Actuator Saturation Problem Research Articles

Practical constrained output feedback formation control of underactuated vehicles via the autonomous dynamic logic guidance

This paper investigates the practical leader-follower formation control issue of underactuated vehicles. To achieve the waypoints-based formation navigation, the autonomous dynamic logic (ADL) guidance is proposed by incorporating the marine practice into the virtual ship-based formation guidance strategy. In the proposed guidance, only a dominant virtual leader is required for constructing the waypoints-based formation reference framework, which shows the simplicity and the practicability. As for the control part, a constrained output feedback algorithm is developed by means of the linear extended state observer (LESO). By constructing the augmented variable, the model uncertainty and unknown disturbances are integrated to be estimated and compensated together. In addition, a second-order dynamic auxiliary system is designed to handle the problem of actuator saturation, where two additional saturation compensation terms are introduced to stabilize the kinematics and the kinetics error dynamics, respectively, and the smoothness of constrained control signals can be guaranteed owing to the modification of Gaussian error function. Using the Lyapunov direct method, all signals in the closed-loop system are proved to be semi-global uniformly ultimately bounded (SGUUB). Finally, two simulation experiments, including the comparative experiment and the formation navigation experiment in the presence of simulated ocean disturbances, are carried out to illustrate the feasibility and the superiority of proposed scheme.

Robust prescribed‐time consensus of multi‐agent systems with actuator saturation and actuator faults

AbstractPrescribed‐time leader‐following consensus problem of multi‐agent systems with actuator saturation is considered in this paper. With the proposed protocol, the convergence time can be assigned off‐line, and actuator saturation problem is solved. A prescribed‐time disturbance and actuator faults observer is designed to estimate the disturbance and actuator faults. At last, numerical simulations show the efficiency of the observer and controller.

Actuator Saturated Fuzzy Controller Design for Interval Type-2 Takagi-Sugeno Fuzzy Models with Multiplicative Noises

In many practical systems, stochastic behaviors usually occur and need to be considered in the controller design. To ensure the system performance under the effect of stochastic behaviors, the controller may become bigger even beyond the capacity of practical applications. Therefore, the actuator saturation problem also must be considered in the controller design. The type-2 Takagi-Sugeno (T-S) fuzzy model can describe the parameter uncertainties more completely than the type-1 T-S fuzzy model for a class of nonlinear systems. A fuzzy controller design method is proposed in this paper based on the Interval Type-2 (IT2) T-S fuzzy model for stochastic nonlinear systems subject to actuator saturation. The stability analysis and some corresponding sufficient conditions for the IT2 T-S fuzzy model are developed using Lyapunov theory. Via transferring the stability and control problem into Linear Matrix Inequality (LMI) problem, the proposed fuzzy control problem can be solved by the convex optimization algorithm. Finally, a nonlinear ship steering system is considered in the simulations to verify the feasibility and efficiency of the proposed fuzzy controller design method.

Extended state observer-based integral line-of-sight guidance law for path following of underactuated unmanned surface vehicles with uncertainties and ocean currents

This article focuses on the problem of path following for underactuated unmanned surface vehicles (USVs) considering model uncertainties and time-varying ocean currents. An extended state observer (ESO)-based integral line-of-sight (ILOS) with an integral sliding mode adaptive fuzzy control scheme is proposed as the main control framework. First, a novel ESO is employed to estimate the surge and sway velocities based on the kinetic model, which are difficult to measure directly. Then, the adaptive ILOS guidance law is proposed, in which the integral vector is incorporated into the adaptive method to estimate the current velocities. Meanwhile, an improved fuzzy algorithm is introduced to optimize the look-ahead distance. Second, the controller is extended to deal with the USV yaw and surge velocity signal tracking using the integral sliding mode technique. The uncertainties of the USV are approximated via the adaptive fuzzy method, and an auxiliary dynamic system is presented to solve the problem of actuator saturation. Then, it is proved that all of the error signals in the closed-loop control system are uniformly ultimately bounded. Finally, a comparative simulation substantiates the availability and superiority of the proposed method for ESO-based ILOS path following of USV.

