Sliding mode control (SMC) has been successfully applied to many practical control problems due to its attractive features such as invariance to matched uncertainties. The characteristic feature of a continuous-time SMC system is that sliding mode occurs on a prescribed manifold, where switching control is employed to maintain the state on the surface. When a sliding mode is realized, the system exhibits some superior robustness properties with respect to external matched uncertainties. However, the realization of the ideal sliding mode requires switching with an infinite frequency. Control algorithms are now commonly implemented in digital electronics due to the increasingly affordable microprocessor hardware although the essential conceptual framework of the feedback design still remains to be in the continuous-time domain. Discrete sliding mode control has been extensively studied to address some basic questions associated with the sliding mode control of discrete-time systems with relatively low switching frequencies. However, the complex dynamical behaviours due to discretization in continuous-time SMC systems have not yet been fully explored. In this thesis, the discretization behaviours of SMC systems are investigated. In particular, one of the most frequently used discretization schemes for digital controller implementation, the zero-order-holder discretization, is studied. First, single-input SMC systems are discretized, stability and boundary conditions of the digitized SMC systems are derived. Furthermore, some inherent dynamical properties such as periodic phenomenon, of the discretized SMC systems are studied. We also explored the discretization behaviours of the disturbed SMC systems. Their steady-state behaviours are discussed using a symbolic dynamics approach under the constant and periodic matched uncertainties. Next, discretized high-order SMC systems and sliding mode based observers are explored using the same analysis method. At last, the thesis investigates discretization effects on the SMC systems with multiple inputs. Some conditions are first derived for ensuring the

<p>Low-sensitivity switched capacitor filters imitating 'R','L' and 'C' can be built by means of capacitances, ordinary switches and voltage inverter switches (VIS). These structures carry the inherent bilinear transformation of their doubly resistively terminated ladder reference filters. This one to one correspondence between the 's-domain' and the 'z-domain' results in the Nyquist criterion being the only limitation on the sampling frequency. This eliminates the necessity for oversampling and VIS filters can be designed for high operating rates.</p><p>Filters based on VIS principle were analysed in previous literatures in the 'phi-domain'. In this thesis work, a successful attempt has been made to formulate an analysis procedure for discrete-time filters based on VIS principle in the 'z-domain'. Significant details have been brought out in comparison with the respective reference filter. A fifth-order lowpass filter has been designed and implemented to exhibit the closeness to the bilinearly transformed continuous-time reference filter. Settling time analysis has been done to justify the need for filters using VIS principle as compared to the filters employing integrator based switched capacitor filter. It is shown that VIS filter can be made to settle within half the period required for a conventional integrator based switched capacitor filter.</p>

Based on a Ph.D. thesis in the Dept. of Electrical Engineering, 1968. / Bibliography: p.125-126.

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Approaching parameter estimation from the discrete-time domain is the dominating paradigm in system identification. Identification of continuous-time models on the other hand is motivated by the fact that modelling of physical systems often take place in continuous-time. For many practical applications there is also a genuine interest in the parameters connected to these physical models. The most important element of time- and frequency-domain identification from sampled data is the discrete-time system, which is connected to the parameters of the underlying continuous-time system. For input-output models, it governs the frequency response from the sampled input to the sampled output. In case of time series, it models the spectrum of the sampled output. As the rate of sampling increase, the relationship between the discrete- and continuous-time parameters can become more or less ill-conditioned. Mainly, because the gathering of the poles of the discrete-time system around the value 1 in the complex plane will produce numerical difficulties while mapping back to the continuous-time parameters. We will therefore investigate robust alternatives to using the exact discrete-time system, which are based on more direct use of the continuous-time system. Another, maybe more important, reason for studying such approximations is that they will provide insight into how one can deal with non-uniformly sampled data. An equally important issue in system identification is the effect of model choice. The user might not know a lot about the system to begin with. Often, the model will only capture a particular aspect of the data which the user is interested in. Deviations can, for instance, be due to mis-readings while taking measurements or un-modelled dynamics in the case of dynamical systems. They can also be caused by misunderstandings about the continuous-time signal that underlies sampled data. From a user perspective, it is important to be able to control how and to what extent these un-modelled aspects influence the quality of the intended model. The classical way of reducing the effect of modelling errors in statistics, signal processing and identification in the time-domain is to introduce a robust norm into the criterion function of the method. The thesis contains results which quantify the effect of broad-band disturbances on the quality of frequency-domain parameter estimates. It also contains methods to reduce the effect of narrow-band disturbances or frequency domain outliers on frequency-domain parameter estimates by means of methods from robust statistics.

