Disturbance Observer-based Control Research Articles

Disturbance Observer-Based Terminal Sliding Mode Tracking Control for a Class of Nonlinear SISO Systems with Input Saturation

This paper focuses on the trajectory tracking control for general nonlinear single-input single-output (SISO) systems in which the output is not directly related to the control input. To address the tracking problem with the consideration of possible model uncertainty, external disturbance, and control input saturation, we employ the input-output feedback linearization technique and design a finite-time disturbance observer-based terminal sliding mode controller to improve the tracking performance and enhance the robustness. The stability analysis is carried out by using the Lyapunov method. To alleviate the chattering while achieving an acceptable control performance, a boundary layer method is adopted for the trade-off between the high-frequency control actions and the bounded unavoidable nonzero steady-state error. The proposed method is evaluated on the two typical nonlinear systems, which are fully linearizable and partially linearizable, respectively, and compared to the state-of-the-art method in terms of tracking and robustness through comprehensive numerical simulations. The results show that the proposed method not only renders the estimated disturbance error tends to be zero in finite time, but also has superiority in the fast reaction to disturbance and small tracking error without high-frequency chattering.

Disturbance observer-based fuzzy fault-tolerant control for high-speed trains with multiple disturbances

Abstract The fault-tolerant control problem is investigated for high-speed trains with actuator faults and multiple disturbances in this paper. Based on the novel train model resulting from Takagi and Sugeno fuzzy theory, a sliding-mode fault-tolerant control strategy is proposed. The norm bounded disturbances which are composed of interactive forces among adjacent carriages and basis running resistances are rearranged by the fuzzy linearity technique. The modeled disturbances described as an exogenous system are compensated by a disturbance observer. Moreover, a sliding mode surface is constructed, which can transform the stabilization problem of position and velocity into the stabilization problem of position errors and velocity errors, i.e., the tracking problem of position and velocity. Based on the parallel distributed compensation method and the disturbance observer, the fault-tolerant controller is solved. Lyapunov theory is used to prove the stability of the closed-loop system. The feasibility and effectiveness of the proposed fault-tolerant control strategy are illustrated by simulation results.

Disturbance Observer-Based Boundary Control for an Antistable Stochastic Heat Equation With Unknown Disturbance

In this paper, a novel control strategy namely disturbance observer-based control is first applied to stabilization and disturbance rejection for an anti-stable stochastic heat equation with Neumann boundary actuation and unknown boundary external disturbance generated by an exogenous system. A disturbance observer-based boundary control is designed based on the backstepping approach and estimation/cancellation strategy, where the unknown disturbance is estimated in real time by a disturbance observer and rejected in the closed-loop, while the in-domain multiplicative noise whose intensity is within a known finite interval is attenuated. It is shown that the resulting closed-loop system is exponentially stable in the sense of both mean square and almost surely. A numerical example is demonstrated to validate the effectiveness of the proposed control approach.

Disturbance and Uncertainty Attenuation for Speed Regulation of PMSM Servo System Using Adaptive Optimal Control Strategy

This paper proposes an adaptive optimal control scheme to minimize the effect of disturbances and uncertainties of permanent magnet synchronous motor (PMSM). In the speed regulation loop, an adaptive speed controller is designed, which not only regulates the speed perfectly but also is robust against wide range variation of parameters and external disturbance of PMSM. Unlike the traditional speed controller, the proposed controller includes an adaptive law to compensate the distorted model parameters and disturbances in real-time, enhancing speed performance. The stability of the proposed speed controller is fully proven by using Lyapunov theory. Meanwhile, a PI-type optimal current controller is established in the inner control loop to achieve the current tracking and limitation. By easily selecting appropriate performance indexes, the proposed controller can balance between control input magnitude and current tracking error. Finally, the validity of the proposed control scheme is verified through simulations and experiments. For a comparative study, four different control strategies, that is, the proposed control, super twisting sliding mode control, PI control and disturbance observer-based control, are carried out to demonstrate the superiority of the proposal.

