Resistance limited permanent magnet segmentation geometry optimization for loss reduction in inverter fed permanent magnet synchronous machines

Inhalt:
Permanent magnet segmentation is a crucial component optimization in permanent magnet synchronous machines. Eddy current losses in permanent magnets lead to temperature increase, permanent demagnetization, and decreased efficiency of the motor. State-of-the-art segmentation consists of either axial segmentation or circumferential segmentation with equidistantly spaced insulation layers. In this paper, an optimization approach for insulation layers in two dimensions will be given. Firstly, various models for the calculation of the eddy current and their limitations are discussed. Based on a simple eddy current model, a lumped equivalent circuit with a set of insulation layers is developed. A parameter optimization, under the assumption of resistance limited eddy currents, is conducted with a discrete gradient descent method to obtain an optimal permanent magnet segmentation in two dimensions. The optimal segmentation is validated with a FEM simulation. Optimization can significantly reduce eddy current losses in permanent magnets with coarse segmentation. With fine segmentations approaching the manufacturing limits, the optimization has negligible benefit compared to conventional segmentation.