Anti-windup Compensator Research Articles

Prescribed-Time Dynamic Positioning Control for USV with Lumped Disturbances, Thruster Saturation and Prescribed Performance Constraints

This work studies the dynamic positioning (DP) control issue of unmanned surface vessels subjected to thruster saturation, error constraints, and lumped disturbances composed of time-varying marine environmental disturbances and model parameter uncertainties. Combining the disturbance-accurate estimation technique and the prescribed performance control strategy, a novel prescribed-time DP control scheme is established to address this challenging problem. In particular, the prescribed-time lumped disturbance observer is designed to accurately estimate external marine disturbances, which guarantees that the estimation error converges to zero within a prescribed time. Subsequently, a prescribed performance control strategy is proposed to guarantee that the positioning errors of DP surface vessels with thruster saturation constraints meet the error constraints requirements within a prescribed time. Furthermore, an anti-windup compensator is presented to mitigate the thruster saturation and improve the robustness of the DP control system. The stability analysis demonstrates that all positioning errors of the closed-loop system can converge to predefined performance constraints within a prescribed time. Finally, the numerical simulation confirms the efficacy and superiority of the proposed PTDP scheme.

Decoupled robust backstepping tracking control for variable stiffness actuated robot with input saturation

Due to the energy storage and release capability introduced by stiffness adjustment, a variable stiffness actuator is essential to achieve human-like energy efficiency for robots. However, it is not trivial to control the strongly coupled and nonlinear system, especially with highly dynamic stiffness variation. In this work, decoupled and robust command filtered backstepping tracking controllers for position and stiffness are proposed. Furthermore, a disturbance observer is introduced to estimate the lumped disturbances caused by directly decoupled dynamics and unmodeling errors. Since the input control torques can be easily saturated due to limited deformation of elastic elements, anti-windup compensation is introduced into the tracking control laws to reduce its negative influence. Thus, by combining the command filtered backstepping controller, disturbance observers, and anti-windup compensation, the stability proof of the proposed composite controller is provided. The tracking control performance is validated through simulations of multi-DoF variable stiffness actuated robots.

Active disturbance rejection control for spacecraft relative motion in libration point orbits subject to actuator saturation and time-delays

This paper proposes a novel active disturbance rejection control (ADRC) scheme to achieve the spacecraft relative pose synchronization in the libration orbits under the constrations of the actuator saturation and time-delays. The relative kinematics and dynamics between two spacecraft are modeled using dual quaternions to avoid singularity. A set of dimensionless variables is introduced to improve computational accuracy. An extended state observer, consisting of a time-delay predictor and an anti-windup compensator, is designed to address actuator saturation and communication time delays. A composite controller is then proposed, based on the designed observer, to mitigate the impact of total disturbances. Finally, two illustrative numerical simulations, including a spacecraft close rendezvous and docking scenario and a formation flying scenario, are provided to verify the effectiveness of the proposed ADRC scheme.

Stability analysis and anti-windup design of saturated switching systems based on multiple Lyapunov functions

Abstract In this paper, employing advanced multiple Lyapunov functions (MLF) technology, we conduct a thorough investigation into the fault-tolerant characteristics of actuator saturation-based systems, particularly those prone to failures. Based on this comprehensive analysis, we carefully design an anti-windup (AW) controller, incorporating an efficient AW compensator and precisely calibrated gains for the dynamic state feedback controller, tailored to meet the specific needs of practical control systems. To further demonstrate the effectiveness of our approach, we also provide a detailed numerical example.

Static anti-windup compensator based on BMI optimisation for discrete-time systems with directional change in controls avoidance

In the paper, a design method of a static anti-windup compensator for systems with input saturations is proposed. First, an antiwindup controller is presented for system with cut-off saturations, and, secondly, the design problem of the compensator is presented to be a non-convex optimization problem easily solved using bilinear matrix inequalities formulation. This approach guarantees stability of the closedloop system against saturation nonlinearities and optimizes the robust control performance while the saturation is active.

