Presence Of Periodic Disturbances Research Articles

Repetitive dynamic matrix control for systems with periodic specifications

This paper proposes a Repetitive Dynamic Matrix Control (RDMC) for systems with periodic specifications. The new algorithm is able to track periodic references and reject repetitive disturbances with a known period based on a modified prediction error. A repetitive version of the Generalized DMC (GDMC) is also proposed such that it can be applied to control open-loop unstable systems. Only the step-response coefficients are required to describe the dynamical system such that the RDMC preserves the modeling simplicity of the Dynamic Matrix Control (DMC). The proposed solution can be interpreted as an extension of the DMC for repetitive control applications. A data-driven filter design is proposed in order to ensure null prediction steady-state error in the presence of periodic disturbances even for unstable open-loop systems. Two case studies are presented to show the usefulness of the proposed strategy for control systems with periodic specification and to illustrate the typical advantages and drawbacks of the proposed repetitive control extension of the DMC algorithm.

Neural network-based adaptive optimal containment control for non-affine nonlinear multi-agent systems within an identifier-actor-critic framework

This paper addresses the adaptive optimal containment control issue for non-affine nonlinear multi-agent systems in the presence of periodic disturbances. To deal with the disturbed internal dynamics, a fourier series expansion-neural networks-based adaptive identifier is designed for each follower, such that the restrictions posed on the system dynamics are released. Then,an adaptive dynamic programming technique is adopted to acquire the optimized virtual and actual controllers under a simplified actor-critic architecture, where the critic aims to appraise control performance and the actor aims to perform control task. Note that the above updating laws are constructed by the negative gradient of a designed function, which is constructed on the basis of the partial derivative of Hamilton-Jacobi-Bellman equation. Finally, simulation results are provided to show the applicability and effectiveness of the containment control scheme.

Modified Repetitive Control Design for Nonlinear Systems With Time Delay Based on T–S Fuzzy Model

In this paper, based on the Takagi-Sugeno fuzzy model approach, a novel output feedback control strategy is developed for a class of continuous-time nonlinear time delay systems via modified repetitive control scheme. The main objective of this paper is to design a fuzzy rule-based modified repetitive controller such that the system output can track any given periodic reference signal even in the presence of periodic disturbances. For this purpose, by employing fuzzy-dependent Lyapunov-Krasovskii functional together with the free-weighting matrix technique, a new set of sufficient conditions is presented in terms of linear matrix inequalities to guarantee the robust stability of the resulting closed-loop system. Based on these conditions and using internal model principle, it is shown that the system output tracks the given reference input within the desired error. Finally, two application-oriented examples are presented to validate the obtained theoretical results in which the proposed control design scheme gives better performance over the existing control scheme.

A Study on Optimal Compensation Design for Meteorological Satellites in the Presence of Periodic Disturbance

Periodic disturbance may cause serious effects on the attitude of meteorological satellites, and the attenuation of periodic disturbance is required. In this paper, a fundamental study on the optimal design of constant compensations against known-law periodic disturbance for meteorological satellites is investigated. An analytical solution for the relationship between the frequency and amplitude ratios and the response of a typical second-order vibration system is firstly derived. The compensation and disturbance torques are determined according to practical engineering. The criteria for designing the optimal compensations are based on the analytical and simulation results. Then, the criteria are applied to a flexible spacecraft actuated by constant control torque in the presence of sustained periodic disturbance. The optimal compensation torque parameters for spacecraft are acquired based on former criteria. The compensate effectiveness of the optimal compensation torque is provided and compared with results of other selections in the frequency and amplitude ratio domain. Numerical simulation results and experimental results clearly demonstrate the good performance of proposed criteria. This work provides a significant reference for the vibration attenuation of meteorological satellites in the present of periodic disturbance.

Fuzzy Sliding‐mode Strategy for Air–fuel Ratio Control of Lean‐burn Spark Ignition Engines

AbstractMinimization of emissions of carbon dioxide and harmful pollutants and maximization of fuel economy for lean‐burn spark ignition (SI) engines relies to a large extent on precise air–fuel ratio (AFR) control. However, the main challenge of AFR control is the large time‐varying delay in lean‐burn engines. Since the system is usually subject to external disturbances and uncertainties, a high level of robustness in AFR control design must be considered. We propose a fuzzy sliding‐mode control (FSMC) to track the desired AFR in the presence of periodic disturbances. The proposed method is model free and does not need any system characteristics. Based on the fuzzy system input–output data, two scaling factors are first employed to normalize the sliding surface and its derivative. According to the concept of the if‐then rule, an appropriate rule table for the logic system is designed. Then, based on Lyapunov stability criteria, the output scaling factor is determined such that the closed‐loop stability of the internal dynamics with uniformly ultimately bounded (UUB) performance is guaranteed. Finally, the feasibility and effectiveness of the proposed control scheme are evaluated under various operating conditions. The baseline controllers, namely, a PI controller with Smith predictor and sliding‐mode controller, are also used to compare with the proposed FSMC. It is shown that the proposed FSMC has superior regulation performance compared to the baseline controllers.

