time disturbance observer (DTDO) for the load following of a modular high-temperature gas-cooled reactor (MHTGR). The common continuous-time MHTGR model is first transformed into a discrete-time form with consideration of model uncertainties, exogenous disturbances, and discretization errors. Then, on the basis of this discrete-time MHTGR model, a DTDO that can estimate the lumped disturbances, composed of model uncertainties, exogenous disturbances, discretization errors, and unmeasured system states, is developed, subsequently being combined with the designed DTITSMC scheme in order to enhance the system robustness. The proposed DTITSMC scheme coupled with the DTDO is novel in that it can be directly implemented on the digital control system of the MHTGR, while at the same time providing an improved load following control performance, owing to the integration of the state-of-the-art sliding mode control techniques, backstepping control techniques, and the disturbance feedforward compensation supported by the disturbance observer techniques. Both the estimation error convergence of the DTDO and the overall system stability are theoretically proved by the Lyapunov stability theory in this paper. Finally, the feasibility and superiority of the proposed DTITSMC scheme coupled with the DTDO over the previous discrete-time linear sliding mode controller (DTLSMC) and discrete-time proportional–integral–derivative controller (DTPIDC) are further confirmed by simulation studies, where in the absence of lumped disturbances, the value of the accumulative absolute load error (AALE) produced by the proposed DTSMPPC scheme coupled with the DTDO is merely 0.0575% and 0.2675% to that of the previous DTLSMC and the optimized DTPIDC, respectively, while in the presence of lumped disturbances, the value of the AALE produced by the proposed DTSMPPC scheme coupled with the DTDO is merely 0.006% and 0.1952% to that of the previous DTLSMC and the optimized DTPIDC, respectively.

Event-Triggering-Learning-Based ADP Control for Post-Stall Pitching Maneuver of Aircraft.

In this article, an improved event-triggering-learning (ETL)-based adaptive dynamic programming (ADP) method for the post-stall pitching maneuver of aircraft is proposed to achieve the robust optimal control and reduce the computational cost. First, a feedforward control with the nonlinear disturbance observer (NDO) technique is designed to attenuate the adverse effects caused by the unsteady aerodynamic disturbances. Subsequently, the ADP method with a critic neural network which is constructed to approximate the value function in the Hamilton-Jacobi-Bellman equation is employed to conduct the optimal control of aircraft. In addition, to reduce the computational cost of learning, the event-triggering (ET) mechanism with an improved ET condition is applied. The Lyapunov stability theory is utilized to prove that all signals in the closed-loop control system are uniformly ultimately bounded. Finally, simulation results are presented to illustrate the effectiveness of the proposed ETL-based ADP method.

Neural Preassigned Performance Control for State-Constrained Nonlinear Systems Subject to Disturbances.

This article addresses the finite-time neural predefined performance control (PPC) issue for state-constrained nonlinear systems (NSs) with exogenous disturbances. By integrating the predefined-time performance function (PTPF) and the conventional barrier Lyapunov function (BLF), a new set of time-varying BLFs is designed to constrain the error variables. This establishes conditions for satisfying full-state constraints while ensuring that the tracking error meets the predefined performance indicators (PPIs) within a predefined time. Additionally, the incorporation of the nonlinear disturbance observer technique (NDOT) in the control design significantly enhances the ability of the system to reject disturbances and improves overall robustness. Leveraging recursive design based on dynamic surface control (DSC), a finite-time neural adaptive PPC strategy is devised to ensure that the closed-loop system is semi-globally practically finite-time stable (SPFS) and achieves the desired PPIs. Finally, the simulation results of two practical examples validate the efficacy and viability of the proposed approach.

