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The magnetic bearing rotor system is affected by internal uncertainties and various forms of external disturbances, which will affect the stability of the active magnetic bearing system. To address this issue, a composite hierarchical anti-disturbance strategy is used to improve the anti-disturbance ability of the magnetic bearing rotor system. The disturbance observer is used to compensate the system's external disturbances, and the controller is used to suppress the system's internal uncertainties. For this purpose, H ∞ controller, disturbance observer (DOB), and linear extended state observer (LESO) are designed, respectively. Then, H ∞ controller is combined with DOB and LESO to form H ∞-DOB and H ∞-LESO composite controllers and prove their stability. Finally, simulation and experiments show that H ∞ -DOB and H ∞ -LESO have better disturbance suppression effects than the H ∞ controller for external disturbances. And when the disturbance frequency or rotor rotation frequency of the system is high, H ∞ -LESO controller has better disturbance suppression effect than H ∞ -DOB. [ABSTRACT FROM AUTHOR]

This article develops a predefined‐time sliding mode control approach for systems with external disturbances and uncertainties through a nonlinear disturbance observer (DO). For addressing predefined‐time stabilization problem of robotic manipulator system, a predefined‐time sliding mode surface is proposed, ensuring system states converge to origin within a predefined‐time once sliding mode surface is attained. Compared to conventional fixed‐time and finite‐time control strategies, a distinctive advantage of this scheme is that system settling time can be explicitly chosen in advance and independent of system states. To achieve predefined‐time performance, a disturbance observer is introduced to generate the disturbance estimate, which can be incorporated into controller to counteract disturbance. To address the systems uncertainty, an adaptive law is employed to estimate the unknown upper boundary of system uncertainties. Finally, the effectiveness and performance of the proposed scheme are illustrated by simulation and experiment. [ABSTRACT FROM AUTHOR]

ABSTRACT To improve tracking control performance in the task space of the Stewart parallel mechanism (SPM) with uncertainties of modeling errors and external disturbances in our developed rust removal sandblasting robot for the surface roughness processing of a bridge's steel box girder, a fixed‐time composite control with variable exponent coefficients (VEC‐FxTCC) approach for multi‐input multi‐output (MIMO) nonlinear robotic systems is developed. Firstly, by devising only one regulation term with a variable exponent coefficient (VEC) function in the system's Lyapunov differential inclusion, a novel VEC fixed‐time stability theorem for the MIMO nonlinear dynamic system is proposed and proven. Secondly, based on the proposed theorem, VEC‐FxTCC is formed by designing and combining a VEC fixed‐time disturbance observer (VEC‐FxTDOB) and a VEC fixed‐time super‐twisting control (VEC‐FxTSTC), in order to achieve fast, steady, and uniformly bounded‐time convergence for SPM's end‐effector tracking, while avoiding singularity. Finally, the effectiveness of the proposed VEC‐FxTCC approach is validated through the simulations and the rust removal sandblasting robot prototype experiments. [ABSTRACT FROM AUTHOR]

To deal with the voltage drop of self‐excited induction generator when the loads are fed, a static synchronous compensator (STATCOM) are used to improve the load capacity of the SEIG and the power quality. Therefore, this paper proposes a Lyapunov‐based control based on a disturbance observer, which constructs a Lyapunov function from the mathematical model and transforms the error‐tracking problem into solving the inner‐loop control law. The control law satisfies the Lyapunov asymptotic stability. To eliminate the impact of model mismatch on the control strategy, a disturbance observer is incorporated into the current inner loop, improving the robustness of inner‐loop. The results demonstrate that the proposed method can reduce the sensitivity to line parameters, enhance inner‐loop robustness, and outperform traditional methods in response speed. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

ABSTRACT The fault estimation and fault‐tolerant control problems of switching stochastic systems with partially unknown nonlinear dynamics, external disturbance, actuator, and sensor faults are studied. A new observer and disturbance observer are constructed to simultaneously estimate the system state, actuator, and sensor faults, as well as modelable disturbances. The dimensions of the proposed adjustable dimension observer are not fixed and can be adjusted within a certain range, and unknown nonlinear dynamics can be decoupled. According to estimated information, fault‐tolerant controller is designed. The sufficient condition is obtained to ensure that the root‐mean‐square gain from the disturbances to the fault reconstruction error is bounded. Finally, two simulation examples are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: The primary objective of this paper is to enhance the efficient utilization of communication resources. To achieve this, the paper delves into the disturbance observer based adaptive heading control strategy for Unmanned Marine Vehicles with event‐triggered and input quantization. Furthermore, in order to mitigate the impact of slow time‐varying external disturbances within the control system, the disturbance observer is employed for estimation. Within the context of a networked control, control input is subjected to quantization via an input quantizer, and the process of input quantization is described by using a linear analytical model. Importantly, no foreknowledge of quantization parameters is necessary for the quantized feedback controllers. Subsequently, the sliding mode control method is combined with event‐triggered mechanismss to design quantization feedback control system. The stability of the closed‐loop system is established in line with the fundamental tenets of Lyapunov stability theory, validating the bounded nature of both observation and heading tracking control errors. The effectiveness of the proposed heading control scheme is further underscored through a series of simulation experiments. [ABSTRACT FROM AUTHOR]

