Effects Of Unknown External Disturbances Research Articles

Truncated predictive tracking control design for semi-Markovian jump systems with time-varying input delays

A state tracking control problem for a class of semi-Markovian jump systems (SMJSs) with input delay and disturbances is addressed in this study. In particular, an improved-equivalent-input-disturbance estimator approach (IEIDEA)-based truncated predictive controller is designed to synchronously compensate the effect of unknown external disturbances and time-varying delay. Specifically, by making use of IEIDEA, the unknown disturbances are estimated with high precision and incorporated into the control input channel, which eases the way to achieve the desired tracking performances. Specifically, the state predictor satisfies the delay-free state-space equation and is used in controller design along with prediction. In accordance with linear matrix inequality framework and Lyapunov stability theory, a set of adequate conditions are established to guarantee the state tracking performance of SMJSs. Finally, the numerical examples with simulation results are provided to validate the efficacy and practicability of the established control technique.

On the robustification of digital event-based stabilizers for nonlinear time-delay systems

In this paper, the robust stabilization problem by means of quantized sampled-data event-based (QSE) controllers is investigated for nonlinear systems affected by state delays and unknown disturbances. In particular, a methodology for the design of robust QSE stabilizers is provided for control-affine nonlinear systems affected by unknown actuation disturbances and unknown measurement errors. Firstly, the notion of Steepest Descent Feedback (SDF), continuous or not, is suitably revised in order to deal with the robustification of event-based controllers. Then, Input-to-State Stability (ISS) redesign methodologies are used to provide the robustification term which is added to the SDF at hand in order to arbitrarily attenuate the effects of unknown external disturbances affecting the considered control scheme. A spline approximation approach is used in order to cope with the problem of the possible non-availability in the buffer of suitable past values of the system state required for the correct application of the proposed robust QSE controller. It is proved that there exist a suitably fast sampling and an accurate quantization of the input/output channels such that: the robust QSE implementation of SDFs, continuous or not, ensures the semi-global practical stability of the related closed-loop system, regardless of the above disturbances, provided that the observation errors affects marginally the new added control term. The stabilization in the sample-and-hold sense theory is used as a tool to prove the results. The provided results include the case of non-uniform quantization of the input/output channels and the case of aperiodic sampling. Applications are presented in order to validate the results.

Adaptive quantized sliding mode attitude tracking control for flexible spacecraft with input dead-zone via Takagi-Sugeno fuzzy approach

This paper addresses the sliding mode control design problem for the flexible spacecraft attitude tracking control system with Takagi-Sugeno fuzzy model based method. In this design, the external disturbance and actuator input dead-zone are considered simultaneously, and the signals between sensors and controller are quantized before transmission over digital communication channels. A quantized adaptive integral sliding mode control law is proposed to ensure that the sliding motion is globally asymptotically stable, and the effects of unknown external disturbances, actuator nonlinearity and quantization errors are compensated via the online adaptive mechanism simultaneously. Moreover, under the proposed digital control law the finite-time reachability of the designed sliding surface can be guaranteed strictly. Finally, simulation results are presented to illustrate the feasibility and effectiveness of the developed quantized spacecraft attitude control method.

Neural Network Based Robust Lateral Control for an Autonomous Vehicle

The lateral motion of an Automated Vehicle (AV) is highly affected by the model’s uncertainties and unknown external disturbances during its navigation in adverse environmental conditions. Among the variety of controllers, the sliding mode controller (SMC), known for its robustness towards disturbances, is considered to generate a robust control signal under uncertainties. However, conventional SMC suffers from the issue of high frequency oscillations, called chattering. To address the issue of chattering and reduce the effect of unknown external disturbances in the absence of precise model information, a radial basis function neural network (RBFNN) is employed to estimate the equivalent control. Further, a higher order sliding mode (HOSM) based switching control is proposed in this paper to compensate for the effect of external disturbances. The effectiveness of the proposed controller in terms of lane-keeping and lateral stability is demonstrated through simulation in a high-fidelity Carsim-Matlab Simulink environment under a variety of road and environmental conditions.

H-Infinity Shifting Control in a Dual-Speed Transmission for Electric Vehicle

To improve the economic and comfort performance of pure electric vehicles (PEV), this paper proposes a novel H-infinity gear-shifting controller for dual-speed Transmissions (DST) to achieve a smooth and swift shifting when considering uncertain disturbances in system. Firstly, the structure as well as the working principle of the DST for PEV are introduced briefly and the mathematical model of the transmission is derived according to the Lagrange equation. Then the gear-shifting process is analyzed and the control problem is formulated according to the clutch status. Next, a robust H-infinity controller is proposed to attenuate the vehicle jerk as well as the clutch sliding energy loss. Simulation results under different working conditions indicate the controller presented have better performance in limiting the effect of unknown external disturbances comparing to a calibrated proportional-integral-derivative (PID) controller.

