Two VHDL-AMS-based models of multi-conductor power cables for EMI simulations

Abstract

Due to the fast switching of the commutation cell in a motor drive system, high-frequency electromagnetic disturbances propagate through cables to reach the loads. Mismatched impedances lead to an overvoltage at the loads terminals. In order to study this EMI issue, accurate circuit models of power cables are required. In this context, this paper proposes two multi-conductor cable models. Our approach takes into consideration the frequency dependence of the cable per-unit-length parameters, the coupling between conductors and propagated induced phenomena. The power cables used in motor drive systems are characterized by their rotational symmetry. Thus, the complexity of the model is reduced by means of both a set of mathematical functions approximating the frequency behavior of the cable and using a modal domain-based transfer matrix. So, the VHDL-AMS frequency model can be easily deduced. Once the model is established, the simulation of any cable length becomes an easy task. The model is implemented in ANSYS Simplorer software. After that, the time domain model is built up based on the vector-fitting algorithm. In order to validate our proposal, a comparison of the common mode and the differential mode frequency responses of the reduced cable model with those of the well-known cascaded cell model and measurements found in the literature is performed. The results demonstrate the accuracy and the speed of our approach in the predefined frequency range. Also, a time-domain comparison between the frequency model and the time model is performed. The results obtained validate the two models.