Low‐gain integral control for a class of discrete‐time Lur'e systems with applications to sampled‐data control

We study low-gain (P)roportional (I)ntegral control of multivariate discrete-time, forced Lur’e systems to solve the output-tracking problem for constant reference signals. We formulate an incremental sector condition which is sufficient for a usual linear low-gain PI controller to achieve exponential disturbance-to-state and disturbance-to-tracking-error stability in closed-loop, for all sufficiently small integrator gains. Output tracking is achieved in the absence of exogenous disturbance (noise) terms. Our line of argument invokes a recent circle criterion for exponential incremental input-to-state stability. The discrete-time theory facilitates a similar result for a continuous-time forced Lur’e system in feedback with sampled-data low-gain integral control. The theory is illustrated by two examples

Non-Fragile Observer-Based Adaptive Integral Sliding Mode Control for a Class of T-S Fuzzy Descriptor Systems With Unmeasurable Premise Variables

The issue of non-fragile observer-based adaptive integral sliding mode control for a class of Takagi–Sugeno (T-S) fuzzy descriptor systems with uncertainties and unmeasurable premise variables is investigated. General nonlinear systems are represented by nonlinear T-S fuzzy descriptor models, because premise variables depend on unmeasurable system states and fuzzy models have different derivative matrices. By introducing the system state derivative as an auxiliary state vector, original fuzzy descriptor systems are transformed into augmented systems for which system properties remain the same. First, a novel integral sliding surface, which includes estimated states of the sliding mode observer and controller gain matrices, is designed to obtain estimation error dynamics and sliding mode dynamics. Then, some sufficient linear matrix inequality (LMI) conditions for designing the observer and the controller gains are derived using the appropriate fuzzy Lyapunov functions and Lyapunov theory. This approach yields asymptotically stable sliding mode dynamics. Corresponding auxiliary variables are introduced, and the Finsler's lemma is employed to eliminate coupling of controller gain matrices, observer gain matrices, Lyapunov function matrices, and/or observer gain perturbations. An observer-based integral sliding mode control strategy is obtained to assure that reachability conditions are satisfied. Moreover, a non-fragile observer and a non-fragile adaptive controller are developed to compensate for system uncertainties and perturbations in both the observer and the controller. Finally, example results are presented to illustrate the effectiveness and merits of the proposed method

Model Reduction by Balanced Truncation

Model reduction by balanced truncation for bounded real and positive real input-stateoutput systems, known as bounded real balanced truncation and positive real balanced truncation respectively, is addressed. Results for finite-dimensional systems were established in the mid to late 1980s and we consider two extensions of this work. Firstly, using a more behavioral framework we consider the notion of a finite-dimensional dissipative system, of which bounded real and positive real input-state-output systems are particular instances. Specifically, we work in a framework where we make no a priori distinction between inputs and outputs. We derive model reduction by dissipative balanced truncation, where a gap metric error bound is obtained, and demonstrate that the aforementioned bounded real and positive real balanced truncation can be seen as special cases. In the second part we generalise bounded real and positive real balanced truncation to classes of bounded real and positive real systems respectively that have non-rational transfer functions, so called infinite-dimensional systems. Here we work in the context of well-posed linear systems. We derive approximate transfer functions, which we prove are rational and preserve the relevant dissipativity property. We also obtain error bounds for the difference of the original transfer function and its reduced order transfer function, in the H-infinity norm and gap metric for the bounded real and positive real cases respectively. This extension to bounded real and positive real balanced truncation requires new results for Lyapunov balanced truncation in the infinite dimensional case, which we also describe. We conclude by highlighting possible future research.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Disappearing Frame.: A Practice-based investigation into composing virtual environment artworks

Through creative art making practice, research seeks to contribute a body of knowledge to an under researched area by examining how key concepts germane to computer based, interactive, three-dimensional, virtual environment artworks might be explicated, potential compositional issues characterised, and possible production strategies identified and/or proposed. Initial research summarises a range of classifications pertaining to the function of interactivity within virtual space, leading to an identification and analysis of a predominant model for composing virtual environment media, characterised as the "world as model": a methodological approach to devising interactive and spatial contexts employing visual and behavioural modes based on the physical world. Following this alternative forms of environmental organisation are examined through the development of a series of artworks beginning with Bodies and Bethlem, and culminating with Reconnoitre: a networked environment, spatially manifest through performative user input. Theoretical corollaries to the project are identified placing it within a wider critical context concerned with distinguishing between the virtual as a condition of simulation: a representation of something pre-existing, and the virtual as potential structure: a phenomena in itself requiring creative actualisation and orientated toward change. This distinction is further developed through an analysis of some existing typologies of interactive computer based art, and used to generalise two base conditions between which various possibilities for practice might be situated: the "fluid" and "formatted" virtual