Output-Based Adaptive Event-Triggered Control of Saturated Systems with Dynamic Anti-Windup Compensator

Output-Based Adaptive Event-Triggered Control of Saturated Systems with Dynamic Anti-Windup Compensator

Prescribed performance based adaptive model-free control for highly flexible spacecraft detumbling rotating satellites

The method, using a servicing spacecraft (SS) mounted with very flexible operation devices (FOD), has shown promising application in detumbling rotating satellites due to its unique advantage of compliant contact processes. The SS is highly flexible, and successful implementation of detumbling rotating satellites is dependent on the advanced controller with high performance. However, the controller design suffers from two problems: (i) since the uncertain dynamics arising from the FOD lead to difficulty in acquiring an accurate dynamic model of the SS, the conventional model-based controllers are unable to achieve high performance; (ii) the large deformation of the FOD caused by contact processes generates impactive disturbance that severely deteriorates the transient and steady-state performances. To address these problems, this paper proposes a prescribed performance based adaptive model-free control for the first time. In the controller design process, a finite-time prescribed performance function is designed to incorporate into the model-free controller, which ensures the user-specified error constraints concerning the convergence rate, overshoot, and tracking accuracy. Meanwhile, an adaptive estimation algorithm is developed to significantly enhance the robustness against the disturbance. Moreover, an anti-windup compensator is constructed to effectively handle the adverse effect of thruster saturation. Simulation results validate the effectiveness of the proposed controller, and further show that the SS can successfully detumble the rotating satellite while achieving prescribed performance.

Antiwindup Compensation for Unstable Rigid-Body Systems with Quantized and Saturated Inputs

It is well known that actuator saturation can cause destabilization and degradation in performance; similar problems are encountered when actuation is quantized. This study proposes the design of an antiwindup compensator for systems with actuators that are limited to a finite number of quantization levels. This combination of discrete-level actuation and saturation poses a unique antiwindup problem that has not yet been solved. To surmount this combined issue, an antiwindup compensator is proposed, which provides ultimate boundedness of the system state within a prescribed region and guarantees that the state does not stray outside a larger compact set. The use of shifted ramp functions enables a less conservative bound on the control-signal error, which yields significantly lower L2 gain bounds compared to a standard sector-bound antiwindup design approach. A numerical simulation example illustrates the effectiveness on a rigid-body system, which inspired this study.

Two-stage anti-windup compensation for systems subject to actuator quantization and saturation

This paper proposes a two stage anti-windup compensation scheme for systems subject to both input saturation and input quantization. The paper makes two main contributions: (i) it proposes a new partitioning of the saturation/quantization nonlinearity; and (ii) it formulates and solves a two-stage anti-windup problem on the basis of this partitioned nonlinearity. The anti-windup compensator contains two distinct elements: one to assuage the effects of quantization, the other to do the same when saturation occurs. Theoretical results provide conditions which must be satisfied in order for the two-stage anti-windup compensator to bestow stability on the resulting closed-loop system. These results are expressed as linear matrix inequalities and naturally lead to algorithms for anti-windup design. Simulation examples illustrate the effectiveness of the techniques.

An Anti-Windup Method Based on an LADRC for Miniaturized Inertial Stabilized Platforms on Unmanned Vehicles in Marine Applications

This paper investigates an anticipatory activation anti-windup approach based on Linear Active Disturbance Rejection Control (LADRC) to address the influences of accelerated saturation on the actuators in a Miniaturized Inertial Stabilized Platform (MISP) with extreme external disturbance. The proposed method aims to eliminate the high-frequency vibrations on the Line of Sight (LOS) of electro-optical devices during actuator saturation. To achieve this, the Linear Extended State Observer (LESO) is modified by adding saturation feedback to the total disturbance observed state variable, which is operated as an anticipatory activation anti-windup compensator. The stability of the proposed controller is discussed, and the gains are optimized by the Linear Matrix Inequality (LMI) constraints though quadratic programming and an H-infinite performance indicator. Additionally, as the multiple activated scheme for anti-windup, the effectiveness of immediate activation in dealing with accelerated saturation is compared and analyzed. These comparisons and verification are implemented through simulations, where the external disturbance is introduced using recorded attitude data from USV sailing. Finally, experiments are conducted on an MISP for a visual tracking system, demonstrating that the anticipatory activation mothed effectively suppresses high-frequency vibrations on the LOS during instances of accelerated saturation.

