Robust Disturbance Research Articles

Robust Adaptive Control of a Free-Floating Space Robot System in Cartesian Space

This paper presents a novel, robust, adaptive trajectory-tracking control scheme for the free-floating space robot system in Cartesian space. The dynamic equation of the free-floating space robot system in Cartesian space is derived from the augmented variable method. The proposed basic robust adaptive controller is able to deal with parametric and non-parametric uncertainties simultaneously. Another advantage of the control scheme is that the known and unknown external disturbance bounds can be considered using a modification of the parameter-estimation law. In addition, three cases are certified to achieve robustness for both parametric uncertainties and external disturbances. The simulation results show that the control scheme can ensure stable tracking of the desired trajectory of the end-effector.

Chemical Process Disturbance Compensation as a Fault Tolerant Control Problem

In general, the control of chemical processes that involve unknown disturbances presents interesting challenges. Research issues have been focused on detailed modelling of the involved phenomena in order to use e.g. robust on-line disturbance compensation procedures or attempting to cancel out the disturbance effect in the feedback control of the chemical system. However, the chemical modelling problem can remain a very difficult challenge due to the unknown or partially-known dynamics occurring in the process under investigation. Therefore, this article proposes a new approach to the disturbance compensation, which is recasted into the theory of robust fault estimation. The disturbances acting in the system can be thus viewed as faults with time-varying characteristics to be estimated and compensated within an output feedback fault-tolerant control scheme. In this way, the limitations arising from the use of model-based approaches are obviated. The unknown input estimation problem is hence embedded inside a control system with required stability and performance robustness. This can be a significant advantage over model-based unknown input compensation methods, in which the detailed modelling of the disturbance term can be essential, and for which robustness with respect to its characteristics is difficult to achieve using purely nonlinear modelling strategies.

Discrete Second-Order Sliding Mode Adaptive Controller Based on Characteristic Model for Servo Systems

Considering the varying inertia and load torque in high speed and high accuracy servo systems, a novel discrete second-order sliding mode adaptive controller (DSSMAC) based on characteristic model is proposed, and a command observer is also designed. Firstly, the discrete characteristic model of servo systems is established. Secondly, the recursive least square algorithm is adopted to identify time-varying parameters in characteristic model, and the observer is applied to predict the command value of next sample time. Furthermore, the stability of the closed-loop system and the convergence of the observer are analyzed. The experimental results show that the proposed method not only can adapt to varying inertia and load torque, but also has good disturbance rejection ability and robustness to uncertainties.

Robust synchronization controller design of a two coupling permanent magnet synchronous motors system

Multi-motor systems have been widely applied in many fields such as industry and transportation. In this paper, a two coupling permanent magnet synchronous motors system is considered. First, the model of the system is established. Then, a novel state equation of the system is obtained by choosing suitable state variables. Based on the state equation, a robust synchronization controller is designed via a cross-coupling idea and interval matrix. In terms of bilinear matrix inequations, sufficient conditions for the existence of the robust controller are derived. Thanks to the suitable choice of state variables, the proposed controllers can deal with load uncertainty without a load observer, and have robustness for environmental and parameter disturbance. In order to verify the effectiveness of the proposed controller, simulations are carried out via Matlab/Simulink soft. Simulation results reflect that the controller has good dynamic, static, and synchronization performance.

A fault detection observer design for LPV systems in finite frequency domain

This paper addresses the fault detection observer design problem for linear parameter-varying systems. Two finite frequency performance indexes are introduced to measure the fault sensitivity and the disturbance robustness. First, the H− index fault sensitivity condition in finite frequency domain is obtained by generalised Kalman–Yakubovich–Popov lemma and new linearisation techniques. Then, with the aid of Kalman–Yakubovich–Popov lemma and projection lemma, the stability and robustness conditions are derived. It turns out that the non-convexity problem which is caused by dealing with the above three conditions can be translated into a bilinear matrix inequality optimisation problem by increasing the dimensions of slack variable matrix. An iterative linear matrix inequality algorithm is proposed to get the solution. The effectiveness of the filter is shown via three numerical examples.

Robust Disturbance Attenuation in Hamiltonian Systems Via Direct Digital Control

AbstractThe discrete‐time robust disturbance attenuation problem for the n‐degrees of freedom (dof) mechanical systems with uncertain energy function is considered in this paper. First, it is shown in the continuous time‐setting that the robust control problem of n‐dof mechanical systems can be reduced to a disturbance attenuation problem when a specific type of control rule is used. Afterwards, the robust disturbance attenuation problem is formulised as a special disturbance attenuation problem. Then, the discrete‐time counterpart of this problem characterised by means of L2 gain is given. Finally, a solution of the problem via direct‐discrete‐time design is presented as a sufficient condition. The proposed discrete‐time design utilizes discrete gradient of the energy function of considered system. Therefore, a new method is also proposed using the quadratic approximation lemma to construct discrete gradients for general energy functions. The proposed direct‐discrete‐time design method is used to solve the robust disturbance attenuation problem for the double pendulum system. Simulation results are given for the discrete gradient obtained with the method presented in this paper. Note that the solution presented here for the robust disturbance attenuation problem give an explicit algebraic condition on the design parameter, whereas solution of the same problem requires solving a Hamilton–Jacobi–Isaacs partial differential inequality in general nonlinear systems.

