Proposed Disturbance Observer Research Articles

Robust exponential arbitrary time control of nonlinear systems with input delay

In this study, we aim to present an exponential arbitrary-time control scheme for nonlinear systems subjected to input time delay and additive disturbances. To this end, a new finite-time controller was developed for certain nonlinear systems, which ensures exponential tracking in a time independent of initial conditions. Due to the presence of unknown disturbances, predictors cannot be directly used to control the system, being a challenging issue. Therefore, to utilize predictor feedback in disturbed nonlinear input delay systems, a disturbance observer was designed. The proposed disturbance observer guarantees the exponential arbitrary time estimation of unknown disturbances. Next, an adaptive exponential arbitrary time controller was designed for the system using the proposed disturbance observer. In addition, the Lyapunov theorem was utilized to prove the disturbance observer and tracking errors converged to the origin in an arbitrary time. In the end, the state tracking error was analyzed accurately. It was ensured that the upper bound of the tracking error was bounded and converged to zero in the adjusted arbitrary time. Ultimately, the main results of this study will be illustrated and validated by simulation and experimental results.

STA-based design of an adaptive disturbance observer for autonomous underwater vehicles: From concept to real-time validation

In this paper, we propose to improve the robustness of the well-known PD controller through an adaptable disturbance observer. The proposed disturbance observer is based on the Super-Twisting Algorithm, and is designed with adaptive gains. The stability analysis of the resulting closed-loop controller/observer is achieved using Lyapunov arguments. Real-time experiments in different operating conditions are conducted to demonstrate the effectiveness and robustness of the proposed methodology, compared to the nominal PD control.

An environmental disturbance observer framework for autonomous surface vessels

This paper proposes a robust disturbance observer framework for maritime autonomous surface vessels considering model and measurement uncertainties. The core contribution lies in a nonlinear disturbance observer, reconstructing the forces on a vessel impacted by the environment. For this purpose, mappings are found leading to synchronized global exponentially stable error dynamics. With the stability theory of Lyapunov, it is proven that the error converges exponentially into a ball, even if the disturbances are highly dynamic. Since measurements are affected by noise and physical models can be erroneous, an unscented Kalman filter (UKF) is used to generate more reliable state estimations. In addition, a noise estimator is introduced, which approximates the noise strength. Depending on the severity of the measurement noise, the observed disturbances are filtered through a cascaded structure consisting of a weighted moving average (WMA) filter, a UKF, and the proposed disturbance observer. To investigate the capability of this observer framework, the environmental disturbances are simulated dynamically under consideration of different model and measurement uncertainties. It can be seen that the observer framework can approximate dynamical forces on a vessel impacted by the environment despite using a low measurement sampling rate, an erroneous model, and noisy measurements.

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

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

Observer-based robust impact angle control three-dimensional guidance laws with autopilot lag

Considering an air-based missile intercepting maneuvering target with desired impact angles, robust guidance laws with autopilot lag in three-dimensional coupling space are presented in this paper. First, combining the fixed-time stability theory and adaptive sliding mode control technique, a novel dual-layer adaptive fixed-time sliding mode disturbance observer is proposed to estimate the unknown target maneuver. The proposed disturbance observer releases the requirement of information on either the target maneuver or its derivative. To achieve interception with the desired impact angles, a novel guidance law based on the nonsingular terminal sliding mode (NTSM) with an exponent coefficient is provided. The proposed control framework prevents singular problems and ensures the fixed-time stability of the guidance system. In addition, autopilot dynamics are taken into consideration, and the dynamics surface control (DSC) method is used to address the nonlinear static feedback system. Meanwhile, the improved fixed-time differentiator is used to acquire the derivative of virtual control laws. This prevents the inherent “differential explosion” of the backstepping technique. The uniform boundedness of the closed-loop system is demonstrated via the Lyapunov method. Finally, numerous numerical simulations are carried out, and the simulation results verify the effectiveness of the proposed guidance laws.

Appointed‐time nonsingular sliding mode control of spacecraft attitude stabilization

AbstractThis paper investigates the appointed‐time attitude stabilization problem of a rigid spacecraft under disturbance and parametric uncertainty. A continuous appointed‐time sliding mode disturbance observer is presented to observe the synthetical disturbance term. To circumvent the singularity problem in terminal sliding mode control, a new nonsingular appointed‐time sliding mode surface is designed by employing the concept of switching control. Based on the observation information deriving from the proposed disturbance observer, an observer‐based nonsingular sliding mode control scheme is developed to stabilize the attitude control system within appointed time which is given by the user. And also, the undesired control chattering phenomenon can be attenuated. The appointed‐time stability of the controlled attitude system is proved by the Lyapunov criteria. The simulation results show that the proposed attitude stabilization control scheme is valid.

