I. Introduction
Nd-Fe-B magnets are widely used for the field excitation of synchronous machines because of their strong magnetization. On the other hand, the conductivity of these magnets is relatively high. As a consequence, the thermal demagnetization is often caused by the eddy currents produced by harmonic fields in the machines [1]–[4]. This is one of the major problems in various applications of the permanent magnet machines. Therefore, the estimation of the eddy current loss of the Nd-Fe-B magnets is indispensable for the machine designs. However, it is very difficult to estimate the magnet eddy current loss in the synchronous machines by measurements because the magnet eddy current loss cannot be separated from the core loss in usual no-load or load tests.