Tobias Reimann

A novel control principle of bi-directional DC-DC power conversion

This paper presents a novel control method for DC-DC power converters with bi-directional power flow and galvanic isolation. A high efficiency is achieved by using a minimal number of power electronic devices working in the soft switching mode. No reverse blocking switches are required. Different circuit variants can be derived from the proposed basic principle. Suitable industrial applications for the new principle of DC-DC conversion are UPS, photovoltaic applications, battery chargers, back-fire applications and auxiliary power supplies.

Modelling of asymmetrical pulse width modulation with frequency tracking control using phasor transformation for half-bridge series resonant induction cookers

A FPGA-based asymmetrical pulse width modulation (APWM) with frequency tracking control method is introduced for half-bridge series resonant induction cookers. Two control loops within FPGA are implemented. Phase-locked loop (PLL) is used as frequency tracking control to keep ZVS over wide range, APWM as power regulation. Large and small signal PSPICE compatible circuit model are obtained by phasor transformation. Dynamic models for half-bridge series resonant induction cooker are extracted from these circuits, and their characteristics are analysed. Finally models are verified and conclusions are given

Envelope Model of Frequency-Duty-Controlled LLC Converters

Tins paper presents envelope model of frequency- duty-controlled LLC converters. With this model, its DC and AC characteristics can be quickly simulated. Moreover, its transfer functions have been solved and analyzed. Thus, the compensator with duty cycle control, variable frequency control, or variable frequency variable duty cycle control can be easily designed using this model.

Design and Implementation of a FPGA-Based Controller for Resonant Inverters

Design and implementation of a PGA-based controller is presented in this paper. First general control scheme for resonant inverter is introduced and the PGA-based controller construction is given. Then the small signal model of the close loop system for a resonant inverter is analyzed. Thus compensator can be designed. Moreover, the key functional blocks within FPGA including variable frequency pulse width modulator (VFPWM), PLL and power control loop are discussed in detail. Finally experimental architecture and results are given.

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.

A half-bridge series resonant inverter for induction cookers using a novel FPGA-based control strategy

Asymmetrical pulse width modulation (APWM) with frequency tracking control strategy is proposed for half bridge series resonant inverter for induction cookers, by which inverter is operated at zero-voltage-switching (ZVS) over wide load range. The FPGA-based full digital control system construction and operation are described. Steady state characteristics, such as normalized output power, turn-off current and average current through switches, are calculated. Some design considerations including selection of snubber capacitor, determination of dead time, ZVS boundary and presetting of phase-locked loop (PLL) are discussed. Finally, experiment results are given

Influences of magnetic inductance, leakage inductance and saturable inductance on an active clamp forward converter

In this paper, the influences of the magnetic inductance, leakage inductance and saturable inductor on the behaviour of the active clamp forward are analyzed, and their mathematic solutions are given. Based on the analysis, the other topology variant is proposed, which can be used to reduce the oscillation across the freewheeling switch and improve the ZVS condition of the auxiliary switch in primary side. This leads to improve the EMI behaviour and efficiency because the low voltage rectifier switches could be used. To verify these analyse, some experimental results are presented.

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.

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.