Academic literature on the topic 'Circulation switching'

SummaryThis study examines contraceptive method switching among married women in the US. It enquires first into the effect of method type and women's socioeconomic characteristics on the risk of switching to each of six methods, including no method, and secondly into the previous methods used by women who adopt specific contraceptive means. The results indicate a great deal of circulation among all method types and of movement to unprotected intercourse. The adoption of sterilization is greatest among women not previously using any contraceptive method.

Abstract Posterior circulation aneurysms are often associated with a higher risk of rupture and compressive symptoms compared to their anterior circulation counterpart. Due to high morbidity and mortality associated with microsurgical treatment of those aneurysms, endovascular therapy gained ascendance as the preferred method of treatment. Flow diversion has emerged as a promising treatment option for posterior circulation aneurysms with a higher occlusion rate compared to other endovascular techniques and a lower complication rate compared to microsurgery. While treatment of saccular and dissecting aneurysms is often associated with comparatively good outcomes, fusiform and dolichoectatic aneurysms should be carefully selected prior to treatment to avoid devastating thromboembolic complications. Occlusion of covered posterior circulation branches showed no correlation with ischemic complications, and appropriate antiplatelet regimen and switching Clopidogrel nonresponders to different antiplatelet agents were associated with lower complication rates following flow diversion of posterior circulation aneurysms.

The thermal model of the well after switching off the flow of drilling mud is considered. The received results are auxiliary for formulation of the general model. The general model in conjunction with temperature data of drilling mud on a surface will allow to reveal layers of the hydrocarbons, penetrated earlier with drilling.

Vanadium-doped zinc telluride (ZnTe:V) thin film sandwiched by two different metal electrodes, that is, Al/ZnTe:V/Cu structure, was deposited onto the glass substrate by e-beam deposition technique in vacuum at a pressure of ~8 × 10−4 Pa. The deposition rate of the film was maintained at 2.052 nms−1. Circulation current was measured through this device as a function of potential difference applied across the structure. The Al/ZnTe:V/Cu structures exhibit memory switching characteristics at atmospheric pressure in room temperature. Switching characteristics of deposited Al/ZnTe:V/Cu structure as a memory device have been investigated in detail for various vanadium compositions, thicknesses of ZnTe:V films as well as various film temperatures, respectively. In all cases, it is seen that the metal/insulator/metal (Al/ZnTe:V/Cu) structures based on ZnTe:V can undergo an electroforming process and exhibit voltage-controlled negative resistance (VCNR) or a new switching process. It is also observed that the electric field, temperature, thickness, and dopant composition have important role in the switching characteristics. Switching characteristics have been interpreted by using a filamentary model. The switching effects of Al/ZnTe:V/Cu device may have important applications in the energy-oriented devices.

In this paper, a switching method is proposed for power device temperature-balancing in a phase-shift full-bridge (PSFB) converter. PSFB is commonly used for applications that require high efficiency, because a zero-voltage switching (ZVS) operation is possible on the primary-side. In PSFB, the circulation current complicates ZVS under a light-load condition, which generates heat. Meanwhile, the heat generated in PSFB creates a temperature deviation between the lagging leg and the leading leg, which shortens the lifetime of the power device, thereby reducing system reliability and efficiency. To solve this problem, previous studies applied a pulse-width modulation (PWM) switching method for light and medium loads, and a phase-shift switching method for the region where ZVS is possible. Although this method has the advantage of easy control, the maximum temperature of the legs of the PSFB increases with medium loads. In this paper, a temperature-balancing algorithm—a temperature-balance control—is proposed to decrease the leg temperature using switching based on position exchanges of the leading leg and lagging leg along with PWM switching. Temperature-balance control minimizes leg temperature deviation under light load conditions. The proposed control method provides a minimum temperature difference between the two legs and high efficiency.

With attention focused on the battle for news ratings between Channels Seven and Nine, an underlying trend has tended to go unnoticed: audiences have been switching off televised news and current affairs programs since the 1990s. Drawing on detailed OzTAM ratings, this article shows how this is particularly true for specific audience segments. Allied with this is the longer-term decline in newspaper circulation. These data raise a central question: are Australians merely switching off ‘outdated’ media such as TV and newspapers (and getting their news from somewhere else such as the internet), or are they switching off the genre of news/current affairs altogether? This article weighs the evidence and concludes that the news audience is fragmenting in particular ways, especially by age, and that some (but certainly not all) groups are going online for news.

The diploma thesis is concerned with switching of vortex circulation in magnetic nanodisks. The results of micromagnetic simulations of hysteresis loops of individual disks with different degrees of asymmetry are presented. The influence of geometric asymmetry of the disk on the shape of the hysteresis loop is discussed as well as switching of vortex circulation in asymmetric nanodisks by external in-plane magnetic field. Simulations of pairs of magnetostatically coupled nanodisks were carried out for different interdisk distances and degrees of asymmetry. By analysing the results of the simulations, the effects of magnetostatic coupling and the asymmetry on resultant circulation of individual vortices were compared and the range of magnetostatic interaction between nanodisks of given dimensions and asymmetry was estimated. Experimental techniques used for fabrication and measurement of the samples are briefly summarized.

Magnetic vortices in ferromagnetic disks are curling magnetization structures characterized by the sense of the spin circulation in the plane of the disk and by the direction of the magnetization in the vortex core. Concepts of memory devices using the magnetic vortices as multibit memory cells have been presented, which brought the high demand for their research in many physical aspects. This work investigates the magnetostatic coupling in pairs of ferromagnetic disks to clarify the influence of nearby disks or other magnetic structures to the vortex nucleation mechanism. To ensure that the vortex nucleation is influenced only by the neighbouring magnetic structures, the randomness of the nucleation process was studied in single disks prior to the work on pairs of disks. We had to ensure that the vortex nucleation is influenced only by the neighbouring magnetic structures and not by an unwanted geometrical asymmetry in the studied disk. Lithographic capabilities were inspected in order to achieve the best possible geometry. Further we present a concept of electrical readout of the spin circulation using the anisotropic magnetoresistance, which allows automated measurements to provide sufficient statistics. To explain the magnetoresistance behaviour, numerical calculations together with magnetic force microscopy measurements are presented.