Robust practical prescribed time trajectory tracking of USV with guaranteed performance

In this paper, a practical prescribed time tracking control scheme is proposed to drive the unmanned surface vehicle (USV) under input saturation and unknown disturbances to track the desired trajectory with guaranteed transient and steady-state performances. First, by employing the logarithmic type barrier Lyapunov function and prescribed time function, the virtual velocity law is designed at the kinematic level. Then, to deal with the unknown disturbances, a prescribed time observer is constructed to achieve perturbation attenuation in a user-defined time. Together with the linear anti-windup compensator, a robust trajectory tracking controller is constructed, which is capable of guaranteeing that all signals in the closed-loop system are uniformly ultimately bounded (UUB) and the tracking error converges to a user-defined compact set in predetermined time with prescribed transient performance. Finally, the effectiveness of the proposed control scheme is validated through Lyapunov theory and numerical studies.

Co-design of Anti-windup Compensator and a Novel Saturation-based Dynamic Event-triggered Mechanism for Asymmetric Saturated System

Co-design of Anti-windup Compensator and a Novel Saturation-based Dynamic Event-triggered Mechanism for Asymmetric Saturated System

Adaptive Controller With Anti-Windup Compensator for Piezoelectric Micro Actuating Systems

Adaptive Controller With Anti-Windup Compensator for Piezoelectric Micro Actuating Systems

Performance-based activation of anti-windup compensation for control of linear systems subject to actuator saturation

In this paper, we propose a performance-based activation mechanism for anti-windup compensation. The signals representing the transient performance of the closed-loop system are passed through a static performance compensator and then injected into the traditional anti-windup activation module and a performance-based anti-windup design framework is developed. The resulting equivalent controller contains the information of the anti-windup compensator and has the potential for improving the performance of the closed-loop systems. Under this new anti-windup design framework, sufficient conditions are established for estimating the domain of attraction and the nonlinear L2 gain of saturated systems. Based on these conditions, we formulate optimization problems to determine the optimal gains of anti-windup and performance compensators for enlarging the domain of attraction and reducing the nonlinear L2 gain. Simulation results show that, compared with the existing methods, our proposed approach has the ability to acquire a significantly larger estimate of the domain of attraction, a significantly tighter estimate of the nonlinear L2 gain, and significantly higher transient quality in reference tracking.

Anti-disturbance control for HVs system subject to nonlinear actuator characteristics with extended state observer

This paper proposes a radial basis function neural network and the actuator fault extended state observer based fast non-terminal sliding mode fault-tolerant control scheme for hypersonic vehicles (HVs) system. The proposed scheme can cope with actuator faults, actuator saturation, parameter uncertainties, and external disturbances for HVs systems, without relying on redundancy as some passive FTC methods do. Moreover, an anti-windup compensator is designed to mitigate the input saturation effects. Furthermore, the finite-time stability of the attitude angle of the HVs system is proved by Lyapunov's theorem. Numerical simulations validate the effectiveness of the proposed scheme.

Division Linearization Zero-Bias Current Control for AMBs–Rotor System With Uncertainties and Saturation

Traditional constant current sum (CCS) distribution strategy is always employed in the nonlinear active magnetic bearing (AMB) system control for linearization, but the bias current in CCS causes extra power consumption and limits the AMBs' capacity. In this paper, a division linearization zero-bias current (DLZBC) distribution strategy is proposed as a substitution for CCS strategy. Under this strategy, a linear active disturbance rejection controller (LADRC) with a static anti-windup compensator (SAWC) is applied to deal with model uncertainties and current saturation. For different types of AMB-supported machines, a partial normalized nonlinear model is established. Subsequently, the performance of the CCS strategy is analyzed, and a DLZBC strategy is presented to reduce the power consumption and transform the system into a linear plant with a lumped uncertain parameter. Afterward, a LADRC is designed to enhance robustness, whose parameters are chosen according to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu -$</tex-math></inline-formula> synthesis framework and are convenient for adjustment practically. For anti-saturation, a SAWC is developed to help the system escape quickly from current saturation and enlarge the stability domain of the saturated system. Comparative simulations and experiments results show that the proposed control method can significantly reduce power consumption and achieve good response in AMB-rotor system.

