Ulf Schwalbe

Advantages of 3-stage-DC/DC-converters for Server Switch Mode Power Supply (SMPS) applications

This contribution deals with the benefits and the challenges of 3-stage DC/DC converters in SMPS applications. They are compared to state of the art 2-stage DC/DC converters for high power and highest efficiency power supplies focusing on server, telecom AC/DC and battery charger applications as a major market for advanced system solutions. The main difference between a 3-stage SMPS and a conventional 2-stage topology is the existence of an extra stage to assume the output power regulation from the main stage. This publication points out the advantages, the problems and the limits of current-fed pre-regulated 3-stage topologies considering the demands. Further on a comparison of different approaches for a voltage-fed post-regulated 3-stage SMPS is presented. This paper also reconsiders the optimal operation frequency regarding the passive components in a resonant mode converter used in the post-regulated circuit. All presented results are extracted from calculations, simulations or practical measurements on the basis of different 800 W demonstrators with 12 V output.

Dimensioning of ultra capacitors used for range extension in electric vehicles

Electric vehicles (EV) require energy storage with high power and high energy-density. A hybrid-storage-system combining battery (high energy density) and ultra-capacitor (high power density) to supply a motor is logical. This paper will present an efficient way of dimensioning the ultra-capacitor of this system. The optimal size is determined by applying real driving cycles to a dynamics simulation. The dynamics model used for the simulation is explained and the results for different driving cycles are presented. In addition a lifetime estimation for the ultra-capacitor (UC) using available datasheets is performed with the same simulation.

Estimating the Limits in System Design for 48 V Automotive Power Applications

The design process in power electronics is driven by increased utilisation level of the used components to gain performance whilst keeping cost low. This article provides an overview on challenges in low-voltage high-current systems, e.g. used in automotive applications. The main content points are: topology selection—single systems vs. cascaded systems, PCB manufacturing technology overview, current measurement methods, bulk capacitor design (ceramic DC link) and PCB design instructions for high-current systems. The PCB design instructions target on optimised thermal design for maximised PCB utilisation and on optimised track design for a low inductance DC link interconnection. The paper bases on calculations, measurements and simulations.

System voltage estimation for a decentralized electromotive drive train system

At present, there are two typical electromotive drive train system (EDTS) configurations on the market. On the one hand, there are high voltage systems for conventional cars with system voltages in the range of 400 V - 800 V. In industrial truck and fork lifter applications, there are low voltage solutions with a system voltage of 80 V. A main question at this topic is: “Which system battery voltage is the best solution for EDTSs?” In future, the development-goals of EDTSs are high efficiency, high power density, low costs and system safety [1]. This paper will show the way of estimating the best system voltage regarding the named development goals. The main focus of the paper is on the system efficiency and losses simulation. Therefore a system simulation with a real measured driving cycle input will be developed.

Comparison of different three-stage DC-DC converter solutions for SMPS applications

Energy savings and the reduction of CO2 emissions is a main topic in todaypsilas power electronics research. Power electronics offers a wide potential for energy savings. This contribution deals with the benefits and the challenges of pre-regulated and post-regulated three-stage DC-DC converters in server applications. They are compared to a state of the art two-stage DC-DC converter. This publication shows the advantages, problems and limits of current fed pre-regulated and voltage fed post-regulated three-stage topologies. The focus is on post-regulated converters and selected technical challenges during the development. Furthermore aspects regarding benefits of resonant gate drive for synchronous rectification MOSFETs and stage synchronisation are discussed. All results are extracted from practical measurements on the basis of different 12 V, and 800 W demonstrators. Efficiency considerations are shown as well.