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In this paper, we study the problem of attitude trajectory tracking of rigid bodies subject to external disturbances. The attitude control problem has been studied in the last decades and novel solutions have been proposed. Nevertheless, most of the proposed controllers only achieve local or almost global asymptotic stability without considering external disturbances. Contrary to other works, we focus on the problem of achieving almost global exponential stability of the attitude tracking errors in the presence of external disturbances using continuous control laws. We propose an attitude trajectory tracking controller based on the exponential coordinates of rotation in combination with a disturbance observer that estimates the exogenous signals. To solve this problem, we adopt a hierarchical approach, where the proposed control law is divided into a kinematic controller (outer control loop) and a velocity tracking controller (inner control loop). To design the disturbance observer, it is assumed that exogenous signals can be generated by a linear exosystem, i.e. the magnitude and phase of the disturbance are unknown. The almost global exponential stability of the closed-loop dynamics' equilibrium point was proved by a strict Lyapunov function. The performance of the proposed approach is assessed by numerical simulations and experimental tests on a low-cost quadrotor. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated skyhook-active disturbance rejection control (ADRC) strategy for vibration reduction of automotive semi-active suspension with MR dampers. Comprehensively considering sprung and unsprung mass, this scheme applies extended state observer to implement switching control of ADRC and skyhook and online estimation and compensation of disturbances such as road excitation, along with the decoupling of sprung and unsprung channels. In addition, the influence of equivalent damping on three vibration characteristic indexes of vehicle acceleration, suspension dynamic deflection, and tire dynamic load is analyzed in the frequency domain, providing a theoretical basis for simulation analysis. Finally, the proposed skyhook-ADRC algorithm was synthetically compared with skyhook and ADRC based on random, convex, and sinusoidal road surfaces, proving its good capability for vibration reduction. [ABSTRACT FROM AUTHOR]

The lateral vibration of the car body affects the lateral stability of high-speed trains (HSTs), and the aim of this study is to design a good control strategy to decrease the lateral vibration of the car body. First, the Maxwell model of the anti-yaw damper was transformed into a Voigt model by the equivalence method, and a modified 17-degree-of-freedom (DOF) lateral vibration model that includes the anti-yaw damper was established. After the design difficulty and control accuracy of the control strategy were weighed, the lateral and yaw motions of the wheelsets were regarded as disturbances, and a disturbance observer of wheelset motions was designed to simplify the 17-DOF model to a 9-DOF lateral vibration model. Second, a model predictive control (MPC) strategy for HST lateral vibration was designed, and the effects of the key parameters on the lateral vibration acceleration of the HST car body and on the iterative computation time of the MPC strategy were studied. In addition, a conditionally triggered model predictive control (CMPC) strategy was proposed. Last, the control effects of the CMPC strategy under the working conditions of speed change, turnout passage, and aerodynamic load were studied by simulation, which verified the validity of the proposed model and control strategy. [ABSTRACT FROM AUTHOR]

The attitude tracking control problem of flexible spacecraft subjected to parameter uncertainties, time-dependent external disturbances, actuator input nonlinearity, and input actuator misalignment is investigated in this paper. Explicitly, the proposed strategy addresses the input actuator misalignment and dead-zone issues that increase the controller design difficulties. Initially, a new second-order sliding mode observer (SoSMO) using an extended state approach is developed by adding a correction function to improve observer performance to estimate unwanted system perturbations. Then, a distinct SoSMO-based integral-type sliding mode control (ISMC) structure is designed in a unified manner to guarantee the asymptotic stability of the closed-loop system. Comparative numerical simulations under input actuator misalignment, the dead-zone nonlinearity, external disturbance, and inertia uncertainty are performed to illustrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

In this study, a new fixed-time sliding mode control approach for trajectory tracking control of robotic manipulator systems is devised, which provides fixed-time convergence, robust stabilization, and high precision. A novel fixed-time non-singular fast terminal sliding mode surface (FNFTSMS) with fixed-time convergence is provided, and with settling time independent of the initial condition of the system and can be pre-determined using design parameters. Furthermore, using adaptive disturbance observer and the suggested FNFTSMS, a new composite robust control approach is developed. The adaptive disturbance observer is intended to boost control performance and compensate for unpredictably occurring disturbances. The Lyapunov stability theory is used to establish the fixed-time stability of sliding surface and system states under the suggested composite control strategy. Finally, numerical simulations are carried out using PUMA560 robot in order to demonstrate the effectiveness and efficacy of the proposed control method in terms of accuracy of tracking, fast response, and convergent speed. [ABSTRACT FROM AUTHOR]

