Characterization of automotive high voltage networks for EMI measurements

One major task in developing electric cars is to control electromagnetic interferences (EMI) of their power train. Fast slew rates in power electronics increase efficiency, but also emitted radio frequency (RF) disturbances. One main approach to reduce EMI within automotive systems is a complete shielding of its high voltage (HV) power network. The shielding of HV power networks changes the system configuration from the used unshielded single core multi wire harness into a coaxial three conductor layout, and therefore the characteristic impedances of the entire power network. Re-cent research shows that line impedance stabilization networks (LISNs) for substitution of low voltage power networks (according to CISPR 25), are not ideal to measure conducted emissions of HV components because of changed characteristic impedances and additional shielding. This paper deals with a method of determining the high-frequency impedances of automotive HV power networks (300 kHz – 200 MHz). A Vector Network Analyzer (VNA) is used to measure Scattering-Parameters of different HV power cables. Matrix conversions allow calculating an impedance network, which is able to represent automotive HV-networks.