Influence of the voltage-dependent output capacitance of SiC semiconductors on the electromagnetic interference in Dc-Dc converters for electric vehicles

The output capacitance C
oss
of power semiconductors is highly dependent on the drain-source voltage. In today's commercially available silicon carbide (SiC) modules an oscillation between C
OSS
and the parasistic module inductances occurs. The battery voltage varies with the state of charge (SoC) between 250 V and 430 V. With a dc-dc converter connected to the battery, the dc-link voltage can be adjusted to optimize system efficiency. In this paper, time-domain measurements are used to show that the non-linearity of C
oss
leads to a module-resonance variation as a function of the output voltage. Conducted-emission measurements with a line impedance stabilization network (LISN) verify that the module oscillation with a frequency above 20 MHz is seen on system level. This leads to increased design effort, because the narrow band interference of the module oscillation frequency varies for different output voltages.