This paper addresses the high‐precision control problem for nonlinear strict feedback systems with external time‐varying disturbances and proposes a novel composite learning control algorithm. Unlike previous research that only uses tracking errors for neural network updates, this paper prioritizes the accuracy of neural network learning. The article uses a selective memory recursive least squares algorithm to construct system information prediction errors, which are combined with tracking errors to update the neural network weights. A new composite learning control algorithm is developed to design dynamic surface control and neural network disturbance observers, which achieves high‐precision control of nonlinear strict feedback systems under external time‐varying disturbance conditions. Lyapunov's method demonstrates the stability of the closed‐loop system and the boundedness of errors. The simulation results show that the proposed control algorithm can effectively estimate system nonlinearity and suppress the impact of disturbances. [ABSTRACT FROM AUTHOR]

This paper exhibits a proportional-type robust current controller for permanent magnet synchronous motors (PMSMs), incorporating the variable bandwidth technique driven by the proposed online auto-tuner and the disturbance observer (DOB) as the subsystems. There are two contributions: (a) the proposed online auto-tuner implements the variable bandwidth for the closed-loop system to boost the transient current tracking performance and (b) the combination of proportional-type feedback controller and DOB eliminates the requirement of the integral action, ensuring the steady-state error rejection property. Moreover, it is proved that the resultant feedback system recovers the target current tracking performance without steady-state errors. The experimental study is conducted to verify the efficacy of the proposed controller using a 700-W prototype PMSM. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, fault estimation (FE) and fault‐tolerant control (FTC) are studied for switched stochastic nonlinear systems with unknown input and faults. The dynamic unknown input observer (DUIO) and disturbance observer are designed, and the system state, faults, and disturbances can be reconstructed. The DUIO designed in this paper is the extension of the traditional unknown input observer (UIO) and the proportional‐integral observer. The unknown input, which contains unmodeled disturbance, uncertainty, can be decoupled by the estimation error system. A dynamic output feedback controller based on observers is designed to compensate for actuator fault and modelable disturbance. The integration scheme of FE and FTC is designed, and the one‐step linear matrix inequalities (LMIs) conditions are constructed, which avoids the coupling of observer and controller parameters. The root‐mean‐square (RMS) gain is used to attenuate the unknown input and unmodelable disturbances in the closed‐loop systems, which can remove some common assumptions. Finally, the feasibility of the proposed method is demonstrated through simulations. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper proposes a novel finite‐time adaptive continuous robust control method for buck converters, combining dynamic sliding mode theory with a mismatched disturbance observer. While traditional sliding mode control can effectively manage matched disturbances, it often falls short when faced with mismatched disturbances, potentially compromising system performance. Our developed control strategy introduces a nonlinear sliding mode‐based disturbance observer and an adaptive continuous robust sliding mode control to guide state variables towards desired values. To mitigate the chattering phenomenon, the proposed controller incorporates a super‐twisting algorithm, ensuring continuous control command behavior. We conducted a rigorous finite‐time stability analysis of the control procedure using Lyapunov theory. Furthermore, comprehensive experimental results demonstrate that our proposed control method significantly reduces disturbance effects and enhances the buck converter's performance in terms of robustness and accuracy. [ABSTRACT FROM AUTHOR]

In this study, a finite-time disturbance observer (FTDOB) with a new structure is originally put forward for the motion tracking problem of a class of nonlinear systems subject to model uncertainties and exogenous disturbances. Compared to existing disturbance estimator designs in the literature, in which the estimation error only converges to the origin asymptotically under assumptions that the first and/or second derivatives are vanishing, the suggested DOB is able to estimate the disturbance exactly in finite time. Firstly, uncertainties (parametric and unstructured uncertainties), unknown dynamics, and external disturbances in system dynamics are lumped into a generalized disturbance term that is subsequently estimated by the proposed DOB. Based on this, a DOB-based backstepping controller is synthesized to ensure high-accuracy tracking performance under various working conditions. The stability analysis of not only the DOB but also the overall closed-loop system is theoretically confirmed by the Lyapunov stability theory. Finally, the advantages of the proposed FTDOB and the FTDOB-based controller over other DOBs and existing DOB-based controllers are explicitly simultaneously demonstrated by a series of numerical simulations on a second-order mechanical system and comparative experiments on an actual DC motor system. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper suggests a neural adaptive command filtered backstepping tracking control strategy for the chaotic permanent magnet synchronous motors with asymmetric prescribed performance constraints. Therefore, enable chaotic permanent magnet synchronous motors (PMSM) to obtain good robustness and better universality in practical industrial environments, and realizes more accurate control effect. The main challenge lies in devising a valid funnel‐like solution within the backstepping frame to handle the asymmetric performance constraints that traditional solutions cannot solve. To achieve this, a novel funnel‐like function is introduced, integrating a performance boundary function independent of initial output error, thereby transforming the system into an unbounded one. Additionally, the “explosion of complexity” with conventional backstepping is mitigated by introducing command filtering and constructing an error compensating system to reduce errors. By combining the theory of Lyapunov function and backstepping technique, the virtual controller and the real controller with adaptive law ensure the stability of the system. The disturbance observer and neural network solve the external disturbance and the uncertain nonlinear problem, respectively. Simulation comparisons confirm the robustness of the proposed control scheme and demonstrate its superiority over existing solutions. [ABSTRACT FROM AUTHOR]

Composite observer based finite time control of nonlinear systems in case of multiple disturbances is studied in this article, wherein the disturbances contain two parts, the first type is the harmonic disturbance with modeling errors, and all other disturbances are classified as the second type, known as lumped disturbances. To give estimation of the harmonic disturbance and the lumped disturbances, a disturbance observer (DO) and the extended state observer are constructed, respectively. On this basis, a finite‐time elegant anti‐disturbance controller is presented by combing DO‐based control, active disturbance rejection control, backstepping technique and the finite time command filter method. Eventually, it is proved that the design method put forward in this article is correct and feasible. [ABSTRACT FROM AUTHOR]