Active Adaptive Observer-Based Fault-Tolerant Control Strategy for a Class of T–S Fuzzy Systems With Unmeasurable Premise Variables

This paper addresses the problem of fault-tolerant output tracking control for a class of Takagi-Sugeno (T-S) fuzzy systems with unmeasurable premise variables subject to additive and multiplicative actuator faults and external disturbances. In nominal conditions, utilizing a quadratic Lyapunov function and non-parallel distributed compensation (non-PDC) technique, the suggested strategy delivers linear matrix inequality (LMI)-based constraints. Simultaneously design of the proportional-integral (PI)-like state feedback controller and fuzzy anti-windup compensator is achieved with the aim of output tracking. In the faulty case, by considering the nominal system as a reference model, a direct adaptive projection-based approach is developed using the T-S fuzzy modeling and control techniques to supply the adaptive fault-tolerant controller components. An enhanced proportional-integral (PI) state/fault observer with unmeasurable premise variables is introduced only to provide the estimation of states to be used in the proposed controller. The overall closed-loop system ensures the uniformly ultimately bounded (u.u.b) solutions for error dynamics. Two examples, subsuming an inverted pendulum and a chaotic power system, have been used to present the merits and efficiency of the suggested approach persuasively.

Reinforcement Learning-Based Fixed-Time Trajectory Tracking Control for Uncertain Robotic Manipulators With Input Saturation.

A fixed-time trajectory tracking control method for uncertain robotic manipulators with input saturation based on reinforcement learning (RL) is studied. The designed RL control algorithm is implemented by a radial basis function (RBF) neural network (NN), in which the actor NN is used to generate the control strategy and the critic NN is used to evaluate the execution cost. A new nonsingular fast terminal sliding mode technique is used to ensure the convergence of tracking error in fixed time, and the upper bound of convergence time is estimated. To solve the saturation problem of an actuator, a nonlinear antiwindup compensator is designed to compensate for the saturation effect of the joint torque actuator in real time. Finally, the stability of the closed-loop system based on the Lyapunov candidate is analyzed, and the timing convergence of the closed-loop system is proven. Simulation and experimental results show the effectiveness and superiority of the proposed control law.

Robust gain-scheduled autopilot design with anti-windup compensation for a guided projectile

Robust gain-scheduled autopilot design with anti-windup compensation for a guided projectile

Adaptive qXE-LMF Filter for Improving Power Quality Using Grid-Supporting Photovoltaic System

In practice, nonlinear electrical loads pose various power quality (PQ) challenges. Driven by these challenges, a parallel combination of a nonlinear load and a photovoltaic (PV) inverter with adaptive quantum normalized-least mean fourth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF) filter is proposed and experimentally validated to detect and compensate for the harmonics in harmonically contaminated currents. A scheme with an adaptive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF using fundamental weight components is used to generate the harmonics in the inverter output current thereby improving the PQ of the grid supply. The resulting grid current is pure and balanced; the PV inverter connected in parallel with the nonlinear load provides reactive and harmonic current support. Practically, the adaptive feature enables the online learning of filter weights of the load current harmonics to guarantee unconditionally balanced sinusoidal grid current. The proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter ensures fast convergence and minimum steady-state oscillations in the grid reference currents. An improved anti-windup PI compensator is used to ensure dc-link voltage stabilization. The practicality of the proposed adaptive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter is experimentally demonstrated using a three-phase four-wire uncontrolled rectifier-based nonlinear load. The experimental results also demonstrate the robustness of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter against changes in solar insolation level and nonlinear loads.