An active disturbance suppression and model predictive control (MPC) strategy is proposed for the quadrotor precision trajectory tracking control problem under disturbance action and model uncertainty. The model predictive controller estimates and compensates the disturbance by the extended state observer (ESO) and disturbance observer (DO) to achieve the position loop accurate control. In the presence of external disturbances and parameter uncertainties, it is demonstrated through simulation experiments that the proposed method improves the robustness to modeling errors and disturbances, while achieving smooth tracking of the reference trajectory. [ABSTRACT FROM AUTHOR]

This article studies an event-triggered fixed-time trajectory tracking control problem of an n-joint manipulator system. Firstly, a fixed-time disturbance observer is proposed to reconstruct the total disturbance composed of external disturbances and model uncertainties, using the estimation as feedforward compensation to enhance the system robustness. Subsequently, based on the backstepping framework, a fixed-time controller with an event-triggering mechanism is designed for the manipulator to ensure the convergence of tracking errors to zero within a fixed time. Additionally, two event-triggering conditions are devised to reduce the transmission time of control input and the computation time of control output. Simultaneously, Zeno behavior is excluded through theoretical proof, validating the fixed-time stability of the closed-loop system. Finally, simulation verification is conducted on a two-joint manipulator, with results confirming the effectiveness of the control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a model predictive control (MPC) approach based on the extended disturbance observer (EDOB) for trajectory tracking of a coaxial octorotor unmanned aerial vehicle (UAV). First, the system dynamic model is derived using Newton–Euler relations in the presence of time‐varying centre of gravity (COG); then, a two‐loop cascade structure is presented to perform the trajectory tracking task. Both loops are controlled using MPC with feedforward compensation based on the EDOB to improve disturbance rejection abilities. When the mass changes, the moment of inertia and COG are affected. The EDOB simultaneously estimates the effects of time‐varying mass, external disturbances, and parametric uncertainties in six degrees of freedom. After obtaining virtual control inputs using designed controllers, constrained control allocation is used to obtain rotors speed in a valid range. The proposed control scheme is evaluated using simulation. The simulation results show the ability of the developed control strategy in accurate trajectory tracking and stable flight in different conditions and being robust to uncertainty and disturbance. [ABSTRACT FROM AUTHOR]

Robot manipulators as an indispensable part of automatic operation are becoming increasingly important in intelligent manufacturing systems, such as grinding and assembly. Although control methods of robot manipulators have been extensively studied, high-precision robots still face new challenges from uncertainties caused by changes in the environment and enhancement of interference. As a consequence, the neural network-based observer is utilized to reduce the influence of uncertainties and external disturbances. In this work, a new kind of nonlinear disturbance observer is designed which could well function with observed states. To improve the control efficiency and response characteristic, a kind of new integral sliding manifold is devised and the control input is generated via backstepping techniques. The stability is proved with Lyapunov theory, and the experimental results are given to demonstrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The non-contact close-proximity formation satellite (NCCPFS) is one of the technical solutions to improve the attitude performance, consisting of a payload module (PM) and a support module (SM). The non-contact Lorentz actuator (NCLA), as the core components of the NCCPFS, directly affect the attitude control performance of the entire satellite. In order to ensure the ultra-high attitude pointing performance and stability of the PM, an in-flight calibration method for the NCLAs based on minimum model error (MME) algorithm and Kalman filtering (KF) with cooperative control strategy is proposed in this article. In this method, the NCLAs generate a periodic nominal torque that causes the attitude of the PM to be periodically deflected. This periodic torque also reacts on the SM, and the SM counteracts this periodic torque through the flywheel to realize the cooperative tracking relative to the PM. Then, the gyroscope data are substituted into the MME algorithm to obtain the angular acceleration of the two modules, and the KF algorithm is adopted to observe the actual output torque of the NCLAs to complete the in-flight calibration of the NCLAs. Numerical simulation results show that the accuracy of the proposed calibration algorithm can reach about 8%, which proves the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances. The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision. Specifically, based on the adaptive backstepping framework, virtual control laws and Lyapunov functions are designed for each subsystem. Three direction interference observers are designed to track the time-varying boundary disturbance. On this basis, the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone. In addition, the stability of the closed-loop system is proven by Lyapunov stability theory. All the system states are bounded, and the vibration offset of the riser converges to a small area of the initial position. Finally, four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper studies leader–follower cooperative control with the slowly-varying environment disturbances of the surface ships, which are mainly caused by wind, wave and current. A disturbance observer is constructed to estimate the slowly-varying environmental disturbances. Based on disturbance observer, the control law of the follower ship is designed by backstepping technique. The disturbance observer-based leader–follower cooperative control scheme is carried out via employing stochastic control theory to analyse the close-loop system. The scheme achieves the follower ship track the leader ship with a certain error range for cooperative movement and all signals are bounded in the mean square. Finally, the results of simulation are listed to verify the scheme. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper is concerned with developing an adaptive method on the basis of a nonlinear disturbance observer (NDO) in order to control a switched nonlinear system in the presence of unknown functions and external disturbances, and under arbitrary switching signals. The proposed approach employs an adaptive backstepping technique, NDO, a fuzzy logic system (FLS), and the particle swarm optimization (PSO) algorithm. Based on a common Lyapunov function (CLF), the adaptive backstepping technique is used to design a nonlinear state-feedback controller. Also, NDO and FLS are stated to estimate the disturbances and the unknown nonlinear functions, respectively. In addition, to improve the performance of the closed-loop system, the PSO algorithm is used to optimize the controller parameters. Finally, simulation examples are taken into account to demonstrate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

