PhD presentations in September 2019: Johannes Voss, Arne Hendrik Wienhausen, Furkan Kaan Titiz & Hafiz Abu Bakar Siddique

Monday, September 09, 2019, 9:00 a.m.

C.A.R.L, Lecture hall 08, Claßenstr., 52072 Aachen


09.00 a.m. Dipl.-Ing. Johannes Voss

„Multi-Megawatt Three-phase Dual-Active Bridge DC-DC Converters: Extending Soft-Switching Operating Range with Auxiliary-Resonant Commutated Poles and Compensating Transformer Saturation Effects“

A high-power dual-active bridge dc-dc converter for a nominal operating voltage of 5 kV is presented. The converter is investigated in terms of soft-switching operation range with additional snubber capacitors. Special attention is paid on the so called soft-switching boundaries and led to a modifi ed auxiliary-resonant commutated pole which allows zero-voltage switching in the entire operation range. Test results up to 3 kV under resonant switching are presented. At medium voltage undesired harmonics in the ac links appear. These harmonics are caused by dc-magnetizing currents in the transformers. A novel compensation control is presented which can be realized very cost effective. The compensation control is verifi ed on a controller-in-the-loop system and fi nally tests at the converter up to a dc-link voltage of 2 kV under quasi-resonant switching are presented.

10.15 a.m. Dipl.-Ing. Arne Hendrik Wienhausen

„High Integration of Power Electronic Converters enabled by 3D Printing“

Since wide-bandgap (WBG) power semiconductors became commercially available, a trend towards increasing power densities of power electronic systems can be observed. The advantages of WBG power components can only be fully exploited in conjunction with low-loss inductive components that are suitable for high switching frequencies. For this reason, a concept for power inductors based on 3D-printed bobbins is developed, featuring excellent high-frequency characteristics. Conventional fl uid coolers typically feature a large volume and a heavy weight, which counteracts a high power density. To minimize size and weight, 3D-printed miniature fl uid coolers are developed. Prototypes of the developed concepts for high-frequency power inductors and 3D-printed fl uid coolers are used to realize a highly-integrated boost converter. Despite the use of discrete power semiconductor devices, a power density of 98 kW/dm³ is demonstrated.


Wednesday, September 18, 2019, 9:00 a.m.

C.A.R.L, Lecture hall 08, Claßenstr., 52072 Aachen

09.00 a.m. Furkan Kaan Titiz, M. Sc.

„A Three-phase Low-voltage Grid-connected Current Source Inverter“

Es handelt sich in dieser Arbeit um einen Stromzwischenkreiswechselrichter, der an einem dreiphasigen Niederspannungsnetz angeschlossen wird. Im Rahmen dieser Arbeit wurden unterschiedliche Aspekte, unter anderen Steady-State Verhalten, DC-Link Induktivität, Modulation der Schalter, harmonische Analyse, Verluste, diskontinuierlicher Betrieb und Modellierung, behandelt. Darüber hinaus wurden Simulationen realisiert, wo ein Regelungsverfahren mit aktiver Dämpfung eingesetzt wurde. Zusätzlich wurde simulativ das Verhalten des Wechselrichters bei Netzstörungen mit einem Photovoltaik-Modul als Eingangsquelle untersucht. Außerdem wurde ein Prototyp aufgebaut, in Betrieb genommen und getestet. Dabei wurden sowohl Steady-State als auch transiente Messungen durchgeführt und Effi zienzwerte aufgenommen.

10.15 a.m. Hafiz Abu Bakar Siddique, M. Sc.
„The Three-Phase Dual-Active Bridge Converter Family: Modeling, Analysis, Optimization and Comparison of Two-Level and Three-Level Converter Variants”

A medium-voltage direct current (MVDC) grid is a potential key enabling technology for the future fl exible grids. To this end, the three-phase dual-active bridge (DAB3) converter is a suitable choice owing to the bidirectional power-transfer capability, high power density and effi ciency, modularity and galvanic isolation. In this work, apart from the conventional DAB3, two alternate DAB3 variants with neutral-point-clamped (NPC) topology on the medium-voltage side are investigated. The NPC bridge can have zero-current (ZC) turn-on of the middle devices apart from the zero-voltage turn-on of the top/bottom devices. The ZC turn-on also enables a dynamic current control in which a
phase-current transient settles down within one-third of the switching cycle without over-/undershoots. Thus, the use of NPC bridge in the DAB3 converter halves the blocking-voltage requirement of the devices while maintaining or improving other favorable characteristics of the converter.