Heat transfer in a three-dimensional rectangular cavity oriented at an angle to the free-stream

We consider a flow of a viscous incompressible heat-conducting fluid over a cubic cavity. The heat transfer on the bottom of the cavity rotated at an angle to the free stream is studied numerically. The numerical algorithm includes a finite-difference approximation in the spatial coordinates, a semi-implicit time integration method, and a modified version of an iterative stabilized method of biconjugate gradients with an algebraic multigrid preconditioner for solving the Poisson equation. The algorithm is designed for the use of multiprocessor computers. Two different inlet flow conditions are considered: a steady-state flow and a steady flow with superimposed periodic perturbations. In the first case, it is shown that the integral heat transfer rate increases monotonically with increase in the cavity rotation angle α. For α = 45°, the increase in the heat flux amounts to 20%. The presence of periodic disturbances may result in up to 3-fold increase in the integral heat transfer rate as compared to the case of the steady-state inlet flow. The enhancement of heat transfer occurs when the frequency of the inlet flow disturbances is close to the frequency of unstable modes of the mixing layer formed at the upper boundary of the cavity.

Iterative learning control: a method that can improve product quality and productivity in manufacturing

As the world moves toward a fully global economy, manufacturers need to search constantly for ways to secure or maintain a competitive advantage. Iterative learning control (ILC) and its sister field, repetitive control (RC), offer software methods to improve the performance of motion control systems, without requiring purchase of expensive high-precision equipment. And these can often translate into improved product quality, or into faster operations with resulting increases in productivity. When a manufacturing operation involves following a desired trajectory, classical feedback control systems repeatedly produce a trajectory different than commanded. ILC, iteratively adjusts the command aiming for zero tracking error in hardware operation. RC instead aims for zero error following periodic commands or in the presence of periodic disturbances. Improving the precision of motion control systems can translate directly into higher product quality. But it can also improve productivity by allowing higher speed operation while maintaining the original accuracy level. Experiments on a robot at NASA Langley Research Center improved the tracking accuracy by a factor of 1000 in 12 iterations. This article is a tutorial presenting a brief introduction to the concepts underlying these relatively new control methods, together with some illustrations from the author's experience, of their potential for improvement in manufacturing operations.

Tuning functions-based output feedback adaptive spacecraft formation flying despite disturbances

This article presents a non-linear adaptive satellite formation control system based on the tuning functions design method using output feedback. A leader spacecraft is orbiting in an elliptic orbit, and a follower satellite is in motion around it. It is assumed that unknown periodic disturbance forces as well as random disturbances are acting on the follower spacecraft, and its mass is not known. Furthermore, only the relative position of the follower satellite, with respect to the leader satellite, is measured for feedback. The objective is to design an adaptive controller so that the follower spacecraft remains in a specific formation with respect to the leader spacecraft. For the purpose of design, first a simplified model including only periodic disturbance inputs is considered, and a canonical representation of the non-linear relative dynamics is obtained. Based on this canonical form, filters are designed to obtain the estimate of the relative velocity of the follower spacecraft and an output feedback adaptive law is derived for the relative position trajectory control. Based on the Lyapunov approach, it is shown that the closed-loop system is globally uniformly stable, and that the adaptive law accomplishes global asymptotic tracking of the reference trajectory in the presence of periodic disturbances. For robustness with respect to random forces in the model, a modified form of the adaptation law using σ-modification is synthesized. Simulation results are presented, which show that the designed output feedback control system achieves precise formation control, despite the periodic and random disturbance forces and parameter uncertainty in the model.

Six-degree-of-freedom synchronised adaptive learning control for spacecraft formation flying

An adaptive learning synchronisation control strategy for six-degree-of-freedom spacecraft formation flying based on the cross-coupling concept is presented. The proposed strategy allows the spacecraft track the desired attitude and position trajectories in a synchronised fashion, in the presence of periodic disturbances and uncertainties in constant parameters. Illustrative simulations of spacecraft formation flying are conducted to verify the effectiveness of the proposed approach.

Airfoil Performance at Low Reynolds Numbers in the Presence of Periodic Disturbances

The boundary-layer separation and wake structure of a NACA 0025 airfoil and the effect of external excitations in presence of structural vibrations on airfoil performance were studied experimentally. Wind tunnel experiments were carried out for three Reynolds numbers and three angles of attack, involving hot-wire measurements and complementary surface flow visualization. The results establish that external acoustic excitation at a particular frequency and appropriate amplitude suppresses or reduces the separation region and decreases the airfoil wake, i.e., produces an increase of the lift and∕or decrease of the drag. The acoustic excitation also alters characteristics of the vortical structures in the wake, decreasing the vortex length scale and coherency. Optimum excitation frequencies were found to correlate with the fundamental frequencies of the naturally amplified disturbances in the separated shear layer. The results suggest that acoustic waves play a dominant role in exciting the separated shear layer of the airfoil. Moreover, low-frequency structural vibrations are found to have a significant effect on airfoil performance, as they enhance the sound pressure levels within the test section.

Self-tuning control in the presence of periodic disturbance

A pseudo-feedforward method is proposed for adapting an incremental self-tuning controller to reject periodic disturbances. The algorithm begins with an estimate of the disturbance frequency. The amplitude and phase of the disturbance are estimated by augmenting the parameter estimation vector. The estimated disturbance can then be used as a feedforward term with the self-tuning controller. A second stage allows for the estimate of the disturbance frequency to be improved using the estimated amplitude. The algorithm has been shown to be robust in simulation examples and on a pilot heat exchanger.