Robust Optimal Disturbance Observer Design for the Non‐Minimum Phase System

AbstractIn this paper, a design strategy of robust disturbance observer is proposed systematically for stable non‐minimum phase systems. This strategy synthesizes the internal and robust stability, relative order and mixed sensitivity design requirements together to establish the optimization function. The optimal solution is obtained by standard H∞ control theory under the condition of guarantying the presented requirements. Simulation results of a rotary mechanical system show the effectiveness of the proposed strategy.

Elegant anti-disturbance control for nonlinear systems based on a robust disturbance observer

A new elegant anti-disturbance control and estimation strategy is presented for a class of nonlinear systems subject to multiple disturbances. As a class of strong-coupled nonlinear systems, the models have measurement error, friction, varying load, and unmodelled dynamics, which can be characterized as two types of disturbances in this framework. One is supposed to be generated by an exogenous system with uncertainty, which represents the disturbance with partial known information. The other is a bounded external disturbance in the H2-norm. The nonlinear robust disturbance observer (DO) based on regional pole placement theory is constructed separately from the controller design to estimate and reject the first type of disturbance, and terminal sliding-mode (TSM) control is used to attenuate the second type of disturbance. By integrating the nonlinear robust DO with TSM control, a new elegant anti-disturbance control scheme based on a robust DO is proposed for a kind of nonlinear system, which can further improve the ability of anti-disturbance for nonlinear systems. Simulations are given to demonstrate the effectiveness of the proposed method.

Estimation and compensation of unknown disturbance in three-axis gyro-stabilized camera mount

Gyro-stabilized camera mounts are used to maintain and stabilize airborne remote sensing sensors, such as aerial cameras, light detection and ranging, and imaging spectrometers, for the purpose of isolating the line-of-sight of optical sensors from disturbing aircraft movements. However, it is difficult to achieve accurate line-of-sight pointing and even the system stability cannot be guaranteed due to the influences of unknown disturbance, such as mass imbalance, gimbal friction, aircraft attitude turbulence and model uncertainty. In order to realize high-precision disturbance rejection and robustness stability, a kind of compound control system is configured and designed in the framework of active fault-tolerant control. The basic idea of this paper is to handle the disturbance as a fault for disturbance compensation by applying online fault estimation and accommodation. Based on H∞ norm sub-optimization, a robust disturbance observer is designed to estimate the fault and then a fault compensator is employed to compensate for it. Based on an exosystem description, the internal model controllers are designed to achieve perfect tracking performance as well as robustness against model uncertainty. Finally, the experimental results demonstrate the effectiveness of the proposed compound control strategy in comparison with the traditional method.

Research on Control by Sliding Form of Variable Structure in Follow-Up System

The article designs a discrete-time sliding mode controller based on reaching law according to the follow-up system’s largely changed loads and strict control criteria for the position. It analyzes the different results by comparison of PID and sliding form of variable structures. Various results from simulation test shows that the control by sliding form of variable structures has better ability to guard load disturbance and parameter robustness.

Hierarchical Sliding Mode Control of an Inverted pendulum

This paper presented a hierarchical sliding mode controller for an inverted pendulum system. The structure characteristic of the inverted pendulum system could be treated as two subsystems. According to the decomposition of cart-inverted pendulum system we select sliding mode surfaces for both subsystems. The sliding mode surfaces of the two subsystems were defined at first. The sliding mode surface of one subsystem was selected as the first layer sliding mode surface. The second layer sliding mode surface was constructed by the first layer sliding mode surface and the sliding mode surface of the other subsystem. The hierarchical sliding mode control law was deduced in terms of Lyapunov stability theorem. Finally, simulation results showed the validity of this control method and its robustness for external disturbances.

Design and Research on Control System of 200Kw Organic Working Fluid Turbine

The power generation system using Organic Rankine Cycle (ORC) is a new technology for energy recovery, but very few people have studied the control system of the organic working fluid turbine at present. This paper put forward the speed and power control strategy about the organic working fluid turbine. The parameters of the speed and power regulators are tuned to insure the steady of speed and power. A series of dynamic simulation experiments are carried out in Simulink. Through the simulation research of robustness and load disturbance experiments, the designed control system have a good effect on accuracy and dynamic response.

Robust disturbance rejection in modified repetitive control system

This study concerns disturbance rejection for a modified repetitive control system (MRCS) that contains a strictly proper plant with time-varying uncertainties. Since an MRCS is affected by both periodic and aperiodic disturbances, and since the disturbances are often unknown, an equivalent-input-disturbance (EID)-based estimator was added to an MRCS to yield an EID-based MRCS that compensates for all types of disturbances. In this system, the repetitive controller ensures tracking of a periodic reference input, and the incorporation of an EID estimate into the control input enables rejection of unknown periodic and aperiodic disturbances. A robust stability condition for the MRCS was established in the form of a linear matrix inequality, and the condition was used to design the parameters of the controller. This design method handles uncertainties and enables the preferential adjustment of the tracking and control performance of the MRCS. Simulation results demonstrate the validity of the method.

