**Motivation:**

The widely spread of information-communication technology (ICT) devices raises a critical issues about conducted electromagnetic interference (EMI) between switching devices and signal transmission. In order to design an effective passive or active filter to mitigate EMI, the actual modal impedances of the involved components should be investigated. In this blog, the SPICE simulation setup is introduced to investigate the frequency response of the common mode (CM) and differential mode (DM) impedance of a complete automotive power train.

A typical powertrain of electric vehicles is illustrated including battery, DC cables, inverter, AC cables and motor. The SPICE model of a automotive power train is built considering both low-frequency functional aspects and high-frequency parasitic effects.

The simulation setups of modal impedance is shown in the next figure, where a) is the differential mode whilst b) is the common mode. Both amplitude and phase of modal impedance of the powertrain can be extracted. The voltage source in the figure contains several sinusoidal sources in series with frequency from 10 kHz to 30 MHz.

The time-domain circuit simulations can be carried out in SPICE, and the frequency response of the CM/DM impedance (amplitude and phase) is afterwards derived using interpolation and Fast Fourier Transform (FFT). The extracted CM/DM impedance provides exhaustive information for effective design and estimation of filter performance.