In this paper, we present a disturbance observer-based point of common connection voltage-modulated direct power control (PCCVM-DPC) system, which increases the robustness of the PCCVM-DPC system. First, the mathematical analysis of the disturbances for the step-up transformer's nonlinearity, the grid voltage harmonics, and the parameter uncertainties is presented. By analyzing the disturbance terms of the PCCVM-DPC system, we present the disturbance observer (DOB) for the PCCVM-DPC system. To assess the efficacy of our approach, we perform comparative studies of the PCCVM-DPC without DOB and PCCVM-DPC with DOB by constructing the simulation environment based on the commercial step-up transformer and ESS inverter datasheet. We have validated that the active and reactive power control performance of the PCCVM-DPC with DOB outperforms the PCCVM-DPC without DOB from the observation that the current total harmonic distortion reduced by more than 40% compared to the PCCVM-DPC without the DOB. [ABSTRACT FROM AUTHOR]

This paper presents a safe-guaranteed backstepping sliding mode heading controller for the underactuated hovercraft in the presence of slew safety constraint and system uncertainties. To begin with, based on the four degrees-of-freedom mathematical model of the hovercraft with system uncertainties, a novel slew rate constraint scheme is proposed to constrain the virtual slew rate of the hovercraft by designing auxiliary dynamic function, and redefine the error constraint envelope according to the prescribed performance control idea to realise the slew rate error constraint. In addition, a second-order fixed time disturbance observer is designed to quickly estimate the uncertainties of the system. Finally, all tracking errors of the closed-loop system are verified global asymptotically stable. The simulation results show that the slew rate can be constrained within the set safety range $r \lt 2.5^\circ /s$ r < 2.5 ∘ / s , and the error signals can converge to 0. [ABSTRACT FROM AUTHOR]

In this paper, the issue of nonlinear remote servosystem with disturbance is studied. A novel robust tracking strategy based on disturbance observer (DO) and dynamic event-triggered (DET) strategy is proposed. Firstly, a non-homogeneous observer based DO is designed, which can accurately estimate external disturbances and their higher-order derivatives. Secondly, a robust control strategy combines backstepping technique with the idea of sliding-mode is proposed with its stability proofed. Thirdly, to optimize network resources utilization for remote control, a novel DET strategy is proposed, which effectively addresses the issues of low sensitivity and poor flexibility in traditional fixed triggered approach. Finally, simulation results demonstrate the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

This study focuses on examining the issues of extended dissipative-based composite anti-disturbance reliable tracking control for stochastic Takagi–Sugeno fuzzy systems afflicted by sensor faults and multiple disturbances. Explicitly, the multiple disturbances include the autonomous Wiener process and non random noises with partly known information that are generated by an exogenous plant. To address the difficulty of estimating the non random disturbance while considering the partially known information, the study incorporates a fuzzy stochastic disturbance observer. Furthermore, to solve the output tracking issue of the system under consideration, a modified repetitive tracking control is implemented. Then, combining the methodologies of disturbance observer-based control technique with modified repetitive control, a composite anti-disturbance reliable tracking control strategy is developed for achieving the intended tracking goal despite the multiple disturbances and sensor faults encountered. Additionally, the proposed approach involves extended dissipativity scheme, which includes $ H_\infty $ H∞, passivity, dissipativity, and $ \mathfrak {L}_2 - \mathfrak {L}_\infty $ L2−L∞ performances in a unified framework. In particular, by employing Lyapunov–Krasovskii functional approach, the essential stability criteria for the proposed closed-loop system are articulated in the form of linear matrix inequalities. Additionally, numerical illustrations are presented to exemplify the application and efficiency of the developed control protocol. [ABSTRACT FROM AUTHOR]

ABSTRACT This article studies the finite‐time control problem for a class of nonlinear chaotic semi‐Markov jump systems with incomplete transition rates described by the T‐S fuzzy model approach. As a means to depict the dynamical properties pertaining to the examined system, parametric uncertainties, faults, external disturbances and input saturation are taken into consideration. The foremost objective of this study is to come up with a composite control mechanism that effectively rejects and attenuates the repercussions of faults and disturbances. In particular, we primarily built a disturbance observer in order to obtain a precise estimation of the external disturbances. After which, the fault diagnosis observer is designated to effectively estimate the faults. Specifically, a composite reliable control mechanism is developed by fusing the output of the constructed observers with the mode‐dependent fuzzy‐rule based state feedback controller. By employing suitable Lyapunov functions in conjunction with the linear matrix inequality technique, a set of mode‐dependent conditions is derived to ensure the finite‐time stochastic boundedness of the underlying closed‐loop and estimation error systems. Following this, the anticipated controller and observer gain matrices are elicited by resolving the established linear matrix inequalities. Thereafter, intending to ascertain the efficacy and usefulness of accrued theoretical findings, simulation results performed on Chua's circuit system is endowed. [ABSTRACT FROM AUTHOR]

In this paper, the attitude control problem of uncertain multi-rotor unmanned aerial vehicles (UAVs) subject to input saturation and external disturbance is considered. First, by introducing a set of low-pass filters, filter-based estimators are utilized for compensating parametric uncertainties to achieve good estimation. Second, a full-order auxiliary system is constructed, which integrates the functions of removing the command filtered error between virtual control and filtered virtual control as well as the deviation between the unsaturated input and the saturated input. In order to deal with the external disturbance more effectively, a filter-based disturbance observer and an adaptive bounding law are developed to suppress it. Simulation results applied to an octorotor system and experimental results applied to a quadrotor system verify the control performance of the proposed method under different conditions. [ABSTRACT FROM AUTHOR]

