This paper examines the frequency-dependent emission of selected commercially available DC/DC converters with rated power up to 1 kW. This involves three devices of the same type each of a DC/DC converter with galvanic isolation and a DC/DC converter without galvanic isolation.
By designing a suitable measurement setup and selecting suitable measurement technology, the emission of these DC/DC converters in the frequency range up to 150 kHz is characterised under different grid-side (i.e. background distortion and impedance characteristics) and device-side conditions (i.e. operating point). The measured data is evaluated and analysed in the frequency domain.
The three DC/DC converters with galvanic isolation have a significant current emission at the switching frequency of the DC/DC converters at ideal (i.e. distortion-free) DC voltage. Furthermore, it is found that the current emission of DC/DC converters of the same type differs in frequency and magnitude due to manufacturing tolerances. Measurements at various load levels also demonstrate a load dependency of the current emission. The results show that the input impedance has very low values and consequently the level of the resulting current emission of the DC/DC converters can significantly
be influenced even by only slight changes of the grid-side impedance. To quantify the current emission, a grouping method is proposed that aggregates multiple frequency components power-equivalently in frequency bands with a defined size.