A Nonlinear Control Approach for Aerial Transportation Systems With Improved Antiswing and Positioning Performance

The aerial transportation system is a kind of nonlinear underactuated mechatronic system, which suspends the cargo beneath the rotorcraft’s fuselage and undertakes two basic missions of rotorcraft positioning and cargo swing suppression. Currently, most available methods need simplifications such as the near hovering hypothesis and dimension reduction operations, which may badly degrade the control performance when state variables get far away from the equilibrium point. In addition, integral terms, which can eliminate the steady errors, are not reflected in controller design and stability analysis processes. To tackle the aforementioned issues, this article provides a novel nonlinear control approach with an elaborately constructed integral term for aerial transportation systems, which not only achieves satisfactory antiswing and positioning performance but also reduces steady errors in practical flight. Meanwhile, the actuating constraint is taken into consideration so as to avoid saturation problems. Without linearization operations, we prove the closed-loop asymptotic stability of the equilibrium by the explicit Lyapunov-based analysis. As far as we know, this article is the first solution for controller design with the consideration of both steady errors elimination and actuating constraints. Finally, several groups of hardware experimental results are provided to validate the effectiveness of the presented control scheme. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This article is motivated by the requirement of effective control schemes for aerial transportation systems. The unexpected cargo swing motion may lead to safety accidents; thus, the dual objective of swing suppression and rotorcraft positioning is the focus of research. Nevertheless, with underactuated property, the cargo swing motion cannot be directly controlled. Up until now, at the cost of model accuracy, most existing methods utilize the simplified models in near hovering state or 2-D transverse plane to reduce the control difficulty. Accounting for the foregoing problems, this article presents a novel control scheme with improved antiswing and positioning performance. With an elaborately constructed integral term, the designed controller could improve the positioning accuracy of the rotorcraft with the guaranteed theoretical analysis. Moreover, to avoid the problem of actuator saturation, the control inputs are restricted in allowable ranges during the transportation process. All these aspects are verified by rigorous theoretical analysis and groups of hardware experiments in different conditions. In future studies, we will apply the suggested control scheme in practical applications.

Disturbance-observer-based control for semi-Markovian jump systems with time-varying delay and generally uncertain transition rate

The analysis result of disturbance-observer-based control (DOBC) for semi-Markovian jump systems (S-MJSs) with time-varying delay and generally uncertain transition rate (TR) is given in this paper. At present, there are still some urgent problems needed to be solved for S-MJSs such that conservative of stability, difficult of obtaining of TR in practical system, and the unexpected transient performance is always inevitable, such as larger overshoots and longer settling time. Unlike the existing methods, the proposed method considers the external disturbance, limitation on domain of control signal, uncertain parameters and time-varying delay in the S-MJSs. The piecewise analysis method for time-varying delay systems is extended to DOBC for S-MJSs. First of all, the sufficient condition of stochastic stability based on S-MJSs with more general TR is derived by piecewise Lyapunov-Krasovskii functional. Then, the disturbance observer is designed for estimating the actual disturbance, and the anti-disturbance controller is designed to deal with the control problem of S-MJSs. Furthermore, the problem of actuator saturation is addressed. Finally, two practical example is employed to testify the correctness of the proposed methods.

Robust attitude control of a 3-DOF helicopter considering actuator saturation

This paper presents a comparative research of robust attitude control for helicopter system. Considering the actuator saturation problem in the controller design process, two control approaches are mainly investigated. A mixed H∞ performance and linear quadratic regulator (LQR) based robust controller is proposed as the first approach, in which the control input is indirectly constrained in the cost function. While a constrained H∞ performance based robust attitude controller is developed as the other approach, in which the actuator saturation problem is directly considered in the dynamical model as well as following controller gain calculation. Based on Lyapunov stability theory, sufficient conditions in terms of linear matrix inequalities (LMI) are given. By using Quanser’s 3-DOF laboratory helicopter platform, comparative simulation and experimental tests are conducted. Payload variation and wind disturbance are all considered in the experimental test. And the results demonstrate the effectiveness as well as different performance of proposed robust attitude controllers.

