The Gate Turn-Off (GTO) Thyristor has the best voltage blocking and current conducting capabilities among all known high power semiconductor devices. To improve its dynamic performances to meet the increased demand in high-performance high-power applications, a special driving technique, namely unity gain turn-off, is studied. Several innovative approaches, which realize this driving requirement, are proposed, analyzed and experimentally demonstrated in this dissertation. The Emitter Turn-Off Thyristor (ETO) is a new family of high power semiconductor devices that is suitable for megawatt power electronics application. ETOs with voltage and current ratings of 4.0~6.0 kV and 1.0~4.0 kA, have been developed and demonstrated. These power levels are the highest in silicon power devices and are comparable to those of the GTO. Compared to the conventional GTO, the ETO has a much shorter storage time, voltage controlled turn-off capability, and a much larger reverse biased safe operation area (RBSOA). These combined advantages make the ETO based power system simpler in terms of dv/dt snubber, di/dt snubber and over current protection, resulting in significant savings at the system level. Experimental and numerical simulation results that demonstrate the advantages of the ETO are presented. A new family of snubberless turn-off GTO, the Resonant Gate Commutated Thyristor (RGCT) is proposed and investigated. By using a transient high commutation voltage, the RGCT can achieve unity turn-off gain and snubberless turn-off capability even with a relatively high gate loop stray inductance. Therefore conventional GTOs with flexible gate lead can be used to achieve the state-of-the-art performance similar to that of the Integrated Gate Commutated Turn-Off thyristor (IGCT). Detailed current commutation analysis and experimental results are presented. A novel equivalent circuit model for the GTO under the unity gain turn-off is proposed. This model is composed of a step current source, which represents the open-base PNP turn-off behavior, in series with a diode that represents the GTO's gate-cathode junction. This equivalent circuit can be used to analyze the turn-off transient behavior of a system employing this GTO. A new mechanism that dominates the failure of the GTO under the unity gain turn-off condition is identified and analyzed. Innovative hybrid GTO-based devices all have significant gate lead stray inductance. During the turn-off transition, this stray inductor will interact with the turn-off voltage source, the junction capacitance of the GTO's gate-cathode, causing effective current injection into the GTO's emitter junction when the voltage on the device is already high. Design guidelines and solutions for different types of GTO-based hybrid devices are provided. / Ph. D.

For many years, power electronics in the high-power area was performed with extremely slow semiconductor switches. These switches, including the thyristor and the Gate Turn-Off (GTO) thyristor, had the capacity to handle very high voltages and currents but lacked the ability to perform high frequency switching. Low-power converters, such as computer power supplies and low horsepower motor drives, have employed high-frequency switching for years and have benefited from very nice output waveforms, good control dynamic performance, and many other advantages compared to low frequency switching. Recent improvements in high-power semiconductor technology has brought switching performance similar to that of the low-power MOSFETs and IGBTs to the high-power area through the advancement of the IGBT's ratings to create the High Voltage IGBT (HVIGBT) and the development of new GTO-derived devices including the Integrated Gate Commutated Thyristor (IGCT) and the Emitter Turn-Off (ETO) thyristor. These new devices all feature high switching speed and the capability to turn off without the requirement for a turn-off snubber. With these new device technologies the high-power field of power electronics can realize dramatic improvements in the performance of systems for utility applications and motor drives. However, with these high-speed switches come new issues relating to noise, protection, performance of diodes, and thermal management in high-frequency applications. This thesis addresses the application of these new devices, especially the ETO and the IGCT. Examples of each device technology (IGBT, IGCT, and ETO) have been characterized in both their switching performance and conduction loss. The tests performed show how these new devices may be applied to various applications. The switching loss, especially related to turn-off, is the dominant factor in the power dissipation of the high-power switches, so knowledge of these characteristics are very important in the system design. To demonstrate the operation of the ETO, two power converters were constructed. The first was a 100 kW DC/DC converter, which demonstrated the operation of the ETO in a typical building block configuration, the half-bridge. The second system, a 1 MegaVolt-Amp (MVA) three-phase inverter, demonstrated the ETO in an application where the switching frequency and power level were both high. The test results demonstrate the expected characteristics of the high-frequency converters. The development of the ETO's gate driver is described. During the inverter testing, a new failure mode was found involving a parasitic diode within the ETO. This failure mode was analyzed and solutions were proposed. One of the proposed solutions was implemented and there were no more failures of this type. Another possible failure mode regarding a circulating current in an IGCT-based system is also analyzed. Soft-switching techniques can help reduce the switching loss in power semiconductor switches. Several topologies were considered for application in the high-power area, and one was selected for further investigation. A prototype Zero Current Transition (ZCT) circuit was developed using an IGCT as the main switch. The turn-off loss was reduced dramatically through the tested ZCT circuit, and the diode recovery was also alleviated. / Master of Science

