Modeling the Dynamic Voltage Distribution in Electric Traction Motor Windings and Its Application on HV Optimal Winding Design

Modern trends for electric traction drives lead to an increased DC link voltage and steeper voltage slopes from novel SiC inverters. This results in higher electrical stress for the insulation system of the stator motor windings. Current motor simulation models lack the precision to investigate the highly dynamic voltage propagation. Consequently, the insulation system is designed inappropriately. To solve this problem, a physically based equivalent circuit model (ECM) is presented for calculating the dynamic voltage distribution. The model is suited for an early design stage and requires neither measurements nor parameter fittings. The ECM structure is strictly linked to physical components in the hairpin stator. This enables the localization of high electrical stress spots in the winding. 2D finite element (FE) models are proposed to calculate the required values of the frequency dependent network elements for the bars in the machine. The bars in the endwinding region are treated with analytical formulas. The ECM is modeled and solved in the frequency domain. Hence, the computational effort is reduced to solving a linear algebraic problem instead of a system of partial differential equations. The model results are validated with measurements in both frequency and time domain. Applications with transient switching events show where locations of high voltage differences can appear inside the slot and the winding heads.