To accurately characterize the high frequency harmonics that appear due to the harness parasitics, a harness model based on real measurements has been used.
A harness can be modeled as a network of resistors, inductors and capacitors:
The harness consists of a positive cable and a negative cable, hence the overall behavior can be modeled as a two-port network. To model the total effect of the network impedances, we will use the impedance matrix.
Since the harness has the same behavior in both directions Z11= Z22 and Z12=Z21, only two values have to be calculated. To obtain these values, two measurements on the harness are performed: one with the opposite end in open-circuit and one with the opposite end in short-circuit.
Introducing the model into LTspice
To be able to simulate the harness model, a T-model based on the calculated impedance matrix was introduced in LTspice:
Since the T-model impedances are based on the real measurement data values, they match the real harness measurements closely. This model has been really useful to design the filter that dampens the high frequency harmonics caused by the parasitic capacitance of the harness.