To prevent flow maldistribution and imbalanced temperature, a disturbance observer-based control strategy is presented for microchannel cooling systems with multiple heat exchangers. A disturbance observer is designed using the extended Kalman filter for estimating the states and disturbance. The performance of the observer is validated using experimental data from a pumped liquid cycle testbed. Disturbance observer-based control is applied to systems with two and three heat exchangers. The findings demonstrate that the wall temperatures and the temperature differences for the heat exchangers could be maintained at the desired values. When the heat exchangers are subjected to heat loads in the form of square, sinusoidal, and sawtooth functions, the temperature fluctuation could be suppressed by 60%-80% and the temperatures could be maintained at the same values. Our research demonstrates that the proposed control strategy has acceptable accuracy and robustness for the system with multiple heat exchangers undergoing various operating situations. [ABSTRACT FROM AUTHOR]

The problem of robust, angular velocity-free control and fault-tolerant control for liquid-filled flexible spacecraft attitude maneuver subject to unknown external disturbances is investigated. Moreover, state variables measurement uncertainty and actuator failures are explored. The liquid sloshing effect of spacecraft fuel is equivalent to a two-order spring-mass model, and the flexible attachments are equivalent to the Euler–Bernoulli beams. The external disturbance, multiple failures of the output actuator, and the coupled interference caused by liquid sloshing and vibrations of flexible attachments are distinguished as continuous and percussive disturbances. First, a fault-tolerant control method against the percussive disturbances is proposed, and the robustness performance and characteristics of this method are analyzed. Then, both continuous and percussive disturbances are considered to propose a new fault-tolerant control method based on a nonlinear disturbance observer, which is used to estimate the integrated disturbance. The Lyapunov stability theory proves that the proposed control strategy can make the state variables converge to a small neighborhood of the origin in finite time. Finally, the numerical simulation is used to verify the effectiveness and robustness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study a neural network-based fault-tolerant controller to improve the tracking control performance of an unmanned autonomous helicopter with system uncertainty, external disturbances and sensor faults, using the prescribed performance method. Design/methodology/approach: To ensure that the tracking error satisfies the prescribed performance, the authors adopt an error transformation function method. A control scheme based on the neural network and high-order disturbance observer is designed to guarantee the boundedness of the closed-loop system. A simulation is performed to prove the validity of the control scheme. Findings: The developed adaptive fault-tolerant control method makes the system with sensor fault realize tracking control. The error transformation function method can effectively handle the prescribed performance requirements. Sensor fault can be regarded as a type of system uncertainty. The uncertainty can be approximated accurately using neural networks. A high-order disturbance observer can effectively suppress compound disturbances. Originality/value: The tracking performance requirements of unmanned autonomous helicopter system are considered in the design of sensor fault-tolerant control. The inequality constraint that the output tracking error must satisfy is transformed into an unconstrained problem by introducing an error transformation function. The fault state of the velocity sensor is considered as the system uncertainty, and a neural network is used to approach the total uncertainty. Neural network estimation errors and external disturbances are treated as compound disturbances, and a high-order disturbance observer is constructed to compensate for them. [ABSTRACT FROM AUTHOR]

