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Descripción
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| The constantly boosting air traffic in aircraft industry, has demanded future aircrafts to evolve towards higher effciency, lower take-off weight, and thus less air pollution. Conventional aircrafts are composed of four different power subsystems after the engine: mechanical, hydraulic, pneumatic and electrical. However there has been an emerging trend to replace the ?first three parts by electrical equipment hich are more efficient, light-weighted, and accordingly less CO2 emissions. Thus aiming at the MEA concept, more electrical power conversion is required which calls for converter topologies that can provide high effciency and high power density. Nowadays the rectifi?ers on the aircraft mainly employ passive solutions involving uncontrolled diode bridges and mains-frequency transformers, even though they are extremely reliable. Thus more enhanced rectifi?er topologies with better performance and controllability, meanwhile complying the corresponding requirements are demanded. In Chapter 2 the overview of the state of the art is provided. Both two-stage structure and single-stage with isolation structure, as candidates for aircraft applications are reviewed and briefly compared. n this dissertation, the standards that the recti?fier systems have to comply are mainly MIL-STD-704F regarding input three-phase voltage, and MIL-STD-461F regarding EMI issues. Besides, galvanic isolation is also a basic requirement for safety concerns. As a contribution, a single-stage isolated three-phase buck-type recti?er topology is proposed. Its operating principle and modulation method in SVM are both thoroughly discussed. Due to the bridge-leg structure, together with suffcient leakage inductance from the transformer, ZVS can be achieved in every switching instant of this recti?fier using the presented asymmetrical modulation sequence. Thus ZVS is an outstanding feature of this topology, which greatly increases the overall effciency of the recti?fier. Detailed analysis on ZVS conditions are presented. Throughout the literature, VIENNA Recti?er III is a topology variation close to the proposed one. However the difference in both phase-leg implementation and modulation sequence make the proposed recti?fier feature less conduction losses, and capability of realizing ZVS which VIENNA Recti?fier III does not have. A detailed comparison is also carried out. In Chapter 4, the design of the proposed recti?er is carried out following the presented design guidelines. Transformer is the key component in the topology, since volt-second balance has to be maintained while achieving sufficient leakage inductance for the ZVS feature. Upon ?finishing the transformer leakage inductance and winding resistance are measured and the results show good accordance to the design. Since the proposed recti?fier features buck-type topology, the input currents present a pulsating waveform. In order to ?lter this pulsating current to a smooth sinusoidal current shape and comply with the MIL-STD-461F standard, a two-stage EMI fi?lter is designed. Simulation results show that at nominal power, the recti?fier together with its EMI fi?lter can comply with the standard and meanwhile maintaining a very low THD and nearly-unity power factor. Next, the voltage and current stresses of all the semiconductor devices in the topology are derived. Output ?lter Lo-Co is also designed. With the diode recti?er on the secondary, ringing effect occurs due to the leakage inductance in the transformer and the parasitic capacitance of the diodes on the secondary. This ringing introduces high voltage peak and high-frequency noises that can cause EMI issues. A passive snubber solution and an active snubber solution are both presented and designed for the recti?fier. Simulation results are shown to prove the functionality of both solutions. Finally a breakdown of total losses estimation is provided at the end of this chapter. | |
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Internacional
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Tipo de Tesis
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Doctoral |
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Calificación
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Sobresaliente |
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Fecha
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