Simulation of Bidirectional Converter for Vechile to Grid and Grid to Vechile Application

This paper represents a bidirectional converter for the application of vehicle to grid and grid to vehicle application. This converter can be used in the application of electric vehicle. And the results have been verified through simulation in MATLAB. The topology can provide an energy bi-directional flow path for energy exchange between the Libattery/supercapacitor (SC) hybrid energy storage system (HESS) of the electric vehicle and the grid. Keywords: bi-directional converter, vehicle, HESS, Li-battery.

MANAGEMENT STRATEGIES FOR ENERGY PROCESSES IN ELECTRIC ROLLING STOCK WITH ON-BOARD ENERGY STORAGE DEVICES

The article deals with the main existing strategies for management strategy of energy exchange processes in the electric rolling stock with onboard capacitive energy storage devices. When considering strategies, it is assumed that the onboard capacitive storage has low power and capacitance. Therefore, this capacitor storage is not able to accept the full amount of regenerative braking energy of the electric rolling stock. The purpose of the paper is to consider and analyze management strategies for energy exchange processes in the electric rolling stock with onboard capacitive energy storages; to define the advantages and disadvantages of each of the existing strategies and propose a concept for the effective management of energy exchange processes in the electric rolling stock. The block diagram of electric rolling stock with the onboard capacitive energy storage which is used for the analysis of management strategies for energy exchange processes is presented. The modes of operation of electric rolling stock with onboard capacitive energy storages are described. Five main strategies for management of energy exchange processes on the electric rolling stock with onboard capacitive energy storages are determined. The advantages and disadvantages of each strategy are set out taking into account the given conditions (characteristics of the electric rolling stock, conditions of the rolling stock motion, oscillograph charts, etc.). The general advantages and shortcomings of each strategy are defined, which allowed to propose the concept of creating an adaptive strategy for managing energy exchange processes in electric rolling stock with onboard capacitive energy storages. The main concept of this management strategy is to implement efficient energy exchange between the traction equipment, the onboard capacitive energy storage, the overhead contact system, both in normal and emergency modes of traction power supply, taking into account the dynamics of energy exchange processes in the overhead contact system, which will generally allow safety and energy efficiency of the transportation process. The obtained research results will contribute to the development and implementation of effective strategies for managing energy exchange processes in the electric rolling stock.

Improvement of the design method of thermal networks: serial connection of heat exchangers

The mathematical model of the system is considered consisting of a series connection of three heating devices. A system of equations based on the energy conservation law is constructed, which turns out to be incomplete. It is shown that, given the known requirements for the system, expressed only in the efficiency of the system, the formalization of design often becomes insoluble. The system of equations is supplemented with expressions in accordance with the hypothesis of the proportionality of the amount of energy in an element and is presented in matrix form. The design task is reduced to determining the elements of the matrix by the value of the determinants. Analysis of the mathematical model made it possible to obtain an expression for the efficiency of the system as a function of energy exchange in its elements. This made it possible to obtain solutions for flows and their relationships in the elements of the system. In addition, the efficiency of inter-network and intra-network energy exchange has been determined, which satisfy the principles of equilibrium and minimum uncertainty in the values of the average parameters of the system. As an application, one of the main parameters, NTU, is considered, which determines the area of heat exchange with the external environment and the mass and dimensional characteristics of the heat exchange system. Models of direct and opposite switching on of flows with variations of flows and the value of the surface of devices when meeting the requirements for the efficiency of the system are considered. The results of comparing the design process with the iterative calculation method are presented and the advantages of the proposed approach are shown

Justification for the use of Markovian Langevin statistics in the modelling of activated surface diffusion.

Low temperature surface diffusion is driven by the thermally activated hopping of adatoms between adsorption sites. Helium spin-echo techniques, capable of measuring the sub-picosecond motion of individual adatoms, have enabled the bench-marking of many important adsorbate-substrate properties. The well-known Markovian Langevin equation has emerged as the standard tool for the interpretation of such experimental data, replacing adatom-substrate interactions with stochastic white noise and linear friction. However, the consequences of ignoring the colored noise spectrum and non-linearities inherent to surface systems are not known. Through the computational study of three alternative models of adatom motion, we show that the hopping rate and jump distributions of an adatom are fixed to within a few percent by the potential energy surface and a new generalized energy exchange rate parameter alone, independent of the model used. This result justifies the use of the Markovian Langevin equation, regardless of the true statistical nature of adatom forces, provided results are quoted in terms of the new energy exchange rate parameter. Moreover, numerous mechanisms for the effect of noise correlations and non-linear friction on the energy exchange rate are proposed which likely contribute to activated surface diffusion and activated processes more generally.