This paper addresses the finite-time control problem of a class of uncertain nonlinear systems subject to input saturation and actuator faults. To approximate the unknown system states, a fuzzy state observer is established where fuzzy logic systems are utilized to estimate the unknown nonlinearities. A nonlinear disturbance observer to estimate the external disturbance of the system. A new finite-time adaptive fuzzy controller is constructed together with the proposed disturbance and state observers, which can guarantee the tracking error into a small neighborhood around zero within finite time. To avoid the tedious and arithmetic problems brought by the traditional backstepping control, the dynamic surface technique is applied, which can effectively reduce the computation burden. It can be proved that not only the boundedness of the closed-loop system states can be guaranteed but also the tracking error is regulated into a small range near the equilibrium in finite time, despite unknown actuator faults and input saturation. Finally, the simulations of two-stage chemical reactor nonlinear system are conducted to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: The direct drive manipulator, which directly links the joint shaft to the motor rotor, is susceptible to external disturbances and model perturbations. When the direct drive manipulator operates with varying payloads, the disturbance observer (DOB) with a constant nominal model struggles to achieve satisfactory performance. To minimize estimation errors caused by disturbance, enhance trajectory tracking accuracy, and improve system robustness, this article proposes a controller parameter self‐tuning strategy with settling time, fused with a nominal model adaptive disturbance observer. Specifically, by optimizing the gain coefficient of the model reference adaptive identification (MRAI), the significant changes in payload at the manipulator's end joint can be quickly and accurately estimated. The inertia introduced by the payload is then employed to continuously update the nominal model of the manipulator, incorporating information about the inertia of the coupling joints. In addition, the controller parameters are updated using a self‐tuning link with settling time, which guarantees that the closed‐loop characteristics of the system remain unaffected by payload changes. Finally, the proposed method was validated using a two‐joint direct drive manipulator. The results demonstrate the robustness of the proposed method in the presence of significant payload changes, and the accuracy of disturbance estimation and the tracking performance of the proposed control strategy is significantly improved. [ABSTRACT FROM AUTHOR]

This paper proposes a novel anti-pitching control algorithm based on algebraic model predictive control (AMPC) for high-speed multihull, in which the heave velocity and pitch angular velocity cannot be measured directly. Specifically, a multihull vertical control model is established with the employed anti-pitching appendages, and the uncertainty of the model as well as the coupling between heave and pitch motion are investigated. To address unmeasurable of the heave velocity and pitch angular velocity, a novel kinematics-based Kalman filter is designed to estimate these states online, which is substantially different from the existing works. Then, the AMPC strategy for varying receding-horizon optimization is proposed, which significantly reduces the amount of online calculation. To estimate the lumped uncertainty, the second-order filter data of input and output is used to design a disturbance observer with less parameters, which can perform feed-forward compensation to enhance the robustness. The convergence of the disturbance observer and the closed-loop system is analyzed mathematically. Finally, the advantages of the proposed anti-pitching control approach are demonstrated in both theory and simulation. • A kinematics based Kalman filter is proposed to reduce the influence of hydrodynamic coefficient uncertainty on signal estimation online. • A varying-horizon AMPC is proposed to simplify the computation of online optimization. • A fixed iterative method is employed to address input saturation constraints. • A disturbance observer with less parameters is presented to estimate the lumped uncertainty based on the second-order low-pass filter. [ABSTRACT FROM AUTHOR]

For the 2–degrees of freedom position tracking problem of the robotized hydraulic-driven roadheader with high nonlinearities and strong uncertainties, a practical disturbance observer–based backstepping sliding cascade control method together with an adaptive compensator is proposed and investigated. The presented methodology mainly includes a continuous nonsingular fast terminal sliding mode with the backstepping technique and the power reaching law with time-varying coefficients used to achieve satisfactory performance against the multi-source disturbances, two disturbance observers used to approximately estimate the unknown dynamics in the mechanical and hydraulic subsystem, respectively. Simultaneously, a continuous robustifying term is also utilized to compensate for the residual disturbances and enhance the robustness. The presented control method doesn't need the precise model thanks to the auxiliary disturbance observer, and can ensure fast convergence and small tracking error thanks to the backstepping sliding cascade control and the adaptive robust compensator. Based on Lyapunov theory, stability of the overall closed-loop system is proved rigorously, and asymptotically bounded tracking performance of the robotic manipulator is guaranteed. Finally, 2–degrees of freedom trajectory tracking experiments are conducted, and comparative results effectively verify the superiorities of the proposed method. [ABSTRACT FROM AUTHOR]

A robust explicit model predictive control (EMPC)-based frequency-adaptive grid voltage sensorless control is developed for a grid-connected inverter (GCI) via a linear matrix inequality (LMI) approach under the model parametric uncertainties as well as distorted and imbalanced grid voltages. In order to ensure the quality of grid currents injected into the utility grid even when the system model parameters vary, the proposed control scheme is accomplished by an enhanced prediction model rather than the conventional prediction model obtained by fixed parameters. Furthermore, an LMI-based observer is integrated with the disturbance observer to improve the reference tracking performance and to reject disturbances. The proposed observer is employed for the grid frequency-adaptive control without the need for grid voltage sensors. The proposed current controller and observer employ the LMI scheme to maintain a stable and robust operation of the GCI. The discrete-time frequency response and pole-zero map analyses are utilized to examine the system performance including the stability and robustness against parametric uncertainties. Comprehensive simulation and experimental tests as well as theoretical analyses clearly validate the robustness of the proposed control scheme under various harsh test conditions with non-ideal and unexpected grid and system parametric uncertainties. [ABSTRACT FROM AUTHOR]

This paper focuses on the adaptive control issue for a class of uncertain nonlinear systems subject to full state constraints and external disturbance. A novel adaptive nonlinear observer is proposed to compensate for disturbance variables in the transformed system. Combining with radial basis function neural networks (RBFNNs) and nonlinear mapping (NM) mechanism, the constrained system is transformed into an unconstrained form and the system uncertainties are effectively handled. Besides that, an adaptive tracking control approach is formulated by invoking backstepping techniques and the event-sampled scheme is utilized to address the sparsity of resources. The adaptive control problem can be addressed with the proposed algorithm, applying the Lyapunov functions, RBF NNs theory, and inequality techniques. Based on the Lyapunov stability theory, it is proved that the system can never violate the specified state constraints and all the closed-loop signals are semiglobally uniformly ultimately bounded (SGUUB). The validity of the proposed approach is well illustrated by a developed numerical example. [ABSTRACT FROM AUTHOR]

Magnetic levitation control technology plays a significant role in maglev trains. Designing a controller for the levitation system is challenging due to the strong nonlinearity, open-loop instability, and the need for fast response and security. In this paper, we propose a Disturbance-Observe-based Tube Model Predictive Levitation Control (DO-TMPLC) scheme combined with a feedback linearization strategy for the levitation system. The proposed strategy incorporates state constraints and control input constraints, i.e., the air gap, the vertical velocity, and the current applied to the coil. A feedback linearization strategy is used to cancel the nonlinearity of the tracking error system. Then, a disturbance observer is implemented to actively compensate for disturbances while a TMPLC controller is employed to alleviate the remaining disturbances. Furthermore, we analyze the recursive feasibility and input-to-state stability of the closed-loop system. The simulation results indicate the efficacy of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents an adaptive neural network (ANN) control scheme based on a disturbance observer that can achieve trajectory tracking control of robotic manipulators under external disturbances and dynamic model uncertainties. Firstly, an ANN controller based on full-state feedback is derived using the backstepping technique to achieve an online approximation of uncertainty. The integral sliding mode surface with a position error is introduced into the controller, which reduces the steady-state error of the system and enhances robustness. Then, a novel disturbance observer is designed to estimate both the approximation errors of the ANN and external disturbances, and to provide compensation for the controller, effectively suppressing the trajectory tracking errors caused by approximation errors and disturbances. Subsequently, the Lyapunov stability theory is utilized to demonstrate the stability of the developed control strategy and the boundedness of all closed-loop signals. Finally, numerical simulations are used to confirm the efficacy of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents a disturbance observer-based sliding mode control strategy of PMSM to address overcurrent and mismatched disturbances. A time-varying disturbance observer is proposed to reduce the influence of mismatched disturbances and estimated peaks. Then, an integral sliding mode control strategy with nonlinear term is designed in permanent magnet synchronous motor control output. Then, the sliding mode surface is constructed by combining the estimates of the mismatched disturbances and the integral sliding mode control. Furthermore, the stability proof of the proposed control strategy is developed. Experimental results are given to validate effectiveness of the proposed control strategy. The proposed control strategy can improve speed control performance under the mismatched disturbances and overcurrent.