Magnetické vortexy jsou charakterizovány směrem stáčení magnetizace a polarizací vortexového jádra, přičemž každá z těchto veličin nabývá dvojice stavů. Ve výsledku jsou tak k dispozici čtyři možné stabilní konfigurace, čehož může být využito v multibitových paměťových zařízeních. Tato dizertační práce se zabývá selektivním zápisem stavů magnetického vortexu v magnetickém disku pulzem elektrického proudu stejně jako jejich následným elektrickým čtením. Před samotnou realizací elektrických měření byla provedena statická měření přepínání stavů vortexu pomocí různých proudových pulzů v kombinaci s technikami MFM a následně MTXM. Následně byl realizován dynamický odečet stavu vortexu kompletně založený na elektrických měřeních. Ovládání cirkulace vortexu je založeno na geometrické asymetrii vytvořené oříznutím magnetického disku a vytvořením fazety. Plochý okraj disku definuje preferenční smysl stáčení cirkulace během procesu nukleace vortexu. Řízení polarity se obvykle provádí ve dvou krocích. V prvním kroku, homogenně magnetizovaná vrstva s kolmou magnetickou anizotropií umístěná na dně disku definuje výchozí polaritu vortexu v době nukleace. V druhém kroku, je-li to nutné, je polarita vortexu přepnuta pomocí rychlého proudového pulzu. Proto je možné nastavit požadovaný stav cirkulace vysláním nanosekundového pulsu s nízkou amplitudou, následované nastavením polarity pikosekundovým pulsem s vysokou amplitudou. Stavy vortexů jsou pak detekovány elektrickou spektroskopií prostřednictvím anizotropní magnetorezistence. Vzorky pro všechna statická a dynamická měření byly připraveny pomocí elektronové litografie v kombinaci s lift-off procesem.

This thesis concerns with specified problems of an electric traction. It deals with the concept of module controlling EC motor of the voltage 24V and the current 100A. There are described possibilities and principles of controlling EC motor in detail. For controlling, the single-purpose IO MC33035, which is directly specified for it, is used. The thesis describes implementation of both testing and final versions of converter for a circulating pump drive of a cooling circuit in locomotives. The convertor is partly universal and can be used in other applications. According to the implemented convertor, a laboratory test and a model protocol were made. In the second part, the concept is described as well as the implementation of DC/DC conventor of output voltage of 24V and which is supplied by 12V battery. The specified output current is 4A. It is used for supplying of the controlling traction vehicle unit and is installed as a boost convertor which contains a resonance conventor. The presentation of measured parameters of the complete convertor is either a part of this thesis.

