Determination of Local Magnetic Material Properties Using an Inverse Scheme

Abstract

The precise knowledge of material properties is of utmost importance for motor manufacturers to design and develop highly efficient machines. Due to different manufacturing processes, these material properties can vary greatly locally and the assumption of homogeneous material parameters for the electrical steel sheets is no longer feasible. The goal of our research project is to precisely determine these local magnetic material properties using a combined approach of measurements, numerical simulations and the applications of inverse methods. In this paper, we focus on the identification of the local linear permeability of electrical sheets considering cutting edge effects. In doing so, the electrical sheets are divided into subdomains, each assigned with a linear magnetic material model. The measurement data are generated artificially by solving the magneto-static case using the finite element (FE) method and overlay these data with a Gaussian white noise. Based on the measured and simulated data, we apply our inverse scheme to determine the parameters of the linear material model. To ensure solvability of the ill-posed inverse problem, a Tikhonov regularization is used and the regularization parameter is computed via Morozov's discrepancy principle.

Inverse Scheme to Locally Determine Nonlinear Magnetic Material Properties: Numerical Case Study

“…Recently, we have proposed an inverse scheme capable of locally determining the change in the linear magnetic property (the linear relationship between B and H via magnetic reluctance) due to the cutting-edge effects. The approach is based on a quasi-Newton method using Broyden's update formula to compute the gradients of the objective function with respect to the local linear magnetic reluctivity [8]. In order to advance the practical relevance, this research paper extends the linear magnetic material model to a nonlinear one and uses the adjoint method (see, e.g., [9]) to compute the gradients of the searched-for parameters, which are the coefficients in all BH-curves.…”