High‐Efficiency Motors Using Soft Magnetic Cores

We have developed a small and highly efficient axial gap motor whose stator core consists of a soft magnetic core. First, the loss sensitivities to various motor design parameters were evaluated by magnetic field analysis. Low sensitivity to the pole number and core dimensions ( ? 2.2 dB) was found for the total loss, which is the sum of the copper loss and the iron losses in the stator core and the rotor yoke. From this we concluded that to improve the motor efficiency, it is essential to reduce the iron loss in the rotor yoke and to minimize the other losses. With this in mind, a prototype axial gap motor was manufactured and tested. The motor has four poles and six slots. The motor is 123 mm in diameter and the axial length is 47 mm. The rotor has parallel magnetized magnets and a rotor yoke with magnetic steel sheets. The maximum measured rotor efficiency is 93%. This value roughly agrees with the maximum calculated efficiency of 95%.