Model Predictive Control for a Voltage Sensorless Grid-Connected Inverter With LCL Filter Using Lumped Disturbance Observer

This paper introduces a disturbance observer-based model predictive control for a voltage sensorless grid-connected inverter (GCI), which minimizes the number of sensor measurements and eliminates the steady-state error by estimating the lumped disturbance in the presence of grid impedance variations. A full-state estimation and lumped disturbance observer are obtained based on the Luenberger observer and gradient steepest descent method, respectively. A cost function, which consists of state error, is used for controller gain design. An optimal full-state observer and controller gains are obtained by solving an optimization problem based on linear matrix inequality. The discrete-time frequency responses analysis of open-loop and closed-loop systems is presented to demonstrate the filter resonance suppression. The robustness of the proposed control against grid impedance variation is analyzed through the pole-zero map approach. Simulations and experiments are conducted for a GCI under the grid impedance variation to demonstrate the theoretical analysis and the efficacy of the proposed control schemes.

Stochastic Anti-Disturbance Flight Control for Helicopter Systems With Switching Disturbances Under Markovian Parameters

In this work, the stochastic anti-disturbance control issue is studied for helicopter systems under multiple random disturbances, in which part disturbances are induced by random noises and others are described by Markovian jump models. Combining the feedback linearization method, backstepping control scheme with nonlinear disturbance observerbased control (NDOBC) technology, a stochastic anti-disturbance flight controller is constructed for full-degree-of-freedom helicopter systems to reject the influence of these disturbances and achieve predefined tracking tasks. Meanwhile, the boundedness in probability of tracking errors is guaranteed via the stochastic Markovian jump control system theory. Finally, an example is given to verify the effectiveness of proposed control methods.

Fault-Tolerant Control of a Variable-Pitch Quadrotor under Actuator Loss of Effectiveness and Wind Perturbations

The actuator fault-tolerant control problem for a variable-pitch quadrotor is addressed under uncertain conditions. Following a model-based approach, the plant nonlinear dynamics are faced with a disturbance observer-based control and a sequential quadratic programming control allocation, where only kinematic data of the onboard inertial measurement unit are required for the fault-tolerant control, i.e., it does not require the measurement of the motor speed nor the current drawn by the actuators. In the case of almost horizontal wind, a single observer handles both faults and the external disturbance. The estimation of the wind is fed forward by the controller, while the actuator fault estimation is exploited in the control allocation layer, which copes with the variable-pitch nonlinear dynamics, thrust saturation, and rate limits. Numerical simulations in the presence of measurement noise show the capability of the scheme to handle multiple actuator faults in a windy environment.

Distributed Disturbance Observer-Based Containment Control of Multi-Agent Systems via an Event-Triggered Approach

This paper studies the containment control problem of linear multi-agent systems (MASs) subject to external disturbances, where the communication graph is a directed graph with the followers being undirected connections. In order to save communication costs and energy consumption, a distributed disturbance observer-based event-triggered controller is employed based on the relative outputs of neighboring followers. Compared with conventional controllers, our observer-based controller utilizes the relative outputs of neighboring followers at the same triggered instant. Furthermore, it is shown that Zeno behavior can be avoided. Finally, the validity of our proposed methodology is demonstrated by a simulation example.

Disturbance observer-based fixed-time control for nonlinear systems with multiple disturbances

The fixed-time control is researched for the nonlinear system subject to multiple disturbances, which contain an external disturbance with unknown frequency and an unknown bounded disturbance. An adaptive nonlinear disturbance observer is devised to estimate the unknown frequency disturbance generated by an exogenous system. On this foundation, a composite fixed-time control scheme is proposed by combining the [Formula: see text] control and the fixed-time theory. It guarantees that the expected control performances of system can be achieved under the existence of multiple disturbances. Eventually, the validity of the control scheme is proved via simulation examples.

