Modeling and Optimization of Bidirectional Dual Active Bridge AC-DC Converter Topologies

摘要

Single-phase, utility interfaced, isolated AC-DC converters with power f actor correction cover a wide range of applications such as chargers for plug-in hybrid electric vehicles and battery electric vehicles, inverte rs for multiple renewable energy sources (e.g. photovoltaic modules), as well as interfaces for residential DC distribution systems and energy s torage systems. Thereby, bidirectional conversion capability enables the development of smart interactive power networks in which the energy sys tems play an active role in providing different types of support to the grid. Examples are vehicle-to-grid concepts, ‘smart home’ concepts, AC m icrogrids, and residential DC distribution systems (DC nanogrids). In the presented work, the main objective is to investigate the feasibility and suitability of a single-stage (1-S) dual active bridge ( DAB) AC-DC converter for the realization of the above mentioned bidirect ional energy conversions. Compared to the commonly used dual-stage (2-S) systems, the 1-S architecture has the potential to benefit the system p erformance with regard to efficiency, volume (power density), number of components (reliability), weight, and costs, due to the effective omissi on of a complete energy conversion stage. In order to validate the prese nted analyses, a second objective is to realize a state-of-the-art (i.e. regarding efficiency and power density) converter prototype system that is designed in order to meet the requirements for future, mode 1 compat ible, on-board electric vehicle battery chargers, interfacing a 400 V DC -bus with the single-phase 230 VAC / 50 Hz mains. Compliance with domest ic power sockets results in a nominal (active) AC charging current of 16 Arms and a nominal power of 3.7 kW. The main challenge to achieve the above objectives lies in addressing the fundamental limitati ons of the existing analyses and circuit implementations of DAB converte rs. These limitations mainly relate to the soft-switching (i.e. by virtu e of zero voltage switching, ZVS) modulation schemes available in litera ture, being especially problematic for DAB converters with large input a nd/or output voltage variations and large power variations, such as is t he case for the 1-S DAB AC-DC architecture at hand. By means of an intro ductory Chapter (i.e. Chapter 2), the shortcomings in the existing analy ses of DAB converters are highlighted, and the selection of the full bri dge - full bridge (FBFB) DAB implementation as the most suitable candida te for the considered AC-DC converter topology is motivated. The subsequ ent chapters discuss the 1-S DAB AC-DC converter in detail: