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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: Chapter 3 outlines the operating principle of the DAB AC-DC converter. T he exact operating range of the DAB DC-DC converter, as the main buildin g block of the 1-S AC-DC architecture, is derived, and a control equatio n for the DAB input current is obtained. Furthermore, the steady-state a nalysis of the DAB is presented and commutation inductance(s) are intr oduced as an essential HF AC-link modification in order to achieve full- operating-range ZVS. Lastly, a novel current-dependent charge-based (C DCB) ZVS verification method is proposed in order to deal with the defic iencies of the existing current-based (CB) and energy-based (EB) ZVS ana lyses; Chapter 4 is devoted to the derivation of full-operating-range ZVS modul ation schemes for the DAB converter. Three different approaches are pres ented, being a numerical approach, an analytical approach, and a semi-an alytical approach, all relying on the CDCB ZVS verification method propo sed in Chapter 3 in order to assure that soft-switching operation with q uasi zero switching losses is obtained within the calculated ZVS regions ; In Chapter 5, the main functional elements of the DAB AC-DC prototype co nverter are designed, employing the values for the circuit level variabl es and the ZVS modulation schemes derived in Chapter 4. State-of-the-art design methods/procedures, models for the component losses, and volume models are combined with custom developed (local) optimization algorithm s in order to obtain a high-efficiency and high-power-density converter design that is in compliance with the specified system requirements; In Chapter 6, first a DC-DC system characterization of the prototype sys tem is presented in order to validate the theoretical analyses, i.e. the steady-state converter model and the ZVS analysis outlined in Chapter 3 , as well as the CDCB ZVS modulation schemes proposed in Chapter 4. Ther eafter, the results of an AC-DC system characterization are given, allow ing to evaluate the performance of the prototype converter with regard t o the reached efficiency and with regard to the quality of the AC input power. Conversion efficiencies higher than 95 % within the major pa rt of the output power range, with a very flat efficiency curve and thus a high partial-load efficiency, are reported. The peak efficiency is ar ound 96 % and the efficiency at nominal power approximately 95.6 %. Moreover, a high power density of 2 kW/liter is obtained. From a b rief comparison with several (similar) dual-stage prototype systems foun d in literature, it is clear that the achieved performance is close to t he absolute state-of-the-art; Chapter 7 concludes the presented work and provides an outlook regarding future research in the field of DAB AC-DC converters. nrpages: 332 status: published |