Disturbance observer-based fixed-time leader-following consensus control for multiple Euler–Lagrange systems: A non-singular terminal sliding mode scheme

This paper focuses on the fixed-time leader-following consensus problem for multiple Euler–Lagrange (EL) systems via non-singular terminal sliding mode control under a directed graph. Firstly, for each EL system, a local fixed-time disturbance observer is introduced to estimate the compound disturbance (including uncertain parameters and external disturbances) within a fixed time under the assumption that the disturbance is bounded. Next, a distributed fixed-time observer is designed to estimate the leader’s position and velocity, and the consensus problem is transformed into a local tracking problem by introducing such an observer. On the basis of the two types of observers designed, a novel non-singular terminal sliding surface is proposed to guarantee that the tracking errors on the sliding surface converge to zero within a fixed time. Furthermore, the presented control algorithm also ensures the fixed-time reachability of the sliding surface, while avoiding the singularity problem. Finally, the effectiveness of the proposed observers and control protocol is further verified by a numerical simulation.

Fixed-time Disturbance Observer-Based Finite-Time Backstepping Control for Hypersonic Vehicle

Due to the severe flight environment, hypersonic vehicles are susceptible to external disturbances and aerodynamic parameter uncertainties, dramatically challenging the precise control and stable tracking. This paper presented a fixed-time disturbance observer (FTDO) to obtain better tracking performance for hypersonic vehicles. The FTDO can improve the tracking performance under external disturbances and aerodynamic parameter perturbations, whose observation time is bounded and does not depend on the initial errors. The backstepping control can guarantee finite-time convergence with the finite-time control technique. A second-order filter is designed to process the complexity explosion problem in the traditional backstepping control and ensure the tracking system’s finite-time stability. Then with Lyapunov theory, it is proved that the control system is stable and convergent in finite time. Finally, three numerical simulation results based on typical conditions are given to show the effectiveness and advantage of the developed control scheme, and external disturbances can be estimated accurately within two seconds. These results have reference value for flight controller design of hypersonic and other aircraft in complex disturbance environments.

Adaptive Sliding-Mode Disturbance Observer-Based Finite-Time Control for Unmanned Aerial Manipulator With Prescribed Performance.

In this article, an adaptive sliding-mode disturbance observer (ASMDO)-based finite-time control scheme with prescribed performance is proposed for an unmanned aerial manipulator (UAM) under uncertainties and external disturbances. First, to take into account the dynamic characteristics of the UAM, a dynamic model of the UAM with state-dependent uncertainties and external disturbances is introduced. Then, note that a priori bounded uncertainty may impose a priori constraint on the system state before obtaining closed-loop stability. To remove this assumption, an ASMDO with a nested adaptive structure is introduced to effectively estimate and compensate the external disturbances and state-dependent uncertainties in finite time without the information of the upper bound of the uncertainties and disturbances and their derivatives. Furthermore, based on the proposed ASMDO, the finite-time control scheme with the prescribed performance is presented to ensure finite-time convergence and implement the specified transient and steady-state performance. The Lyapunov tools are utilized to analyze the stability of the proposed controller. Finally, the correctness and performance of the proposed controller are illustrated through numerical simulation comparisons and outdoor experimental comparisons.

Active Fault Diagnosis and Control of a Morphing Multirotor Subject to a Stuck Arm

In this paper, we propose a fault tolerant control law for a morphing quadrotor, where the considered morphing ability is that of extendable/telescopic arms. This quite recent class of systems is able to provide a good trade-off between payload capabilities, maneuverability, and space occupancy. However, such degrees of freedom require dedicated servomotors, which in turn implies more possible faults. Thus, the problem of diagnosis for the telescopic servo motors subject to a stuck fault is considered. System symmetries are exploited and used in a residual generator design, which triggers an active fault isolation/identification phase. External disturbances are also taken into account and estimated through a nonlinear disturbance observer. A classical double-loop controller closes the loop, providing an overall control system structure that follows the disturbance observer-based control paradigm. The control scheme is validated through realistic numerical simulations, and the closed-loop performances are analyzed.

Disturbance observer-based fuzzy adaptive optimal finite-time control for nonlinear systems

This paper investigates the issue of disturbance observer-based fuzzy adaptive optimal finite-time control in light of the backstepping approach for strict-feedback nonlinear systems with bias fault term and full state constraints. Considering that external disturbance and bias fault signal can affect the stability of control and control quality, a disturbance observer is constructed to track the external disturbances and bias fault online. A disturbance observer-based finite-time control strategy is proposed to achieve optimized control by utilizing the fuzzy logic system approximation-based adaptive dynamic programming method under the critic-actor framework. The purpose of the critic is to evaluate control performance and the role of the actor is to execute control behaviour. In addition, it is proved that the proposed fuzzy adaptive optimal finite-time scheme not only realizes all signals in closed-loop system are bounded, but also ensures that system states are restricted within specific sets. Finally, simulation results are shown to demonstrate the effectiveness of the proposed control strategy.

