http://www.ifac-papersonline.net/ en Copyright 12:18 AM Thursday 23, 2013 IFAC-PapersOnline http://www.ifacpapersonline.com 12:18 AM Thursday 23, 2013 12:18 AM Thursday 23, 2013 ET webmaster@ifac-papersonline.net webmaster@ifac-papersonline.net http://www.ifac-papersonline.net/Detailed/53227.html 04:00 PM Wednesday 31, 1969 http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53229.html 04:00 PM Wednesday 31, 1969 A revolution in control theory thought happened in the early 1970’s when the dominant focus of research shifted from optimality to robustness in response to unexpected failures of optimal control theory to produce feedback control designs capable of tolerating normal differences between design models and reality. The robustness concept has since become such an integral part of present day control theory that it is difficult to imagine that time long ago when the concept lacked a clear mathematical representation and the tools of multivariable robustness analysis were yet to be identified. We shall revisit that time to examine the events that facilitated, and necessitated, this remarkable paradigm shift. Next, looking to the future, we will consider how failures of robust control designs to cope with incorrect uncertainty estimates are beginning to spur control theorists to consider data-driven problem formulations for estimation and control that tacitly question the roles of basic concepts like ‘true model and uncertainty bounds’, stochastic noise models and even Bayesian probability. We will discuss how and why Karl Popper’s scientific logic of unfalsification seems to be emerging as a central concept in these data-driven problem formulations, and how the unfalsification concept might again shift the focus of mathematical research in the areas of estimation and control. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53231.html 04:00 PM Wednesday 31, 1969 In this paper we discuss numerical strategies to find periodic orbits of nonlinear dynamic system. These orbits shall be open-loop stable and robust with respect to bounded disturbances. For this aim, we review and extend existing techniques from the field of reachability analysis and ellipsoidal calculus to compute robust positive invariant tubes for nonlinear dynamic systems. We suggest a conservative approximation strategy for robust stability optimization providing guarantees on the region of attraction. The technique is tested by applying it to an inverted spring pendulum for which robust and open-loop stable orbits exist. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53233.html 04:00 PM Wednesday 31, 1969 Finite-time state-feedback stabilization of a class of continuous-time nonlinear systems with conic type nonlinearities, bounded feedback control gain perturbations, and additive disturbances is presented. Sufficient conditions for the existence of a robust and resilient linear finite-time state-feedback controller for this class of systems are derived. Then, using linear matrix inequality techniques, solutions for the controller gain and the upper bound on the gain perturbations are obtained. The developed controller is robust for all unknown nonlinearities lying in a hyper-sphere and all admissible disturbances. Furthermore, it is resilient against any bounded perturbations that may modify the controller’s gain by at most a prescribed amount. We conclude the paper with a numerical example illustrating the applicability of the main result. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53235.html 04:00 PM Wednesday 31, 1969 In this paper a time-delayed acceleration measurement is used to linearize a second order nonlinear system. A theoretical foundation is developed, and a control strategy is presented which handles the challenges related to classical linearization. Utilizing the acceleration measurement to directly cancel the nonlinearities constitute a feedforward approach which increases robustness with respect to unmodeled dynamics and model uncertainties. Due to the time-delay, one or more perturbation terms dependent on a previous state of the system appears. This work outlines a stability criterion which these terms must satisfy in order for the linearization to be valid, where it is shown that the performance of the scheme is dependent on the measurement time-delay. The proposed method proves feasible when compared to two other nonlinear control strategies, including a conventional linearization control law and a sliding mode control law. In comparison, the feedforward linearization features robust performance without aggressive control input. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53237.html 04:00 PM Wednesday 31, 1969 A robust Kalman conjecture is defined for the robust Lur’e problem. Specifically, it is conjectured that the nonlinearity’s slope interval for which robust absolute stability is guaranteed corresponds to the robust interval of the uncertain plant. We verify this robust Kalman conjecture for first-order plants perturbed by various norm-bounded unstructured uncertainties. The analysis classifies the appropriate stability multipliers required for verification in these cases. Robust control of Lur’e-type nonlinear systems satisfying this novel conjecture can therefore be designed using linear robust control methods. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53239.html 04:00 PM Wednesday 31, 1969 This paper considers the output synchronization of nonlinear agents with gain-bounded uncertainty in the input-output stability framework. Communication among the agents is constrained by the topology of the associated directed graph. A sufficient condition for achieving the robust synchronization is derived in terms of a matrix inequality under the assumption that the nominal dynamics of the agents satisfy a certain passive properties. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53241.html 04:00 PM Wednesday 31, 1969 In the modeling of stochastic nonlinear systems it is often necessary to consider the existence of uncertainties about some parameters of the system or in the distribution implied by the stochastic shocks, and in this setting, the control policy can be obtained by the rules of robust control theory. To present a different way to handle control systems in this scenario, this paper introduces a theoretical framework for continuous-time stochastic nonlinear systems in which the Control Variations Increase the state Uncertainty (CVIU systems). This type of system can be applied in several areas of science and engineering, due to its ability in dealing with complex stochastic systems, for which the dynamics are not completely known. In particular, the paper applies this model to a problem of fishery management in an unknown environment, and establishes a harvesting rule for it based on the CVIU approach. Using dynamic programming and tools from nonsmooth analysis, the control solution indicates the existence of a region in the state space in which the optimal harvesting is of no variation, yielding periods of inaction. This behavior obtained from optimality is somehow expected from the cautionary nature of controlling underdetermined systems. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53243.html 04:00 PM Wednesday 31, 1969 New algorithms for estimation of the frequencies of oscillating waveform signals are described. Model of the signals is presented in the form of linear difference equation with unknown coefficients, which define the frequencies and amplitudes. Coefficients are estimated utilizing the property of the persistence of excitation of oscillating signals. Exponentially damped and oscillating signals are described in a unified framework. A property of excitation is proved for exponentially damped signal that contains a single frequency via diagonal dominance of an information matrix. Two applications of this frequency estimation technique are considered. The first one is filtering of the wind speed signal in wind turbine control applications, and the second one is the frequency estimation of exponentially damped signal motivated by the engine knock detection applications. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53245.html 04:00 PM Wednesday 31, 1969 This paper deals with robust estimation of speed and rotor flux for sensorless control of motion control systems which use induction motors as actuators. Due to the observability lack of five and six order Extended Kalman Filters, speed is here estimated by means of a Total Least Square algorithm with Neural Adaptive mechanism. This allows the use of a fourth-order Kalman Filter for estimating rotor flux and to filter stator currents. To cope with motor-load parameter variations, a descriptor-type robust Kalman Filter is designed taking explicitly into account these variations. The descriptor-type structure allows direct translation of parameter variations into variations of the coefficients appearing in the model. This, in turn, brings to some simplifications in the design of the filter. Simulation experiments are shown with the aim of verifying the goodness of the whole estimator. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53247.html 04:00 PM Wednesday 31, 1969 The thermal behavior of high-temperature fuel cell systems is characterized by a large variety of parameters which are not directly accessible for measurements. To derive mathematical models for the dynamics of such systems, it is essential to identify the parameter values on the basis of knowledge about the current operating conditions. After an offline parameter identification with suitable experimental data, the values are further adjusted by online state and parameter estimation. In previous work, various approaches have been employed for the offline parameter identification of fuel cell systems. These approaches include the application of commercial local optimization procedures and novel interval arithmetic routines which aim at a global optimization within a bounded parameter range. Since it could be shown that interval procedures provide system parameterizations with an improved approximation quality, further alternative algorithms are investigated in this paper for the parameter identification of fuel cell systems. These algorithms make use of a sensitivity analysis of suitable performance criteria. These performance criteria can be employed both offline for parameter identification and online for state and disturbance estimation. Numerical results show the advantages of the sensitivity-based procedure in comparison with the above-mentioned estimation approaches. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53249.html 04:00 PM Wednesday 31, 1969 We propose a multi-model adaptive control scheme for uncertain linear parameter varying plants based on the concept of model unfalsification. The approach relies on examining the ability of a pre-computed set of plant-controller candidates and choosing the one that is best able to reproduce observed in- and output signal samples. The ability to reproduce observations is measured as an easily computable signal norm. Compared to other related approaches, our procedure is designed to be able to handle significant measurement noise and closed-loop correlations between output measurements and control signals. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53251.html 04:00 PM Wednesday 31, 1969 This paper proposes an approach to blind system identification for disturbance rejection control. We first identify plant dynamics with unknown disturbance, based on a well-known FIR (Finite Impulse Response) approximation technique for BSD (Blind Signal Deconvolution) in terms of independence of signals. Since we are more interested in the system itself than signal deconvolution, we adopt polynomial matrix fraction with a given degree structure, and then adjust the coefficients by projecting the FIR learning law to this parameter space of modest dimension. Finally we design feedback control for disturbance rejection via the identified system representation. Numerical simulation for a simple example is carried out to illustrate the proposed approach. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53253.html 04:00 PM Wednesday 31, 1969 In this paper, a comparison of polytopic and norm-bounded approach is sought for stability analysis of networked control systems (NCS) with uncertain time-varying delays. The delays are considered to be general in the sense that these could be either smaller or greater than the sampling time. For stability analysis, first the continuous-time NCS plant is represented remodeled into tan equivalent discrete time one. The uncertainties in the NCS model arises due to the time varying delays are modeled using both polytopic and norm-bounded approach. Considering a state-feedback controller, LMI conditions are used to exploit the stability region in the controller and delay parameter plane using two numerical examples. It is observed that the norm-bounded approach is slightly conservative whereas higher computational complexities are involved in the polytopic one. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53255.html 04:00 PM Wednesday 31, 1969 Paper studies the problem on robust networked static output feedback model predictive controller design that stabilizes uncertain system with guaranteed cost. The upper bound of the time-delay is assumed to be bigger than sampling time. Control design is based on sufficient robust stability condition formulated as a solution of bilinear matrix inequality BMI. The example illustrates the viability of the proposed output feedback design method. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53257.html 04:00 PM Wednesday 31, 1969 This paper concerns the stabilization of two-input two-output (TITO) discrete-time linear time-invariant (LTI) systems over parallel additive white noise (AWN) channels, in which each individual channel is independently constrained in SNR. Necessary and sufficient conditions for stabilizability are obtained on the SNR's of the channels, in terms of the unstable poles and non minimum phase zeros of the plant, for both state and output feedback control. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53259.html 04:00 PM Wednesday 31, 1969 This paper studies stabilization of Networked Control Systems (NCS) with communication constraints, dynamic quantization, variable delay and variable sampling intervals. The system sensor nodes are supposed to be distributed over a network. The scheduling of sensor information towards the controller is ruled by the classical Round-Robin protocol. We develop a {it time-delay approach} for this problem by presenting the closed-loop system as a continuous-time switched system with multiple and {it ordered time-varying delays}. Firstly, the input-to-state stability conditions in term of Linear Matrix Inequalities (LMIs) are derived via appropriate Lyapunov-Krasovskii-based methods. Then on the basis of input-to-state stability conditions, we propose a zooming algorithm that allows to provide the exponential stability. Polytopic uncertainties in the system model can be easily included in the analysis. The efficiency of the method is illustrated on the batch reactor %and on the cart-pendulum benchmark problem. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53261.html 04:00 PM Wednesday 31, 1969 In this paper a modified Euler transformation is introduced and studied. The main merit of this transformation is to outperform stability preservation (with respect to the traditional Euler transformation) besides preserving the matrix sparseness. This is particular appealing in the analysis of positive systems since it is shown that stability is preserved independent of the sampling period. A brief collection of results for switched systems has been also provided. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53263.html 04:00 PM Wednesday 31, 1969 In order to achieve high accurate pointing with robustness to system uncertainty, inertial Line of Sight stabilization loop controllers are designed with a specific structure related to the nature of the disturbances to be rejected. For this problem, H-infinity Loop Shaping synthesis is efficiently used, but the resulting controllers are of high order because of the order of the synthesis model and weighting filters which are useful to shape the loop regarding synthesis objectives. In this paper, reduced order controllers are investigated through recently developed tools that recast the fixed order H∞ synthesis problem as a nonsmooth optimization problem. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53265.html 04:00 PM Wednesday 31, 1969 This paper presents new control laws synthesis methods applied to the attitude control of flexible structures. These methods are based on the structured H-infinity synthesis and the acceleration sensitivity formulation. First the theoretical background is presented on the structured H-infinity synthesis and the acceleration sensitivity problem. Then these methods are applied on an academic spring-masses example, which is representative of a flexible structure. Finally, a conclusion of the use of these methods for the attitude control of flexible space structures is proposed. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53267.html 04:00 PM Wednesday 31, 1969 Par2 is a two degrees of freedom high-speed and high-accuracy pick-and-place parallel robot. Considering trajectory accelerations at the order of 10g in its 3.5 kg charged end-effector, significant vibrations show up immediately after reaching a stop position, consequently jeopardizing operation cycle times. These vibrations, measured by three orthogonally oriented accelerometers, are particularly less damped in the direction normal to the trajectory plane. In order to actively minimize these vibrations, piezoelectric patches are wrapped around the robot arms. For this system, an identified model interconnected with an H-infinity controller are calculated. Laboratory experiments attest the adequacy of the controller. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53269.html 04:00 PM Wednesday 31, 1969 Synthetic biology is highly valued in the recent decade. In a previous study, Elowitz and Leibler (Nature, vol. 403, pp. 335-338, 2000) have construct a biological oscillator in consisting of three genes, and found out its mathematical expressions. Designing the optimal transcription rates of mRNA and the decay rates of protein concentration to track desired sinusoidal signal and achieve the best oscillation have been becoming a challenge problem. Actually, design of an oscillator can be regarded as a tracking design problem from the control engineer’s viewpoint. Genetic algorithm (GA) bears the feature of searching the global optimum for the optimization problem. However, subject to the fixed solution structure, the results may not be the cheap ones. In this paper, we introduce the real structure genetic algorithm (RSGA) to solve the design problem of synthetic biological oscillators. The design approach is shown to be capable of yielding genetic oscillators with a cheaper structure. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53271.html 04:00 PM Wednesday 31, 1969 This paper presents the application of an H∞ control technique to the control of a HAPD (High Altitude Performance Demonstrator) aircraft having redundant surfaces. The interaction of the controlling moments and forces with the aircraft flexible modes requires a careful use of the control resources in the frequency domain also considering that aerodynamic surface deflections are limited in amplitude and angular rates. A fixed structure H∞ control problem design, inspired by the classical minimum norm allocation control approach, is formulated and solved in terms of Linear Matrix Inequalities. Numerical simulations on the full nonlinear model of the HAPD including flexibility modes are carried out to show the effectiveness of the proposed technique on the whole flight envelope which is covered using a parameter dependent formulation of the linearized model plants. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53273.html 04:00 PM Wednesday 31, 1969 Vibration reduces the ability of a camera to detect far away targets which leads to the use of stabilized platforms. Despite of much research on stabilized platforms, the need of more accurate systems still exists as a consequence of sensor resolution improvements. The stabilization problem is the problem of attenuating persistent disturbances which is a suitable case-study for l_1 control problem. In this paper, a robust l_1 controller is designed for a nonlinear gyro-stabilized system based on LMI approach. The performance of the introduced controller is evaluated by simulation and real-time implementation and is compared with a Proportional-plus-Integral (PI) controller with a notch filter. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif http://www.ifac-papersonline.net/Detailed/53275.html 04:00 PM Wednesday 31, 1969 Multivariable Quantitative Feedback Theory (QFT) is applied to a bank-to-turn missile plant for disturbance rejection specifications. The plant is first partially decoupled over the plant uncertainty to reduce the interaction index to below unity for frequencies around and higher than the expected closed-loop system bandwidth. QFT methodology is then applied to design a diagonal controller to meet the disturbance rejection specifications. The resulting fully populated controller is able to meet the design specifications, which was not achievable using a diagonal controller because of the interaction and delay in the system. http://www.ifac-papersonline.net/static/luna/images/ifac/icon-download.gif