Switching Transient Shaping by Application of a Magnetically Coupled PCB Damping Layer

Hartmann, Michael,Musing, Andreas,Kolar, Johann W. The Korean Institute of Power Electronics 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

An increasing number of power electronic applications require high power density. Therefore, the switching frequency and switching speed have to be raised considerably. However, the very fast switching transients induce a strong voltage and current ringing. In this work, a novel damping concept is introduced where the parasitic wiring inductances are advantageously magnetically coupled with a damping layer for attenuating these unwanted oscillations. The proposed damping layer can be implemented using standard materials and printed circuit board manufacturing processes. The system behavior is analyzed in detail and design guidelines for a damping layer with optimized RC termination network are given. The effectiveness of the introduced layer is determined by layout parasitics which are calculated by application of the Partial Element Equivalent Circuit (PEEC) simulation method. Finally, simulations and measurements on a laboratory prototype demonstrate the good performance of the proposed damping approach.

Influence of Surface Roughness of Tools on the Friction Stir Welding Process

Hartmann, Michael,Bohm, Stefan,Schuddekopf, Sven The Korean Welding and Joining Society 2014 대한용접·접합학회지 Vol.32 No.6

Most publications on friction stir welding describe phenomena or results with given process parameters like feed rate, rotation speed, angle and depth of penetration. But without a complete documentation of tool design, the results under the same process parameters are completely different. For this purpose, the Institute of Cutting and Joining Manufacturing Processes (tff), University of Kassel investigated the influence of tool roughness on the friction stir welding process. Therefore a defined surface finish was produced by turning and die sinking. As basis of comparison the constant parameters were rotation speed, feed rate, tilt angle and a heel plunge depth. Sound butt-welds were produced in aluminium alloy 6082 (AlMgSi1) with 1.5 mm sheet thickness with a turned reference tool with a surface of $Ra=0.575{\mu}m$ in position controlled mode. The surfaces are manufactured from a very fine to a very rough structure, classified by the VDI-classes with differences in the arithmetical mean roughness. It can be demonstrated with the help of temperature measures, that less heat is generated at the surfaces of the shoulder and the pin by the higher roughness due to lower active friction contact surface. This can also be seen in the resulting wormhole defects.

Switching Transient Shaping by Application of a Magnetically Coupled PCB Damping Layer

Michael Hartmann,Andreas Musing,Johann W. Kolar 전력전자학회 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.2

An increasing number of power electronic applications require high power density. Therefore, the switching frequency and switching speed have to be raised considerably. However, the very fast switching transients induce a strong voltageand current ringing. In this work, a novel damping concept is introduced where the parasitic wiring inductances are advantageously magnetically coupled with a damping layer for attenuating these unwanted oscillations. The proposed damping layer can be implemented using standard materials and printed circuit board manufacturing processes. The system behavior is analyzed in detail and design guidelines for a damping layer with optimized RC termination network are given. The effectiveness of the introduced layer is determined by layout parasitics which are calculated by application of the Partial Element Equivalent Circuit (PEEC) simulation method. Finally, simulations and measurements on a laboratory prototype demonstrate the good performance of the proposed damping approach.

Influence of Surface Roughness of Tools on the Friction Stir Welding Process

Michael Hartmann,Stefan Böhm,Sven Schüddekopf 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.6

Most publications on friction stir welding describe phenomena or results with given process parameters like feed rate, rotation speed, angle and depth of penetration. But without a complete documentation of tool design, the results under the same process parameters are completely different. For this purpose, the Institute of Cutting and Joining Manufacturing Processes (tff), University of Kassel investigated the influence of tool roughness on the friction stir welding process. Therefore a defined surface finish was produced by turning and die sinking. As basis of comparison the constant parameters were rotation speed, feed rate, tilt angle and a heel plunge depth. Sound butt-welds were produced in aluminium alloy 6082 (AlMgSi1) with 1.5 mm sheet thickness with a turned reference tool with a surface of Ra = 0.575 µm in position controlled mode. The surfaces are manufactured from a very fine to a very rough structure, classified by the VDI-classes with differences in the arithmetical mean roughness. It can be demonstrated with the help of temperature measures, that less heat is generated at the surfaces of the shoulder and the pin by the higher roughness due to lower active friction contact surface. This can also be seen in the resulting wormhole defects.