Effective Position Error Compensation in Sensorless Control Based on Unified Model of SPMSM and IPMSM

Sliding mode observer (SMO) has attracted extensive attention in the field of medium- and high-speed sensorless control of permanent magnet synchronous (PMSM) because of its strong robustness and stability. However, the traditional methods are vulnerable to dc bias caused by measurement errors and parameter changes. Therefore, an improved SMO algorithm by disturbance observer compensation is proposed in this article. The algorithm unifies the mathematical models of surface PMSM and interior PMSM. Besides, a band-pass filter (BPF) is used to replace the traditional low-pass filter, so it can effectively suppress dc bias and high-frequency noise. In addition, at any BPF center frequency, the proposed disturbance observer with LPF characteristics can perfectly compensate the position error caused by the digital filter in real time. Moreover, through sensitivity analysis, the influence of model uncertainty on the observation position is studied, and an adaptive extended state observer is added to mitigate the influence of parameter mismatch on the performance, and hence improving the estimation accuracy. Finally, a triple redundant permanent magnet assisted synchronous reluctance motor is taken as an example to verify the feasibility and effectiveness of the proposed observer.

Anti-Disturbance Boundary Control for a Wave Equation With Input Disturbance

In this article, we investigate the exponential stabilization issue of a wave equation with the external input disturbance, which is described by a nonlinear exogenous system. A novel disturbance observer is constructed to estimate the unknown input disturbance. Then, based on the proposed disturbance observer, a boundary control strategy is developed to cancel the effect of disturbance and stabilize the system. The exponential stability is proven by employing the Lyapunov’s direct method. This method can be extended to a class of flexible systems described by the hyperbolic partial differential equation met in the practical engineer area. The example of a nonuniform flexible string system is given, where the effectiveness of the proposed strategy is evaluated based on simulations.

Composite anti-unwinding attitude control of spacecraft under actuator saturation and angular velocity limits

Spacecraft attitude control employs quaternion representation to avoid singularity issues and obtain global maneuver stability. However, it has redundancy associated, resulting in dual equilibrium points. The attitude control may confront the unwinding phenomenon due to the presence of the equilibria. In this paper, an anti-unwinding controller for spacecraft stabilization in the presence of external disturbances and inertial uncertainties, angular velocity limit, actuator saturation and faults is presented. Specifically, a modified extended state observer (ESO) is designed to obtain total disturbance estimates of the rigid-body spacecraft. Auxiliary parameters are added in the design to avoid initial high estimates in the proposed ESO design resulting in faster convergence. The proposed disturbance observer is to release the assumption that requires the estimated disturbance to be constant or varying at slow rates. Using the ESO estimates, a particular back-stepping-SMC (ESO-BTSMC) controller is devised to formulate anti-unwinding control law for spacecraft stabilization. Lyapunov stability theory is employed to prove closed-loop stability of system and estimation error convergence. Comparative simulations are performed to demonstrate the performance of the proposed control scheme. It is found that the proposed control scheme gives smooth and precise control performance along with faster transient response. Additionally, it also alleviates the chattering phenomenon.

Online temperature distribution estimation of lithium-ion battery considering non-uniform heat generation characteristics under boundary cooling

Lithium-ion batteries (LIBs) generate a lot of heat in the course of use, which will lead to a highly uneven distribution of the temperature, thus affecting the accuracy of battery modeling, parameter estimation and thermal management. In order to solve this potential threat, an on-line temperature distribution estimation method of LIB considering non-uniform heat generation under boundary cooling is proposed in this paper. Firstly, a thermal model of tab area is constructed by using lumped parameter method based on the analysis of the heat generation and heat transfer mechanism, and this tab thermal model is regarded as the first kind of boundary condition of the cell core. Secondly, a difference equation of the temperature distribution of the core area is constructed by using the heat balance method, and the boundary conditions and convection coefficient model are also deduced. Finally, a disturbance observer is designed to estimate the state and disturbance simultaneously to further improve the accuracy of temperature estimation. Additional stability analysis shows the convergence of the proposed disturbance observer. Experiments and verification demonstrate that the proposed method is effective and has better estimation performance compared with the other traditional methods under four different cycles, and the estimation error is less than 1.5 °C.

