Robust control of Cassette Multi-functional Mover for ITER remote handling tasks

This paper deals with uncertain model structures, model validation and robust performance analysis of active magnetic bearings. The dynamics of active magnetic bearing systems are characterized by their instability and complex dynamics of rotor and electromagnets. The feedback control is indispensable to stabilize the system, further the closed-loop systems of magnetic bearings should have robustness for stability and performance against model uncertainties. First we derive a nominal mathematical model of AMBs as a linear state-space model under some assumption and idealization, then we consider the discrepancy between the real physical systems and the obtained nominal design model. This discrepancy can be expressed as the structured uncertainties by Linear Fractional Transformation. These uncertainties include linearization error, parametric uncertainties, unmodeled dynamics, and gyroscopic effect. Then we set the interconnection structure which contains the above structurally represented uncertainties. Next we design a robust controller which achieves robust performance condition. Finally, we validate the interconnection structure with the nominal model and uncertainties, and analyze the robustness of stability and performance of the closed-loop system via the mixed structured singular value.

Robust tracking control for vehicle electronic throttle using adaptive dynamic sliding mode and extended state observer

Covariance matrix adaptation evolution strategy based design of fixed structure robust H∞ loop shaping controller

Robust control of an industrial boiler system; a comparison between two approaches: Sliding mode control & [formula omitted] technique

The automatic pouring of molten metal from a ladle into a mold by a robot requires an high-precision tracking control of the flow rate. Due to the hydrodynamics of the liquid metal, the model of the pouring process is highly nonlinear which has to be considered for the model-based design of the tracking control. The two design approaches studied in the paper combine a feedforward and a feedback control in order to obtain a precise and robust tracking performance. Thereby, the property of differential flatness is used for the design of the tracking control, and the unmeasured states are reconstructed for the feedback control by an unscented Kalman filter. Two proposed control schemes are compared by simulations of the automatic pouring robot together with the pouring process.

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

High damping ratio and fast settling time are very challenges for improving the stability performance in power system. In this paper, an energy capacitor system (ECS) is applied in a two-area multi-machine power system to provide the transient stability enhancement. The algorithm for designing the robust damping controller of the ECS is based on the loop shaping control. The results from the design are the control parameters of the ECS damping controller with the constraint that the size of the ECS must satisfy the criteria of damping consideration. From the simulation results, it can be found that the ECS can effectively enhance the damping of power system oscillations. Moreover, the combination of ECS and the existing power system stabilizers (PSSs) allows exceptional performance and more desirable size of ECS.

Sufficient conditions for robust stability of multivariable quadratic dynamic matrix controllers with an end condition (EQDMC) are developed, and the effect of these conditions on closed‐loop performance is examined. Hard and soft constraints on process inputs and outputs, and process modeling uncertainty are present Modeling uncertainty is quantified in the time domain as upper and lower bounds on the coefficients of a finite pulse response process model. The robust stability conditions that we develop involve the prediction and control horizon lengths, and a set of inequalities that the move‐suppression coefficients in the on‐line EQDMC objective function must satisfy. These conditions imply that for processes with modeling uncertainty, the move‐suppression coefficients could be quite large and quite sensitive to the control horizon length and process modeling errors. This could make the EQDMC controller conservative, thus significantly deteriorating performance. To determine the optimal control horizon length corresponding to the best robust performance of the EQDMC controller for a class of disturbances, follow the proposed EQDMC controller design methodolo∼. To illustrate this methodology simulations on an SISO example and a 2 × 2 subsystem of the Shell Standard Control Problem are presented.

This thesis addresses stable inversion based output tracking control and its applications to robotic systems. It considers the non-causal invertibility (stable inversion) problem of control systems in its various aspects including properties of stable inverses and algorithms for constructing stable inverses. Then, the stable inversion approach is applied to solve a control problem of long-standing interest: output tracking control for non-minimum phase nonlinear systems. A minimum energy property of stable inverses is firstly established. The property claims that given any desired output trajectory, out of infinitely many possible inverse solutions, the one provided by the stable inversion process is the only one that has finite energy. Based on this property, a numerical procedure is developed to provide an efficient approach to construct stable inverses. Secondly, a new output tracking control design is developed. The design incorporates stable inverses and assumes a controller structure of feed-forward plus feedback. It achieves high precision tracking together with closed-loop stability. Furthermore, when system uncertainties are considered and assumed to satisfy the so-called matching conditions, a modified controller structure is presented and the corresponding robust tracking performance is discussed. Finally, the stable inversion based tracking control design is applied to three flexible robotic systems. The first study is output tracking control of a flexible-joint robot. The application demonstrates how the new design deals with the undesirable non-minimum phase property and achieves desired output tracking. The second application is tip trajectory tracking for a two-flexible-link manipulator. This thesis, for the first time, addresses the problem of stable tip trajectory tracking without any transient or steady-state errors for such non-minimum phase systems. In the third application, a new optimal motion control strategy for a flexible space robot is presented. The space robot system is assumed to consist of a two-link flexible manipulator attached to rigid space-craft. Optimality is in the sense that a performance index measured by maneuvering time, control effort, and structural vibrations is minimized while the interference from the manipulator to spacecraft is kept satisfactorily small. Studies on three applications demonstrate that the stable inversion based control design is very effective on output tracking for various robotic systems. This approach is expected to perform equivalently well for many other realistic non-minimum phase nonlinear systems.

