The three-phase dual-active bridge converter family : modeling, analysis, optimization and comparison of two-level and three-level converter variants
Aachen / E.ON Energy Research Center, RWTH Aachen University (2019, 2020) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (xii, 236 Seiten) : Illustrationen, Diagramme
With increasing integration of the intermittent renewable energy sources (RES), the inflexibility of the conventional alternating current (AC) grids is becoming more evident. To cope with the problem, one of the possible solutions is to employ the medium-voltage direct current (MVDC) grid at the distribution level where most of the RES are connected. Since MVDC grids are based on power-electronic converters, these are highly dynamic and enable a precise power-flow control without marring the system efficiency. 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 efficiency, 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 semiconductor devices while maintaining or improving other favorable characteristics of the converter. Moreover, owing to more control parameters, it is possible to achieve better controllability even with smaller value of transformer leakage inductance. Lastly, the effects of dead time and transformer winding resistance are investigated and compensated in the control loop of DAB3 converter.
Siddique, Hafiz Abu Bakar
de Doncker, Rik W.