This thesis is mainly devoted to the investigation of speed control methods for three phase cage induction motors with particular emphasis being given to Direct Torque Control (DTC) improved techniques.Classical Direct Torque Control has inherent disadvantages such as: problems during starting resulting from the null states, the compulsory requirement of torque and flux estimators, and torque ripple. In the classical DTC induction motor drive a voltage vector is applied for the entire period, and this causes the stator current and electromagnetic torque exceeds its reference value early during the cycle, causing a high torque ripple. Switching cycles then follows this, in which the zero switching vectors are applied in order to reduce the electromagnetic torque to reference value. This thesis suggests a technique based on applying to the inverter the selected active states just enough time to achieve the torque and flux references values. The rest of the switching period a null state is selected which won't almost change both the torque and the flux. Therefore, a duty ratio has to be determined each switching time. By means of varying the duty ratio between its extreme values (0 up to 1) it is possible to apply any voltage to the motor. The optimum duty ratio per sampling period is a non-linear function of the electromagnetic torque error, the stator flux position and the working point, which is determined by the motor speed and the electromagnetic torque. It is obvious that it is extremely difficult to model such an expression since it is a different non-linear function per working point. Therefore, this thesis is focused on performing a fuzzy-logic-based duty-ratio controller, where the optimum duty ratio is determined every switching period. Additionally, this Fuzzy Controller is adaptive and may be applied to any induction motor.A stator flux reference optimum controller is also designed, which not only helps to achieve a smaller torque ripple, but also reduces the reactive power consumption of the drive taken from the main supply. This is achieved by changing the stator flux reference value with reference being made to the correspondent torque reference value. Therefore, the stator flux reference value chosen is to be just of sufficient value to produce the desired torque Simulated results are shown in order to compare the classical DTC and the Fuzzy Logic based DTC.The control algorithms have been implemented on a PC/DSP based board that facilitates the use of parallelism in software design. A 1.5kW, three-phase induction motor drive has been designed and experimental data obtained from it in order to verify the results achieved by simulation.

En problemes d'assignació de recursos, normalment s'han de tenir en compte les incerteses que poden provocar canvis en les dades inicials. Aquests canvis dificulten l'aplicabilitat de les planificacions que s'hagin fet inicialment.Aquesta tesi se centra en l'elaboració de tècniques que consideren la incertesa alhora de cercar solucions robustes, és a dir solucions que puguin continuar essent vàlides encara que hi hagi canvis en l'entorn. Particularment, introduïm el concepte de robustesa basat en reparabilitat, on una solució robusta és una que pot ser reparada fàcilment en cas que hi hagi incidències. La nostra aproximació es basa en lògica proposicional, codificant el problema en una fórmula de satisfactibilitat Booleana, i aplicant tècniques de reformulació per a la generació de solucions robustes. També presentem un mecanisme per a incorporar flexibilitat a les solucions robustes, de manera que es pugui establir fàcilment el grau desitjat entre robustesa i optimalitat de les solucions. / Resource allocation problems usually include uncertainties that can produce changes in the data of the problem. These changes may cause difficulties in the applicability of the solutions.This thesis is focused in the elaboration of techniques that take into account such uncertainties while searching for robust solutions, i.e. solutions that can remain valid even if there are changes in the environment. Particularly, we introduce the concept of robustness based on reparability, where a robust solution is one that can be easily repaired when unexpected events occur. Our approach is based in propositional logic, encoding the problem to a Boolean formula, and applying reformulation techniques in order to generate robust solutions. Additionally, we present a mechanism to incorporate flexibility to the robust solutions, so that one can easily set the desired degree between optimality and robustness.

The thesis involves the development and implementation of a new and robust control system based on permeability trends but at the same time capable of reducing aeration proportionally to permeate flux. Permeability was made a key parameter for directly comparing temporary changes in membrane performance. Transmembrane pressure and flux were gathered every 10 seconds and permeability values were automatically calculated; different mathematical algorithms were applied for the signal filtering of on-line data. Short term and long term permeability trends were compared once a day, and a control action was applied proportionally to the short term/long term permeability ratio without exceeding the aeration flow recommended by the membrane suppliers. / El treball presentat a la tesi inclou el desenvolupament i la implementacio d’un nou sistema de control robust basat en les tendencies de la permeabilitat i, al mateix temps, capac de reduir l’aeracio de forma proporcional al flux de permeat. S’ha seleccionat la permeabilitat com el parametre clau per comparar directament els canvis temporals en el funcionament de les membranes. La pressio transmembrana i el flux es mesuren cada 10 segons i llavors la permeabilitat es calcula automaticament. El senyal de les dades recollides en linia es filtra adequadament mitjancant diversos algoritmes matematics. L’algoritme de control compara diariament una tendencia a curt termini de la permeabilitat amb una tendencia a llarg termini de la permeabilitat, i s’aplica una accio de control proporcional al quocient de les dues tendencies, sense excedir mai el cabal d’aeracio recomanat pels fabricants de membranes.