This paper investigates anti-disturbance synchronization for Lur'e systems using a hierarchical composite control mechanism. This mechanism integrates two control approaches: disturbance observer-based control and switchedgain event-triggered control, ensuring the H∞ exponential stability of the synchronization-error system in the presence of multiple disturbances. A condition on the H∞ exponential stability is derived utilizing a piecewise-defined and timedependent Lyapunov function and several inequalities. Based on the condition, a co-design is proposed for the gains of the event-triggered controller and disturbance observer. For comparison, the hierarchical composite control with a fixed gain is also investigated, and the corresponding design approach is presented. Finally, the effectiveness of the proposed composite anti-disturbance synchronization control mechanism is validated through an example involving master-slave Chua's circuits. [ABSTRACT FROM AUTHOR]

The article presents a novel control strategy for cable-driven aerial manipulators (UAMs) aimed at enhancing impedance control during contact operations in complex environments. A fractional-order nonsingular terminal sliding mode control (FONTSMC) integrated with a disturbance observer (DOB) is proposed to improve the robustness and precision of the UAM under lumped disturbances. This developed approach utilizes the flexibility of fractional calculus, the finite-time stability of nonsingular terminal sliding mode, and the real-time disturbance estimation capabilities of the DOB to ensure smooth and compliant contact interactions. The effectiveness of the proposed control strategy is validated through comprehensive simulation studies, which demonstrate significant improvements in control performance, stability, and disturbance rejection when compared to traditional methods. The results indicate that the FONTSMC-DOB framework is highly suitable for complex aerial manipulation tasks, offering both theoretical and practical insights into the design of advanced control systems for UAMs. [ABSTRACT FROM AUTHOR]

Achieving faster convergence, smaller transient overshoots, and higher steady‐state tracking accuracy is essential to improve the efficiency, robustness, and applicability of robotic manipulators. This article introduces an innovative adaptive fixed‐time uniform prescribed performance controller for the manipulator facing model uncertainties and unknown disturbances. Initially, by designing a modified prescribed performance function inspired by variable superposition, this study redefines the unified prescribed performance control problem into a simplified parameter selection problem. This approach allows for the incorporation of varied performance metrics within a singular control scheme, addressing both transient and steady‐state performances concurrently without shifting control frameworks. Then, to alleviate computational demands, an adaptive neural network employing a single‐parameter weight update technique compensates for uncertainties of the manipulator dynamic model. Additionally, a disturbance observer is designed to mitigate the impact of non‐parametric disturbances. Moreover, integrating fixed‐time theory with the Lyapunov stability analysis method guarantees the convergence of all error signals to a near‐zero compact neighborhood at a fixed time. Finally, the advantages and comprehensive performance of the proposed method are confirmed by numerical simulations and real‐world experiments. [ABSTRACT FROM AUTHOR]

In this paper, we proposed several disturbance observer‐based matrix‐weighted consensus algorithms. A new disturbance observer is firstly designed for linear systems with unknown matched or mismatched disturbances representable as the multiplication of a known time‐varying matrix with a unknown constant vector. Under some assumptions on the boundedness and persistent excitation of the regression matrix, the disturbances can be estimated at an exponential rate. Then, a suitable compensation input is provided to compensate the unknown disturbances. Second, disturbance‐observer based consensus algorithms are proposed for matrix‐weighted networks of single‐ and double‐integrators with matched or mismatched disturbances. We show that both matched and mismatched disturbances can be estimated and actively compensated, and the consensus system uniformly globally asymptotically converges to a fixed point in the kernel of the matrix‐weighted Laplacian. Depending on the network connectivity, the system can asymptotically achieve a consensus or a cluster configuration. The disturbance‐observer based consensus design is further extended for a network of higher‐order integrators subjected to disturbances. Finally, simulation results are provided to support the mathematical analysis. [ABSTRACT FROM AUTHOR]

This article investigates a class of multi-agent systems (MASs) with known dynamics external disturbances, where the communication graph is directed, and the followers have undirected connections. To eliminate the impacts of external disturbance, the technologies of disturbance observer-based control are introduced into the containment control problems. Additionally, to save communication costs and energy consumption, a distributed disturbance observer-based event-triggered controller is employed to achieve containment control and reject disturbance. Furthermore, designing the event-triggered function using an exponential function is beneficial for a time-dependent term while ensuring the exclusion of Zeno behavior. Finally, a numerical simulation is provided to validate the effectiveness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents issues related to the damping of torsional vibrations in a system with elastic coupling. A novel PI-based control structure with additional feedback from torsional torque and its derivative is proposed. For the estimation of the required variables, the integral observer is proposed. Analytical expressions are presented to enable the selection of parameters of the control system. The relationship between the considered system and popular structures with a PI controller and one additional feedback from torsional torque and the derivative of torsional torque is pointed out. The proposed control structure is tested under simulation and experimental studies. [ABSTRACT FROM AUTHOR]

