Ningsu Luo

Semiactive Control Methodologies for Suspension Control With Magnetorheological Dampers

Suspension systems are one of the most critical components of transportation vehicles. They are designed to provide comfort to the passengers to protect the chassis and the freight. Suspension systems are normally provided with dampers that mitigate these harmful and uncomfortable vibrations. In this paper, we explore two control methodologies (in time and frequency domain) used to design semiactive controllers for suspension systems that make use of magnetorheological dampers. These dampers are known because of their nonlinear dynamics, which requires the use of nonlinear control methodologies for an appropriate performance. The first methodology is based on the backstepping technique, which is applied with adaptation terms and H∞ constraints. The other methodology to be studied is the quantitative feedback theory (QFT). Despite QFT is intended for linear systems, it can still be applied to nonlinear systems. This can be achieved by representing the nonlinear dynamics as a linear system with uncertainties that approximately represents the true behavior of the plant to be controlled. The semiactive controllers are simulated in MATLAB/Simulink for performance evaluation.

A linear matrix inequality approach to robust fault detection filter design of linear systems with mixed time-varying delays and nonlinear perturbations

Accepted version of an article in the journal: Journal of the Franklin Institute-Engineering and Applied Mathematics. The definitive version can be found on Sciverse: http://dx.doi.org/10.1016/j.jfranklin.2010.03.004

ROBUST STABILIZATION OF A CLASS OF UNCERTAIN TIME DELAY SYSTEMS IN SLIDING MODE

This paper addresses the problem of robust stabilization of a class of uncertain systems subject to internal (i.e., in the state) point delays, external (i.e., in the input) point delays and nonlinear disturbances by using sliding mode control. Methods for the design of sliding mode controllers based on state feedback, static output feedback and dynamic output feedback, respectively, are proposed. Sufficient conditions for the asymptotic stability and robustnesss of the closed–loop systems are given under a wide class of admissible nonlinear disturbances.

A note on the stability of linear time-delay systems with impulsive inputs

This brief derives sufficiency-type stability results for time-delay linear systems with constant point delays under impulsive inputs of impulses of state-dependent amplitudes occurring separately through time. It is proved that the amplitudes of the impulses and the time intervals between impulses may be chosen sufficiently large if the delay-free dynamics is sufficiently stable compared to the delayed one. It is also seen that faster input impulses of appropriate amplitudes and signs may achieve stabilization if the delay-free dynamics is not exponentially stable.

Design of linear observers for a class of linear hybrid systems

This paper deals with the design of linear observers for a class of linear hybrid systems. Such systems are composed of continuous-time and digital substates and possess, in general, coupling dynamics between both substates. Two observer prototypes based on the prediction error are proposed. The first is based on the observation of an extended discrete system at sampling instants. The discrete extended state is composed of the sampled values of the continuous substate at sampling instants and the digital substate. The estimation of the continuous substate in between sampling instants is made by using the plant parametrization and the sampled prediction error at the preceding sampling instant. The continuous-time state estimates are reinitialized at each new sampling instant by taking values from the corresponding components of the discretized substate of the observer of the auxiliary discrete extended system. The second observer prototype estimates the continuous-time substate for all time from initial conditions which are taken only when the estimation algorithm starts. The observer involves feedback information of the current observation error, that of the preceding sampling instant and that associated with the estimation of the discrete system. As a result, the discontinuities of the estimated substate at sampling instants, which typically occur with the use of the first prototype, are not present in this observation scheme. The exponential convergence to zero of both prediction and observation errors may be ensured under observability and detectability assumptions Furthermore, prescribed pole placement of the state estimation error is achieved under observability of the discrete extended plant. Also, prescribed pole placement of the combined dynamics of the extended plant and observation error can be obtained. For that purpose, the extended hybrid plant is assumed to be controllable when the linear control input is generated from measurements of the state observation. in both observation prototypes.

Modeling and Identification of a Small-scale Magnetorheological Damper

Magnetorheological (MR) dampers are promising devices for vibration mitigation in structures due to their low cost, energy efficiency, and fast response. To use these dampers efficiently it is necessary to have models that describe their behavior with a sufficient precision. However, because a precise modeling of these devices using the laws of physics is an arduous task, semi-physical models are used to describe their behavior instead. Two of these models are explored in this article: a normalized version of the Bouc-Wen model and the Dahl friction model. A methodology for identification is proposed, and the obtained models are tested and validated experimentally.

Semiactive vibration control of offshore wind turbine towers with tuned liquid column dampers using H ∞ output feedback control

This short paper addresses the problem of vibration in wind turbine towers. These structures are subject to winds and waves causing undesirable vibrations that affect the structure integrity and system performance. In order to mitigate the vibrations of the tower, a controllable tuned liquid column damper is placed on its top. We propose the use of H∞ control techniques to formulate a control law. Furthermore, the controller uses output feedback to avoid the dependence on the knowledge of the states of the system. Simulation results illustrate the design procedure proposed in this paper.

Frequency domain control based on quantitative feedback theory for vibration suppression in structures equipped with magnetorheological dampers

This paper addresses the problem of designing quantitative feedback theory (QFT) based controllers for the vibration reduction in a structure equipped with an MR damper. In this way, the controller is designed in the frequency domain and the natural frequencies of the structure can be directly accounted for in the process. Though the QFT methodology was originally conceived of for linear time invariant systems, it can be extended to nonlinear systems. A new methodology is proposed for characterizing the nonlinear hysteretic behavior of the MR damper through the uncertainty template in the Nichols chart. The resulting controller performance is evaluated in a real-time hybrid testing experiment.

Wind turbine control and monitoring

Maximizing reader insights into the latest technical developments and trends involving wind turbine control and monitoring, fault diagnosis, and wind power systems, Wind Turbine Control and Monitoring presents an accessible and straightforward introduction to wind turbines, but also includes an in-depth analysis incorporating illustrations, tables and examples on how to use wind turbine modeling and simulation software. Featuring analysis from leading experts and researchers in the field, the book provides new understanding, methodologies and algorithms of control and monitoring, computer tools for modeling and simulation, and advances the current state-of-the-art on wind turbine monitoring and fault diagnosis; power converter systems; and cooperative & fault-tolerant control systems for maximizing the wind power generation and reducing the maintenance cost. This book is primarily intended for researchers in the field of wind turbines, control, mechatronics and energy; postgraduates in the field of mechanical and electrical engineering; and graduate and senior undergraduate students in engineering wishing to expand their knowledge of wind energy systems. The book will also interest practicing engineers dealing with wind technology who will benefit from the comprehensive coverage of the theoretic control topics, the simplicity of the models and the use of commonly available control algorithms and monitoring techniques.

An LMI approach to vibration control of base-isolated building structures with delayed measurements

In this article, we address a convex optimisation approach to the problem of state-feedback H ∞ control design for vibration reduction of base-isolated building structures with delayed measurements, where the delays are time-varying and bounded. An appropriate Lyapunov–Krasovskii functional and some free-weighting matrices are utilised to establish some delay-range-dependent sufficient conditions for the design of desired controllers in terms of linear matrix inequalities. The controller, which guarantees asymptotic stability and an H ∞ performance, simultaneously, for the closed-loop system of the structure, is then developed. The performance of the controller is evaluated by means of simulations in MATLAB/Simulink.