Academic literature on the topic 'Adaptive disturbance attenuation'

This paper investigates the adaptive feedback passification and disturbance attenuation problems for a class of switched nonlinearly parameterized systems. First, a state-dependent switching law and a set of adaptive feedback controllers with new control inputs are designed to render the resulting closed-loop system passive for a class of switched nonlinearly parameterized systems without external disturbance. Then, the new control inputs are designed to solve the disturbance attenuation problem. Second, a set of adaptive feedback controllers and a composite state-dependent switching law are designed to solve the adaptive feedback passivity-based disturbance attenuation problem for a class of cascaded switched nonlinearly parameterized systems. A numerical example shows the effectiveness of the proposed method.

This paper presents the adaptive controller design for brushed permanent magnet DC motor used in velocity-tracking applications based on worst-case approach. We first formulate the robust adaptive control problem as a nonlinearH∞-control problem under imperfect state measurement, and then solve it using game-theoretic approach. The controller guarantees the boundedness of closed-loop signals with bounded exogenous disturbances, and achieves desired disturbance attenuation level with respect to the unmeasured exogenous disturbance inputs and the measured disturbance inputs. The strong robustness properties are illustrated by a simulation example.

In this paper, an adaptive composite anti-disturbance control structure is constructed for a class of non-linear systems with dynamic non-harmonic multisource disturbances. The key point of this paper is that a kind of non-harmonic disturbance, which has non-linear internal dynamics and complex features, is involved. A non-linear exogenous system is employed to describe the dynamic non-harmonic disturbances and several useful assumptions are introduced. By introducing a non-linear damping term, a novel adaptive non-linear disturbance observer is constructed. Based on the disturbance/uncertainty estimation and attenuation (DUEA) schemes, a composite anti-disturbance control structure is synthesized. Meanwhile, a new sufficient condition is derived and the stability of the closed-loop system is proved. Several illustrative examples are employed to demonstrate the effectiveness of the proposed method.

We present a systematic procedure for designing H∞-optimal adaptive controllers for a class of single-input single-output parametric strict-feedback nonlinear systems that are in the output-feedback form. The uncertain nonlinear system is minimum phase with a known relative degree and known sign of the high-frequency gain. We use soft projection on the parameter estimates to keep them bounded in the absence of persistent excitations. The objective is to obtain disturbance attenuating output-feedback controllers which will track a smooth bounded trajectory and keep all closed-loop signals bounded in the presence of exogenous disturbances. Two recent papers (Pan and Bas¸ar, 1996a; Marino and Tomei, 1995) addressed a similar problem with full state information, using two different approaches, and obtained asymptotically tracking and disturbance-attenuating adaptive controllers. Here, we extend these results to the output measurement case for a class of minimum phase nonlinear systems where the nonlinearities depend only on the measured output. It is shown that arbitrarily small disturbance attenuation levels can be obtained at the expense of increased control effort. The backstepping methodology, cost-to-come function based H∞ -filtering and singular perturbations analysis constitute the framework of our robust adaptive control design scheme.

The problem of designing an adaptive backstepping controller for nonlinear static var compensator (SVC) system is addressed adopting two perspectives. First, instead of artificially assuming an upper bound or inequality scaling, the minimax theory is used to treat the external unknown disturbances. The system is insensitive to effects of large disturbances due to taking into account the worst case disturbance. Second, a parameter projection mechanism is introduced in adaptive control to force the parameter estimate within a prior specified interval. The proposed controller handles the nonlinear parameterization without compromising control smoothness and at the same time the parameter estimate speed is improved and the robustness of system is strengthened. Considering the short-circuit ground fault and mechanical power perturbation, a simulation study is carried out. The results show the effectiveness of the proposed control method.

La tesi presenta recenti sviluppi nel progetto di leggi di controllo non lineari per motori ad induzione e generatori sincroni: tecniche di controllo robuste, adattative, in retroazione dallo stato o dall'uscita sono utilizzate per tali sistemi elettromeccanici descritti da equazioni differenziali ordinarie, deterministiche e ¯nito-dimensionali e possibilmente caratterizzati da incertezze come parametri non noti (costanti o tempovarianti). I motori ad induzione, che, grazie alla loro più semplice struttura, sono più affidabili e meno costosi di quelli a magneti permanenti, a riluttanza variabile e in corrente continua, sono difficili da controllare per diverse ragioni: le dinamiche sono intrinsecamente non lineari e multivariabile (due ingressi di controllo e due uscite da controllare) ; non tutte le variabili di stato e non tutte le uscite da controllare possono essere disponibili per la retroazione; sono presenti parametri critici incerti, come la coppia di carico, tipicamente non nota in tutti i motori elettrici e la resistenza rotorica, che può variare fino al 100 % durante il funzionamento a causa del riscaldamento del rotore. La disponibilità di potenti DSP a basso costo e i progressi nell'elettronica di potenza hanno reso algoritmi complessi implementabili anche per motori ad induzione di media e piccola taglia, che, in tal modo, sono effettivamente in grado di sostituire i motori elettrici usati, ammesso che siano garantite alte prestazioni dinamiche ed elevata e±cienza: ciò ha motivato intensi sforzi di ricerca nel progetto di controllori non lineari per motori ad induzione. In modo analogo, la stabilizzazione transitoria e la regolazione della tensione per sistemi di potenza sono problemi di controllo classicamente di±cili: tutti i modelli dinamici che sono stati proposti per una singola macchina connessa a un in ¯ n ite bu s mostrano una intrinseca natura non lineare e, di conseguenza, diversi punti di equilibrio stabili e instabili. Primi studi miravano alla determinazione di regioni di stabilità delle condizioni operative desiderate, via funzioni di Lyapunov, cosi da studiare l'effetto delle improvvise perturbazioni meccaniche e elettriche che possono destabilizzare il sistema e forzare il singolo generatore ad essere disconnesso dalla rete. Il problema consiste dunque nel mantenere la velocità del generatore prossima alla velocità sincrona quando perturbazioni occorrono (stabilizzazione transitoria) e regolare la tensione di uscita al corrispondente valore di riferimento nel caso di perturbazioni costanti e permanenti (regolazione della tensione in uscita). A tal riguardo, i controllori lineari realmente impiegati, progettati sulla base di approssimazioni lineari attorno alle condizioni operative, non sono in grado di sostenere le forti perturbazioni che tipicamente occorrono nei sistemi di potenza: controllori non lineari sono di conseguenza richiesti. La tesi è suddivisa in due parti: la prima parte (motore ad induzione) è formata dai capitoli 2, 3 e 4, mentre la seconda parte (generatore sincrono) consiste dei capitoli 5 e 6. I capitoli 2 e 3 affrontano il problema del controllo di motori ad induzione senza sensore di velocità: l'esistenza di uno schema di controllo globale è esplorata nel capitolo 2 mentre una legge di controllo non lineare adattativa è progettata nel capitolo 3. Il capitolo 4 è dedicato al progetto di un controllore non lineare per motori ad induzione sen so rless: uno schema di controllo in retroazione dall'uscita è proposto. I capitoli 5 e 6 concernono il problema del controllo di un generatore sincrono con incertezze nei parametri: nel capitolo 5, un controllore non lineare robusto adattativo è presentato per la stabilizzazione transitoria, mentre il capitolo 6 propone una legge di controllo non lineare robusta adattativa che garantisce sia stabilizzazione transitoria che regolazione della tensione in uscita.
The thesis incorporates recent advances in the design of nonlinear control laws for induction motors and synchronous generators: robust, adaptive, state or output feedback control techniques are used for both these electro-mechanical systems which are modelled by ¯nite dimensional, deterministic ordinary differential equations and are possibly affected by uncertainties, such as unknown constant and time-varying parameters. Induction motors, which, due to their simpler construction, are more reliable and less expensive than those permanent magnet, switched reluctance and d.c. motors are di±cult to control for several reasons: their dynamics are intrinsically nonlinear and multivariable (two control inputs and two outputs to be controlled); not all of the state variables and not all of the outputs to be controlled may be available for feedback; there are critical uncertain parameters such as load torque, which is typically unknown in all electrical drives, and rotor resistance, which, due to rotor heating, may vary up to 100% during operations. The availability of low cost powerful digital signal processors and advances in power electronics made complex algorithms implementable even for medium- and small-size induction motors, which, in this way, could replace currently used motors provided that high dynamic tracking performance along with highpower efficiency are achieved: this is what motivated intense research efforts in induction motor control design. In analogous way, transient stabilization and voltage regulation for power systems are classically difficult control problems: all the dynamic models which have been developed for a single machine connected to an in¯nite bus show an intrinsic nonlinear nature and, consequently, there are several stable and unstable equilibrium points. Early studies aimed at determining the stability regions of desired operating conditions by means of Lyapunov functions in order to study the effect of perturbations. In fact, sudden mechanical and electrical perturbations may drive the system outside its stability region and force the generator to be disconnected from the network. The transient stabilization and voltage regulation problem consists in the design of an excitation control which keeps the generator speed close to the synchronous speed when perturbations occur (transient stabilization) and regulates the output voltage to the corresponding reference value in the case of permanent constant perturbations (voltage regulation). To this purpose, linear controllers are actually employed which are designed on the basis of linear approximations around operating conditions: only small perturbations and deviations from operating conditions can be handled. It is clear that nonlinear controllers are required to handle the large perturbations that typically occur in power systems. The thesis is divided into two parts: Part I (induction motor) consists of Chapters 2, 3 and 4 while Part II (synchronous generator) consists of Chapters 5 and 6. Chapters 2 and 3 address the problem of controlling a speed-sensorless induction motor: the existence of a global controller is explored in Chapter 2, while a nonlinear adaptive control scheme is developed in Chapter 3. Chapter 4 is devoted to nonlinear control design for a sensorless induction motor: an output feedback control algorithm is proposed. Chapters 5 and 6 address the problem of controlling a synchronous generator with parameter uncertainty: a nonlinear robust adaptive transient stabilizing control is presented in Chapter 5, while Chapter 6 proposes a nonlinear robust adaptive transient stabilizing and output regulating control algorithm.

