Investigating the conducted EMI issues in fighter aircraft power supplies

Abstract

A power supply might have passed the MIL standards, however retrofitting it into a system may still have compatibility issues. To investigate such issues in power supplies fitted in a fighter aircraft, modeling and simulations of one such power supply is carried out with the help of PSPICE. Conducted EMI performance of this power supply is analyzed and various steps towards EMI mitigation, like use of snubber circuits and RC gate control, are studied with the help of simulations. The DC bus is modeled by taking into account the transmission line parameters. When power supplies having high frequency switching rates are connected across this DC bus, they generate switching reflections. The interaction between these inter-connected on board power supplies produces time varying loads whose sudden rise and fall times generate high frequency signals on the common DC bus voltage, which, in turn, causes increased EMI. An experimental set-up is established in the laboratory to verify the simulation results. All the results of this study are presented. It is observed that by proper modeling and with the help of simulation tools, the EMI issues can be studied at the design stage itself which saves both time and costs, as there is no need to construct a prototype for EMI investigations.