Developments of Control and Design strategies for Slotless Permanent Magnet Motors using High Energy Density Magnets

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As one of strategies for saving energy in global environmental conservation, the efficiency improvements of electric motor drive systems have been promoted in home appliances and industrial applications. Among them, Slotless Permanent Magnet Synchronous Motor (slotless PMSM) using recently developed rare-earth magnets with high energy density have been received much attention from a standpoint of effective use of rare-earth magnets. An aim of this project was to develop the optimum design and control strategies for high efficiency slotless PMSM and during research period we had made achievements as follows.1. Considering that winding inductance value is important for designing high efficiency slotless PMSM, we proposed the new optimum design strategy modifying the design strategy of the first prototype. We made the second prototype according to the result of the optimum design using three-dimensional Finite Element Analysis (3D-FEM) and experimentally evaluated the drive performances. As a result, it was confirmed that the second prototype could realize the decrease in carrier loss by 25% compared to the first prototype.2. By using 3D-FEA, we identified the fact that the decrease in the winding inductance and the increase in the winding resistance for an increase in frequency are due to the eddy current loss on the surface of Ne-Fe-B permanent magnets. Based on the above investigation, we proposed a method for the quantitative prediction of the carrier loss at the design stage of slotless PMSM and confirmed the effectiveness of the proposed method by the experiments using the second prototype.