Common-Mode Impedance Prediction of a High Frequency Hairpin Stator Winding Based on FEM and Modified Nodal Analysis

Abstract

With the widespread use of inverters with increasing switching frequencies in three-phase AC machines, parasitic and harmful bearing currents with high frequencies may occur. To predict this problem in the design stage, the common-mode impedance can be used. Therefore, the aim of this paper is to propose a valid high frequency stator winding model based on transmission line theory, to identify the parameters of the high frequency machine behavior and to examine their influence. The proposed model is then used to calculate the common-mode impedance of an example machine for a wide frequency range. A cascaded solving algorithm for model parameter identification and efficient computation of the resulting network is given as well. Further, the parameters of the high frequency machine behavior will be varied. The result of the calculation performed using the model obtained and the influence of the model parameters are validated with a laboratory measurement on the chosen machine equipped with a hairpin winding. Thus the presented model, for the time being, only includes assumptions based on hairpin windings. Recommendations on further model extensions are derived from the results.