Die vorliegende Arbeit behandelt den Modularen Mehrpunktstromrichter M2C, der eine aufstrebende Mehrpunktstromrichtertopologie im Mittelspannungs- und Hochspannungsbereich ist. Die modulare Struktur des Stromrichters enthält in einem Stromrichterzweig eine Reihenschaltung aus identischen Submodulen (Zellen) und einer Spule. Der gesamte Stromrichter ist aus sechs Zweigen aufgebaut. Somit hängt die Anzahl der Spannungsstufen in den Leiter-Leiter-Spannungen von der zunächst beliebigen Anzahl der Submodule ab. Zur Untersuchung dieser komplexen Stromrichtertopologie werden zwei Simulationsmodelle hergeleitet: das kontinuierliche Modell und das diskrete Modell. Dafür wird das elektrische Schaltbild durch ein gewöhnliches Differenzialgleichungssystem beschrieben, wobei die Schaltzustände der Leistungshalbleiter durch sogenannte Schaltfunktionen abgebildet werden. Das kontinuierliche Modell verwendet Schaltfunktionen, die Werte in einem kontinuierlichen Intervall annehmen können. Bei Vorgabe der Zweigströme und Sternpunktspannung können die Lösungen der anderen Systemgrößen analytisch berechnet werden. Für den allgemeinen Fall ist dies numerisch möglich. Im Gegensatz dazu verwendet das diskrete Modell diskrete Schaltfunktionen. Es wird durch numerische Integrationsverfahren mit dem Schaltungssimulator MATLAB/Plecs simuliert. Eine spezielle Eigenschaft dieses Stromrichters sind seine inneren, an den Ein- und Ausgangsklemmen nicht messbaren Ströme: die sogenannten Kreisströme. Diese Stromanteile werden erstmalig mathematisch im Zeitbereich definiert und die Harmonischen hergeleitet, die sich für einen symmetrischen Betrieb des Stromrichters ergeben. Für das diskrete Modell wird eine Zweigstromregelung implementiert. Die Anfangswerte der Spulen und Kondensatoren werden durch die analytischen Gleichungen des kontinuierlichen Modells so berechnet, dass sich der eingeschwungene Zustand ergibt. Der M2C besitzt keinen großen, sondern viele verteilte Energiespeicher: die Submodulkondensatoren. Die gespeicherte Energie sollte symmetrisch verteilt sein. Dafür werden drei Möglichkeiten der Energieänderung hergeleitet und deren Effektivität gezeigt. Eine andere Untersuchung betrifft die Stromaufteilung innerhalb der Submodule auf den jeweils oberen und unteren Leistungshalbleiter. Dabei wird die Stromaufteilung für verschiedene Phasenwinkel und Kreisströme gezeigt. Der Einfluss der schwankenden Kondensatorspannungen auf die Leiter-Leiter-Spannungen sowie die Anzahl der Spannungsstufen in den Leiter-Leiter-Spannungen werden mit dem diskreten Modell untersucht. Die Genauigkeit der Simulationsmodelle wird mit Hilfe eines Prototyps des M2Cs überprüft, der von der Fa. Siemens entwickelt wurde. Es werden charakteristische Strom- und Spannungsverläufe gemessen und den simulierten Verläufen der beiden Simulationsmodelle gegenübergestellt. Die Auslegung des Leistungsteils gliedert sich in die Auslegung der Submodulkondensatoren und die der Leistungshalbleiter. Zuerst wird die Kapazität der Submodulkondensatoren auf der Grundlage von drei verschiedenen Kondensatorspezifikationen mit Hilfe eines iterativen Algorithmus minimiert. Dies wird sowohl für kreisstromfreie als auch für optimierte kreisstrombehaftete Betriebsweisen mit dem kontinuierlichen Modell durchgeführt. Im nächsten Schritt werden die Leistungshalbleiter mit dem diskreten Modell dimensioniert. Dafür wird ein Stromfaktor definiert, der eine ideale Parallelschaltung von mehreren Leistungshalbleitern beschreibt. Die Verluste, die Verlustverteilung sowie die Sperrschichttemperaturen in den Leistungshalbleitern für verschiedene Phasenwinkel zeigen das Verhalten des Stromrichters in verschiedenen Arbeitspunkten
This thesis deals with the Modular Multilevel Converter M2C, an emerging and highly attractive multilevel converter topology for medium and high voltage applications. One of the most significant benefits of the M2C is its modular structure - the converter is composed of six converter arms, where each arm consists of a series connection of identical submodules (cells) and an inductor. Thus, the number of distinct voltage levels available for the line-to-line voltages is proportional to the number of submodules, which is in principle arbitrary. For the investigation of this complex converter topology, two simulation models - a continuous model and a discrete model - are derived. For this purpose, the electrical circuit is described by a system of ordinary differential equations where the switching states of the power semiconductors are represented by the so-called switching functions. The continuous model results from the analytical solution of the differential equations with a continuous interpretation of the switching functions. In contrast, the discrete model uses discrete switching functions and is computed using numeric integration methods with MATLAB/Plecs. One aspect of particular significance with the M2C is the topic of inner currents: the so-called circulating currents. In this thesis, these current components are defined mathematically in the time domain for the first time and the harmonics of the circulating currents for symmetrical operation of the converter are derived. For the discrete model, closed-loop control of the arm currents is implemented. Initial values for the inductors and capacitors are derived using the analytical equations of the continuous model. The M2C has several distributed energy storage elements: the submodule capacitors. The stored energy must be distributed evenly amongst these capacitors. To achieve this, three methods of energy distribution are presented. Another focus of this investigation is the current sharing between the upper and lower power semiconductor within the submodules. For different load phase angles and circulating currents, the current distribution is depicted. The influence of the floating capacitor voltages on the line-to-line voltages as well as the of number of discrete voltage levels in the line-to-line voltages are investigated with the discrete model. The accuracy of the simulation models is verified by experimentation with a prototype of the M2C from the company Siemens. The experimental results are compared with simulation results from the two simulation models. The dimensioning of the power components of the elecrical circuit is divided into two parts: the first for the submodule capacitors and the second for the power semiconductors. Initially, the capacitance of the submodule capacitors are minimized by an iterative algorithm on the basis of three different capacitor specifications. This computation is done using the continuous converter model for converter operation neglecting circulating currents and with optimized circulating currents. In the next step, the power semiconductors are dimensioned using the discrete model and assuming a defined current factor, which describes the ideal parallel connection of several semiconductors. The losses, the loss distribution, and the junction temperatures in the power semiconductors for different load phase angles describe the behavior of the converter for different operating points

碩士
國立交通大學
電控工程研究所
102
In this study, the droop method is used to share the current for parallel bidirectional full-bridge converters. Each converter is operating independently without connections between modules and without modification of the control structure. In the parallel converters, the effect of switching strategy on the reduction of circulating current is studied. The simulation and experimental waveforms are also provided to demonstrate the results.

The objective of the research is to design an electro-optic control for the Active Vertical Coupler-based Optical Cross-point Switch (OXS). The electronic control should be implemented on Printed Circuit Board (PCB) and therefore the design will include the PCB design as well. The aim of the electronic control board is to process the headers of the packets prior to entering the OXS to be switched and from the information in the headers, determine the state that the OXS should be configured in. It should then configure the optical cross-point accordingly. The electronic control board should show flexibility in the sense that it can handle different types of traffic and resolve possible contention that may occur. The research seeks to understand the problems associated with Photonic Packet Switching (PPS) networks. Two of the main problems identified in a PPS network are contention resolution and the lack of variable delays for storing optical packets. The OXS was analyzed and found to meet the requirements for future ultra-high speed PPS network technology with its high extinction ratio, wide optical bandwidth, ultra-fast switching speed and low crosstalk levels. Photonic packets were generated with 4-bit, 8-bit or 16-bit headers at a bit rate of 155 Mbit/s followed by a PRBS (Pseudo Random Bit Sequence) payload at 10 Gbit/s. Different scenarios were created with these types of packets and the electro-optic control and OXS were subjected to these scenarios with the aim of testing the flexibility of the electro-optic control to control the OXS. These scenarios include:

• Fixed length packets arriving synchronously at one input of the OXS. Some packets are destined for output 1, some are destined for output 2 and some are destined for output 3, therefore realizing a 1-to-3 optical switch.
• Eight variable length packets arriving synchronously at the OXS at one input, all of them destined for one output. The electro-optic control should open the switch cell for the correct amount of time.
• Three variable length packets arriving synchronously and asynchronously at one input of the OXS. Some packets are destined for output 1 while other packets are destined for output 2. The electro-optic control should open the correct switch cell for the correct amount of time.
• Two fixed length packets arriving at the OXS synchronously on different input ports at the same time, both destined for the same output port. The electro-optic control should detect the contention and switch the packets in such a way as to resolve the contention.
The electro-optic control and OXS managed to switch all these types of data traffic (scenarios) successfully and resolve the contention with an optical delay buffer. The success of the results was measured in two ways. Firstly it was deemed successful if the expected output sequence was measured at the corresponding output ports. Secondly it was successful if the degradation in quality of the packet was not drastic, meaning the output packets should have an BER (Bit Error Rate) of less than 10-9. The quality of the packets was measured in the form of eye diagrams before and after the switching and then compared. The research resulted in the design and implementation of a flexible electro-optic control for the OXS. The problem of contention was resolved for fixed length synchronous packets and a proposal is discussed to store packets for variable lengths of time by using the OXS. This electro-optic control has the potential to control the OXS for traffic with higher complexities and make the OXS compatible with future developments.
Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2008.
Electrical, Electronic and Computer Engineering
MEng
unrestricted