The emergence of small and affordable satellites has led to rapid growth in the number of launched satellites over the past two decades. To save costs, small satellites often use mass-produced electronic components not explicitly designed for the radiation environment of space, which reduces reliability and makes them unsuitable for higher orbits. Improved radiation protection would enable small satellites to operate in high radiation environments and increase their reliability. This work investigates how small satellite electronics can be protected against the high radiation environment of geostationary transfer orbit on the example of the Foresail-2mission. Foresail-2 is a planned 6U CubeSat mission to the Earth radiation belts and is intended to use consumer-grade electronics components. In this harsh environment, most semiconductor devices require radiation shielding. The Space EnvironmentInformation System of the European Space Agency was used to analyse expected particle spectra along the planned orbit through the radiation belts. These particle spectra were then used in Monte-Carlo simulations based on the Geant4 particle transport toolkit to simulate the performance of different shielding configurations. Several thousand multilayer shielding configurations were simulated to optimise the material composition and layer structure of multilayer shielding. The best multilayer configurations against the combined proton and electron spectra of the Earth’s radiation belts use materials with low proton numbers on top of materials with high proton numbers and can significantly outperform conventional aluminium shielding. However, the usage of alternative materials might introduce significant overhead in the design and manufacturing of the satellite structure. Additionally, the influence of satellite structure geometry and openings in the shield was analysed. Even a 1 cm2 opening in the shield can increase the total ionising dose received by electronic components over a mission lifetime by more than an order of magnitude. In conclusion, the work recommends an aluminium body of 6 mm or equivalent multilayer shielding for the Foresail-2 mission to reduce the radiation level to a tolerable level for consumer-grade electronics, while openings in the satellite body should be avoided or covered up with additional shielding. / FORESAIL