Aiming at the accurate speed tracking control of electric vehicles (EV) driven by permanent magnet synchronous motors (PMSM) under external load torque disturbances, this paper proposes an approach for prescribed performance back-stepping control based on a disturbance observer. Firstly, a controller was designed using the back-stepping technique, and a second-order sliding mode differentiator was introduced to approximate the derivative of the virtual control law, which can solve the "differential explosion" problem in traditional back-stepping control techniques. Secondly, in order to reduce the influence of motor load disturbances in the driving process of EV, a novel disturbance observer was proposed, bolstering the anti-interference capability of system. In addition, to achieve the preset high transient and steady-state speed tracking performance, a prescribed performance control strategy was incorporated to guarantee tracking errors within predefined boundaries. Finally, the Lyapunov function was utilized to verify the system stability. The simulation results showed that, compared with traditional PI control, the designed controller significantly increased motor speed tracking precision by more than 5 times, demonstrating a superior speed tracking performance and enhanced anti-interference capability.

This paper proposes an adaptive speed control strategy for DC motors using a DC/DC converter (in buck and boost modes) based on the inverse optimal control (IOC) approach. Our proposal leverages the robust theoretical framework of IOC to derive a control law that ensures the stability and optimal performance of nonlinear dynamical systems through the Lyapunov theory. The control law is designed to minimize a specified cost function, implicitly supporting the optimality of the control strategy. An integral action is incorporated into the IOC approach to enhance performance, ensuring asymptotic stability without affecting convergence properties. The control strategy was implemented on buck and boost converter/DC motor systems. In addition, a disturbance observer technique was utilized for real-time load torque estimation, ensuring precise and efficient control to tackle the challenge posed by unknown and time-varying load torques. Simulations in PLECS and experimental results demonstrate the superiority of the proposed IOC approach compared to conventional cascaded PI control. Our approach reports significantly faster response times and reduced settling times in both buck and boost converter configurations, showcasing its potential for efficient and robust DC motor speed control applications.

Unmanned aerial vehicles (UAVs) are ideal for tasks such as inspections in confined spaces, owing to their maneuverability and independence from terrain constraints, unlike terrestrial robots. However, the aerodynamic effects in confined spaces are greater than that in open areas, because of the propeller-induced flow (PIF). This research addresses this issue as a robust-control challenge and develops a frequency-based robust-control solution. Preliminary experiments reveal that robust control is more suitable than feed-forward control, because of the complex relationships between flight and environmental conditions. To counteract the PIF-based aerodynamic effects in confined spaces, we propose a frequency-based robust controller employing a nonlinear disturbance observer (NDO). The NDO gain design is based on wind-gust frequencies. Comparative experiments, including static and dynamic scenarios, are conducted between the conventional controllers (proportional-integral–derivative and geometric controllers) and proposed robust solution. The results demonstrate improved quadrotor performance compared to that of nonrobust controllers, exhibiting enhanced hovering and navigation within a 0.4 m narrow space under 3 m/s wind when using a Crazyflie. This research provides valuable insights for improved safety and control in confined environments and serves as a guide for developing advanced control strategies and safety protocols for potential real-world applications.

This paper focuses on enhancing lateral motion stability in an independent drive electric vehicle (IDEV) under various uncertainties such as parameter variations, external disturbances, and input time delay. Initially, a new mathematical model for the IDEV is developed, accounting for these uncertainties. Further, a sliding mode predictive control (SMPC) utilizing an adaptive reaching law (ARL) is designed to alleviate the chattering effects, expedite reaching time and mitigate the impact of input time delay. Additionally, two virtual control signals are generated to improve tracking accuracy. An optimal control allocation technique is then introduced to map virtual control signals to actual control inputs. To further enhance control robustness and path-tracking accuracy, disturbance observer and delay estimator are designed to accurately estimate unknown disturbances and input time delay, with feedback incorporated into the SMPC. Simulation and hardware-in-the-loop (HIL) experiments are performed for two specific driving maneuvers and the results demonstrate the effectiveness of the proposed ARL-SMPC design.