Disturbance Observer-Based Safe Tracking Control for Unmanned Helicopters with Partial State Constraints and Disturbances

In this paper, a disturbance observer-based safe tracking control scheme is proposed for a medium-scale unmanned helicopter with rotor flapping dynamics in the presence of partial state constraints and unknown external disturbances. A safety protection algorithm is proposed to keep the constrained states within the given safe-set. A second-order disturbance observer technique is utilized to estimate the external disturbances. It is shown that the desired tracking performance of the controlled unmanned helicopter can be achieved with the application of the backstepping approach, dynamic surface control technique, and Lyapunov method. Finally, the availability of the proposed control scheme has been shown by simulation results.

Mismatched disturbance compensation enhanced robust H∞ control for systems with nonvanishing uncertainties/disturbances

AbstractThis article proposes a robust control method based on disturbance observer techniques for systems subject to mismatched uncertainties/disturbances. In the existing composite robust control methods with disturbance compensation, only matched uncertainties/disturbances, that is, the uncertainties/disturbances acting on the same channels as the control inputs, are feedforward compensated, while the mismatched ones are only attenuated in a conservative manner. It should be highlighted that if the mismatched uncertainties/disturbances are nonvanishing, the controller generally requires excessive control energy to suppress the effects of uncertainties/disturbances, where the control gains must be designed to ensure robust properties at the expense of sacrificing nominal tracking and/or stabilization performances. To address this problem, this article further introduces the compensation of mismatched uncertainties/disturbances into the robust control. Moreover, to attenuate the effects of observation errors, sufficient conditions for the asymptotic and robust stability of error systems are established. Finally, the proposed controller is applied to a DC–DC buck converter system feeding constant power load. Experimental results confirm its feasibility and efficiency.

Load following control of a PWR with load-dependent parameters and perturbations via fixed-time fractional-order sliding mode and disturbance observer techniques

This paper is concerned with the fixed-time fractional-order sliding mode control (FTFOSMC) approach using fixed-time disturbance observer (FTDO) for the load following problem of a pressurized water reactor (PWR), in the presence of load-dependent parameters and perturbations. First, by integrating the merits of the fixed-time stability theory and the disturbance observer technique, an FTDO which can ensure fixed-time convergence is constructed to estimate perturbations induced by model uncertainties, external disturbances, and unmeasured states. Then, an FTFOSMC strategy with the help of the disturbance observer is proposed to achieve strong robustness against perturbations and high-precision load following performance. The fixed-time stability of the closed-loop system is theoretically demonstrated by Lyapunov’s theorem. Finally, comparative simulation results are presented to illustrate the superiority of the overall proposed control strategy.

Sliding-mode-based chaos suppression of coronary artery systems

Since coronary artery disease is the leading global cause of mortality and morbidity, this paper investigates the chaos suppression of coronary artery systems. The motivation of the paper is to discuss and analyze coronary artery disease in the field of dynamics. Firstly, the mathematic model of coronary artery systems is formulated and the properties of this model are illustrated by bifurcation diagram, information entropy analysis, phase plane trajectory, and Poincaré section. With regard to the uncertainties of coronary artery systems, the disturbance observer technique is adopted. Meanwhile, the smooth second-order sliding mode controller is designed to suppress the chaos phenomenon. In light of the combination of the controller and observer, the stability of such a closed-loop system is proven in the sense of Lyapunov. Finally, some numerical simulations demonstrate the feasibility and validity of such design.

Combination of Functional and Disturbance Observer for Positive Systems with Disturbances

This technique note proposes two classes of functional and disturbance observers for positive systems with structural and non-structural disturbances, respectively. A positive functional observer is first proposed for positive systems by introducing the estimation of disturbance to the observer. By developing the disturbance observer technique, a positive disturbance observer is designed to supply the estimation of disturbance in the functional observer. Then, a new unknown input observer is constructed for positive systems. A matrix decomposition method is employed to design the observer gains. All conditions are described in terms of linear programming. The corresponding algorithms are addressed for computing the presented conditions. Finally, two examples are provided to verify the effectiveness of the theoretical findings.