Stabilisation of a Flexible Spacecraft Subject to External Disturbance and Uncertainties

This paper addresses the problems of vibration reduction and attitude tracking for a flexible spacecraft subject to external disturbances and uncertainties. Based on Hamilton’s principle, flexible spacecraft is modelled by a coupled nonlinear partial differential equation with ordinary differential equations. Adaptive boundary control scheme is adopted to stabilize the vibration displacement of flexible appendage into a small neighbourhood of original position and simultaneously maintain attitude angle within the desired angle region. Two disturbance adaptive laws are constructed to attenuate the effect of unknown external disturbances. The well posedness of the controlled system is proven by using the semigroup theory. The proposed adaptive boundary control scheme can guarantee the uniform boundedness of the closed-loop system. Numerical simulation results illustrate the effectiveness of the proposed control scheme.

Event-triggered adaptive fault-tolerant control for multi-agent systems with unknown disturbances

This paper presents an event-triggered consensus control protocol for a class of multi-agent systems with actuator faults, sensor faults and unknown disturbances. The adaptive neural network compensation control method is introduced to solve the problem of sensor faults. The event-triggered mechanism is developed to reduce the communication burden. In the control design process, the radial basis function neural networks are used to approximate the unknown nonlinear functions, and a nonlinear disturbance observer is used to eliminate the effect of unknown external disturbances. Furthermore, based on the graph theory and Lyapunov stability theory, it is further shown that the consensus tracking errors are semi-globally uniformly ultimately bounded. Finally, the simulation example illustrates the effectiveness of the designed control protocol.

3D trajectory tracking control of an underactuated AUV based on adaptive neural network dynamic surface

This paper addresses the 3D trajectory tracking control of an underactuated autonomous underwater vehicle (AUV) under uncertain model parameters and unknown external disturbances. A dynamic surface control scheme based on neural network and adaptive technique is proposed. In controller design, the first-order integral filters are employed to estimate derivative of virtual control, which avoid repeated derivative of virtual control. To deal with the effect of unknown external disturbances and uncertain model parameters, the neural network and adaptive technique are combined to approximate unknown nonlinear functions. All of the error signals in the closeloop system are uniformly ultimately bounded based on Lyapunov stability theory. Simulation studies and comparisons with adaptive dynamic surface control scheme illustrate the effectiveness and superiority of the proposed control scheme.

Finite-Time Adaptive Fuzzy-Neural-Network Control of Active Power Filter

In this paper, an adaptive fuzzy-neural-network (AFNN) control using nonsingular terminal sliding mode control is proposed for active power filter (APF) as a current controller to attenuate the effect of unknown external disturbances and modeling uncertainties. First, the dynamic model for APF is built in which both the system parameter variations and external disturbance are considered. Then, a nonsingular terminal sliding mode control based on the backstepping (NTSMB) approach is presented for the current control system to solve singularity point problem and realize the fast and finite-time convergence. Moreover, AFNN is designed to relax the requirement of the prior knowledge of system parameters to improve the robustness of NTSMB. In the AFNN strategy, AFNN framework is designed to mimic the NTSMB, where the parameters are adjusted online by the adaptive law derived from the projection algorithm and the Lyapunov stability analysis, to guarantee tracking performance and stability of the closed-loop system. Simulation studies demonstrate that the proposed control methods exhibit excellent performance in both steady-state and transient operation compared to traditional sliding mode control. Experimental results are provided using a fully digital control system in order to validate the performance of the proposed controller.

Switching Logic-Based Nonlinear Feedback Control of Offshore Ship-Mounted Tower Cranes: A Disturbance Observer-Based Approach

We propose, in this paper, an observer-based nonlinear feedback controller for four degrees of freedom (4-DOF) offshore ship-mounted tower cranes, which includes a robust-type term to address the observation uncertainty, and a switching logic tuning mechanism to update the involved unknown parameter. As a typical nonlinear underactuated mechatronic system, unlike the land-fixed tower cranes, an offshore ship-mounted tower crane also suffers from persistent disturbances caused by sea waves or currents, which leads to many difficulties and challenges in the controller design of such systems. Existing offshore crane control methods require either linearizations or approximations when performing analysis; moreover, most of them are only applicable for simplified 2-DOF crane models, and the ranges of system state errors cannot be guaranteed during the overall process. Motivated by these facts, to achieve simultaneous accurate jib/trolley positioning and fast payload swings suppression against complex unknown external disturbances, in particular, a disturbance observer is first designed in this paper, based on which a novel nonlinear switching logic-based control scheme for offshore cranes with jib rotation and horizontal transportation is proposed. As far as we know, the proposed method yields the first observer-based feedback closed-loop control without simplification operations to the original 4-DOF offshore tower crane dynamics and achieves the first asymptotic stability of the closed-loop system’s equilibrium point for offshore cranes. To support the theoretical derivation, the corresponding stability analysis of the closed-loop system’s equilibrium point is implemented by Lyapunov techniques. Numerous simulation and hardware experimental results are presented to demonstrate the superior performance of the proposed method. Note to Practitioners —This paper is motivated by the issue of controlling a four- degree-of-freedom (4-DOF) offshore ship-mounted tower crane system under the effects of unknown external disturbances. In practical applications, the persistent disturbances caused by sea waves or currents can always happen and make the offshore crane operation very challenging. Moreover, it brings more difficulties in the controller design for such a system due to its nonlinear underactuated property. Existing control approaches for offshore cranes are developed based upon linearized or oversimplified crane models or require exact model knowledge, and they may not work well in the presence of harsh sea conditions. Toward this end, this paper suggests a new control approach for 4-DOF offshore tower cranes suffering from sea wave effects to achieve a satisfactory performance. The asymptotic stability of the closed-loop system’s equilibrium point is derived, implying that the accurate jib/trolley positioning and fast payload swings suppression against complex unknown external disturbances are achieved simultaneously. Preliminary physical experiments implemented on a self-built offshore tower crane hardware test bed verify the effectiveness and the robustness of the proposed observer-based control method. In the future research, we will apply the suggested control approach to industrial offshore crane systems to improve their working efficiency.

