Modulation and dynamic control of intelligent dual-active-bridge converter based substations for flexible dc grids

• Modulation und dynamische Steuerung von auf intelligenten Dual-Active-Bridge-Umrichtern basierenden Umspannwerken für flexible Gleichstromnetze

Hu, Jingxin; de Doncker, Rik W. (Thesis advisor); Kolar, Johann W. (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2019)
Book, Dissertation / PhD Thesis

In: E.ON Energy Research Center 69. Ausgabe : PGS, Power Generation and Storage Systems
Page(s)/Article-Nr.: 1 Online-Ressource (VI, 138 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2019

Abstract

This dissertation proposes improved modulation and dynamic control of high-power three-phase dual-active bridge (DAB3) dc-dc converters to enhance the operating performance and functionalities of intelligent dc substations in dc-grid applications. With the increasing integration of renewable energies, energy storage systems and the emerging fast charging stations for electric vehicles, dc distributions grids present numerous advantages e.g. higher efficiency, higher power capability and higher flexibility compared to existing ac grids. The key enabling component of flexible dc grids is the intelligent dc substation based on high-power dc-dc converters, which needs to achieve high efficiency over a wide voltage and power range, control the power flow and grid voltage dynamically, and ride through dc short-circuit faults. By employing the proposed asymmetrical duty cycle control method, the soft-switching range of the DAB3 converter is significantly extended over a wide voltage range especially in light-load conditions. Thereafter, the dissertation also introduces a novel method to control the transformer winding current and magnetizing flux of the DAB3 converter instantaneously and simultaneously under transient conditions. Thereby, the dc substation can control the power flow dynamically without causing transformer core saturation. Finally, a dc fault ride-through method for the DAB3 converter is proposed, which enables the breakerless protection of dc grids.