Die vorliegende Arbeit behandelt den Modularen Mehrpunktstromrichter M2C, der eine aufstrebende Mehrpunktstromrichtertopologie im Mittelspannungs- und Hochspannungsbereich ist. Die modulare Struktur des Stromrichters enthält in einem Stromrichterzweig eine Reihenschaltung aus identischen Submodulen (Zellen) und einer Spule. Der gesamte Stromrichter ist aus sechs Zweigen aufgebaut. Somit hängt die Anzahl der Spannungsstufen in den Leiter-Leiter-Spannungen von der zunächst beliebigen Anzahl der Submodule ab. Zur Untersuchung dieser komplexen Stromrichtertopologie werden zwei Simulationsmodelle hergeleitet: das kontinuierliche Modell und das diskrete Modell. Dafür wird das elektrische Schaltbild durch ein gewöhnliches Differenzialgleichungssystem beschrieben, wobei die Schaltzustände der Leistungshalbleiter durch sogenannte Schaltfunktionen abgebildet werden. Das kontinuierliche Modell verwendet Schaltfunktionen, die Werte in einem kontinuierlichen Intervall annehmen können. Bei Vorgabe der Zweigströme und Sternpunktspannung können die Lösungen der anderen Systemgrößen analytisch berechnet werden. Für den allgemeinen Fall ist dies numerisch möglich. Im Gegensatz dazu verwendet das diskrete Modell diskrete Schaltfunktionen. Es wird durch numerische Integrationsverfahren mit dem Schaltungssimulator MATLAB/Plecs simuliert. Eine spezielle Eigenschaft dieses Stromrichters sind seine inneren, an den Ein- und Ausgangsklemmen nicht messbaren Ströme: die sogenannten Kreisströme. Diese Stromanteile werden erstmalig mathematisch im Zeitbereich definiert und die Harmonischen hergeleitet, die sich für einen symmetrischen Betrieb des Stromrichters ergeben. Für das diskrete Modell wird eine Zweigstromregelung implementiert. Die Anfangswerte der Spulen und Kondensatoren werden durch die analytischen Gleichungen des kontinuierlichen Modells so berechnet, dass sich der eingeschwungene Zustand ergibt. Der M2C besitzt keinen großen, sondern viele verteilte Energiespeicher: die Submodulkondensatoren. Die gespeicherte Energie sollte symmetrisch verteilt sein. Dafür werden drei Möglichkeiten der Energieänderung hergeleitet und deren Effektivität gezeigt. Eine andere Untersuchung betrifft die Stromaufteilung innerhalb der Submodule auf den jeweils oberen und unteren Leistungshalbleiter. Dabei wird die Stromaufteilung für verschiedene Phasenwinkel und Kreisströme gezeigt. Der Einfluss der schwankenden Kondensatorspannungen auf die Leiter-Leiter-Spannungen sowie die Anzahl der Spannungsstufen in den Leiter-Leiter-Spannungen werden mit dem diskreten Modell untersucht. Die Genauigkeit der Simulationsmodelle wird mit Hilfe eines Prototyps des M2Cs überprüft, der von der Fa. Siemens entwickelt wurde. Es werden charakteristische Strom- und Spannungsverläufe gemessen und den simulierten Verläufen der beiden Simulationsmodelle gegenübergestellt. Die Auslegung des Leistungsteils gliedert sich in die Auslegung der Submodulkondensatoren und die der Leistungshalbleiter. Zuerst wird die Kapazität der Submodulkondensatoren auf der Grundlage von drei verschiedenen Kondensatorspezifikationen mit Hilfe eines iterativen Algorithmus minimiert. Dies wird sowohl für kreisstromfreie als auch für optimierte kreisstrombehaftete Betriebsweisen mit dem kontinuierlichen Modell durchgeführt. Im nächsten Schritt werden die Leistungshalbleiter mit dem diskreten Modell dimensioniert. Dafür wird ein Stromfaktor definiert, der eine ideale Parallelschaltung von mehreren Leistungshalbleitern beschreibt. Die Verluste, die Verlustverteilung sowie die Sperrschichttemperaturen in den Leistungshalbleitern für verschiedene Phasenwinkel zeigen das Verhalten des Stromrichters in verschiedenen Arbeitspunkten.:Kurzbeschreibung i Abstract iii Danksagung v Abbildungsverzeichnis xi Tabellenverzeichnis xvii Abkürzungsverzeichnis xix 0 Einleitung 1 1 Stand der Technik bei Mittelspannungsstromrichtern 3 1.1 Neutral-Point-Clamped Voltage Source Converter . . . . . . . . . . . . . . 5 1.2 Cascaded H-Bridge Voltage Source Converter . . . . . . . . . . . . . . . . 8 1.3 Flying Capacitor Voltage Source Converter . . . . . . . . . . . . . . . . . 10 2 Modularer Mehrpunktstromrichter 13 2.1 Aufbau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2 Prinzipielle Funktionsweise . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2.1 Spannungserzeugung durch die Submodule . . . . . . . . . . . . . 15 2.2.2 Symmetrierung der Kondensatorspannungen . . . . . . . . . . . . 16 2.2.3 Kreisströme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Stand der Technik . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.4 Strukturelle Eigenschaften . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.1 Vorteile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.2 Nachteile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.5 Motivation der Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3 Modellierung des Modularen Mehrpunktstromrichters 25 3.1 Verlust- und Sperrschichttemperaturberechnung von IGBT-Modulen . . . . 25 3.1.1 Stromfaktor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.2 Verlustberechnung . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.2.1 Durchlassverluste . . . . . . . . . . . . . . . . . . . . . 27 3.1.2.2 Schaltverluste . . . . . . . . . . . . . . . . . . . . . . . 28 3.1.3 Thermisches Ersatzschaltbild . . . . . . . . . . . . . . . . . . . . . 30 3.2 Modellierung eines Antriebs mit Modularem Mehrpunktstromrichter . . . . 31 3.2.1 Schaltungsmodell mit einem Submodul pro Zweig . . . . . . . . . 31 3.2.2 Differenzialgleichungssystem für das Schaltungsmodell mit einem Submodul pro Zweig . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2.3 Das diskrete Modell . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.2.4 Das kontinuierliche Modell . . . . . . . . . . . . . . . . . . . . . . 37 4 Analyse und Simulation des Modularen Mehrpunktstromrichters 43 4.1 Kreisströme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.1.1 Definition der Kreisströme . . . . . . . . . . . . . . . . . . . . . . 44 4.1.2 Harmonische der Kreisströme für den symmetrischen Betrieb . . . 45 4.2 Verfahren zur Erzeugung der Schaltsignale des diskreten Modells . . . . . . 49 4.3 Annahmen für die Simulation . . . . . . . . . . . . . . . . . . . . . . . . . 54 4.3.1 Daten des exemplarischen Simulationsmodells . . . . . . . . . . . 54 4.3.2 Anfangswertbestimmung . . . . . . . . . . . . . . . . . . . . . . . 56 4.3.2.1 Spulenströme . . . . . . . . . . . . . . . . . . . . . . . 56 4.3.2.2 Kondensatorspannungen . . . . . . . . . . . . . . . . . . 58 4.4 Analyse der Simulationsergebnisse . . . . . . . . . . . . . . . . . . . . . . 61 4.4.1 Verläufe charakteristischer Stromrichtergrößen . . . . . . . . . . . 61 4.4.2 Vergleich des kontinuierlichen und des diskreten Modells . . . . . . 69 4.4.3 Möglichkeiten der Verschiebung der gespeicherten Energie der Submodulkondensatoren . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4.3.1 Änderung der gespeicherten Energie einer Stromrichterphase . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 4.4.3.2 Verschiebung der gespeicherten Energie innerhalb einer Stromrichterphase . . . . . . . . . . . . . . . . . . . . . 86 4.4.3.3 Änderung der gespeicherten Energien unter Verwendung der Sternpunktspannung . . . . . . . . . . . . . . . . . . 94 4.4.4 Stromaufteilung innerhalb der Submodule . . . . . . . . . . . . . . 95 4.4.5 Einfluss der schwankenden Kondensatorspannungen auf die Leiter- Leiter-Spannungen . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5 Messtechnische Überprüfung der Simulationsmodelle 109 5.1 Versuchsaufbau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.2 Messergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.2.1 Modularer Mehrpunktstromrichter mit dreiphasiger induktiver Last 112 5.2.2 Modularer Mehrpunktstromrichter mit Maschinenlast . . . . . . . . 123 6 Auslegung des Leistungsteils 133 6.1 Kondensatorspezifikation . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2 Iterativer Algorithmus zur Bestimmung der minimalen Submodulkapazität . 135 6.3 Kreisstromfreier Betrieb . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.3.1 Auslegung der Submodulkondensatoren . . . . . . . . . . . . . . . 136 6.3.1.1 Vorgehensweise . . . . . . . . . . . . . . . . . . . . . . 136 6.3.1.2 Ergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.3.2 Auslegung der Leistungshalbleiter . . . . . . . . . . . . . . . . . . 143 6.3.2.1 Leistungshalbleiteraufwand . . . . . . . . . . . . . . . . 143 6.3.2.2 Verlustverteilung . . . . . . . . . . . . . . . . . . . . . . 145 6.4 Betrieb mit optimierten Kreisströmen . . . . . . . . . . . . . . . . . . . . 148 6.4.1 Auslegung der Submodulkondensatoren . . . . . . . . . . . . . . . 148 6.4.1.1 Algorithmus . . . . . . . . . . . . . . . . . . . . . . . . 148 6.4.1.2 Ergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.4.2 Auslegung der Leistungshalbleiter . . . . . . . . . . . . . . . . . . 157 6.4.2.1 Leistungshalbleiteraufwand . . . . . . . . . . . . . . . . 157 6.4.2.2 Verlustverteilung . . . . . . . . . . . . . . . . . . . . . . 159 7 Zusammenfassung der Dissertation 163 Literaturverzeichnis 169
This thesis deals with the Modular Multilevel Converter M2C, an emerging and highly attractive multilevel converter topology for medium and high voltage applications. One of the most significant benefits of the M2C is its modular structure - the converter is composed of six converter arms, where each arm consists of a series connection of identical submodules (cells) and an inductor. Thus, the number of distinct voltage levels available for the line-to-line voltages is proportional to the number of submodules, which is in principle arbitrary. For the investigation of this complex converter topology, two simulation models - a continuous model and a discrete model - are derived. For this purpose, the electrical circuit is described by a system of ordinary differential equations where the switching states of the power semiconductors are represented by the so-called switching functions. The continuous model results from the analytical solution of the differential equations with a continuous interpretation of the switching functions. In contrast, the discrete model uses discrete switching functions and is computed using numeric integration methods with MATLAB/Plecs. One aspect of particular significance with the M2C is the topic of inner currents: the so-called circulating currents. In this thesis, these current components are defined mathematically in the time domain for the first time and the harmonics of the circulating currents for symmetrical operation of the converter are derived. For the discrete model, closed-loop control of the arm currents is implemented. Initial values for the inductors and capacitors are derived using the analytical equations of the continuous model. The M2C has several distributed energy storage elements: the submodule capacitors. The stored energy must be distributed evenly amongst these capacitors. To achieve this, three methods of energy distribution are presented. Another focus of this investigation is the current sharing between the upper and lower power semiconductor within the submodules. For different load phase angles and circulating currents, the current distribution is depicted. The influence of the floating capacitor voltages on the line-to-line voltages as well as the of number of discrete voltage levels in the line-to-line voltages are investigated with the discrete model. The accuracy of the simulation models is verified by experimentation with a prototype of the M2C from the company Siemens. The experimental results are compared with simulation results from the two simulation models. The dimensioning of the power components of the elecrical circuit is divided into two parts: the first for the submodule capacitors and the second for the power semiconductors. Initially, the capacitance of the submodule capacitors are minimized by an iterative algorithm on the basis of three different capacitor specifications. This computation is done using the continuous converter model for converter operation neglecting circulating currents and with optimized circulating currents. In the next step, the power semiconductors are dimensioned using the discrete model and assuming a defined current factor, which describes the ideal parallel connection of several semiconductors. The losses, the loss distribution, and the junction temperatures in the power semiconductors for different load phase angles describe the behavior of the converter for different operating points.:Kurzbeschreibung i Abstract iii Danksagung v Abbildungsverzeichnis xi Tabellenverzeichnis xvii Abkürzungsverzeichnis xix 0 Einleitung 1 1 Stand der Technik bei Mittelspannungsstromrichtern 3 1.1 Neutral-Point-Clamped Voltage Source Converter . . . . . . . . . . . . . . 5 1.2 Cascaded H-Bridge Voltage Source Converter . . . . . . . . . . . . . . . . 8 1.3 Flying Capacitor Voltage Source Converter . . . . . . . . . . . . . . . . . 10 2 Modularer Mehrpunktstromrichter 13 2.1 Aufbau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2 Prinzipielle Funktionsweise . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2.1 Spannungserzeugung durch die Submodule . . . . . . . . . . . . . 15 2.2.2 Symmetrierung der Kondensatorspannungen . . . . . . . . . . . . 16 2.2.3 Kreisströme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Stand der Technik . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.4 Strukturelle Eigenschaften . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.1 Vorteile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.2 Nachteile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.5 Motivation der Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3 Modellierung des Modularen Mehrpunktstromrichters 25 3.1 Verlust- und Sperrschichttemperaturberechnung von IGBT-Modulen . . . . 25 3.1.1 Stromfaktor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.2 Verlustberechnung . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.2.1 Durchlassverluste . . . . . . . . . . . . . . . . . . . . . 27 3.1.2.2 Schaltverluste . . . . . . . . . . . . . . . . . . . . . . . 28 3.1.3 Thermisches Ersatzschaltbild . . . . . . . . . . . . . . . . . . . . . 30 3.2 Modellierung eines Antriebs mit Modularem Mehrpunktstromrichter . . . . 31 3.2.1 Schaltungsmodell mit einem Submodul pro Zweig . . . . . . . . . 31 3.2.2 Differenzialgleichungssystem für das Schaltungsmodell mit einem Submodul pro Zweig . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2.3 Das diskrete Modell . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.2.4 Das kontinuierliche Modell . . . . . . . . . . . . . . . . . . . . . . 37 4 Analyse und Simulation des Modularen Mehrpunktstromrichters 43 4.1 Kreisströme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.1.1 Definition der Kreisströme . . . . . . . . . . . . . . . . . . . . . . 44 4.1.2 Harmonische der Kreisströme für den symmetrischen Betrieb . . . 45 4.2 Verfahren zur Erzeugung der Schaltsignale des diskreten Modells . . . . . . 49 4.3 Annahmen für die Simulation . . . . . . . . . . . . . . . . . . . . . . . . . 54 4.3.1 Daten des exemplarischen Simulationsmodells . . . . . . . . . . . 54 4.3.2 Anfangswertbestimmung . . . . . . . . . . . . . . . . . . . . . . . 56 4.3.2.1 Spulenströme . . . . . . . . . . . . . . . . . . . . . . . 56 4.3.2.2 Kondensatorspannungen . . . . . . . . . . . . . . . . . . 58 4.4 Analyse der Simulationsergebnisse . . . . . . . . . . . . . . . . . . . . . . 61 4.4.1 Verläufe charakteristischer Stromrichtergrößen . . . . . . . . . . . 61 4.4.2 Vergleich des kontinuierlichen und des diskreten Modells . . . . . . 69 4.4.3 Möglichkeiten der Verschiebung der gespeicherten Energie der Submodulkondensatoren . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4.3.1 Änderung der gespeicherten Energie einer Stromrichterphase . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 4.4.3.2 Verschiebung der gespeicherten Energie innerhalb einer Stromrichterphase . . . . . . . . . . . . . . . . . . . . . 86 4.4.3.3 Änderung der gespeicherten Energien unter Verwendung der Sternpunktspannung . . . . . . . . . . . . . . . . . . 94 4.4.4 Stromaufteilung innerhalb der Submodule . . . . . . . . . . . . . . 95 4.4.5 Einfluss der schwankenden Kondensatorspannungen auf die Leiter- Leiter-Spannungen . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5 Messtechnische Überprüfung der Simulationsmodelle 109 5.1 Versuchsaufbau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.2 Messergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.2.1 Modularer Mehrpunktstromrichter mit dreiphasiger induktiver Last 112 5.2.2 Modularer Mehrpunktstromrichter mit Maschinenlast . . . . . . . . 123 6 Auslegung des Leistungsteils 133 6.1 Kondensatorspezifikation . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2 Iterativer Algorithmus zur Bestimmung der minimalen Submodulkapazität . 135 6.3 Kreisstromfreier Betrieb . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 6.3.1 Auslegung der Submodulkondensatoren . . . . . . . . . . . . . . . 136 6.3.1.1 Vorgehensweise . . . . . . . . . . . . . . . . . . . . . . 136 6.3.1.2 Ergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . 140 6.3.2 Auslegung der Leistungshalbleiter . . . . . . . . . . . . . . . . . . 143 6.3.2.1 Leistungshalbleiteraufwand . . . . . . . . . . . . . . . . 143 6.3.2.2 Verlustverteilung . . . . . . . . . . . . . . . . . . . . . . 145 6.4 Betrieb mit optimierten Kreisströmen . . . . . . . . . . . . . . . . . . . . 148 6.4.1 Auslegung der Submodulkondensatoren . . . . . . . . . . . . . . . 148 6.4.1.1 Algorithmus . . . . . . . . . . . . . . . . . . . . . . . . 148 6.4.1.2 Ergebnisse . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.4.2 Auslegung der Leistungshalbleiter . . . . . . . . . . . . . . . . . . 157 6.4.2.1 Leistungshalbleiteraufwand . . . . . . . . . . . . . . . . 157 6.4.2.2 Verlustverteilung . . . . . . . . . . . . . . . . . . . . . . 159 7 Zusammenfassung der Dissertation 163 Literaturverzeichnis 169

