Wideband Impedance Measurements and Modeling of DC Motors for EMI Predictions

In electromagnetic interference prediction, dc motors are usually modeled as a source and a series impedance. Previous researches only include the impedance of the armature, while neglecting the effect of the motor´s rotation. This paper aims at measuring and modeling the wideband impedance of a dc motor under operating conditions. These measurements are performed by injecting a small signal, using a method based on conducted susceptibility measurement setups as described in military standards. Different setups are developed to cover a wideband, from 0 Hz up to 200 MHz. The measurements provide satisfying results for the wideband impedance of the rotating dc motor, and the setups´ validation is discussed. Finally, the resulting impedance is modeled as a passive impedance network.