With the increasing reliance on unmanned logistics through drone technology, the challenge of efficiently transporting heavy cargo has emerged. The study delves into the complexities of multi-drone cargo transportation, focusing on the stability of transported goods. To address the limitations of single drones in carrying heavy loads, we propose the integration of a disturbance observer-based (DOB) controller to effectively estimate disturbances without intricate calculations or additional sensors and specific knowledge of the cargo’s characteristics, thereby enhancing cargo movement stability. This estimated disturbance is countered by dynamically adjusting the drone’s inclination, reducing the cargo swing angle, and maintaining formation to ensure a balanced weight distribution during transportation. In addition, we investigate the impact of positional accuracy on overall performance and find that a PID controller combined with the DOB controller outperforms both standalone PID control and the combination of PID and formation control relative to the desired reference. Real-world experiments, which have rigorously validated the efficacy of our proposed method, demonstrate its ability to neutralize disturbances and stabilize drones within constrained areas quickly, instilling confidence in its reliability and effectiveness.

This study addresses the control of second-order dynamic systems in the presence of uncertainties and disturbances using an optimized Active Disturbance Rejection Control (ADRC) approach. To achieve practical implementation, a Reduced-Order Generalized Proportional Integral (GPI) observer is introduced to estimate potentially time-varying grouped disturbances within a second-order system The optimized ADRC method is developed by incorporating the information generated by the reduced-order GPI Observer (GPIO) into the output prediction. This approach aims to achieve an optimal tracking performance, particularly in scenarios characterized by disturbances and uncertainties. For numerical validation, simulations were conducted on three distinct second-order system models: a power converter, Direct Current (DC) motor, and nonlinear two-tank system. The simulation results underscore the robustness of the proposed control solution compared to a Proportional Integral Derivative (PID) controller designed using the pole assignment method and a traditional GPI controller. The proposed ADRC approach ensures precise reference tracking even in the presence of disturbances and parametric uncertainty, thereby demonstrating its effectiveness in practical applications.

This paper presents a guaranteed-cost disturbance observer and controller design to achieve accurate path tracking control for a powered paraglider (PPG) in the presence of unknown rudder trim and wind disturbances. The key contribution of this paper is a theoretical approach that ensures given flight control performance even in the presence of these unknown variables. Due to the complex and highly nonlinear nature of PPG dynamics, our approach utilizes a nonlinear control framework based on Takagi-Sugeno fuzzy models. Although this paper designs a nonlinear controller that compensates the rudder input not only with the trim but also with the wind estimated by the disturbance observer, it successfully derives guaranteed-cost design conditions that allow the separate design of the disturbance observer and the nonlinear controller within this framework. In addition, the influence of observer estimation errors on control performance degradation is discussed in terms of considering the upper bound of given control performance. The effectiveness of the proposed approach is demonstrated through extensive flight simulations using a high-precision PPG simulator, which accurately models the real-world flight dynamics of two rigid bodies with seven degrees of freedom. This validates the practical utility of the guaranteed-cost disturbance observer and controller design in maintaining control performance under unknown rudder trim and wind disturbances.

In a bilateral control system, reducing the information-transmission channel between the master and slave systems has advantages, such as suppressing data traffic, reducing stored data, and simplifying the control-system design. The position/force hybrid-control-type bilateral control system can realize stable and highly transparent bilateral control; however, it requires four transmission channels between the master and slave systems to transmit the position and force information. Several types of conventional two-channel controllers are difficult to operate and contact with hard environments. A two-channel controller with a performance equivalent to that of a four-channel controller exists, but it still requires local position control loops. Therefore, this study proposes a force-symmetric type two-channel bilateral control system based on force control systems with robust acceleration controllers using second-order disturbance observers (DOBs) among higher-order DOBs. Bilateral control systems have two control goals: synchronization of the position of the master-slave system, which is a position-related control goal, and artificial realization of the law of action-reaction between the master-slave system, which is a force-related control goal. Methods using low-order DOBs, such as zero- and first-order DOBs, cannot achieve the position-related control goal. In contrast, the proposed method can achieve both the position and force control goals simultaneously, even though it only has force transmission channels and control loops. This study also showed that the performance of the proposed two-channel bilateral control system is equivalent to that of a four-channel bilateral control system that transmits both position and force information. The effectiveness of the proposed method was confirmed through experiments.