AbstractSchistosomes are blood flukes that parasitize humans, apes, cattle, and other animals. In these definitive hosts they are bisexual, and lay eggs which are shed to fresh water where they complete an asexual cycle in different snails, ending in the release of cercariae which infect the definitive hosts to complete the life cycle.Seven of over 100 species of schistosomes are human pathogens, causing disease in different organs depending on the parasite species. Racial and genetic factors are involved in susceptibility, severity, and sequelae of infection.Morbidity is induced by the host’s immune response to schistosomal antigens. The latter include tegument, microsomal, gut, and oval antigens. The former are important in the process of invasion and establishment of infection, oval antigens in formation of granulomata which lead to fibrosis in different sites, and the gut antigens constitute the main circulating antigens in established infection, leading to immune-complex disease, particularly in the kidneys. The host immunological response includes innate and adaptive mechanisms, the former being the front line responsible for removing 90% of the infecting cercarial load. Adaptive immunity includes a Th1 phase, dominated by activation of an acute inflammatory response, followed by a prolonged Th2 phase which is responsible for immunity to re-infection as well as progression of tissue injury. Switching from Th1 to Th2 phases is controlled by functional and morphological change in the antigen-presenting cells, which is achieved by molecules of host as well as parasitic origin.Many cells participate in parasite killing, but also in the induction of tissue injury. The most potent of these is the eosinophil, which by binding antibodies to the parasite, particularly immunoglobulin E, facilitates parasite elimination. However, this process is complex, including agonist as well as antagonist pathways, which provide escape mechanisms for the parasite to survive, thereby achieving a delicate balance that permits schistosomes to live for decades in the infected host.

