En aquesta Tesi es proposa una nova estructura de control amb l'objectiu de solucionar el conflicte entre rendiment i robustesa en l'esquema de realimentació tradicional. La teoria matemàtica de la factorització coprimera permet proposar un configuració de control basada en observador. És el que es denomina configuració Observador-Controlador i es fa servir de diferents maneres. La primera proposta enfoca la millorar les prestacions de robustesa com a una alternativa al disseny d'un controlador robust. Amb la intenció d'aconseguir un bon rendiment en presència de pertorbacions i d'incerteses procedim de la següent manera: en primer lloc, dissenyem un sistema de control per realimentació estàndard per tal de satisfer els requeriments de seguiment a referència; en segon lloc, millorem les propietats de robustesa sense alterar les propietats de seguiment del sistema de control inicial. Aquesta estratègia es basa en la generació d'un complement pel sistema de control nominal mitjançant una estructura fonamentada en la configuració Observador-Controlador. Els sistema de control resultant funciona de tal manera que la planta estarà controlada només pel controlador per realimentació nominal quan no hi hagi ni incerteses ni pertorbacions externes i el controlador per a la robustificació estarà actiu només en presencia de incerteses i/o pertorbacions externes.La segona proposta afronta l'objectiu d'aconseguir un bon rendiment en presència de pertorbacions i d'incerteses. En aquest cas, desenvolupen un controlador de dos graus de llibertat (2-DOF) i procedim de la següent manera: primer, dissenyem un sistema de control per realimentació basat en observador per tal de garantir un nivell mínim d'estabilitat robusta; segon, dissenyem un prefiltre per tal de garantir robustesa en les propietats de llaç obert. Malgrat les dues propostes no es basen en una reformulació en termes del factor de Youla, es possible fer una parametrització basada en Youla per tal de caracteritzar el conjunt de tots els observadors per una planta nominal. En essència, les dues propostes es poden veure com a estructures de dos graus de llibertat. Tot i que l'esquema de la primera proposta no s'adapta a una estructura de 2-DOF clàssica, amb un prefiltre i una part per realimentació, podem considerar-la com a tal pel fet que aconsegueix una complerta separació de propietats. En aquest cas, el controlador inicial s'ocupa de les especificacions de seguiment a referència per a la planta nominal i el controlador per a la robustificació s'encarrega de la millora, si cal, les prestacions de robustesa nominals. / In this Thesis, we shall propose a new controller architecture to try to completely overcome the conflict between performance and robustness in the traditional feedback framework. The proposed control configuration comes from the coprime factorization approach and, in such a context, a somewhat uncommon observer-based control configuration is derived. It is the Observer-Controller configuration and it is used in different arrangements.The first proposal deals with the robustness enhancement problem as an alternative to the design of a robust control system. With the lofty goal of achieving high performance in the face of disturbances and uncertainties we proceed as follows: first, an initial feedback control system is set for the nominal plant to satisfy tracking requirements and second, the resulting robustness properties are conveniently enhanced while leaving unaltered the tracking responses provided by the initial controller. The approach is based on the generation of a complement for the nominal control system by means of an structure based on the Observer-Controller configuration. The final control system works in such a way that the plant will be solely controlled by the initial nominal feedback controller when there is neither model uncertainties nor external disturbances and the robustification controller will only be active when there is model uncertainties and/or external disturbances. The second proposal also addresses the goal of high performance in the face of disturbances and uncertainties. In this case, a two degrees-of-freedom (2-DOF) control configuration is developed. We proceed as follows: first, an observer-based feedback control scheme is designed to guarantee some levels of stability robustness and second, a prefilter controller is computed to guarantee robust open-loop processing of the reference commands. Despite both proposals are not based on a reformulation in terms of the Youla parameter, it is possible to perform a Youla parametrization to characterize the set of all observers for the nominal plant. Essentially, both proposals can be considered as 2-DOF control configurations. The first presented proposal do not fit the standard 2-DOF control scheme made up with a feedback controller and a prefilter controller. Nevertheless, it can also be seen to lie in the 2-DOF control configuration in the sense that a complete separation of properties is achieved. In such case, the tracking properties of the nominal plant are attained by a controller and the robustness properties are considered and enhanced if necessary by the Observer-Controller configuration.

This thesis is an experimental study of shear effect of a two-degree-of-freedom cylinder in fluid flow in terms of different mass ratio. This study is done using an elastic cylinder of high natural frequency, and the free stream velocity is 0.2m/s to 1.5m/s. The results show that as mass ratio increases, the motion of cylinder becomes more stable and small, and the frequency response of cylinder self-excited is bigger than vortex-shedding response when spring constant is bigger enough. Thus it is not easy to observe the vortex-shedding frequency variation with respect to various velocities by dint of cylinder vibration. When it come to the shear effect, the effect of shear flow could decreases the drag force, and increases the lift force. Orbits of cylinder vibration is not symmetric; the displacement is more significant on low velocity side.

This thesis presents a parallel-series two-bridge DC/DC converter topology with the ability to operate with ZVS over a wide input and load range. The intended application is power conditioning systems (PCS) of photovoltaic (PV) arrays used in hybrid renewable energy system architectures. The proposed topology provides two degrees of freedom which allows the PV-PCS to regulate the DC-link voltage, while tracking the maximum power point (MPP) of the PV array. This topology distributes the main power into two bridges and the phase-shift between the two bridges and provides another degree of freedom for the PCS to track the MPP. The proposed topology is also able to achieve soft-switching over a wide range. The power conditioning system shows a modular structure to efficiently transfer the power to the load as the main power is divided between two bridges. In addition, the proposed control scheme provides complete decoupling between the input side controller from the output side controller in order to perform MPPT and regulate the the DC-link voltage simultaneously. A 2kW Experimental prototype has been provided to validate the feasibility and performance of the converter. Experimental results prove that the converter is able to regulate the DC-link voltage and track the maximum power extracted from the PV array simultaneously. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-04-18 19:51:43.405