• An adaptive backstepping controller based on nonlinear filter Lyapunov function is designed. • Integration of body control objectives and hard constraints into one control variable. • An adaptive backstepping bottom controller based on nonlinear disturbance observer is designed. • Conduct stability analyses of zero-power systems to ensure that safety performance indicators are bounded. • Backstepping dynamic surface control is used to avoid the derivative explosion phenomenon. In order to improve the ride comfort and handling stability of the electro-hydraulic active suspension system, a hierarchical control strategy is proposed. For the active suspension system with body mass uncertainty and safety constraints, an enhanced constraint adaptive backstepping controller is designed to generate the target force of body vertical motion. When dealing with constraints, nonlinear filters are introduced, backstepping technology and quadratic Lyapunov function are used to combine the control target and domain constraints, and the vertical displacement of the body and the suspension deflection control index are synthesized into a single controlled variable, so that the control variable converging to zero meets the suspension dynamic displacement limit. The ride comfort and safety of the active suspension system are improved. Secondly, stability analysis is conducted on the zero dynamic error system to ensure that all safety performance indicators are bounded. The effects of external disturbances, parameter uncertainties and modelling errors on the force tracking accuracy of asymmetric cylinder electrohydraulic systems are addressed. A backstepping dynamic surface control method based on a nonlinear perturbation observer is proposed, which estimates the composite perturbation terms such as modelling error and external perturbation, and uses the estimated value of the nonlinear observer to design a feedforward compensating control term to offset the effect of the composite perturbation on the system performance. In addition, the dynamic surface control method is used to calculate the derivative of the target force input, which avoids the derivative explosion phenomenon and reduces the computational complexity of the system. Simulation test results show that this method reduces the computational complexity of the system and improves the control performance. And under random and bumpy road conditions, the root-mean-square value of sprung mass acceleration performance index is reduced by 48.354 % and 72.677 % compared with passive suspension, which improves the ride comfort of the vehicle. [ABSTRACT FROM AUTHOR]

An adaptive fractional-order sliding mode control method using a disturbance observer is proposed for position tracking of a quadrotor. The mathematical model of the quadrotor considering disturbance is derived using the Euler–Lagrange equations. The model is divided into two fully actuated and underactuated subsystems. The proposed controller as the result of combining fractional calculus and the sliding mode method is designed for both subsystems separately. Furthermore, a disturbance observer is designed which deals with actuator fault, uncertainty, and wind disturbance. The stability of the closed-loop system is proved using Lyapunov theory and finite-time convergence of the variables to the desired values is guaranteed. In the numerical simulation, position tracking despite the actuator faults and effects of load and wind disturbance are investigated. Finally, the simulation results validate the superior performance and robustness of the proposed controller against actuator fault and wind disturbance and the results of controllers are compared. [ABSTRACT FROM AUTHOR]

Aiming to address the problem of underactuated unmanned surface vehicles (USVs) performing fixed-point operations at sea without dynamic positioning control systems, this paper introduces an original approach to positioning control: the virtual anchor control method. This method is applicable in environments with currents that change slowly and does not require prior knowledge of current information or vessel motion model parameters, thus offering convenient usability. This method comprises four steps. First, a concise linear motion model with unknown disturbances is proposed. Then, a motion planning law is designed by imitating underlying principles of ship anchoring. Next, an adaptive disturbance observer is proposed to estimate uncertainties in the motion model. In the last step, based on the observer, a sliding-mode method is used to design a heading control law, and a thrust control law is also designed by applying the Lyapunov method. Numerical simulation experiments with significant disturbances and tidal current variations are conducted, which demonstrate that the proposed method has a good control effect and is robust. [ABSTRACT FROM AUTHOR]

This paper clarifies the theoretical similarities and differences between the exosystem-model-based disturbance observer and the model error compensator. In 1972, Johnson proposed the exosystem-model-based disturbance observer. This observer is constructed against the augmented system model, which consists of nominal plant and disturbance-generating models. Ohnishi et al. proposed to cancel out the effect of uncertainties with its estimated disturbance. Furthermore, in 2013, Okajima et al. proposed the model error compensator, which compensates for the error between the output of the nominal plant model and the measurement outputs of the actual plant. The theoretical differences among these control structures have yet to be fully understood. Therefore, this paper theoretically investigates the relation and shows the superiority of the exosystem-model-based disturbance observer to the model error compensator in its freedom to assign the behavior of the uncontrollable modes. This superiority enables the exosystem-model-based disturbance observer to suppress output fluctuations against uncertainties effectively. This effect is shown by a numerical example.

A model predictive control (MPC) method based on the vector field guidance law is proposed to improve the effectiveness of path following and collision avoidance for ships. First, the path following and collision-avoidance problems are transformed into heading-control problems by the vector field guidance law. Then, the first-order Nomoto response model is adopted as the ship dynamic model for the model predictive control. Considering the input limitation of the rudder angle, the disturbance observer is introduced to compensate the model error and the environmental disturbances. The stability of the designed path following control system is verified by the Lyapunov theory. Finally, a collision avoidance strategy based on the vector field guidance law is designed to enable the ship to avoid collision autonomously in the process of path following. The simulation results indicate that the proposed methods can make the ship track the target path accurately and realize collision avoidance under the impacts of wave disturbances.

Abstract This paper exhibits a proportional-type robust current controller for permanent magnet synchronous motors (PMSMs), incorporating the variable bandwidth technique driven by the proposed online auto-tuner and the disturbance observer (DOB) as the subsystems. There are two contributions: (a) the proposed online auto-tuner implements the variable bandwidth for the closed-loop system to boost the transient current tracking performance and (b) the combination of proportional-type feedback controller and DOB eliminates the requirement of the integral action, ensuring the steady-state error rejection property. Moreover, it is proved that the resultant feedback system recovers the target current tracking performance without steady-state errors. The experimental study is conducted to verify the efficacy of the proposed controller using a 700-W prototype PMSM.

