Effect of Dimensional Variation on Magnet Temperature Estimation in Interior Permanent Magnet Synchronous Motors

Various methods for estimating magnet temperature in interior permanent magnet synchronous motors have been proposed to further enhance their performance. However, the effect of dimensional variations of motor parts on the accuracy of temperature estimations has been infrequently addressed. In this study, we investigated the effect of dimensional variations on the accuracy of magnet temperature estimated from voltage induced in the motor, applying electromagnetic field analysis. We obtained following results: (1) The maximum estimation error was 14.5°C owing to the variations in the IEEJ D-model; (2) the magnet slot thickness and air gap strongly affected the accuracy, and d-axis inductance also significantly changed; (3) the air gap had approximately seven times the effect on the amount of the inductance change as that of the slot thickness. These results can be qualitatively explained using the equivalent magnetic circuit method, although quantitative differences occurred in estimations of the analysis because some parts of the magnetic flux are not considered in this method.