Quick and reliable computational methods for optimized orbital transfers are crucial for projects at preliminary stages. They enable an initial, realistic sizing of the propulsion subsystem, one of the major components of satellite design. This thesis work, conducted at ReOrbit Oy, presents a minimum-time optimal trajectory for the orbit raising of a micro-satellite from GTO to GEO, assuming continuous firing by electric propulsion. The Delta-v requirements resulting from this simulation lead to the selection of an appropriate electric propulsion system, elaborating on the design of its configuration in terms of fuel and thrust requirements. This is done by taking into account, other than the major contribution given by the orbit raising, additions due to in-orbit maneuvers performed twice a day over a 10-year lifetime, like station-keeping corrections and reaction wheels desaturation. The optimization method is a direct-indirect hybrid for low-thrust orbital maneuvers, employing Pontryagin’s Minimum Principle for the transcription into a nonlinear programming problem. The initial guess required to start the optimizer is obtained with Lyapunov control theory. An orbital averaging technique is implemented, enabling fast computation of multiple trajectories during the optimization. Disturbances from the J2 zonal harmonic, solar radiation pressure, third-body effects of the Sun and Moon, and atmospheric drag up to 1500 km of altitude are included in the dynamic model. Eclipse conditions are assessed with a cylindrical shadow model, as the solar electric propulsion experiences a zero thrust period when in Earth’s shadow. The electric propulsion system configuration is determined with trade-off studies and comparisons between different suppliers. The chosen outline includes 4 Xenon thrusters, with complementary power processing units and propellant management systems, resulting in a total transfer time of less than 4 months. The same propulsion system is employed both for the transfer trajectory and the in-orbit maneuvers, by changing the thruster’s configuration once in GEO. / Snabba och pålitliga beräkningsmetoder för optimerade växlingar mellan omloppsbanor är avgörande för projekt i preliminära skeden. De möjliggör en initial, realistisk dimensionering av framdrivningssystemet, ett av huvudkomponenterna i satellitdesign. Detta examensarbete, utfört vid ReOrbit Oy, presenterar en tidsoptimerad bana för en mikrosatellits banhöjning från GTO till GEO, förutsatt kontinuerlig avfyring med elektrisk framdrivning. Simuleringens resulterande Delta-v-krav leder till valet av ett lämpligt elektriskt framdrivningssystem, med utarbetande av dess konfiguration vad gäller bränsle- och drivkraftskrav. Detta uppnås genom att ta hänsyn till (förutom bidraget från växlingen av omloppsbanan) tillägg från manövrar i omloppsbana som utförs två gånger om dagen under en 10-årig livstid, som t.ex. korrigeringar för stationshållning och avmättning av svänghjul. Optimeringsmetoden är en direkt-indirekt hybrid för manövrar i omloppsbanor med låg drivkraft, som använder Pontryagins minimiprincip för omskrivning till ett icke-linjärt programmeringsproblem. Den första gissningen som krävs för att starta optimeraren erhålls med Lyapunovs reglerteori. En teknik for omloppsutjämning implementeras, vilket möjliggör snabb beräkning av flera banor under optimeringen. Störningar från zonövertonen J2, solstrålningstryck, tredjekroppseffekter från solen och månen och luftmotstånd upp till 1500 km höjd ingår i den dynamiska modellen. Förmörkelseförhållanden uppskattas med en cylindrisk skuggmodell, då den elektriska solframdrivningen undergår ett skede utan drivkraft inom jordens skugga. Det elektriska framdrivningssystemets konfiguration bestäms med avvägningsundersökningar och jämförelser mellan olika leverantörer. Förslaget på utformning inkluderar 4 Xenon raketmotorer, med kompletterande kraftbearbetningsenheter och drivmedelshanteringssystem, vilket resulterar i en total överföringstid på mindre än 4 månader. Samma framdrivningssystem används både för överföringsbanan och manövrarna inom omloppsbanorna, genom att ändra motorns konfiguration när satelliten är i GEO.

With the rapid development of computers and their proven usability in manufacturing environments, simulation-based optimisation has become a recognised tool for proposing near-optimal results related to manufacturing system design and improvement. As a world-leading manufacturer within their field, Volvo GTO in Skövde, Sweden is constantly seeking internal development and has in recent years discovered the possibilities provided by flow simulation. The main aim of this thesis is to provide an optimal buffer size of a new post-assembly and packaging line (Konpack) yet to be constructed. A by-product of the flow simulation optimisation project in form of a flow simulation process evaluation was also requested. The simulation project started with a pre-study including the development of the frame of reference and an analysis of the literature focused on merging Lean philosophy with simulation-based optimisation. The simulation model was built based on both historical and estimated data. The optimisation results showed different buffer size alternatives depending on the throughput to be achieved, these are discussed, and near-optimal solutions presented for decision-making. Additionally, four experiments were carried out, both contributing to the model’s credibility as well as providing new and valuable insight to the stakeholders. The conclusions drawn from the optimisation and experiments indicate that Konpack will be able to meet the established throughput goals, provided that the suggested near-optimal solutions are considered. The experiments also unanimously point to the fact that Konpack has a built-in overcapacity, utilizable by optimising certain suggested input parameters. Additionally, an evaluation of the completeness of the standard simulation process employed by Volvo GTO is provided, concluding that no major changes are needed. Nevertheless, there is always room for improvement. Hence, future work regarding the flow simulation process at Volvo GTO is proposed.

Techn. Hochsch., Diss., 2003--Aachen.

Once a satellite has completed its operational period, it must be removed responsibly in order to reduce the risk of impacting other missions. Geostationary Transfer Orbits (GTOs) offer unique challenges when considering disposal of spacecraft, as high eccentricity and orbital energy give rise to unique challenges for spacecraft designers. By leveraging small satellite research and integration techniques, a deployable drag sail module was analyzed that can shorten the expected orbit time of launch vehicle stages in GTO. A tool was developed to efficiently model spacecraft trajectories over long periods of time, which allowed for analysis of an object’s expected lifetime after its operational period had concluded. Material limitations on drag sail sizing and performance were also analyzed in order to conclude whether or not a system with the required orbital performance is feasible. It was determined that the sail materials and configuration is capable of surviving the expected GTO environment, and that a 49 m2 drag sail is capable of sufficiently shortening the amount of time that the space vehicles will remain in space.

Advancements in the power electronics systems have been directly related to the availability of improved power semiconductor devices. The device performance greatly determines the efficiency, reliability, volume, and cost of the power electronics system. This dissertation is dedicated to develop an advanced high power semiconductor device, the emitter turn-off (ETO) thyristor, which is targeted to improve the limitations of the present high power devices. Major improvements in electrical and mechanical designs of the ETO for high power and high frequency operation are proposed which result in improved snubberless turn-off capability, low conduction loss, and low gate drive power consumption of the new generation ETO. A revolutionary self-power generation method of the ETO is proposed. Different from the conventional high power devices which require the external power input for their gate drivers, ETO achieves complete optically controlled turn-on and turn-off and all the internal power required is self-generated. This advancement will have a major impact to high power converter designs. A novel integrated method to eliminate the dead-time requirement is proposed for ETO. This method not only improves the output waveform quality but also increases the reliability and reduces the cost of the high power PWM voltage source converters. With this unique function, the upper and the lower ETO's within a converter phase leg can receive the ideal complementary (without dead-time) PWM signals and solve shoot-through problems. Method to measure the ETO current and transfer the current information to a PWM signal is proposed. Based on the ETO's built-in current sensor, the over-current protection function of the ETO is designed as well. The experimental results show that the built-in current sensor has a very high precision, and the over-current protection function can effectively protect the ETO during the short circuit faults. In order to improve ETO's turn-off capability, a comprehensive investigation of the turn-off failure mechanism of the ETO was performed. A series of simulations and experiments are carried out to study the ETO turn-off operation. The detail turn-off failure mechanisms are presented. The conditions to cause the ETO failure are addressed. The approaches to improve the ETO's turn-off capability are discussed. / Ph. D.

This paper focuses on the Double Fed Induction Machine in the Pumped Storage Power Plants. It includes listing of this plants in the world, where such a technology is used; principle of Double Fed Induction Machine, its usage with variable speed, advantages and disadvantages and also experience of its usage.

Les progrès réalisés ces dernières années dans la commande des onduleurs MLI à deux niveaux de tension pilotant en vitesse variable des machines asynchrones de moyenne et grande puissance ont permis d'améliorer sensiblement les performances. L'utilisation récente des onduleurs MLI à trois niveaux de tension est très prometteuse en raison de la capacité de cette nouvelle structure d'onduleur à améliorer la qualité des courants dans la machine et à étendre sa commande à des domaines de puissance supérieurs à 2 MW. Nous définissons le principe de calcul et les limites de validité des principales techniques de modulation sinusoïdales à trois niveaux. Certaines d'entre elles se révèlent être tout à fait adaptées et performantes pour commander la machine dans les zones de faible vitesse. Nous proposons ensuite une méthode systématique de construction d'une commande optimisée. Les signaux sont calculés pour minimiser les harmoniques de courant et les pulsations de couple. Cette méthode est appliquée à un exemple concret, et la commande est implantée sur le microcontrôleur 80C196KC. La simulation des régimes établis permet d'affiner les études qualitatives des signaux. La bonne concordance entre les résultats expérimentaux et les résultats théoriques permet de confirmer la conservation des caractéristiques des signaux par la méthode de génération en temps réel. L'étude de l'association de la commande optimisée et d'une loi de contrôle vectoriel permet enfin de prouver la faisabilité d'un tel contrôle. Elle permet d'envisager l'amélioration des performances des entraînements de grande puissance en régimes permanent et transitoire simultanément.