The robust stabilisation for a general class of disturbed nonlinear systems subject to state-dependent uncertainties is addressed in this paper. Different from most existing results, the lumped uncertainty, including external disturbances and model uncertainties, is relaxed to be bounded by some nonlinear functions rather than constants in this paper. Based upon the classical design procedure of disturbance observer-based control (DOBC), a new continuous saturation-based dynamic controller is proposed to estimate the lumped uncertainty. By the delicate design of several compact sets, the qualitative robust stability of the closed-loop system is guaranteed in the sense that all the signals of the closed-loop system can converge to an arbitrarily small compact set in a finite time. Furthermore, when the external disturbances are constants, the semi-global asymptotic stability can also be guaranteed by the proposed controller. Finally, the relationship between system uncertainties and observer gain is shown by a numerical simulation example.

ROBUST ANALYSIS OF DISTILLATION COLUMN DYNAMICS

The book is examined in the context of its suitability for a first engineering course in feedback control. The text covers several topics normally included in the most current introductory feedback control texts, including: transfer functions and state-space descriptions; Routh-Hurwitz and Nyquist stability criteria; and state-feedback and linear-quadratic regulator theory. It also includes more contemporary topics, such as: robust stability and performance for unstructured perturbations; strong stabilization and Youla parameterization; generalized plants and H/sub/spl infin// design; and H/sub/spl infin// optimization by model matching and interpolation theory. Short appendices are included on normed linear spaces, matrix and abstract algebra, and state-space system manipulations. The material is well presented, with careful proofs of key results. Each chapter includes numerical examples, together with a good list of homework exercises. Some Matlab functions for computing numerical solution are mentioned, but the discussion of software is limited. Unfortunately, the mathematical level of the test is too high, at least for most programs in the United States. The book also omits several standard topics associated with engineering course on feedback control, such as modeling of physical systems, root-locus analysis, digital control, and an introduction to nonlinear systems. As it is, the book would make a very good test for a graduate engineering course in linear feedback control. It could also be a valuable reference for graduate engineering students or applied mathematics students interested in research in the control area.

A novel robust scheme for Transfer Alignment (TA) is proposed for improving the accuracy of the navigation of a Hypersonic Cruise Vehicle (HCV). The main goal is to instil robustness in the safety and accuracy of the attitude determination, despite mode uncertainties. This article focuses on Robust Sparse-Grid Quadrature Filtering (R-SGQF) using two given robust factors for norm-bounded model uncertainties in non-linear systems. Missile dynamic and measurement model uncertainties are established to validate TA technologies. The nominal stability of the R-SGQF is defined by estimating error dynamics. The technique gives sufficient conditions for the R-SGQF in terms of two parameterised Riccati equations. Robust stability is analysed using Lyapunov theory and the accuracy level of the Sparse-Grid Quadrature (SGQ) algorithm. Embedding the SGQ technique into the robust filter structure, R-SGQF is not only of robust stability against uncertainty but also of higher accuracy. The simulation results of the TA algorithm demonstrate that attitude determinations validate the effectiveness of the R-SGQF algorithm.

An H∞-Based optimal vibration isolation system using patch-type piezoelectric actuators and sensors, suitable for application on high-precision manufacturing equipment that is being affected by external disturbances, has been designed. Reductions of the force transmitted through the structure range from approximately 5 to 30 dB in the frequency band of interest. Robust stability, nominal performance and robust performance have all been verified using the structured singular value, μ, and simulation testing for the set of plants within a derived uncertainty set. In addition, the H∞ controller is compared to an LQG-optimal controller designed for the same structure. The LQG controller, while achieving nominal performance comparable to the H∞ controller and being of significantly lower order, was shown to be unstable via μ-analysis and simulation testing. Thus, the LQG design should not be applied to a machine where there is significant in-band model uncertainty. Use of light-weight patch-type piezoelectric actuators and sensors provides a low-cost, easily-installable way of applying this technique to manufacturing equipment requiring isolation from low-frequency disturbances.

Linear quadratic state feedback regulators make the resulting closed-loop systems stable enough, i.e. they realize robust stabilization. Many attempts at robust stabilization using linear quadratic regulators have been reported. One of the major trends of formulating uncertainty in systems is to express perturbed parameters as the sum of two terms, i.e. nominal values and the deviation from them. In this paper, it is assumed that the upper and lower bounds for each uncertain parameter can somehow be estimated. This enables us to dispense with nominal values. The main aim is to contrive a robust feedback stabilization law for systems with parameters falling into certain ranges via a linear quadratic regulator based only upon information on their bounds. The systems under consideration are therefore those having interval system matrices (in which each element has the above-mentioned two-sided bounds). A certain feedback law is a stabilizing law for a system with an interval system matrix if and only if the same feedback law remains so for systems with system matrices whose entries are all possible combinations of the endpoints of their variation range.