Finite Time Convergence Incremental Nonlinear Dynamic Inversion-Based Attitude Control for Flying—Wing Aircraft with Actuator Faults

In this paper, a two-loop fault-tolerant attitude control scheme is proposed for flying-wing aircraft with actuator faults. A regular nonlinear dynamic inversion (NDI) control is used in the outer attitude loop, and a finite time convergence incremental nonlinear dynamic inversion (FINDI) control combined with control allocation strategy is used in the inner angular rate loop. Prescribed performance bound (PPB) is designed to constrain the tracking errors within a residual set, so the prescribed system performance can be guaranteed. An optimal anti-windup (AW) compensator is introduced to solve the actuator saturation problem. Simulation results demonstrate the effectiveness of the proposed approach.

Distributed Adaptive Sliding Mode Control for Vehicle Platoon with Uncertain Driving Resistance and Actuator Saturation

Vehicle platoon has been demonstrated to be a promising driving pattern for its prominent advantages in enhancing traffic safety, improving highway capacity, and increasing fuel economy as well as reducing carbon emissions. However, the uncertain driving resistance and saturated actuator output decay the control performance and may even lead to the instability of a vehicle platoon. Therefore, a distributed adaptive sliding mode control algorithm for vehicle platoon with uncertain driving resistance and actuator saturation is proposed in this paper. First of all, sliding mode control technique, together with the coupled sliding surface (CSS) method, is adopted to design the vehicle platoon control algorithm and an adaptive updating law is proposed to estimate the unknown driving resistance coefficients. Then, for the problem of actuator saturation, an antiwindup compensation-based approach is utilized to attenuate the integral windup of the adaptive platoon control laws in the case of actuator saturation. In addition, considering the chattering problem inherent in sliding mode control, a sigmoid-like function sgn⋅ is deployed to weaken the influence of chattering, which is expected to enhance the driving comfortableness. Both theoretical analysis and numerical simulation verify the feasibility and effectiveness of the proposed vehicle platoon algorithm.

Distributed fault-tolerant control of modular and reconfigurable robots with consideration of actuator saturation

A novel decomposition-based distributed robust fault-tolerant control method is proposed for modular and reconfigurable robots based on joint torque sensing. The designed robust controller compensates for both model uncertainties and a class of actuator faults. In addition, the proposed scheme does not require a fault detection and diagnosis module, avoiding time delay associated with it. Furthermore, a radial basis function neural network-based compensation scheme is proposed to deal with the actuator saturation problem, which is especially critical when actuator fault has to be tolerated by the control system. Simulation results have shown the effectiveness of the presented method.

A robust constrained control approach for flexible air‐breathing hypersonic vehicles

AbstractThis article investigates the robust adaptive control system design for the longitudinal dynamics of a flexible air‐breathing hypersonic vehicle (FAHV) subject to parametric uncertainties and control input constraints. A combination of back‐stepping and nonlinear disturbance observer (NDO) is utilized for exploiting an adaptive output‐feedback controller to provide robust tracking of velocity and altitude reference trajectories in the presence of flexible effects and system uncertainties. The dynamic surface control is introduced to solve the problem of “explosion of terms.” A new NDO is developed to guarantee the proposed controller's disturbance attenuation ability and to performance robustness against uncertain aerodynamic coefficients. To deal with the problem of actuator saturation, a novel auxiliary system is exploited to compensate the desired control laws. The stability of the presented NDO and controller is analyzed. Simulation results are given to demonstrate the effectiveness of the presented control strategy.

Stability Analysis of a Proximate Time Optimal Controlled Electrostatic Suspension System Using Piezo Actuator via Lyapunov Functional Approach

An electrostatic suspension of silicon wafer using proximate time optimal control has been successfully developed. In this system, the movable electrodes which are supplied by constant voltage and actuated by the piezoelectric (PZT) actuator are used instead of stationary electrodes like previous systems. The changing of the gap length between movable electrodes and the suspended object will create varying capacitances that can control the electrostatic forces. To overcome the problem of actuator saturation of the piezo actuator, a proximate time optimal control is used to stabilize the system. The system stability is theoretically investigated using Lyapunov’s function. The constant voltage supplying to the electrode is an important parameter, and it is also determined. The paper presents series of the simulation and experimental results that prove completely suspension of 4-inch silicon wafer without any mechanical contact.