Abstract Continuous Circulation Systems (CCS) have been around since the JIP between Shell, BP, Statoil, BG, Total and Eni in October 2000. Initial reports of these systems demonstrated that while cumbersome, the use of CCS is of benefit to drilling ERD wells. Continuous circulation keeps cuttings moving out of the wellbore, reducing or eliminating the time required to circulate clean any high-angle section before making a drill pipe connection or before tripping out of the hole. Continuous Circulation over each connection enhances the management of Equivalent Circulating Density(ECD) to control the bottom hole pressure on the well by never switching off the pumps, therefore the wellbore never experiences an Equivalent Static Density(ESD). Through this mechanism, the application of CCS has also been proven to manage bottom hole pressure constantly, which in conjunction with good drilling practices for torque and drag management, are key factors in drilling any Extended Reach Drilling(ERD), Complex or High Pressure/High Temperature (HPHT) well.

The paper presents the results of the OECD/NEA benchmark transient ‘Switching off one main circulation pump at nominal power’ analyzed as a boundary condition problem by the coupled system code ATHLET-BIPR-VVER. Of primary interest are the comparisons done for the local in-core parameters — assembly outlet coolant temperatures at 93 measured points and SPND powers at 7 layers of 64 fuel assemblies. Revealed are some sources of inaccuracy and methods are proposed to be decreased. An important step is done for the future performing of uncertainty and sensitivity analysis in the frame of the OECD/NEA activities.