ObjectiveTo address the problem of ultra-short baseline (USBL) relative navigation and positioning during the dynamic docking of an autonomous underwater vehicle (AUV) in shallow water, a compensated unscented particle filter (CUPF) algorithm based on a disturbance observer is proposed. MethodsThe CUPF algorithm compensates for missing values in the USBL data based on the dead reckoning model, estimates the unknown disturbances in the dynamic docking of the AUV using observer technology and filters outliers in the USBL data combined with the unscented particle filter to realize the estimation of the AUV's state. Results The lake trial data shows that the proposed CUPF algorithm can effectively remove outliers and fill in missing values for USBL positioning with a speed estimation error of less than 15% and computation time reduced by 57% compared with traditional methods. ConclusionsThe CUPF algorithm can improve the positioning accuracy of USBL while smoothing the AUV motion trajectory and state estimation by fully utilizing relative measurement information for AUV docking.

This study addresses a novel strategy to enhance the accuracy and reliability of direct yaw-moment controller for vehicle directional stability. In the proposed method, some complementary terms are added to the bicycle model, as a reduced-order vehicle model to upgrade its content toward the actual model. The controller designed by the enhanced bicycle model compensates for perturbations such as unmodelled dynamics, parametric uncertainties and wind forces. Therefore, a reliable model-based controller is achieved to control vehicle directional stability in various maneuvers. The limitations of external yaw moment are modeled using a constrained optimization problem. Simulation studies are conducted in the CarSim software considering detailed vehicle dynamics and wind forces. The results demonstrate the superior efficiency of the constrained controller, developed by the enhanced bicycle model, compared with the researches in which the perturbation is not estimated for being used by the controller. During a severe lane-change maneuver, for instance, estimating the disparities between the bicycle model and the CarSim model causes the root mean square of the yaw rate tracking error to decrease from 0.237 to 0.005 )rad(. Importantly, the calculated external yaw moment is also reduced from 980.13 to 557.4 )N.m). In another path tracking test, a comparison with the linear quadratic method, indicates 74% reduction in the RMS of the yaw rate tracking error and 19% reduction in the RMS of the control effort. The obtained results imply that the proposed controller can remarkably improve the tracking accuracy with much lower control efforts through estimating the model perturbations. [ABSTRACT FROM AUTHOR]

In this article, the sliding mode control (SMC) of fractional nonlinear systems (FNSs) with disturbances di(t)$$ {d}_i(t) $$ is studied. First, a useful fractional power‐rate inequality DαV(x(t))≤−μVβ(x(t))$$ {D}^{\alpha }V\left(x(t)\right)\le -\mu {V}^{\beta}\left(x(t)\right) $$ for β∈(0,1)$$ \beta \in \left(0,1\right) $$ is extended to a more general form β>0$$ \beta >0 $$. Based on the generalized inequality, the method of a modified fractional integral SMC is completed, in which the parameter of the symbolic function is extended to ς>1/2$$ \varsigma >1/2 $$ and γ>1/2$$ \gamma >1/2 $$. This increases the degree of freedom of the sliding mode surface (SMS). Then, the SMC of FNSs is studied for the cases of known and unknown disturbances. In the case of known disturbance, it is proved by the generalized inequality and quadratic Lyapunov function method that the state of the FNSs can converge asymptotically to zero on the SMS. For the case of unknown disturbance, a fractional disturbance observer is used to estimate the disturbance by introducing auxiliary variables zi(t)=di(t)−δxi(t)$$ {z}_i(t)={d}_i(t)-\delta {x}_i(t) $$. The disturbance estimation error d˜i(t)$$ {\tilde{d}}_i(t) $$ of the proposed FNSs is proved to be bounded. An equivalent global control law is obtained and asymptotic convergence of the FNSs under the action of the controller is proved. Finally, two numerical simulation examples are given to verify the feasibility of the method proposed in this article. [ABSTRACT FROM AUTHOR]

Abstract This study focuses on the highway platoon driving mode and proposes a distributed adaptive control algorithm based on an observer. Firstly, the adaptive observer is designed to compensate for the effect of unknown driving resistance and thus enhance the adaptation ability of the system to uncertainty. Secondly, an auxiliary system is introduced to specifically address actuator saturation constraints, ensuring the stability of the platoon driving in extreme conditions. Lastly, combining an event‐triggered mechanism, a control strategy is designed to achieve the stability of the entire platoon while maximizing the conservation of communication resources. The algorithm's viability and efficiency are confirmed through simulation outcomes.

This paper investigates the attitude tracking control problem for the cruise mode of a dual-system convertible unmanned aerial vehicle (UAV) in the presence of parameter uncertainties, unmodeled uncertainties and wind disturbances. First, a fixed-time disturbance observer (FXDO) based on the bi-limit homogeneity theory is designed to estimate the lumped disturbance of the convertible UAV model. Then, a fixed-time integral sliding mode control (FXISMC) is combined with the FXDO to achieve strong robustness and chattering reduction. Bi-limit homogeneity theory and Lyapunov theory are applied to provide detailed proof of the fixed-time stability. Finally, numerical simulation experimental results verify the robustness of the proposed algorithm to model parameter uncertainties and wind disturbances. In addition, the proposed algorithm is deployed in a open-source UAV autopilot and its effectiveness is further demonstrated by hardware-in-the-loop experimental results.

Abstract For a class of chain non‐holonomic systems with external disturbance and function constraints, the tan‐type barrier Lyapunov function is used to solve the constraints of the system, and then the non‐linear disturbance observer is used to deal with the disturbance so that the disturbance error eventually converges exponentially. The control strategy designed by the backstepping method can effectively ensure that signals are bounded without violating the respective constraints. Through the simulation design of a three‐stage wheeled mobile robot, the effectiveness of the control scheme is verified again by the results.

