An Improved Model for Circulating Bearing Currents in Inverter-Fed AC Machines

In this paper, a general lumped parameter bearing current model is presented. The lumped parameters are derived from the analytical descriptions of the bearing current paths and the numerical field simulations based on the finite element method. The model considers frequency dependence. The resulting model delivers the common mode current and the circulating bearing current is determined by modeling the magnetic coupling between the common mode current path and the circulating bearing current path. The derived circuit can be applied to AC machines and is verified by measurements of a permanent magnet excited synchronous machine, which is supplied by an off-the-shelf motor drive inverter.