After the review of single-phase converter topologies and detailed examination of several candidates, a non-resonantly coupled parallel resonant DCIDC converter is identified as being the most appropriate high frequency linked topology. The steady-state characteristics of the chosen converter with both variable frequency and phase shift control have been examined using state-plane analysis. These theoretical predictions are confirmed with time-domain simulation and comprehensive measurements from a 3.0 kVA prototype. The power losses resulted from real devices and components account for the discrepancies. Hybrid control has been employed for stand-alone applications. By contrast, phase-shift control only at a reduced switching frequency provides better output performance and higher conversion efficiency. Under light loads, a look-up correction table has been developed to improve the output performance further. The prototype efficiency is measured to be 94% under full load. Integral compensator and phase shift control only have been utilized for grid-connected applications. A damping resistor has been added to damp the resonant oscillation of the output filter. Similarly, a correction table is introduced under light load. An additional compensator, increased DC gains and phase margin compensation have been introduced to improve the output performance further. The impact of the grid-connected converter on the grid voltage is also examined.

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No description available.

No description available.

An induction generator offers advantages in terms of its low cost, simplicity, robust construction, nature protection against short circuits and ease of maintenance in today’s renewable energy industry. However, the need for an external supply of reactive power (to produce a rotating magnetic flux wave) limits the application of an induction machine as a standalone generator. It is possible for an induction machine to operate as a Self-excited Induction Generator (SEIG) if capacitors are connected to the stator terminals in order to supply the necessary reactive power to achieve generating electrical energy in remote areas. Poor voltage and frequency regulation is the main drawback of a SEIG as the system is highly dynamic under variable load conditions. The regulation of speed and voltage does not result in a satisfactory level although many studies have been focused on this topic in the past. Therefore, the aim of the thesis is to provide a better understanding of the behaviour of a smooth airgap, selfexcited, squirrel cage induction generator as a nonlinear dynamic system when operating under a variety of load conditions, which would hopefully contribute to the development of a better regulated/controlled, viable SEIG system. Allowing for the cross-saturation nonlinear effect, a mathematical Simulink, d -q axis model of the SEIG system utilising currents as state space variables is developed and verified by both the experimental results and numerical analysis. The SEIG computer model is constructed and tested using Matlab/Simulink R2010b throughout the thesis. The self-autonomous system is shown to exhibit a transition from a stable periodic orbit to a quasi-periodic orbit (leading to likely chaotic motion) through a Neimark bifurcation, as a result of small changes in the values of system parameters (such as load resistance, load inductance, rotational speed and self-excitation capacitance). This characteristic dynamic behaviour of the SEIG system is firstly identified in this work and is verified experimentally using a laboratory test rig. The stability of the periodic and quasi-periodic orbits exhibited by the SEIG system when feeding an inductive load ( RL) is numerically analysed and the movement of the eigenvalues of the system’s characteristic matrix when changing a system parameter is presented to verify the qualitative change in system behaviour from a stable period-one orbit to unstable quasi-periodicity. Eigenvalue technique is successfully applied to assess the stability of the period-one and quasi-periodic orbits of the SEIG when feeding variable load conditions.

Power electronics is the key technology for connecting flexible ac transmission system devices and renewable power generation to the ac grid. Among the ac to ac converters, the matrix converter represents a promising alternative power electronics technology to back to back converters. It does not incorporate any storage elements which minimises the size and weight of the converter. In addition, with the introduction of the reverse blocking insulated gate bipolar transistor, its efficiency can surpass that of back to back converters. A new approach in controlling the matrix converter output current is introduced. The approach depends mainly on logic circuitry and facilitates power system applications using the matrix converter. Furthermore, it can provide sinusoidal output current under asymmetry voltage conditions. The output current quality is at the expense of the input current in this case. Both sinusoidal input and output currents cannot be achieved under asymmetry voltage conditions due to the lack of any storage elements. Matrix converter suitability to power system applications such as flexible ac transmission and embedded generation, is investigated particularly under asymmetrical ac supply conditions. The effect of the absence of an intermediate storage element, on the output power and current quality is considered. The utilization of the proposed control technique in a unified power flow controller, which is the most versatile flexible ac transmission system device, is investigated. The restriction on unified power flow controller operation due to the absence of any intermediate storage element in the matrix converter is also studied. Special attention is given to asymmetry ac voltage condition effects and how to mitigate this problem for embedded generation. Extraction of the positive and negative sequence components is essential in obtaining non-oscillatory output power, and a dual current controller is used to this end.