Summary: This paper addresses the problem of fixed‐time (F‐T) control for unmanned aerial vehicle (UAV) formation under unknown input disturbances to achieve moving target tracking. First, a kinematic model with uncertainties is employed to analyze the transient response of the UAV formation accurately. Next, based on a fast F‐T lemma, an F‐T disturbance observer is constructed to estimate the unknown disturbances. Subsequently, based on the designed observer and fast F‐T lemma, a distributed F‐T guidance law that controls multi‐UAV to track a moving target in a desired formation is introduced. Then, through rigorous mathematical proof, it is established that the control strategy enables the formation system to achieve F‐T stability, and the convergence time is independent of the system's initial states. Finally, the validity of the proposed control method is demonstrated through numerical simulation and presented in a realistic visual simulation scenario created using Unreal Engine 4 (UE4). [ABSTRACT FROM AUTHOR]

This study focuses on the highway platoon driving mode and proposes a distributed adaptive control algorithm based on an observer. Firstly, the adaptive observer is designed to compensate for the effect of unknown driving resistance and thus enhance the adaptation ability of the system to uncertainty. Secondly, an auxiliary system is introduced to specifically address actuator saturation constraints, ensuring the stability of the platoon driving in extreme conditions. Lastly, combining an event‐triggered mechanism, a control strategy is designed to achieve the stability of the entire platoon while maximizing the conservation of communication resources. The algorithm's viability and efficiency are confirmed through simulation outcomes. [ABSTRACT FROM AUTHOR]

This article primarily focuses on the finite‐time fault‐tolerant tracking control problem of quadrotor unmanned aerial vehicle (UAV) systems. Our main innovation points are: (1) A simple cubic form of Lyapunov function is applied to the design of the position ring controller of the quadrotor UAV; (2) The command filtering technology effectively solves the challenge of derivation of complex coupling matrixs in the controller design process; (3) An improved disturbance observer and a variable threshold event‐triggered mechanism are applied in the Quadrotor UAV system. In summary, the overall approach combines the backstepping method and finite‐time Lyapunov stability to prove the finite‐time stability of all the signals in the system. Finally, the effectiveness and rationality of the algorithm are verified through simulation experiments and its application on an actual simulation platform. [ABSTRACT FROM AUTHOR]

In this paper, a disturbance observer‐based adaptive neural backstepping integral sliding mode control (BISMC) is developed for a flexible joint robot (FJR) with the integration of an adjustable stiffness rotary actuator (ASRA). This system suffers from unknown system dynamics, external disturbance, and the influence of variable stiffness, which is a challenge for achieving precision tracking performance. Considering the lumped disturbances in FJR generated by the hydraulic system and the stiffness modulation of the ASRA, we investigate the structural dynamics nonlinear model of the FJR system, including hydraulic actuator dynamics. While other linear control strategies are applied for the FJR, the proposed controller uses BISMC, neural networks (NN), and nonlinear disturbance observers to deal with the disadvantages mentioned above. Radial basis function neural networks (RBFNN) are designed to tackle unknown nonlinear functions, and the disturbance observers are introduced to compensate for the influence of the variable stiffness, disturbance, and the approximation error caused by NN. Simulations and experiments are independently implemented to demonstrate the effectiveness and feasibility of the proposed controller. Results exhibit that the integral absolute error‐index is reduced by 20.4% when the proposed method is deployed for the experiment with a multistep trajectory. [ABSTRACT FROM AUTHOR]

To eliminate the influence of unknown disturbance and uncertainty on vehicle longitudinal control, the layered vehicle longitudinal control system based on disturbance observer and terminal sliding mode control was designed. The disturbance observer was used to observe the system disturbance in real time and realize the feedback compensation of system for reducing the switching gain of sliding mode control and suppressing the chattering problem of sliding mode control. The stability of the control system was proved by Lyapunov function, and the joint simulation experiments were conducted by Carsim/ Simulink. The results show that under the two simulation conditions, the controller has good tracking effect on the reference speed, and the maximum speed error is only 0.22 m/s. The disturbance observer can accurately and quickly estimate the system disturbance with the estimation error of only 0.003 14, and the switching logic actuator performs well. Compared with the traditional sliding mode control, the designed controller has better stability with decreased chattering problem of sliding mode control, and the stable tracking of vehicle longitudinal speed is realized. [ABSTRACT FROM AUTHOR]

Accurate sensing and control are important for high-performance formation control of spacecraft systems. This paper presents a strategy of disturbance estimation and distributed predefined-time control for the formation of multi-spacecraft systems with uncertainties based on a disturbance observer. The process begins by formulating a kinematics model for the relative motion of spacecraft, with the formation's communication topology represented by a directed graph for the formation system of the spacecraft. A disturbance observer is then developed to estimate the disturbances, and the estimation errors can be convergent in fixed time. Following this, a disturbance-estimation-based sliding mode control is proposed to guarantee the predefined-time convergence of the multi-spacecraft formation system, regardless of initial conditions. It allows each spacecraft to reach its desired position within a set time frame. The results of the analysis of the multi-spacecraft formation system are also provided. Finally, an example simulation of a five-spacecraft formation flying system is provided to demonstrate the presented formation control method. [ABSTRACT FROM AUTHOR]

Summary: This article delves into the adaptive heading tracking control of unmanned surface vehicle (USV) by incorporating an event‐triggered mechanism and signal quantization. The primary objective is to save communication resources while alleviating the burden of signal transmission. To address time‐varying external perturbations inherent in the control system, a disturbance observer is employed for precise estimation. Additionally, a linear model is introduced to delineate the procedure of quantization. By furnishing the controller with purpose‐designed quantized control input, the adaptive tracking control system can effectively track desired input without requiring any prior knowledge of the quantized parameters. The article substantiates its claims by demonstrating the system's stability in the absence of quantization considerations and the bounded nature of quantization errors through a series of presented lemmas. Further, the stability of the USV heading control system, integrated with an event‐triggered mechanism and signal quantization, is proofed in accordance with Lyapunov stability theory. Finally, the proposed strategy's efficacy and practical applicability are validated through experimental simulations. [ABSTRACT FROM AUTHOR]