In this work, the problem of active attenuation of disturbances with uncertain and possibly time-varying characteristics is addressed. The focus is on situations in which the uncertainty set is large, that is, the possible operating conditions of the system subject to disturbances can be different so that a single robust controller cannot ensure satisfactory performance levels. These situations underline the importance of control solutions able to reconfigure their action in real-time. The first part of this work is focused on the description of two different case studies, namely an active suspension system and an adaptive optics system, as well as on an overview of relevant contributions within the literature related to this subject. The solution that we propose is described in the second part; this method relies on the Adaptive Switching Control (ASC) paradigm, which has emerged as an alternative to classical Adaptive Control. In ASC, a finite family of candidate controllers is pre-synthesized off-line, and a supervisory logic has to select the potentially best one to be put in feedback with the plant. Particular attention is devoted to both performance and stability of the overall switching system. Finally, as an extension of the solution based on ASC, in the third part of this work an algorithm is proposed which combines both switching and tuning, aiming at preserving the beneficial features of the two different approaches, while possibly overcoming their drawbacks. The effectiveness of the proposed solutions is validated by means of simulation tests performed in the context of the two considered case studies.

This paper presents a procedure for designing an adaptive H∞ controller to reject sinusoidal disturbances with unknown constant frequencies. The proposed adaptive controller identifies the tonal frequencies in the disturbance and updates the controller to attenuate these frequencies. The controller design builds upon a closed-form solution for a simplified single-frequency attenuation problem. An application to optical beam jitter control illustrates the design procedure and its properties.