Estimation of Common-Mode Current Coupled to the Communication Cable in a Motor Drive System

Electromagnetic interference (EMI) couplings between a motor drive and an adjacent communication network induce a considerable common-mode (CM) current in a communication cable, which has a serious impact on the performance of the communication network. In order to estimate the CM current, it is necessary to study the coupling mechanism between the motor drive and the communication network. In this paper, a commercial motor drive system with an RS485 communication circuit is used for analysis. The conducted and near-field coupling paths are analyzed and modeled. By integrating the models of coupling paths with the EMI models of the motor drive and the dc/dc converter, an estimation model of the CM current coupled to the communication cable is built. Furthermore, online measurement methods and numerical simulation are presented to extract the impedance parameters of the conducted and near-field coupling paths. The estimation model is validated by comparing the simulated currents with the measured currents in the two configurations. This model is applicable for estimating the CM current coupled to the communication cable in various configurations.