Investigation of Magnetic Material Degradation Caused by Stator Manufacturing as a Source of NVH and Core Losses in Electric Drives

During the development of modern electric drives, vibroacoustic quality is one of the most critical parameters alongside motor performance and efficiency. One source of poor vibroacoustic characteristics is the inhomogeneity and imperfection of the soft magnetic materials found in the electrical machine. The primary indicators of these defects are the selected electrical steel and the machining processes used for the stator (waterjet cutting, laser cutting, punching). These inhomogeneities excite the mass-spring-damper oscillating system through higher-order harmonics induced in the air gap. The objective of the present research is the identification of these air-gap harmonics, for which this study aims to perform a systematic investigation chain starting from closed magnetic circuit measurements and building up to measurements loaded with an air gap. This is based on classical Epstein measurements, followed by induction measurements conducted in the air gap of a C-core. The test specimens were fabricated from M400-50A electrical steel using three different machining methods. The results show that the machining process has a significant impact on the magnetic characteristics, and the exit angle of the induction vectors measurable in the air gap also deviates from the ideal.