Finite-Time Attitude Tracking Control for Hypersonic Flight Vehicles with Actuator Saturation

This paper investigates finite-time attitude tracking control strategies for hypersonic flight vehicles (HFVs) with parameter uncertainties, external disturbances, and actuator saturations by applying sliding model control, adaptive mechanism, and nonlinear disturbance observer techniques. A nonlinear dynamic model of HFV attitude system in reentry flight phase is established. Then, a basic attitude control method of the HFV system is designed based on a terminal sliding mode control (TSMC) scheme to accommodate the system-lumped disturbance torques and guarantee the finite-time stability. To relax the prior knowledge of bounded lumped disturbance of the TSMC-based HFV attitude system, an adaptive TSMC (ATSMC) scheme is proposed. In order to relax the limit of compound uncertainties and attenuate chattering phenomenon of the TSMC-based HFV attitude system, a nonlinear disturbance observer-based TSMC (DO-TSMC) scheme is presented, which enhances the disturbance attenuation and robust tracking performance. Finally, simulation results of a generic X-33 nonlinear model exhibit the effectiveness of the proposed TSMC, ATSMC, and DO-TSMC schemes.

APF-based intelligent navigation approach for USV in presence of mixed potential directions: Guidance and control design

This paper investigates the real-time intelligent navigation approach for unmanned surface vehicle (USV), considering constraints of the randomly moving target and multiple static or moving obstacles. In the scheme, an intelligent guidance principle is developed by employing the traditional dynamic virtual ship (DVS) structure and the artificial potential field (APF) technique. The improved design for repulsive potential field can guarantee the reasonable obstacle avoidance capability. Especially, the amended repulsive terms are derived by the velocity and orientation factors of moving obstacles. Combining with the APF-based guidance, the robust neural path following control algorithm is proposed by employing the minimal learning parameter (MLP) and the nonlinear disturbance observer (DOB) technique. For merit of the improved design of DOB, the attitude of USV can be effectively stabilized to that of virtual ship. That can derive the state-of-art trade-off between the complicated control law and the hardware computing burden. Through the Lyapunov synthesis, all states of USV are with the semi-globally uniform ultimate bounded (SGUUB) stability. Two experiments have been illustrated to verify the obstacle avoidance and dynamic tracking performance of the proposed strategy.

Modeling and Control of Spacecraft with Multiple Active Pointing Ultra-Quiet Platforms

Future high-resolution space-based astronomical observation and remote sensing require space telescope with long focal length or space interferometer with long baseline. In these systems, multiple payloads will be placed over a large spacecraft structure and work in coordination to fulfill the mission tasks. However, structure flexibility and various disturbances present challenges for precision control of the payloads. In this article, each payload is placed on an active pointing ultra-quiet platform for simultaneous steering and active/passive vibration isolation, and the associated modeling and control problems are addressed. First, dynamic equations are formulated for a flexible spacecraft with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> platforms. In these equations, relative motion variables are used for the platforms, so that the equations are simple yet suitable for control design and analysis. Then, two typical coordination schemes for the platforms are identified, and the corresponding control goals are defined. Finally, the controllers for both the schemes are designed based on the disturbance observer technique, and their performance, including steady-state disturbance rejection and transient-state agility, is evaluated via numerical simulation.

Fixed‐time non‐singular terminal sliding mode control with globally fast convergence

This paper investigates a fixed-time terminal sliding mode (TSM) control scheme of second-order non-linear uncertain systems. A globally fast fixed-time stable system is proposed, and the convergence time is established with the Lyapunov method. Then, a novel non-singular TSM utilising the proposed fixed-time stable system and an auxiliary polynomial function is constructed. Meanwhile, a fixed-time disturbance observer technique is employed to estimate the matched lumped perturbation. Globally fast fixed-time convergence of the closed-loop system is guaranteed with the phase plane analysis and Lyapunov tools, and the upper bound of the settling time independent of the initial conditions can be predefined by the controller parameters. Finally, the simulation results of a single inverted pendulum system are included to confirm the validity of the proposed methodology while comparing with some popular TSM control strategies.

