Mission profile optimized modularization of hybrid vehicle DC/DC converter systems

Vehicles based on electrical drive trains become more and more attractive due to rising oil prizes and environmental reasons. In these vehicles usually different and/or varying voltage levels for the drive and the energy storage elements are employed in order to fully utilise the components and increase the system efficiency. The DC- links with different voltage levels are interconnected by bidirectional DC-DC converters. Due to the high power levels the converters are often realised by interleaved smaller units for increasing part load efficiency and power density. In this paper an procedure for optimising the nominal power levels, operating points and distribution of silicon area of interleaved/parallel connected DC-DC converters is presented. There, the aim is to optimise the overall system efficiency for a given mission profile of the electric vehicle (e.g. NEDC/FTP-75) and to determine the optimal distribution of a fixed amount of silicon area between the parallel units for minimal losses. For demonstrating the performance of the method a 48 kW test system is optimised, where an improvement of more than 21% compared to equal parallel connected units is shown. There, the calculations are based on measurements on a 12 kW bidirectional prototype DC-DC converter designed for electric vehicles.