Circulating Type Motor Bearing Current in Inverter Drives

To facilitate understanding of the differences between the two types of inverter-induced bearing currents which appear in induction motor drives, a review of the previous noncirculating type of bearing current theory is given. A brief introduction to the concept of coupling current in drive systems follows. This article then proposes an explanation to the generation of a circulating-type of bearing current in inverter-fed motor drives. The theory is backed up by the experimental measurement of bearing currents. Finally, a solution to these bearing currents, of both circulating and noncirculating types, is also proposed.