Experimental Validation of a Prediction Method for Bearing Currents in Traction Drive Systems

This paper presents a proposed measuring PCB for bearing currents in a traction drive system. The bearing currents of three bearings are first predicted by a novel calculation methodology over a speed range for different DC-link voltages and inverter voltage gradients. The common-mode (CM) current, CM voltage, and bearing voltage were then measured for the different setups and operating points. A comparison of the predicted bearing currents with the corresponding measurements is also presented. The measured values are in good agreement with the calculations. Variations of parameters show that higher voltages, steeper voltage edges, and higher switching frequencies lead to higher CM currents. Finally, a design methodology for a CM choke for the tested drive is presented and simulated, which shows that the CM current can be reduced.