Optimal design of medium-frequency high-power converters
DIRECTORS: Alfred Rufer, Philippe Barrade UNIVERSITY: EPFL (École Polytechnique Fédérale de Lausanne)
In the last decades, the interest in renewable energies and electrification of traction systems is increasing. In this new context, power electronic plays an essential role, since it allows converting and controlling effectively electric power with static converters.
The evolution of energy and transport systems needs the development of power electronic converters with higher efficiency, lower cost, higher reliability, higher power density and greater functionality. A great contribution of these goals will be made by new high-power semiconductor devices with better frequency features, as well as advanced power topologies and soft-switching techniques, which permit the extension of the frequency range of power converters, and consequently the reduction of magnetic components. A good example of these systems are medium-frequency power conversion systems, also known as Power Electronic Transformers, which are able to convert electric power in the same way as conventional low-frequency transformers but with additional features: volume and weight reduction, power control, etc.
The emergence of new magnetic and semiconductor materials, new power devices and novel power circuits offer a very wide range of possibilities for designers. The main drawback of high-power Power Electronic Transformers is the high number of design parameters, and the difficulty of handling them on a particular design. The advantages of new technologies, as computers, allow implementing new design methodologies based on optimization algorithms, solving the present difficulties and improving conventional design methodologies. The motivation of this work stems from the need to develop a novel design methodology for high-power isolated converters which allows to reach optimal parameters (e.g. semiconductors, operation frequency, topology, cooling system, etc.) according to some objectives (e.g. weight, volume, efficiency, cost, etc.) and considering the specifications of industrial applications. The proposed design methodology is based on a sequential design at different levels, starting with the definition of the global decision of the system structure and going then to the detailed design of all the elements with custom designs and databases with commercial components. Therefore, new multidisciplinary models are required with different level of abstraction, from the approximate models with low computation cost to accurate analytical models considering parasite behavior of high-power semiconductors. The presented design methodology is implemented in a computer tool and applied in a medium-voltage medium-frequency railway application. Experimental measurements of a configurable isolated reduced-scale prototype and the development of various medium-frequency transformers verify the developed new models and the methodology.