Disturbance-observer-based fixed-time control for 6-DOF spacecraft rendezvous and docking operations under full-state constraints

The problem of fixed-time control is addressed for the autonomous proximity of non-cooperative targets with full-state constraints, input saturation, parameter uncertainties, and matched and unmatched disturbances. A six degrees of freedom (6-DOF) relative motion model for non-cooperative targets is constructed. Combining with a radial basis function neural network (RBF-NN), a fixed-time disturbance observer is proposed to estimate system disturbances. Model items and assumptions for the boundedness of the derivatives of the disturbances are not required in the proposed disturbance observer. The back-stepping technique provides an adaptive fixed-time controller to stabilize the full-state constrained relative error system and a unified framework for dealing with constrained and unconstrained cases is proposed by designing a coordinate transformation method. The fixed-time stability of the relative error system is guaranteed by the proposed controller regardless of the constraints. Finally, two simulation scenarios validate the effectiveness and robustness of the developed controller design.

Event‐driven fault‐tolerant attitude control of spacecraft with finite‐time disturbance observer under input saturation

AbstractThis paper investigates the attitude stabilization problem for a bandwidth‐constrained spacecraft subjected to model uncertainty, external disturbances, actuator faults, and saturated input. The proposed attitude controller is developed by combining the disturbance observer with an event‐trigger technique to provide disturbance attenuation meanwhile respecting the constraint on the wireless control network. The proposed disturbance observer estimates the lumped disturbance within a finite time, and its output is then fed to the composite control law. The presented control scheme relaxes the use of a priori upper bound knowledge of disturbance and resolves the unwinding problem in the quaternion‐based attitude representation. The closed‐loop stability analysis under the proposed algorithm shows the uniformly ultimately bounded convergence of state trajectories. Moreover, the designed event trigger approach avoids the Zeno behavior. The numerical simulation with comparative analysis illustrates the efficacy of the proposed controller in terms of convergence time, steady‐state bound, rate of control update, and energy consumption.

State Space LS-SVM as a Disturbance Observer in Sliding Mode Control of a Quadrotor UAV

This paper proposes the approach of employing state space least squares support vector machine (SS LS-SVM) as a disturbance observer in the sliding mode control of a quadrotor. SS LS-SVM, which was recently introduced by the authors, is adopted for the disturbance estimation task in this study. A quadrotor type unmanned aerial vehicle is considered as the system of interest to apply and assess the performance of SS LS-SVM as a disturbance observer. Quadrotor continuous time mathematical model is taken into account in a standard integrator based on Euler discritization. Both parametric uncertainties and external disturbances are lumped in a disturbance term and added to the nominal model. That term is approximated by SS LS-SVM in an output error prediction context by minimizing the state estimation error via gradient descent as the training method. The proposed disturbance observer works in collaboration with a standard nonlinear observer. It is only necessary for estimating the system states using the measured system output while SS LS-SVM performs the estimation of disturbance. SS LS-SVM enables placement of a native LS-SVM directly in a state equation. Simulation results indicates the significant performance of closed loop disturbance estimation by the SS LS-SVM disturbance observer and based on that, robustness of the employed control method is empowered.

Variable gain based composite trajectory tracking control for 4-wheel skid-steering mobile robots with unknown disturbances

This paper investigates the trajectory tracking problem for 4-wheel skid-steering mobile robots (SSMRs) with unknown disturbances. A novel variable gain based composite disturbance rejection control approach is proposed. By designing a variable gain disturbance observer, the unknown uncertainty and external disturbance are estimated. Then, a novel time-varying sliding surface and nonsingular terminal sliding mode controller (NTSMC) are proposed, and the estimation of disturbance is incorporated in the controller to achieve the active disturbance rejection. It is shown that, with the proposed disturbance observer and controller, the tracking error is guaranteed to converge within a predefined time. Moreover, the control allocation for motors is also considered, which can allocate the virtual driving force to obtain the motor driving torque commands for the four wheels. Finally, the stability and the tracking performance of the proposed control scheme are verified respectively by theoretical analysis and comparative experiments.

Disturbance observer-based control with adaptive neural network for unknown nonlinear system

This paper presents an adaptive neural network controller based on a disturbance observer to compensate the disturbance caused by neural network approximation for a class of unknown nonlinear systems. The proposed adaptive neural network control with an updated parameters mechanism is not subject to the restriction of compact set assumption for satisfying the universal approximation property. The neural network approximation error can be compensated online through the proposed disturbance observer. The proposed method eliminates the need to obtain an exact system model before applying the ideal controller. The effectiveness of the proposed method is validated by numerical simulations.

Consensus Cooperative Encirclement Interception Guidance Law for Multiple Vehicles against Maneuvering Target

This paper studies a cooperative encirclement interception guidance law against a maneuvering target that utilizes a leader–follower control scheme. The control design is decoupled into two parts. In the line-of-sight (LOS) direction, a fixed-time distributed disturbance observer is presented to estimate the maneuvering of the target. Based on the proposed disturbance observer, the guidance law is designed for the followers to guarantee that each follower’s total flight time achieves consensus with that of the leader. In the normal direction of the LOS, the control command is designed to realize the encirclement interception with a predefined-time consensus protocol. The convergence of the guidance algorithm is proven by the Lyapunov stability theory. Numerical simulations are provided to demonstrate the effectiveness and superiority of the proposed cooperative-guidance law.

Output feedback sliding mode control based on adaptive sliding mode disturbance observer

In this paper, an adaptive sliding mode disturbance observer is designed to counteract the disturbance actively. By designing the adaptive laws, the assumptions on the disturbance are relaxed in the proposed observer, its first derivative upper bound is considered to be unknown. Based on the proposed disturbance observer, an output feedback sliding mode controller is constructed for the continuous-time linear systems with unknown external disturbance. The proposed controller incorporates only the system output information and has less chattering of the control input. The feasibility of the proposed strategy is shown by numerical simulations.

Time-varying disturbance observer based on sliding-mode observer and double phases fixed-time sliding mode control for a T-S fuzzy micro-electro-mechanical system gyroscope

This paper proposes a new disturbance observer concept based on the information of the estimated and measured signals for a micro-electro-mechanical system. First, the sliding-mode observer based on the linear matrix inequality was designed to estimate the states of a micro-electro-mechanical system gyroscope. Second, a new disturbance observer was proposed for estimating perturbations of the T-S fuzzy micro-electro-mechanical system gyroscope. Third, the double phase’s fixed-time sliding-mode control was designed to control the positions and velocities of the MEMS system. The proposed disturbance observer input signals were taken into account from the measured and estimated signals. Two cases of high magnitudes and high frequencies disturbances were used to test the power of the proposed disturbance observer. Fourth, the Lyapunov condition was used to verify the corrections of the proposed controller and observer. Finally, the simulation by using MATLAB software was used to show the power of the proposed methods. The achievements of the small reaching-time, small tracking error, and stable steady-states under the vibration form outside of the system.

Cooperative Platoon Control for Uncertain Networked Aerial Vehicles With Predefined-Time Convergence

In this paper, the predefined-time cooperative platoon control problem with constrained communication range for uncertain networked aerial vehicles is considered. The uncertain networked aerial vehicles are subjected to external disturbance and parameter uncertainties. A novel adaptive sliding mode disturbance observer is first designed for single uncertain networked aerial vehicle with an RBFNN estimator to guarantee the control performance. By embedding a dynamic control gain associated with the predefined convergence time, the proposed disturbance observer is proved to be uniformly ultimate boundedness (UUB) stable by the time transformation approach. Then the dynamic gain technology is combined with the prescribed performance control to design the platoon controllers for uncertain networked aerial vehicles. With the proposed disturbance observer and the distribute controller, the platoon can be achieved within the predefined time. The proposed approach can simultaneously guarantee the system stabile without any initial conditions and system parameters. Finally, some simulation experiments are given to verify the effectiveness of the proposed protocols.

Rolling-optimized model predictive vibration controller for offshore platforms subjected to random waves and winds under uncertain sensing delay

In this paper, we investigate the vibration control problem in an offshore platform control structure. A model predictive controller is designed under internal model principle (IMP) and model predictive control (MPC) on the basis of linear quadratic optimal theory, where a rolling-optimized observer is taken to observe and estimate mixed external disturbance. Firstly, a steel jacket offshore platform is modelled as a single-degree-of-freedom (SDOF) vibration system subjected to varying waves and winds containing sensing delay. And the process of finding a vibration suppression controller is summarized as a global optimization problem. Secondly, an optimal quadratic regulator is proposed to attenuate the structure vibration, which naturally adopts IMP considering the varying dynamics of marine disturbance. Data-driven MPC method is then adopted to deal with leading disturbance items. Thirdly, a rolling-horizon optimal algorithm is applied to the proposed disturbance observer so that desired predictive states in deriving the optimal control law are obtained regardless of disturbance sensing delay. Lyapunov stability of the proposed control strategy is proved and comparable simulation experiments are conducted with other controllers.