Disturbance observer-based boundary control for a suspension cable system moving in the horizontal plane

This paper addresses the suppressing problem of cable vibration and the positioning control design for a suspension cable system of a helicopter with disturbances. Hamilton’s principle is applied to obtain a distributed parameter system for the suspension cable system of a helicopter. Two observers are employed to restrain the effect of unknown external disturbances. Based on the proposed disturbance observers and Lyapunov’s direct method, two boundary control laws are designed, which are provided by the actuators at the top and bottom boundaries of the suspension cable, respectively. Under the proposed control laws, the oscillation amplitude and the error between the bottom boundary payload and the desired point are proven to be uniformly ultimately bounded. Moreover, they will converge to a small neighbourhood of zero by selecting proper design parameters. Meanwhile, some sufficient conditions are provided to guarantee the validity of the proposed control laws. Finally, simulation results show the rationality and effectiveness of the control scheme developed in this paper.

Globally exponential synchronization criterion of chaot-ic oscillators using active control

This research paper focuses the globally exponential synchronization between two identical and two nonidentical chaotic oscillators. With the help of Lyapunov direct method and using the active control technique, suitable algebraic conditions are obtained analytically that establish the globally exponential synchronization. The proposed globally exponential synchronization criterion is more general and much less conservative than the previously published works. A comparison, based upon the synchronization speed, cost and quality have been performed with our study of the previously published results. The effect of unknown external disturbances has also been discussed. Numerical simulation results are presented to illustrate the performance and efficiency of this study.

Partial stabilization of underactuated post-capture combination with inaccurate measurement information and unknown disturbances

This paper aims to address the attitude stabilization issue of post-capture combination with underactuated actuators, measurement inaccuracy and unknown external disturbances during on-orbit servicing. A precise and practical form of underactuated attitude dynamics is proposed for the asymmetric combination with two control torques. With the adopted partial stabilization strategy, a sliding mode controller is first proposed to achieve partial stabilization of the combination against the effect of unknown external disturbances. Through the additional consideration of the measurement inaccuracy in the inertia tensor and the mass centroid, an underactuated adaptive sliding mode controller with compensation laws is proposed in presence of uncertainties and disturbances. Numerical simulations validate the effectiveness of proposed partial attitude stabilization controllers.

Whole-Range Nonlinear Large Disturbance Attenuation Controller Design for Turbo Generator Steam Valve Systems

For a class of strongly nonlinear reheat-type turbo generator steam valve control problem, a whole-range nonlinear adaptive large disturbance attenuation control scheme is investigated based on the Minimax and adaptive Backstepping method. The effect of unknown external disturbances on the rotor angle and the rotor speed of the generator are considered. The Minimax method is used to reduce effectively the conservativeness of the disturbance treatment, which is brought by the estimation of the upper bound of the disturbance and the inequality scaling. The purpose is to ensure the robustness and insensitivity to effects of large disturbances of the closed-loop system. By considering the effect of the short-circuit ground fault and the mechanical power of disturbances, an application of the single-machine infinite-bus system is researched. Simulation results show that the control scheme can effectively improve the dynamic process of the transient stability of the power system. Compared with the conventional nonlinear controller, the control scheme has more advantages for large disturbances, and the process of controller design is simple and intuitive.

Replacement of Lyapunov Function by Locally Convergent Robust Fixed Point Transformations in Model-Based Control a Brief Summary

Lyapunov’s 2ndMethod is a popular approach in the model-based control of nonlinear systems since normally it can guaranteeglobal asymptotic stability. However, the cost of the application of Lyapunov function frequently can be inefficient and complicated parameter tuning process containing unnecessary number of almost arbitrary control parameters, and vulnerability of the tuning process against not modeled, unknown external disturbances. Improved versions of the original, model-based tuning are especially sensitive to the external perturbations. All these disadvantages can simply be avoided by the application of robust fixed point transformations at the cost of giving up the guarantee of global asymptotic stability. Instead of that simple,stable iterative controlof local basin of attraction can be constructed on the basis of an approximate system model that can well compensate the effects of unknown external disturbances, too. Since the basin of convergence of the method in principle can be left, setting the three adaptive parameters of this controller needs preliminary simulation investigations. These statements are illustrated and substantiated via simulation results obtained for the adaptive control of various physical systems.