Composite anti-disturbance control for ship dynamic positioning systems with thruster faults

Anti-disturbance control problem is studied for ship dynamic positioning systems with model uncertainties and ocean disturbances under thruster faults. For the ocean disturbance, a stochastic disturbance observer (SDO) is established to give the online estimation. For thruster faults, an adaptive law is used to evaluate, which is obtain from Lyapunov function. For model uncertainties, a robust control term with adaptive technology is used to attenuate it. Then, a composite anti-disturbance control (CADC) strategy is raised by combining disturbance observer-based control (DOBC), adaptive technology, and robust control term, which makes the position and yaw angle of ship reach the desired values. Finally, the simulation example proves the validity of the controller.

Design and disturbance rejection control of a piezoelectric nanopositioning stage

The article covers structural design and disturbance rejection control of a flexure-based compliant piezoelectric nanopositioning stage. The stage is devised using four-bar amplification mechanisms, auxiliary guiding mechanisms, and a compound parallelogram mechanism. Static and dynamic models of compliant mechanisms are analyzed based on a compliance matrix method. A modified Prandtl-Ishlinskii (PI) model with dead zone operators is used to describe the asymmetric hysteresis. Then, a global electromechanical dynamic model is built and identified. A comprehensive disturbance rejection controller (CDRC) combining a robust H∞ control and a disturbance observer-based (DOB) control is proposed for high trajectory tracking accuracy and anti-disturbance performance. The trajectory tracking accuracy of the stage can be up to 3 nm in experiments. As amplitudes of reference signals increases, relative tracking errors gradually decrease. System instability and oscillation caused by strong external disturbances are also reduced. Experimental results prove the effectiveness of the developed CDRC.

선형 파라미터 변형 시스템에 대한 이벤트-트리거 외란 관측기 기반 강인 제어

In this paper, an event-triggered disturbance observer-based robust control strategy is proposed for linear parameter-varying systems. In the proposed control strategy, the disturbance observer estimates the plant’s states and external disturbances, and the robust tracking controller uses the estimated values to compensate for the external disturbance. The scenario of the transmission of the estimated values from the disturbance observer through shared networks was considered. An event-triggered observer scheme was proposed to reduce communication resources while ensuring the stability of the closed-loop system. A stability analysis was performed by considering external disturbances. The simulation results demonstrated that the output follows the desired value, compensating for external disturbances.

Performance Analysis of Learning-Based Disturbance Observer for Pulsed Superconducting Cavity Field Control

The use of Disturbance Observer-based (DOB) control is widespread in stabilizing the electromagnetic field in superconducting radio frequency cavities to facilitate beam acceleration in particle accelerators. Repetitive disturbances such as beam loading and Lorentz force cavity detuning are compensated by DOB control, and their suppression is enhanced through the incorporation of a learning scheme into the conventional disturbance observer. This paper evaluated the performance of a learning-based disturbance observer for compensating beam loading and cavity detuning in pulsed superconducting radio frequency cavities and proposes modifications for better field stability. A superconducting cavity baseband model for π-mode was simulated in Matlab/Simulink with a trapezoidal beam pulse as the input disturbance and different cavity detuning values to analyze the controllers’ performance. The simulations were conducted for multiple observer filter bandwidths to evaluate the performance of the learning-based disturbance observer under plant model uncertainties and different detuning values. The results demonstrate that the learning-based disturbance observer yields faster convergence to the reference input and lower tracking errors during the flat top of pulse voltage in comparison to conventional disturbance observer control.

Active control for system with multiple microchannel heat exchangers using disturbance observer

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.

Disturbance observer-based backstepping control for leader–follower ships with disturbances

ABSTRACT 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.