The disappearing frame: a practice-based investigation into composing virtual environment artworks

Through creative art making practice, research seeks to contribute a body of knowledge to an under researched area by examining how key concepts germane to computer based, interactive, three-dimensional, virtual environment artworks might be explicated, potential compositional issues characterised, and possible production strategies identified and/or proposed. Initial research summarises a range of classifications pertaining to the function of interactivity within virtual space, leading to an identification and analysis of a predominant model for composing virtual environment media, characterised as the "world as model": a methodological approach to devising interactive and spatial contexts employing visual and behavioural modes based on the physical world. Following this alternative forms of environmental organisation are examined through the development of a series of artworks beginning with Bodies and Bethlem, and culminating with Reconnoitre: a networked environment, spatially manifest through performative user input. Theoretical corollaries to the project are identified placing it within a wider critical context concerned with distinguishing between the virtual as a condition of simulation: a representation of something pre-existing, and the virtual as potential structure: a phenomena in itself requiring creative actualisation and orientated toward change. This distinction is further developed through an analysis of some existing typologies of interactive computer based art, and used to generalise two base conditions between which various possibilities for practice might be situated: the "fluid" and "formatted" virtual.

Faux Queens: an exploration of gender, sexuality and queerness in cis-female drag queen performance

This research explores the cultural implications of cis-women performing as drag queens; focusing on straight-identified performers.The exegesis and creative production examine intersections between heterosexual and queer identities, and whether straight-identified faux queens may be queered by performance practice. Drawing on practice-led research, autoethnography and in-depth interviews, the thesis explores challenges in negotiating cis-gender iterations of drag and discusses ways that faux queen performances maintain the challenge of queer and resist reincorporation

Optimal control and model reduction for wave energy systems: A moment-based approach

Following the sharp increase in the price of traditional fossil fuels, in combination with issues of security of supply, and pressure to honor greenhouse gas emission limits, much attention has turned to renewable energy sources in recent years. Ocean wave energy is a massive and untapped resource, which can make a valuable contribution towards a sustainable, global, energy mix. Despite the fact that ocean waves constitute a vast resource, wave energy converters (WECs) have yet to make significant progress towards commercialisation. One stepping stone to achieve this objective is the availability of appropriate control technology, suchthatenergyconversionisperformedaseconomicallyaspossible,minimisingthedelivered energy cost, while also maintaining the structural integrity of the device, minimising wear on WEC components, and operating across a wide range of sea conditions. Suitable energy-maximising control technology depends upon the availability of two fundamental ‘pieces’: A control-oriented dynamical model, describing the motion of the WEC, and a model-based optimal control framework, able to efficiently compute the corresponding energy-maximising control law, subject to a set of constraints, defined according to the physical limitations of the device. FollowingtherequirementsforsuccessfulWECcontrol,andbothusingandextendingkeytools arising from the framework of model reduction by moment-matching, this thesis presents two main contributions. Firstly, this monograph proposes a comprehensive moment-based model reduction framework, tailored for WEC systems, addressing linear and nonlinear model reduction cases, providing a systematic method to compute control-oriented models from complex target structures. These approximating models inherit steady-state response characteristics of the target system, via the proposed moment-matching reduction framework. Secondly, by recognising that, besides being a powerful model reduction tool, the parameterisation of the steady-state response of a system in terms of moment-based theory can be explicitly used to transcribe the energy-maximising control problem to a finite-dimensional nonlinear program, a comprehensive moment-based optimal control framework, tailored for WEC systems, is proposed. This framework considers both linear and nonlinear optimal control cases, while also including robust solutions with respect to both system, and input uncertainty, providing an efficient method to compute the energy-maximising control law for WECs, under different modelling assumptions. Throughout this thesis both model reduction, and optimal control frameworks, are presented for a general class of WEC devices, and their performance is analysed via multiple case studies, considering different devices, under different sea state conditions