Voltage stability is critical in electrical power systems, and automatic voltage regulators play a crucial role in maintaining voltage levels within permissible limits. Due to their simplicity and effectiveness, traditional Proportional-Integral-Derivative (PID) controllers have been widely used in automatic voltage regulation. However, they may not always perform optimally in complex power systems with varying operating conditions and external disturbances. This research introduces an integrated approach of employing a 3-degrees of freedom-PID-Acceleration (3-DOF-PIDA) controller coupled with a disturbance observer-based control strategy. This combination is embedded with a simple but effective salp swarm optimisation algorithm. This novel control approach of the combined 3-DOF-PIDA, disturbance observer and salp swarm optimisation will enhance the voltage regulation of the system. The proposed novel control strategy incorporates an acceleration component to continuously adjust its parameters based on system dynamics. Simultaneously, the disturbance observer is responsible for estimating and compensating for external disturbances, further improving the system’s performance. The salp swarm optimization is applied to optimize both the PIDA control parameters and the disturbance observer’s parameters in the automatic voltage regulation system to find optimal solutions that improve voltage regulation and disturbance rejection capabilities. The results are established by performing statistical and graphical analyses with time-varying step load fluctuations, and under various system parameter variations. The results are validated by comparisons to five popular optimization algorithms found in the reviewed literature. The investigations demonstrate that this new proposed approach provides outstanding performance, in the presence of substantial system parameter fluctuations and uncertainties.

This paper presents a novel Robust Feedback Linearization (RFBL) controller for Quadrotor Unmanned Aerial Vehicle (UAV) when subjected to external disturbances. A Robust Feedback Linearization controller is achieved by augmenting the conventional Feedback Linearization-based control with the Supertwisting Algorithm in the outer loop. To estimate the external disturbances acting on a quadrotor a Nonlinear Harmonic Disturbance Observer (NHDO) is patched with the robust controller. The efficacy and superiority of the results can be seen in terms of tracking error, rise time and robustness to disturbances when comparing it with other three robust controllers i.e. Integral Sliding Mode Controller (ISMC), Terminal Synergetic Controller (TSC) and Finite-Time supertwisting controller. Lyapunov’s stability analysis is performed to prove stability while numerical simulation is carried out using MATLAB/Simulink. The results are also validated by testing the system in a Hardware-In-Loop (HIL) environment on the MicroLabBox dSPACE RTI-1202 platform.

Based on a line-of-sight (LOS) guidance law for a curve parametrized path, a finite-time backstepping control is proposed for the kinematic path-following of an underactuated autonomous surface vehicle (ASV). Finite-time observer is utilized to estimate the unknown external disturbances accurately. The first-order Levant differentiator is introduced into the finite-time filter technique, such that the output of filter can not only approximate the derivative of the virtual control, but also avoid the singularity problem of real heading control. The integral terminal sliding mode is employed to improve the tracking performance and converging rate in the surging velocity control. By virtue of Lyapunov function, all the signals in the closed-loop system can be guaranteed uniformly ultimate boundedness, and accurate path-following task can be fulfilled in finite time. The simulation results and comparative analysis validate the effectiveness and robustness of the proposed control approach.

Abstract This paper presents a leader-follower formation control of multiple mobile robots by position-based method using a fisheye camera. A fisheye camera has a wide field of view and recognizes a wide range of objects. In this paper, the fisheye camera is first modeled on spherical coordinates and then a position estimation technique is proposed by using an AR marker based on the spherical model. This paper furthermore presents a method for estimating the velocity of a leader robot based on a disturbance observer using the obtained position information. The proposed techniques are combined with a formation control based on the virtual structure. In this paper, the formation controller and velocity estimator can be designed independently, and the stability analysis of the total system is performed by using Lyapunov theorem. The effectiveness of the proposed method is demonstrated by simulation and experiments using two real mobile robots.

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.

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.

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.

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.

This article introduces an innovative trajectory tracking control methodology for a marine vessel with disturbances. The vessel is driven to track a predetermined trajectory while preventing the constraint violation of the position error. A universal barrier Lyapunov function (BLF) is, for the first time, established to resolve the variable constraint. It should be emphasized that the devised barrier function can handle constraint types including time-varying, time-invariant, symmetric, and asymmetric forms, and it can be employed to devise control schemes for unconstrained systems. Consequently, in comparison to the current BLF-based techniques for vessels, it can be flexible for dealing with practical control issues with or without constraints. A simplified disturbance observer performs estimations of ocean disturbances. It is proven that all the error variables can be exponentially stabilized to a small neighborhood close to the equilibrium point, while violations of the constraints on the position error never occur. The feasibility of the theoretical discoveries is shown by the outcomes of the final simulation.