Optimal design of a synchronous DC-DC converter using analytical models and a dedicated optimization tool

The aim of this paper is to present an optimization approach of static converters using analytical models and a dedicated tool. Indeed, tools like Saber, Pspice or Simplorer are effective means for the power electronics structure time-domain studies. However, if these structures have an ac input and a high switching frequency (various time scales), or if several aspect studies are taken into account, time-domain simulation becomes painful and expensive in memory and computing time. The study of electromagnetic compatibility (EMC) performances is also difficult because of the line impedance stabilizer network (LISN) time-constants which come to penalize the time-domain simulation. In addition, in sizing and optimization process, results in short computing times are needed, so the time-domain simulation may be too time consuming. In this way, the paper proposes to carry out a compromise between the model accuracy and the tool rapidness and recommends the use of analytical models to optimize the passive element volume of static converters by respecting EMC standards, by minimizing the whole dissipated losses (conduction and switching semiconductor losses, core and copper inductor losses, capacitor losses) and by constraining the semiconductor junction, the winding and the magnetic circuit temperatures. This optimization approach is applied to a 42 V-14 V dc-dc converter for the automotive domain (output power 1 kW). The developed optimization procedure is validated by numerical simulation and measures.