Das Projekt „MEDIWA“

<p><strong><em>Me</em></strong><em>teorological <strong>D</strong>rivers of Mass and Energy Exchange between <strong>I</strong>nland <strong>W</strong>aters and the <strong>A</strong>tmosphere (MEDIWA)</em></p> <p>Die genaue Quantifizierung des Stoff- und Energieaustausches zwischen Binnengewässern und der bodennahen Luftschicht ist von großer wissenschaftlicher und praktischer Bedeutung. So sind zum Beispiel genaue Abschätzungen der auftretenden Verdunstungsraten essentiell für die Steuerung und Betriebsführung von Talsperren und Stauseen sowie für eine erfolgreiche Realisierung von Flutungsvorhaben in Bergbaufolgelandschaften. In gleicherweise sind Kenntnisse des Wärmewärmehaushalts bzw. des Wärmeaustauschs eines Gewässers mit der Atmosphäre sowie ein exaktes Wissen über den an der Wasseroberfläche stattfindenden Gasaustauschs wichtig, um die wasserwirtschaftlichen Steuermöglichkeiten effizient zur Optimierung und Verbesserung der Wassergüte in Gewässern einsetzen zu können.</p> <p>Exakte, direkte Messungen des an der Wasseroberfläche stattfindenden Stoff- und Energieaustauschs sind möglich, aber sehr teuer und technisch extrem aufwendig. Daher werden Stoff- und Energieflüsse (z.B. Verdunstungsraten) meist mit Hilfe von verschiedenen numerischen Modellen aus einfacher zu messenden limnologischen und meteorologischen Variablen abgeschätzt. Die Genauigkeit derartig bestimmter Austauschraten ist jedoch sehr stark abhängig von (i) der Komplexität des eingesetzten Modells, (ii) der Parametrisierung der Modellgleichungen und (iii) der Repräsentativität und Genauigkeit der zur Verfügung stehenden Eingangsdaten. In der Praxis treten dadurch oftmals Konfliktsituationen auf, da die für den Einsatz genauer, komplexer Modelle notwendigen Umweltmessdaten in vielen Anwendungsfällen nicht oder nicht in ausreichender Qualität bereitstehen. Dieser Sachverhalt führt in Konsequenz dazu, dass der Stoff- und Energieaustausch eines Gewässers meist nur sehr überschlägig quantifiziert werden kann. Ergänzend ist festzuhalten, dass auch komplexe Modelle nach wie vor erhebliche Defizite und Schwächen in der Nachbildung der in Gewässern ablaufenden Prozesse haben. Insgesamt sind die Möglichkeiten zur Modellierung des Stoff- und Energiehaushalts von Gewässern somit stark verbesserungsbedürftig.</p> <p>Mit dem Ziel Stoff- und Energieflüsse von Binnengewässern auf Grundlage allgemein verfügbarer Umweltgrößen genauer modellieren und prognostizieren zu können, sollen in dem Projekt -MEDIWA- die an der Wasseroberfläche stattfindenden Austauschprozesse intensiv messtechnisch untersucht werden. Auf Grundlage der gewonnenen Messdaten sollen Methoden entwickelt werden, um die Verlässlichkeit von Modellabschätzungen zu verbessern. Komplexe Zusammenhänge und Prozessketten sollen aufgelöst und durch mathematische Gleichungen beschreibbar gemacht werden. Im besonderem Fokus steht dabei die Analyse und quantitative Beschreibung, wie die zeitliche und räumliche Variabilität meteorologischer Steuergrößen den Stoff und Energiehaushalt eines Gewässers beeinflusst. In unserem Tagungsbeitrag wollen wir das Projekt vorstellen und erste Ergebnisse der gegenwärtig noch laufenden Messungen präsentieren. Insbesondere wollen wir die Aspekte der räumlichen Heterogenität meteorologischer Steuergrößen auf den Stoff- und Energiehaushalt eines Gewässers diskutieren und im Hinblick auf die Zielvorhaben des Projektes erörtern.</p>

Thermal transport in beta-gallium oxide thin-film using non-gray Boltzmann transport equation

Phonon transport in β-Ga2O3 thin films and metal–oxide field effect transistors (MESFETs) are investigated using non-gray Boltzmann transport equations (BTE) to decipher the effect of ballistic-diffusive phonon transport. The effects of domain size, and energy dissipation to various phonon modes and subsequent phonon-phonon energy exchange on the thermal transport and temperature distribution is investigated using non-gray BTE. Our analysis deciphered that domain size plays a major role in thermal transport in β-Ga2O3 but energy dissipation to various phonon modes and subsequent phonon-phonon energy exchange does not affect the temperature field significantly. Phonon transport in β-Ga2O3 MESFETs on diamond substrate is investigated using coupled non-gray BTE and Fourier model. It is established that the ballistic effects need to be considered for devices with β-Ga2O3 layer thickness less than 1 µm. A non-gray phonon BTE model should be used near hotspot in the thin β-Ga2O3 layer as the Fourier model may not give accurate temperature distribution. The results from this work will help in understanding the mechanism of phonon transport in the β-Ga2O3 thin films and energy efficient design of its FETs.