Switching Transient Shaping of RF Power MOSFETs for a 2.5 ㎒, Three-Phase PFC

Michael HARTMANN,Andreas MUSING,Johann W. KOLAR 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

To increase the power density of active rectifiers, the switching frequency and switching-speed have to be raised considerably. However, the very fast switching transients induce a strong voltage and current ringing. In this paper, a novel magnetically coupled damping layer is introduced for attenuating these unwanted oscillations. The proposed damping layer can be implemented using standard materials and printed circuit board manufacturing processes. The system behavior is analyzed in detail and design guidelines are given. The effectiveness of the introduced layer is determined by layout parasitics, which are calculated with the Partial Element Equivalent Circuit method and compared to impedance measurements. The performance of the damping layer is demonstrated by simulations and verified via measurements on a laboratory prototype.

European Academic Harmonization and Accreditation and Their Effects on Publication

Michael Hartmann,John Pearson 사람과세계경영학회 2010 Global Business and Finance Review Vol.15 No.2

Over the past two decades, a number of forces have compelled European governments to reevaluate their disparate academic systems and to work toward common standards for academic degrees. European academic ministers have chosen to sacrifice some of their autonomy in order to establish academic credential transparency and mobility across Europe. Since two major types of academic business schools have developed in Europe, the American system and the German system, this article recaps the historical development of the two academic systems and documents the changes which have been published in a variety of conferences, joint declarations, and extensive reports. The effects of harmonization have begun to alter the structure of doctoral programs and research institutions across Europe and will impact programs across the globe. This paper examines the history of these academic changes and explores the future opportunities and challenges for the global academic setting.

Defect Detection in Friction Stir Welding by Online Infrared Thermography

Kryukov, Igor,Hartmann, Michael,Bohm, Stefan,Mund, Malte,Dilger, Klaus,Fischer, Fabian The Korean Welding and Joining Society 2014 대한용접·접합학회지 Vol.32 No.5

Friction Stir Welding (FSW) is a complex process with several mutually interdependent parameters. A slight difference from known settings may lead to imperfections in the stirred zone. These inhomogeneities affect on the mechanical properties of the FSWed joints. In order to prevent the failure of the welded joint it is necessary to detect the most critical defects non-destructive. Especially critical defects are wormhole and lack of penetration (LOP), because of the difficulty of detection. Online thermography is used process-accompanying for defect detecting. A thermographic camera with a fixed position relating to the welding tool measures the heating-up and the cool down of the welding process. Lap joints with sound weld seam surfaces are manufactured and monitored. Different methods of evaluation of heat distribution and intensity profiles are introduced. It can be demonstrated, that it is possible to detect wormhole and lack of penetration as well as surface defects by analyzing the welding and the cooling process of friction stir welding by passive online thermography measurement. Effects of these defects on mechanical properties are shown by tensile testing.

Defect Detection in Friction Stir Welding by Online Infrared Thermography

Igor Kryukov,Michael Hartmann,Stefan Böhm,Malte Mund,Klaus Dilger,Fabian Fischer 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.5

Friction Stir Welding (FSW) is a complex process with several mutually interdependent parameters. A slight difference from known settings may lead to imperfections in the stirred zone. These inhomogeneities affect on the mechanical properties of the FSWed joints. In order to prevent the failure of the welded joint it is necessary to detect the most critical defects non-destructive. Especially critical defects are wormhole and lack of penetration (LOP), because of the difficulty of detection. Online thermography is used process-accompanying for defect detecting. A thermographic camera with a fixed position relating to the welding tool measures the heating-up and the cool down of the welding process. Lap joints with sound weld seam surfaces are manufactured and monitored. Different methods of evaluation of heat distribution and intensity profiles are introduced. It can be demonstrated, that it is possible to detect wormhole and lack of penetration as well as surface defects by analyzing the welding and the cooling process of friction stir welding by passive online thermography measurement. Effects of these defects on mechanical properties are shown by tensile testing.