Modified robust external force control with disturbance rejection with application to piezoelectric actuators

In micromanipulation applications, controlling the force exerted on the object is of great importance. In such cases, any uncontrolled forces may damage the object or cause system failure. However, the presence of disturbances such as impedance uncertainties and hysteresis can strongly degrade force control performance and even lead to instability. Therefore, accurate force control when internal and external disturbances occur is a significant challenge. Conventional control methods usually have a number of restrictive conditions especially on the disturbance bounds. To rectify those issues, a modified robust disturbance rejection-based force control approach is proposed in this paper. For this purpose, an appropriate disturbance observer is utilized to estimate the disturbance effect regardless of amplitude. Then a robust control method is employed to achieve the disturbance-free desired dynamic. A modification is also performed to rectify the need for acceleration measurement in the control design. Finally, the force control for an unknown environment in the presence of disturbances is accomplished. The efficiency of the proposed approach is evaluated through simulation studies and compared with the well-known PI method. The experimental results validate the force control performance for the micropositioning piezoelectric actuator.

Some results on disturbance attenuation for Hamiltonian systems via direct discrete‐time design

SummaryThe disturbance attenuation and robust disturbance attenuation problems for Hamiltonian systems in the discrete‐time setting are considered and some new results are presented. The new results are derived utilizing the recently presented dissipativity equality obtained by adding the dissipation rate function to the classical dissipativity inequality. A selection of the dissipation rate function yields new results. These results include a condition on the dissipation structure of the system to achieve the desired disturbance attenuation level and gives direct construction of optimal control laws for any desired disturbance attenuation level. The results remove the need to solve Hamilton–Jacobi–Isaacs inequalities. Copyright © 2014 John Wiley & Sons, Ltd.

Estimation of Load Disturbance Torque for DC Motor Drive Systems Under Robustness and Sensitivity Consideration

This paper presents multiple methods for the design of a robust disturbance torque estimator. The benefit of these designs is that they ensure robust estimation in the presence of model uncertainties and/or noise. It is shown that these estimation schemes can be used to estimate both constant and nearly constant disturbance torques. In order to design the observers, the nominal plant model is expanded to incorporate uncertainties. Various cases for the design of the observer are presented. All of the cases are tested on a real system using varying degrees of model uncertainty to ensure that robust estimation is achieved. The results are validated using an in-line torque sensor and are presented accordingly.

Quantitative Feedback Control of Multiple Input Single Output Systems

This paper presents a robust feedback control solution for systems with multiple manipulated inputs and a single measurable output. A structure of parallel controllers achieves robust stability and robust disturbance rejection. Each controller uses the least possible amount of feedback at each frequency. The controller design is carried out in the Quantitative Feedback Theory framework. The method pursues a smart load sharing along the frequency spectrum, where each branch must either collaborate in the control task or be inhibited at each frequency. This reduces useless fatigue and saturation risk of actuators. Different examples illustrate the ability to deal with complex control problems that current MISO methodologies cannot solve. Main control challenges arise due to the uncertainty of plant and disturbance models and when a fast-slow hierarchy of plants cannot be uniquely established.

Fault Detection in Finite Frequency Domain for Takagi-Sugeno Fuzzy Systems With Sensor Faults

This paper is concerned with the fault detection (FD) problem in finite frequency domain for continuous-time Takagi-Sugeno fuzzy systems with sensor faults. Some finite-frequency performance indices are initially introduced to measure the fault/reference input sensitivity and disturbance robustness. Based on these performance indices, an effective FD scheme is then presented such that the generated residual is designed to be sensitive to both fault and reference input for faulty cases, while robust against the reference input for fault-free case. As the additional reference input sensitivity for faulty cases is considered, it is shown that the proposed method improves the existing FD techniques and achieves a better FD performance. The theory is supported by simulation results related to the detection of sensor faults in a tunnel-diode circuit.

Simulation on Active Disturbance Rejection Control

A highly robust active disturbance rejection controller (ADRC) is developed in this paper. The proposed ADRC consists of a tracking differentiator (TD) in the feed forward path, an extended state observer (ESO), and a nonlinear state error feedback control law (NLSEF) in the feedback path. The control theory, the structure of ADRC and the controller design are presented. LabVIEW is used for modeling, simulation and analysis of the dynamic system. Simulation results show that the proposed ADRC has excellent control performance, especially outstanding adaptability and robustness external disturbances and model uncertainties.

Active Queue Management Based on State Variable Feedback Control

A new AQM algorithm based on state variable feedback control (SPC) is proposed. The future dynamic queue length in data buffer predicted by state space model is successfully introduced into feedback data's advanced prediction to compensate feedback delay. Finally, the control requirement of congestion is converted to optimal control objective function, and drop probability is obtained by solving the optimal problem. The simulation results show that the queue length with SPAQM algorithm reaches the desired value with minimal tracking error and lower drop probability. SPAQM algorithm has better performance than PID algorithms and RED algorithms in terms of disturbance rejection, stability, and robustness.