Effects of switching frequency modulation on EMI performance of a converter using spread spectrum approach

A novel approach to simulate the EMI emissions comparable to EMC standards (CISPR 16/22) from the point of view of average (AV) and quasi-peak (QP) detection are presented. In addition an algorithm to convert the high-resolution FFT data to correspond with the defined measurement bandwidths is presented. A homodyne receiver approach was found to be useful for modeling the frequency selective process of EMI measurement equipment. The developed methods can be effectively used to study the effect of spread-spectrum technique to reduce EMI emissions. It was noticed that in order to optimize EMI in respect to AV detection a low frequency jittering is optimal. From a QP detection point of view it is favorable to apply a modulation frequency in the order of the same magnitude as the measurement of the bandwidth demanded.