Orientador: Ricardo Tokio Higuti / Coorientador: Edvaldo Assunção / Banca: Rodrigo Cardim / Banca: Joaquim Miguel Maia / Resumo: Sistemas de controle de temperatura são necessários em diversos setores da indústria e pesquisa científica. Neste trabalho propõe-se um sistema de controle de temperatura para líquidos, que será utilizado em uma célula de medição de propriedades de líquidos por ultrassom. O sistema de controle tem como requisito atingir uma variação máxima de 0,01C em regime permanente. Os atuadores térmicos empregados são células de efeito Peltier e utilizam-se circuitos de potência do tipo ponte H para injetar ou retirar calor do objeto de interesse. São utilizados sensores de temperatura do tipo resistivos (RTDs), que são lineares e muito utilizados na indústria como referência para medição de temperatura. É utilizado um controlador proporcional, integral e derivativo (PID) digital, sintonizado a partir de um experimento em que o sistema é realimentado através de um controlador do tipo relé. A partir dos resultados desse experimento utilizam-se métodos diretos, como o de Ziegler-Nichols, para a sintonização dos coeficientes. Em seguida um ajuste fino é feito a partir dos coeficientes gerados por esses métodos. Um controlador PID capaz de atingir as meta de variação máxima de 0,01C é implementado. Com essa baixa oscilação no regime permanente concluiu-se que é possível realizar medidas de velocidade de fase de ondas de ultrassom propagando-se em água destilada com variação máxima de 0,05 m/s em torno do valor médio / Abstract: Temperature control systems are required in several industry and scientific research areas. This work proposes a liquid temperature control system applied to an ultrasonic mea- surement cell for liquids. The control system requires a maximum steady state deviation of 0,01C. Thermoelectric coolers (TEC) work as thermal actuators with H bridge power circuits to pump heat to or from the object of interest. Resistive temperature detectors (RTD) are used in this work, which are linear and widely used in the industry as temperature measurement reference. A proportional, integral and derivative (PID) digital controller is tuned using relay feedback identification with direct tuning methods, such as Ziegler-Nichols'. To improve the results a fine tuning is implemented from the parameters estimated by the direct methods. A PID controller capable of achieving the 0,01C maximum variation goal is implemented. With this low steady-state oscilation it is possible to measure phase velocity of ultrassound waves in distilled water with maximum variation of 0,05 m/s around the mean value / Mestre

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M.Sc. (Mathematical Statistics) / This dissertation deals with the computation of nonlinear control strategies for an autonomous vehicle. The vehicle consists of two wheels attached to an axle. It is assumed that both wheels roll without slipping leading to nonholonomic constraints. A third order nonlinear kinematic model of the vehicle is derived from these constraints. It is further assumed that the vehicle has builtin feedback controllers independently regulating the rotational velocities of the wheels (using electric motors as actuators). Thus, the vehicle is maneuvered by applying a separate rotational velocity reference command to the feedback controller of each wheel. The closed loop system dynamics from the reference command to the wheel rotational velocity is approximately modelled by a first order system. This leads to a fifth order nonlinear state-space model for the vehicle. The above-mentioned reference commands constitute the control input variables of the vehicle model and are subject to amplitude constraints. Firstly, a methodology is developed for computing reference command strategies to drive the autonomous vehicle from a specified initial state to a desired final state in a given time and such that a circular obstacle is avoided. The vehicle performs the required maneuver whilst satisfying all the specifications and constraints. Secondly, feedback reference command laws are developed such that a specified point just ahead of the vehicle asymptotically tracks a given reference trajectory in the horizontal plane. The feedback control law steers the vehicle onto the reference path from any initial position and keeps it moving on the path. Thirdly, the stochastic system performance is evaluated when the above-mentioned tracking control strategy is applied and the initial state of the vehicle is a random vector.

The thesis begins with an overview of the four types of error that are generated in digital filters which arise from two sources. The first source is the quantisation of time through the sampling process which gives rise to the first error type - algorithmic error. The second source of error is the quantisation of amplitude due to finite wordlength effects. Coefficient representation error (coefficient error), ADC quantisation error (ADC error) and multiple-word truncation error (truncation error) are all effects of amplitude quantisation. The shift operator commonly used in digital filters is prone to sensitivity problems especially at high sampling rates. Alternative filter operators are reviewed and advantages and disadvantages of their use are identified in enhancing the performance of digital filters. The measurement of algorithmic error and coefficient error can be carried out deterrninistically whilst ADC error and truncation error need to be treated stochastically. The thesis presents a technique to separate the deterministic error and the stochastic error in a composite output signal from a digital filter that is implemented using a high-Ievellangnage with floating-point arithmetic. This technique represents a method for validating the error analysis techniques. The error analyses presented in the thesis are used as tools to improve the performance of emulated digital filters. Each different error form varies in an individual manner with respect to changes in the sampling period. By careful selection of a sampling rate the filter performance can be improved by ensuring that the magnitudes of all the error forms are consistent with each other. Similar techniques can be used to improve the performance of digital compensators in c1osedloop control systems. Careful consideration of the duration of the sampling interval needs to be observed to ensure that the stability of the closed-loop system is adequate. This method of determining the controller parameters is used to exploit the digital control hardware to its fullest potential, and is automated in software; details are described in the thesis.

