Common-mode current analysis focused on grounding structures of shielded cable and power converter chassis

Grounding structure of the shielded cable at the high voltage battery side and that of the power converter chassis have significant influences on common-mode current emitted from a converter such as a DC-DC converter in electric vehicles. In this paper, the equivalent circuit focused on the common-mode current is established to comprehend the circuit functionality of the grounding structures. From a 3D electromagnetic simulation, the grounding structure of the shield is assumed to act as a common-mode noise source converted from the noise generated by the converter. Simultaneously, it is confirmed that the common-mode current of the whole shielded cable is equivalent to the current flowing in the exterior of the shield. Thus we hypothesize the equivalent circuit considering the grounding structure of the shield as a noise source, the exterior of the shield as a transmission line, and the power converter chassis including its grounding structure as a termination. To verify above hypothesis, the frequencies of the common-mode current peak caused by the impedance mismatch of both the exterior of the shield and the converter chassis including its grounding structure is calculated by using the equivalent circuit. The calculated peak frequencies show good agreements with measurements within 3% of errors, which indicates the validity of the hypothesis.