Un-terminated Common-Mode EMI Model of DC-Fed Motor Drives

Terminal electromagnetic interference (EMI) models of power converters have been shown to successfully predict conducted emissions up to at least 30 MHz. These models can accurately predict the input side EMI of converters for changes in the source impedance but only for a fixed load. In other words these models cannot predict the input side EMI for changes in the load side parameters. Such terminated EMI models have limited utility as they cannot be used for converters that have a strong coupling between the input and output side EMI. Moreover, in aerospace applications, the conducted EMI standards (DO-160) dictate limits on the noise currents in all power lines and cable bundles, thus compelling development of models that can predict the EMI on both sides of the power converters. The proposed un-terminated EMI terminal model in this paper directly predicts the input and output side common-mode (CM) noise currents in a motor drive system for changes in both source and load side impedances. Such models can be very useful in understanding how EMI filters and harnesses affect the overall EMI in a motor drive system. The model runs in the frequency-domain and is validated by experiments.