Diesel generation is used worldwide to provide prime power or as a backup should the mains electricity supply be lost. This thesis presents a model of a diesel generating set (gen-set) to simulate its behaviour following a sudden application of load. Load acceptance is of particular interest in standby applications where the site load is connected through a breaker to an unloaded gen-set, The quality of a gen-set's voltage and frequency are of the most concern when supplying a load. During large load acceptances, transient voltage and frequency deviations can be so large that lights will extinguish, contactors drop out, and permanent damage can occur to sensitive electronics. In extreme cases the load can cause the engine to stall. The increasing desire to predict the magnitude of these deviations from nominal values has identified the need to have an accurate gen-set model. The model presented in this thesis was developed in order that the voltage and frequency transients could be recreated and examined in the simulation environment. There is considerable detail included, with models of the engine, governor, synchronous machine and voltage regulator, and many of their component parts. The control signals and other interaction are also included, so that the gen-set's behaviour during load acceptance can be analysed. The gen-set model has been extensively validated against plant measurements under a number of test scenarios and is shown to remain accurate. The model has also been used to predict a number of potential performance enhancements which could be implemented on the gen-set in the future.

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Ce travail a pour objectif de développer des méthodes de détection, localisation et caractérisation de défauts sur une maquette de turboalternateur. Les défauts abordés ici sont le court-circuit entre les spires du rotor et les excentricités rotoriques. Les méthodes seront, par la suite, adaptées à l’étude des machines de 900 et 1300 MW du parc nucléaire d’EDF. Pour cela, la maquette d'essais a été modélisée par deux approches, analytique et numérique par éléments finis. Des méthodes pour détecter et localiser les défauts rotoriques ont ensuite été développées. Les résultats de simulations utilisant les deux approches et des essais expérimentaux ont étés analysés et comparés. Ils ont montré une bonne concordance et démontré une bonne aptitude de la méthode proposée à la détection et localisation des défauts. Différents cas de défauts, associés à plusieurs points de fonctionnement de la machine, ont été étudiés et ont montré la bonne fiabilité des méthodes de détection développées. / The aim of this work is to develop methods to detect, locate and recognise faults in a turbogenerators of reduced scale. In the framework of this study, only short-circuit defects in the rotor windings and rotor eccentricities were investigated. The developed methods would be adapted to the machines of EDF nuclear plant of 900 and 1300 MW. First the studied machine was modelled using an analytical approach and a numerical model based on the finite element method. Then, the methods to detect and locate the rotor faults were developed. The results obtained from simulations using both approaches and experimental measurements were analysed and compared. They showed a good agreement and demonstrated a good capacity of the method proposed to detect and locate the faults. Several fault cases, at different operating points of the machine, were studied and they showed the good reliability of the method.

La prise en compte des pertes fer dans les machines électriques est une étape cruciale lors du processus de conception. L’objectif de ce travail a donc été de valider l’implémentation d’un modèle de pertes fer tout en effectuant une modélisation précise des machines électriques étudiées. Le choix s’est porté sur l’utilisation de modèles de calcul des pertes en post-traitement d’un code par éléments finis. Ainsi, différents modèles analytiques ont été comparés en régime sinusoïdal et non sinusoïdal (sans cycles mineurs) en termes de précision, afin de choisir le plus adapté pour une implantation dans code_Carmel. Par ailleurs, nous avons montré que la prise en compte des cycles mineurs peut être améliorée en remplaçant le terme classique de Steinmetz par un modèle d’hystérésis ou par un modèle analytique adapté. L’implémentation et la précision du modèle analytique ont été évaluées d’abord sur des systèmes simples puis sur plusieurs machines tournantes. La comparaison des résultats simulés avec les mesures issues des essais à vide montre une bonne concordance et démontre la capacité du modèle à estimer les pertes fer avec une bonne précision pour une large gamme de machines électriques et pour les deux types d’alimentations utilisés (sinusoïdale et MLI). / Taking into account the iron losses in electromechanical machines is a crucial step during the design process. The aim of this study was to validate the implementation of an iron loss model at the same time performing an accurate modelling of the electrical system. Our choice was to use models in a post-processing stage of a finite element code. Thus, four analytical models were compared for, sinusoidal and non-sinusoidal supply, (without minor cycles) in terms of accuracy, in order to choose the most suitable to be implanted in code_Carmel. We have shown that the inclusion of minor loops can be improved by replacing the classical Steinmetz term by a hysteresis model or by a suitable analytical model. The implementation and the accuracy of the analytical model were evaluated first on simple systems, and after on several rotating machines. Comparing the simulated results with measurements ones showed good agreement and demonstrated the ability of the model to estimate the iron losses with good accuracy for a wide range of electrical machines and for different supply (sinusoidal and PWM).