EMC performance of two topologies of DC-DC converters for aeronautic applications

The increase in electric power demands and the project to develop a high voltage DC power distributions system in future aircrafts has created the need for a new generation of DC/DC power converters. The design of these systems has to take into account the stringent electromagnetic compatibility requirements typical of aeronautic applications, which combined with strict weight and volume restrictions make it often very difficult to comply with the emissions limits established in the applicable electromagnetic compatibility norms. In this context it is highly advisable to incorporate electromagnetic compatibility considerations from the beginning of the design process. In this work we perform a through comparison of two candidate topologies for 270VDC/28VDC and 540VDC/28VDC 3kW power converters in terms of emission of conducted noise. We compare two topologies with four switches in the high voltage side: a full bridge and a three level NPC converter. We show that a careful modeling of the parasitic effects that cause noise emissions allows for obtaining valuable preliminary conclusions in the simulation stage of the design process. Also, we take advantage of the circuit models developed to compare these converters in terms of output voltage spectrum distortion and efficiency. We have found some differences between the performance of the converters in function of the input voltage and the topology. In particular, we have found that the three level converter is slightly less efficient and does not provide significant improvement in terms of reduction of common mode noise. We explain this apparent paradox by close analysis of the effect of the parasitic elements that model capacitive couplings in the converter.