Barrier Lyapunov Function Based Controller Design for Euler-Lagrange Systems with Reduced Control Effort

In this paper, a novel nonlinear controller is designed for Euler- Lagrange (EL) systems while satisfying user-defined safety-constraints in position variables. The EL systems, which are highly popular for modeling a variety of non-linear mechanical plants like aircraft, spacecraft, quad-rotors, robotic manipulators, etc., critically demand safety-constraint satisfaction during trajectory tracking applications. Barrier Lyapunov Function (BLF) is widely used for systematically designing the controller to prevent safety-constraint violation during trajectory tracking. By proving the boundedness of BLF in a closed loop, safety-constraint satisfaction is analytically guaranteed. The fundamental principle of BLF is that if the states are reaching close to the boundary of a safe region, the high control input is applied to the system to push states far inside the boundary. In practical scenarios, such a high control effort requirement may lead to the critical problem of actuator saturation. This work alleviates the issue of high control effort requirements in the BLF framework. The proposed BLF-based controller is capable of guaranteeing safety-constraint satisfaction with less control effort, making the design practically viable. Simulation results validate significant improvement in terms of reduction in control input magnitude of the proposed algorithm in contrast to conventional BLF-based control algorithms.

Adaptive path following control of a stratospheric airship with full-state constraint and actuator saturation

In this paper, the path following problem is addressed for a stratospheric airship subject to full-state constraint, input saturation and external disturbances. A novel full-state constrained path-following algorithm, which ensures that all states of the system remain in the predetermined intervals, is proposed based on the theories of barrier Lyapunov function, vector field guidance, adaptive backstepping control and saturation compensator. Firstly, an error-constrained vector field (ECVF) guidance law is presented to handle the position tracking error, which can navigate the stratospheric airship along the predefined path and guarantee that the error is limited by the time-varying asymmetric constraints. Secondly, a state-constrained adaptive attitude controller is introduced to track the desired attitude calculated by the ECVF, in which a saturation compensator of virtual control law is employed to handle the problem of angular velocity constraint. Finally, a state-constrained adaptive velocity controller is designed to maintain an appropriate scheduled velocity. Furthermore, two auxiliary design systems are used to deal with the actuator saturation problem, and adaptive laws are developed for handling dynamic couplings and unknown disturbances. Stability analysis implies that all signals in the closed-loop system are uniformly ultimately bounded, and all path-following state constraint requirements are never violated. Meanwhile, the effectiveness of the proposed control algorithm is demonstrated by comparative simulation results.

Nussbaum gain adaptive control scheme for moving mass reentry hypersonic vehicle with actuator saturation

This paper addresses an actuator saturation problem of the moving mass hypersonic vehicles (HSVs) in the reentry phase. The saturation nonlinearity is modeled using a hyperbolic tangent function and the concomitant time-varying coefficients problem is handled via Nussbaum gain technique. Then backstepping technique is applied in control design and the explosion of complexity in traditional backstepping design is avoided by utilizing dynamic surface control. Subsequently, a Nussbaum gain adaptive controller is constructively framed to deal with the actuator saturation. Based on the disturbance observers, the robustness of the proposed controller is enhanced. The semiglobal stability of the closed-loop system is ensured via Lyapunov synthesis. Finally, numerical simulation results are presented to show the effectiveness of the designed control scheme.

Model-Free Cooperative Adaptive Sliding-Mode-Constrained-Control for Multiple Linear Induction Traction Systems.

In order to deal with the speed cooperative control problem in the multiple linear induction traction systems consists of multiple linear induction motors, a model-free cooperative adaptive sliding-mode-constrained-control strategy is proposed considering the input magnitude and rate constraints which may cause the problem of actuator and integral saturation. First, the equivalent circuit topology of the single motor in the system is investigated. Besides, the system is considered as the multiagent system with fixed communication topology due to the interaction between adjacent motors. Then, the output observer is presented to estimate the output and the estimation algorithm of pseudo-partial derivative parameter and uncertainties is proposed. Based on the above, the proposed control scheme is presented by designing an integral sliding-mode surface containing the systematic error and an anti-windup compensator is added to eliminate the saturation. Finally, the simulations of the proposed control strategy for multiagent systems are carried out to demonstrate the effectiveness and superiority of the proposed control strategy.

Super-twisting algorithm-based integral sliding mode control with composite nonlinear feedback control for magnetic levitation system

The paper aims to discuss the issues of actuator saturation and external disturbance in the magnetic levitation (maglev) system. The proposed technique is composed of composite nonlinear feedback (CNF) and super-twisting algorithm (STA)-based integral sliding mode (ISM) control to tackle the problem of actuator saturation and external disturbances simultaneously. The composite nonlinear feedback scheme comprises of linear feedback law which provides stability and fast response whereas the nonlinear feedback law takes care of input saturation and reduces the overshoot. The super-twisting algorithm (STA)-based integral sliding mode (ISM) controller is designed for disturbance rejection. A super-twisting algorithm-based approach is applied on ISM scheme to eliminate the chattering effect and make it continuous in nature for its direct implementation to the physical maglev system. The designed scheme is successfully tested on real-time feedback instruments model of the maglev system.

Asymmetric error-constrained path-following control of a stratospheric airship with disturbances and actuator saturation

Abstract This paper addresses the asymmetric error-constrained path-following problem of a stratospheric airship with external disturbances and actuator saturation. A path-following algorithm is proposed based on the theories of tan-type barrier Lyapunov function, vector field guidance, adaptive sliding mode control, and radial basis function neural network (RBFNN). First, to satisfy the asymmetric tracking error-constrained requirements of airship position, an asymmetric error-constrained vector field (AECVF) guidance law is presented, which can navigate the stratospheric airship along the predefined path and guarantee that the tracking error is limited by the error constraints. Second, an adaptive sliding mode attitude controller is introduced to track the desired attitudes calculated using the AECVF with disturbances. Finally, an adaptive velocity controller is added to the control algorithm to maintain an appropriate velocity. Moreover, an RBFNN saturation compensator is introduced to solve the actuator saturation problem caused by the low maneuverability. Stability analysis indicates that all the signals in the closed-loop system are uniformly ultimately bounded. Meanwhile, simulation results demonstrate the effectiveness of the proposed control algorithm.

Consensus Tracking for Teleoperating Cyber-physical System

In this paper, we investigate the consensus tracking problem for teleoperating cyber-physical system (TCPS) under time-varying delay and actuator saturation constraints. Due to the introduction of communication network, variable propagation time delays are considered in cyber element. In addition, actuator saturation problem is investigated in physical element, which is caused by the physical restrictions on robots. Then, a novel distributed consensus tracking controller is proposed in the presence of time-varying delay and actuator saturation. Meanwhile, sufficient conditions are provided to show that the consensus tracking controller can stabilize the master-slave TCPS. Finally, simulations and experiments are performed to validate our proposed results. It is shown that the consensus controllers can guarantee the asymptotic stability of single-master-multi-slave TCPS.

Synchronization of multiple 3-DOF helicopters under actuator faults and saturations with prescribed performance

The distributed cooperative control strategy is proposed to make the networked nonlinear 3-DOF helicopters achieve the attitude synchronization in the presence of actuator faults and saturations. Based on robust adaptive control, the proposed control method can both compensate the uncertain partial loss of control effectiveness and deal with the system uncertainties. To address actuator saturation problem, the control scheme is designed to ensure that the saturation constraint on the actuation will not be violated during the operation in spite of the actuator faults. It is shown that with the proposed control strategy, both the tracking errors of the leading helicopter and the attitude synchronization errors of each following helicopter are bounded in the existence of faulty actuators and actuator saturations. Moreover, the state responses of the entire group would not exceed the predesigned performance functions which are totally independent from the underlaying interaction topology. Simulation results illustrate the effectiveness of the proposed control scheme.