This paper addresses the vibration reduction and disturbance attenuation problems of a flexible arm, which is modelled as a fourth-order partial differential equation. The main control objectives lie in reducing the influence of the disturbance, steering the flexible arm to the desired angular position and suppressing the vibration, simultaneously. To achieve the objectives, firstly, two different disturbance observers are designed. Secondly, we construct boundary controllers based on the two designed disturbance observers and boundary measurable signals. Then, with the two disturbance observers, the boundary disturbance compensation is achieved, and with the designed boundary controllers, the uniform boundedness of the flexible arm is guaranteed. Moreover, the well-posedness of the closed-loop system under the designed boundary controllers is discussed by means of the operator semigroup theory. Finally, the effectiveness and advantages of the proposed controllers are demonstrated through simulations and physical experiments. [ABSTRACT FROM AUTHOR]

In this paper, the secure communication of the electroencephalogram (EEG) signal is presented via the wireless protocol. To obtain the goal of secure communication, a new stability condition for providing a new disturbance observer (DO) to estimate the attacked signals of the secure communication system is proposed. Herein, the fractional-order calculus was used to obtain the goal of the stability design. To meet the goal of the construction of the master and slave, the fractional-order chaotic system was used. First, the Takagi-Sugeno fuzzy was used to remodel the master and slave systems with support of the Grunwald–Letnikov approximation technique from continuous time to discrete time domain. Second, the DO was equipped to the slave system to reject the unwanted on both public channels and uncertain values on the master and slave sides. Third, the sliding mode control was designed based on the given stability theorem. Fourth, the stability was provided based on Lyapunov condition. Final, the simulation by using MATLAB software and experiment by using the ESP8266 chips with the wireless communication were provided to show the effectiveness of the proposed theories. [ABSTRACT FROM AUTHOR]

Reconfigurable variable stiffness actuator (RVSA) has attracted increasing attention in robotics due to its safety, compliance, and robustness. However, the control of the RVSA is challenging due to nonlinear factors such as high-order nonlinear dynamic, model uncertainties, time-varying model parameters, and disturbances. In this paper, firstly, a lightweight RVSA structure with both passive and active nonlinear variable stiffness characteristic is developed. Secondly, a dynamic surface backstepping control method based on a radial basis neural network and disturbance observer (DSBC-RBFNN-DOB) is proposed to achieve position control of the lightweight RVSA with matched and unmatched uncertainties. To address solve the "complexity explosion" and noise problems in traditional backstepping control, the dynamic surface backstepping control (DSBC) method is used to design the controller. Then, a method based on radial basis neural network (RBFNN) and disturbance observer (DOB) are used to compensate for the matched and unmatched uncertainties in the link and motor. In this method, the matched uncertainties are compensated using RBFNN, and the DOB is integrated to compensate RBFNN approximation errors and unmatched uncertainties. Through Lyapunov stability analysis, the semi-global boundedness of the controller is proven. Finally, the proposed method is simulated and actually implemented, verifying the effectiveness of the method. Simulation and experimental results show that the root mean square error (RMSE) of the proposed method is only 0.97277° and 0.6418°, respectively. Compared with PID, DSBC, and DSBC-RBFNN, the error reduction percentages in simulation (experiment) are 85.6 % (88.9 %), 49.4 % (88.4 %) and 36.1 % (80.0 %) respectively. • A lightweight reconfigurable variable stiffness actuator with smaller mass and more compact structure is proposed.. • A dynamic surface backstepping control method based on neural network and disturbance observer is proposed. • A method of uncertainty and disturbance estimation combining neural network and disturbance observer is proposed. • Experiments and simulations were conducted under the condition of actively changing stiffness. [ABSTRACT FROM AUTHOR]

This paper presents a disturbance observer‐based controller for a class of multi‐actuator systems that possess passivity properties. By distributing the input and aggregating the output using the same vectors, the original plant is transformed into an aggregation‐and‐distribution plant (ADP), which is also passive. Based on the ADP, this paper derives the conditions for the controller to sufficiently ensure that the overall system has a finite L2‐gain. The conditions can be checked via the passivity notation of several transfer functions. It is not required to establish the overall system's dynamical equation, thereby alleviating the design burden. The additional objective can be attained by performing an optimization on the aggregation/distribution vectors. Several practical applications are introduced as motivating examples, and the effectiveness of the proposed method is demonstrated by the integration of motion control and energy management for electric vehicles. [ABSTRACT FROM AUTHOR]

This paper explores the problem of relative attitude stabilization between a noncooperative target interest surface (NCTIS) and a bandwidth‐restricted spacecraft subjected to parameter uncertainties, exogenous disturbance, actuator faults, and input saturation. The proposed angular velocity estimator provides the rotational angular velocity of NCTIS. The proposed control scheme uses a dynamic surface control framework with the finite time disturbance observer to attenuate multi‐source disturbances, and it deals with the restricted communication resources by employing a dynamic event‐triggered mechanism. The presented scheme relaxes the prior upper bound of total disturbance and improves the traditional event‐triggered technique. Stability analysis shows the ultimate uniform boundedness of the closed‐loop system's state trajectory. In addition, the Zeno‐free behavior can be guaranteed in the design. Comparing numerical simulation results with advanced techniques shows the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]