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Sensor integrity plays a crucial role in automatic control and system monitoring, both in achieving performance and guaranteeing safety. Conventional approaches in sensor failure detection demand precise process models and abundant central computing power. This thesis describes the development and the evaluation of a novel local sensor validation scheme which is independent of the underlying process and is applicable to a wide variety of sensors. A signal-based in-situ sensor validation scheme is proposed. Typical sensor failures are classified according to their signal patterns. To avoid the ambiguity between genuine failures and legitimate measurand variations, a pair of decomposition filters are designed to partition the sensor output; and attention is focused on characteristics beyond the measurement signal bandwidth, which is the only essential process-related variable required. In addition, the application of decimating filters is explored, both as a relief to the analog anti-aliasing filter and as an enhancement in signal discretization. An expression is derived relating the oversampling rate and the attainable improvement in signal resolution. Based on a period of failure-free observation, a whitening filter is identified by modelling the decomposed sensor signal as a stochastic time-series. Significant progress is achieved by a deliberate injection of bandlimited random noise to ensure signal stationarity and to avoid inadmissible leakage of measurement signal into the innovation sequence. The adopted failure detection strategy is primarily innovation-based. Pertinent sensor signal information is extracted recursively by a collection of efficient and robust signal processing algorithms. Its validity is continuously monitored by statistical tests on which a series of precursory failure alarms are formulated. Any aberration detected is then diagnosed under the supervision of a simple rule-based system. The practicality, efficacy and flexibility of the proposed scheme are successfully demonstrated by a bench-top thermocouple experiment and extensive synthetic simulations.

Hallucinations are often considered a sign of psychotic illness, but are also common in other diagnostic groups and individuals without mental health problems. This thesis uses Perceptual Control Theory (PCT), a cybernetic model which explains behaviour and cognition in terms of control processes regulating ongoing perception according to internally represented goals, as a theoretical framework to understand hallucinations. First, a theoretical/conceptual paper (Paper 1) examines how PCT provides an integrated account of (i) the mechanisms responsible for the formation of hallucinations, (ii) their phenomenological heterogeneity, (iii) the interaction between these mechanisms and environmental factors that might contribute to the formation of hallucinations, and (iv) the processes leading to different affective reactions to hallucinatory experiences (e.g. distress). The main implications of this model are discussed in the context of pertinent theoretical and empirical literature, and relevant clinical and research implications are considered. Second, this thesis includes an empirical investigation (Paper 2) examining two PCT-informed hypotheses in a cross-section of 22 clinical and 18 non-clinical individuals with auditory verbal hallucinations (“hearing voices”), namely (i) that the content of voices will be thematically linked to the participants’ personal goals, and (ii) that affective reactions to voices will depend on the extent to which voices facilitate and/or interfere with important personal goals. The analysis revealed that 82.5% of participants reported voices that thematically matched at least one of their reported goals. As predicted, affective reactions to voices were strongly associated with measures of interference and facilitation of goals, even when controlling for important covariates (e.g. participants’ history of mental health difficulties; voices’ content, frequency and duration).Finally, a critical evaluation is provided (Paper 3), where the methodological strengths and limitations of the work presented in the present thesis are discussed with the aim to reflect on the research process, and inform future investigations into the topics considered in this thesis.

Over the last decade infinite poles and zeros have been recognised as having fundamental relevance to the analysis of the dynamical behaviour of a system. Indeed even the classical theory of characteristic root loci alludes to the existence of infinite zeros without defining them as such whilst the significance of the infinite poles has more recently emerged in the study of non-proper systems.

The effect of the implementation of constant output feedback on a general rational transfer function matrix has long been of interest. More recently, interest has been shown in the properness of closed-loop systems when such constant output feedback is applied to a general open-loop G(s) which is given either in terms of a state space realisation or as a matrix fraction description. In the first part of this work the effect of constant output feedback on a general composite system is considered and a simple sufficient condition for properness of such a system is derived.