Volume optimization of a PFC flyback structure under electromagnetic compatibility, loss and temperature constraints

The aim of this paper is to present an analytical optimization approach of a flyback structure in PFC mode. Indeed, softwares 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), time-domain simulation becomes painful and expensive in memory and computing time. The study of EMC performances is also difficult because of the line impedance stabilizer network (LISN) time-constants which comes 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 a flyback structure by respecting EMC standards, by minimizing the whole losses dissipated in the structure (conduction and switching semiconductor losses, core and copper losses in the transformer) and by constraining the semiconductor junction, the winding and the magnetic circuit temperatures. Firstly, analytical models of the flyback structure for these various optimization aspects are developed, validated by numerical simulation or measures and integrated in an optimization process. Then, the optimization results are presented and validated thanks to a measurement workbench of the flyback structure.