On the common mode current due to circuit asymmetry in three-phase motor drive systems

This paper deals with the analytical investigation of common-mode current generation due to asymmetry in the three-phase load of a motor drive system. Load asymmetry is typically due to parasitic turn-to-turn capacitances included in the high-frequency circuit model of motor coils. It is shown that, in case of load asymmetry, generation of common mode current is due not only to the zero-sequence voltage source, as in the conventional analysis, but a further contribution is given by the space vector components of the voltage source. To this aim, rigorous circuit representation of such contribution is derived.