A High-Frequency DC-DC Converter for the Next Generation Train (NGT) CARGO HFC Concept

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Kurzfassung

The German Aerospace Center’s (DLR) Next Generation Train (NGT) CARGO vehicle concept comprises two catenary-powered end cars and several battery-powered intermediate wagons. Each end car uses a catenary-based traction system with a conventional traction transformer rated at 10.5 MW for connection to 25 kVAC/50 Hz and 15 kVAC/16.7 Hz railway electrification networks. In addition, the system is re-configurable and allows for connection to 3 kVDC and 1.5 kVDC catenaries. The intermediate cars utilize lower voltage (800 Vnom) Li-ion NMC battery packs (585 Vmin to 910 Vmax) for self-powered driving of up to 25 kilometers between charges. In order to extend the driving range of the individual intermediate wagons when running in non-electrified lines, static or dynamic opportunity charging methods have been considered. Another solution is to hybridize the individual traction systems by utilizing the concept of hydrogen Fuel-Cell-based Range Extenders (FCRE). In a fuel-cell hybrid traction system, the fuel-cell stacks have relatively larger response times due to the nature of the energy conversion processes taking place within the individual cells and due to limitations related to the air supply sub-systems. Therefore, dynamic power is usually delivered by battery packs, which are capable of handling high power peaks faster. The average power demand is provided by the fuel-cell system with the aim to keep the batteries’ State-of-Charge (SoC) levels within a certain range. As the complexity of the system and its controls increases, the design of a suitable interface that provides both good power regulation and galvanic isolation between sources and loads becomes a challenge. In addition, as the different sub-systems operate with a variety of different operating states on different voltage levels, handling a wide range of voltage inputs and power flow combinations becomes a problem. Towards the direction of overcoming these challenges for the NGT CARGO’s FCRE configuration, this work presents a fuel-cell hybrid traction system concept based on cascaded rectifier setups (in the end cars) and multi-port bidirectional isolated DC-DC converters (in the intermediate cars). In the proposed setup, the conventional traction transformers and rectifiers are eliminated, replaced by cascaded rectifier Input-Series-Output-Parallel (ISOP) setups, which provide the main DC-link voltage. Lower-rating isolation stages are used in the end and intermediate cars, essentially resulting in a modular, distributed traction system (see Fig. 1). The aforementioned isolated DC-DC converters utilize Silicon Carbide (SiC) power MOSFET modules for reduced conduction and switching losses, which allows for usage of higher switching frequencies and thus reduced material, weight and volume of magnetic elements. In addition, a Medium Frequency Transformer (MFT) provides the galvanic isolation between several ports (i.e. several sources and loads). With regards to the requirements of the NGT CARGO vehicle concept, the objective of this study is to present a preliminary design and a power/voltage regulation method for the isolated multi-port setup and demonstrate its validity through simulation. Furthermore, the losses of the DC-DC converter are characterized and an estimation of its power density is derived.

Verfügbare Versionen dieses Eintrags

• A High-Frequency DC-DC Converter for the Next Generation Train (NGT) CARGO HFC Concept. (deposited NICHT SPEZIFIZIERT)
  • A High-Frequency DC-DC Converter for the Next Generation Train (NGT) CARGO HFC Concept. (deposited 16 Aug 2018 09:54) [Gegenwärtig angezeigt]