A unique double gear fuel pump system with operation mode switching capability for aircraft engines was developed to solve the heat management problem of current high efficiency turbofan engines and improve Specific Fuel Consumption (SFC). Mode switching from parallel operations to series operations was found to reduce the discharge flow and pump work to nearly half. This resulted in the reduction of the rise in fuel temperature due to the fuel re-circulation at the high altitude low Mach number flight condition. Air Cooled Oil Cooler (ACOC) is usually required for sufficient oil cooling at decent or approach flight conditions. Since fuel consumption at those conditions is not very high, most of the gear pump discharge fuel flow proportional to the engine speed is returned to the fuel pump inlet resulting in significant heating. The ACOC that provides additional cooling capability degrades SFC due to not only increased weight but also wasted fan discharge air. By reducing fuel temperature rise at the pump at those flight conditions, the necessity of ACOC may be eliminated. Further, it is shown that a reduction by half of the double gear pump weight can be achieved by increasing pump speed twice (2x) without incurring a durability penalty. Extensive tests showed sufficient steady state pump performance, switching characteristics, and durability.

A valveless shear-driven micro-fluidic pump design (SDMFP) for hemodynamic applications is presented in this work. One of the possible medical and biomedical applications is in-vivo hemodynamic (human blood circulation) support/assist. One or more SDMFPs can be inserted/implanted into vascular lumens in a form of a stent/duct in series and/or in parallel (bypass duct) to support blood circulation in-vivo. A comprehensive review of various micro-pump designs up to about mid 2000’s is given in [1,2]. Many of micropump designs considered are not suitable for in-vivo or even in-vitro medical/biomedical applications. Operating principles, design, and SDMFP features are given in [3]. A particular design used in cardiovascular applications has no moving valves. SDMFP with Gourney-flap type valves to support high-pressure applications are developed for other applications. SDMFP could be fully bi-directional and can control its operation on the run using embedded microcontrollers and sensors. Estimated efficiency is high with low leakage resulting in low power consumption. Proprietary “fish-scale” surface coating ShearQ™ designs are implemented to improve unidirectional flow pumping efficiency. Bi-directional feature may be especially critical when clogging of blood vessels is detected. By automatically and temporarily switching into the reverse-mode operation and retrogressive flow, while inducing suction-head for a short time periods it is hoped that possibly blood conduits can be cleared/unclogged and the normal forward-flow operation resumed. Such may be an important feature if SDMFP is used in-vivo, such as, in coronary arteries which are prone to clogging leading to cardiac-arrest.

A real-time version of the Nodal Expansion Method (NEM) code is developed and implemented into Kozloduy 6 full-scope replica control room simulator. Combined with an enhanced thermal-hydraulics and I&C models the whole package is a high-fidelity simulation tool for operator training and various other applications. The fidelity and accuracy of simulation with emphasis on reactor core model is illustrated through comparison with plant-specific data. The transient of ‘Switching-off of One of the Four Operating Main Circulation Pumps at Nominal Reactor Power’ as described in OECD/NEA Kalinin 3 Coolant Transient Benchmark is an example of an asymmetric core scenario with a range of parameter changes. Simulation results concerning fuel assembly power and axial power distribution during the transient are compared with records from Kalinin 3 in-core monitoring system. Main operating parameters of nuclear steam supply system of a VVER-1000/V320 series units vary to a considerable degree. While Kalinin 3 benchmark specification contains very good description of the transient, as well as record of many parameters of the unit, the document provides only superfluous description of the reference unit. In such a case, an approach based on a ‘generic’ V320 model by default introduces deviations which are difficult to quantify. There are several examples which warrant discussion. One example is core coolant flow and pressure loss during the transient. Pump head and pressure loss across reactor vessel are measured and recorded and in-core monitoring system provides estimation of core coolant flow, which is quite high in comparison with some other V320 units (e.g. by about 5 % larger). Without more detailed pressure loss data across the main circulation loop and specific pump characteristics, however, one can only guess how much simulation is off the mark. Another detail of the same problem is coolant flow through a specific fuel assembly. The presence of a fuel assembly of different design (TVS-M type) surrounded by TVSA type fuel assemblies shall be thoroughly considered, because secondary sources indicate significant differences in fuel assembly pressure loss coefficients between the two types. Coolant flow affects coolant (and fuel) temperature profile and thus neutron cross-sections. Yet another example, even more strongly affecting our ability to interpret simulation results is core power reconstruction provided by the in-core monitoring system of the unit. The SPND (Self-Powered Neutron Detector) current readings are subject of conversion by an algorithm based upon simulated spatial neutron flux distribution across the reactor core. While error estimation of the parameters in stationary conditions is available from secondary sources, there is no reliable estimation of error magnitude during the transient.

The use of non-motorized means of transport such as the bicycle, brings many benefits to the user and for the city in terms of costs and health for the first and decreased environmental pollution for the city. To find the optimal location for placement of the different parties to public bike, aims to attract the usual user and potential, have the feasibility of switching modes without any restrictions, while generating the ability to balance the demands users towards sustainable modes of transport, with special attention to cycling and public bike loan. The implementation of this methodology is performed in the municipality of Murcia (Spain) due to the opening of its public bicycle system MUyBICI which will have 60 benches, with a total of 1,200 posts anchor and put into circulation 600 public bicycles. As selection criteria to be considered for the optimal location of the beds, the existing network of bike paths were considered, roads used by all users of the public highway, a description of travel and a database information with different land uses and socioeconomic data transport areas. In this paper an analysis model and application for optimal design of banking locations for Murcia MUyBICI service occurs. Specifically, they define what are the best locations to attract a larger number of users, in order to achieve a change in the percentage of the modal split of the municipality, increasing the number of users MUyBICI service. This work comes under the direction of the Bicycle Office of Murcia, part of the ALEM (Local Agency for Energy and Environment) service under the Department of Environment of the City of Murcia.DOI: http://dx.doi.org/10.4995/CIT2016.2016.4090