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This paper discusses an accurate magnetic field analysis that addresses stress distribution in the magnetic core by using the finite-element method (FEM) to estimate motor characteristics. This analysis method consists of the following steps: 1) measurement of the magnetic characteristics of electrical steel sheets in a state where stress is added; 2) calculation of deformation and stress distribution using structural analysis; 3) preprocessing of the magnetic field analysis, which generates the FEM mesh taking account of the deformation by stress and the changes of the magnetic properties in each of the core elements corresponding to stress distribution; and 4) magnetic field analysis using the data measured in step 1) and the FEM mesh generated in step 3). As an example, a result of a permanent magnet motor's cogging torque calculation is shown, focusing on stress in the stator core resulting from shrink fitting into the frame. As a result, the cogging torque waveform was shown to differ depending on the shape and the materials of the frame.

The stress that acts on the core by installing a stator in a frame influences the performance of a motor. To reflect this influence in the equipment design, the stress dependence of the magnetic property was examined for non-oriented electrical steels, which are the core materials. This time, the stress dependence of the magnetic power loss in the range of ±225 MPa was evaluated for high-grade non-oriented electrical steel sheets of 0.5 mm thickness, and the following results were obtained. (1) The influence on the magnetic power loss is larger under compression than under tensile stress. The loss increases rapidly with an increase in the compressive stress. However, when the stress exceeds -50 MPa, the saturation tendency of the loss gradually becomes strong. (2) The influence of the stress on the magnetic power loss is different in the rolling direction and the traverse direction. (3) A greater magnetic power loss that occurs with compressive stress is mainly due to an increase in hysteresis loss, and the eddy current loss also increases slightly. It is thought that this slight increase in the eddy current loss that occurs with compressive stress depends on the change in the anomalous loss.

In this paper we show a novel motor design method, considering stress distribution in the motor core. This method consists of several steps as follows: (a) measurement of magnetic characteristics of the electrical steel sheets in the state where the stress is added, (b) calculation of deformation and stress distribution using structural analysis, (c) pre-process of the magnetic field analysis, which makes FEM mesh deformed by the stress and changes the properties of each elements of the core corresponding to the distribution of the stress, and (d) magnetic field analysis using the measured data by step-(a) and the FEM mesh generated by step-(c). As an example, we show a result of cogging torque calculation of permanent magnet motors, considering the stress in the stator core resulting from shrink fitting in the frame. As a result, we show that the cogging torque waveform is different depending on the shape of the frame