It has been well known that the architecture of insect compound eyes contributes outstanding capability for precise and efficient observation of moving objects. If this technique can be transferred to the domain of engineering applications, significant improvement on visual tracking of moving objects will be greatly expected. The brightness variation, caused by relative velocity of the camera and environment in a sequence of images, is called optical flow. The advantage of the optical-flow-based visual servo methods is that features of the moving object do not have to be known in advance. Therefore, they can be applied for general positioning and tracking tasks. The purpose of this thesis is to develop a visual servo system with trinocular cameras. For mimicking the configuration of compound eyes of insects, the arrangement of the divergent trinocular cameras is applied. In order to overcome possible difficulties of unknown or uncertain parameters, an image servo technique using the robust discrete-time sliding-mode control algorithm to track an object moving in 2D space is developed.

One of the commonly used simulation approaches is process orientation. This is based on the use of nodes (or blocks) that perform functions in series. In spite of the compactness and ease of learning that characterize process-based simulation, many languages are somewhat complex, primarily the result of the large number of nodes that users have to deal with and the considerable gulf between a user's abstract notion of the model and the details required to implement it. This paper describes a process-based simulation system that integrates object-oriented programming, visual interactive simulation and graphical model specification. Object-oriented programming techniques and simulation seem to be a natural match. The process classes are represented as network blocks or network nodes, and the process as a network diagram or directed graph. Arcs connect the nodes and specify the next step in the process. Each block type has its own icon. Developing an application model requires selecting a set of nodes, connecting them, and specifying the parameters (such as activity durations and random number streams) of the nodes through dialog boxes or inspection panels. Nodes have been designed to accomplish the major requirements in simulation modeling, including creation and termination of entities, attribute assignment, branching, queues and resources, activity specification and statistics collection and display. Additional system features include: statistics manipulation for steady state results, execution trace utilities, and limited animation capabilities. The system has been implemented for the NeXT programming environment using Objective-C. The NeXT includes an extensive object-oriented user interface library, relatively powerful hardware, and a modern multi-tasking and virtual memory operating system. Objective-C allows object-oriented concepts such as inheritance and subclassing while adding only a few constructs to that of the C language. The system modeling environment developed in this research enhances the applicability and usability of high level modeling tools. The program also provides a platform for further work on the distribution of the modeling process over several cooperating, communicating applications. / Graduation date: 1992

Low-sensitivity switched capacitor filters imitating 'R','L' and 'C' can be built by means of capacitances, ordinary switches and voltage inverter switches (VIS). These structures carry the inherent bilinear transformation of their doubly resistively terminated ladder reference filters. This one to one correspondence between the 's-domain' and the 'z-domain' results in the Nyquist criterion being the only limitation on the sampling frequency. This eliminates the necessity for oversampling and VIS filters can be designed for high operating rates. Filters based on VIS principle were analysed in previous literatures in the 'phi-domain'. In this thesis work, a successful attempt has been made to formulate an analysis procedure for discrete-time filters based on VIS principle in the 'z-domain'. Significant details have been brought out in comparison with the respective reference filter. A fifth-order lowpass filter has been designed and implemented to exhibit the closeness to the bilinearly transformed continuous-time reference filter. Settling time analysis has been done to justify the need for filters using VIS principle as compared to the filters employing integrator based switched capacitor filter. It is shown that VIS filter can be made to settle within half the period required for a conventional integrator based switched capacitor filter.

This thesis focuses on decentralized deadbeat output regulation of discrete-time nonlinear plants that are composed of multiple agents. These agents interact, via scalar-valued signals, in a known structured way represented with a graph. This work is motivated by applications where it is infeasible and/or undesirable to introduce control action within each plant agent; instead, control agents are introduced to interact with certain plant agents, where each control agent focuses on regulating a specific plant agent, called its target. Then, two analyses are carried out to determine if regulation is achieved: targeting analysis is used to determine if control laws can be found to regulate all target agents, then growing analysis is used to determine the effect of those control laws on non-target plant agents. The strength of this novel approach is the intuitively-appealing notion of each control agent focusing on the regulation of just one plant agent. This work goes beyond previous research by generalizing the class of allowable plant dynamics, considering not only arbitrary propagation times through plant agents, but also allowing for non-symmetrical influence between the agents. Moreover, new necessary and sufficient algebraic conditions are derived to determine when targeting succeeds. The main contribution of this work, however, is the development of new easily-verifiable conditions necessary for targeting and/or growing to succeed. These new conditions are valuable due to their simplicity and scalability to large systems. They concern the positioning of control agents and targets as well as the propagation time of signals through the plant, and they help significantly with design decisions. Various graph structures (such as queues, grids, spiders, rings, etc.) are considered and for each, these conditions are used to develop a control scheme with the minimum number of control agents needed.

The thesis considers the problems of designing a dynamic output feedback controller to discrete time systems with polytopic uncertainty so that the closed-loop systems are DR stable with their transfer matrices having H2 norm and H¡Û norm bounded by a prescribed value ru. The formar part of the thesis provides less conservative LMI conditions for H2 and H¡Û analysis and the output feedback control of discrete system than those appeared in the current research. While the latter part of the thesis extend the current research to DR stable with H2 and H¡Û design. Finally, numerical examples are illustrated to show improvement of the propered result.