Distributed Coordinated Control for Fixed-Wing UAVs With Dynamic Event-Triggered Communication

Compared with most existing results concerning unmanned aerial vehicles (UAVs) wherein two-degree or only attitude/longitudinal dynamics are considered, this paper proposes an event-based fault-tolerant coordinated control (FTC) for multiple fixed-wing UAVs such that the consensus tracking of velocity and attitude is achieved in the presence of actuator faults, external disturbances and modeling uncertainties. More precisely, as opposed to static event-triggered communication mechanisms, a dynamic event-triggered communication mechanism (DECM) is devised to schedule the connected communications while avoiding the unnecessary information exchanges among UAVs, which reduces the communication burden and saves on the network resources. Meanwhile, the Zeno phenomenon is excluded in terms of guaranteeing that the period between two consecutive triggering communication is lower bounded by a positive constant. Moreover, the actuator fault, external disturbance as well as model uncertainty are treated as the lumped disturbances and estimated via the disturbance observer technique. By strict Lyapunov arguments, all closed-loop signals are proved to be uniformly ultimately bounded (UUB) and the tracking errors of velocity and attitude converge to a residual set around origin. Finally, simulation results are presented to illustrate the validity and superiority of proposed event-based control scheme.

Active-Damping Speed Tracking Technique for Permanent Magnet Synchronous Motors With Transient Performance Boosting Mechanism

This article exhibits a novel solution to the speed tracking problem of permanent magnet synchronous motors (PMSMs) subject to parameter and load uncertainties. The resultant cascade structured solution is designed to give the speed tracking capability to the closed-loop system, which depends on only the nominal PMSM parameter information. This article provides two novel contributions: 1) a variable performance target system describing the desired perfect tracking nature with boosting feedback gains and 2) a robust control law forcing the target tracking system to be invariant through the utilization of active-damping pole-zero cancellation and disturbance observer techniques. The prototype 1-kW PMSM experimental set confirms the practical advantages of the proposed system compared to the recent autotuning controller.

Composite SOSM controller for path tracking control of agricultural tractors subject to wheel slip

In the work, the path tracking control methods are developed for autonomous agricultural tractors subject to wheel slip constraints by using second-order sliding mode (SOSM) and finite-time disturbance observer (FDOB) techniques. First of all, the path tracking error dynamics derived from the kinematic model is given and applied to controller design. In order to deal with the inevitable chattering problem existing in the conventional first-order sliding mode (FOSM) controller, a SOSM controller is constructed by regarding the controller derivative as the new control law, which means that the practical control law can be seen as an integration of the SOSM controller. Through a combination of the FDOB and the designed SOSM controller, the composite path tracking controller is further constructed to avoid high control gains in the designed SOSM controller. The strict Lyapunov stability analysis is carried out to ensure that the sliding variable can be finite-time stabilized to the origin under the proposed control algorithms. Finally, the comparative simulation results confirm that the developed guidance laws can achieve good tracking performance and strong robustness even in the presence of slipping effects.

Disturbance observer‐based tracking control with prescribed performance specifications for a class of nonlinear systems subject to mismatched disturbances

AbstractThis work investigates simultaneous prescribed performance tracking control and mismatched disturbance rejection problems for a class of strict‐feedback nonlinear systems. A novel control scheme combining prescribed performance control, disturbance observer technique, and backstepping method is proposed. The disturbance estimations are introduced into the design of virtual control law design in each step to compensate the mismatched disturbances. To further improve the control performance, a prescribed performance function characterizing the error convergence rate, maximum overshoot, and steady‐state error is used to construct the composite controller. The proposed controller guarantees transient and steady‐state performance specifications of tracking error and provides much better disturbance attenuation ability simultaneously. Rigorous stability analysis for the closed‐loop system is established by direct Lyapunov function method. It is shown that all the states in the resulting closed‐loop system are stable, and the tracking error evolves within the prescribed performance boundaries and asymptotically converges to zero even in the presence of mismatched external disturbances. Finally, theoretical results are illustrated and demonstrated by two simulation examples.