PROBLEM TO BE SOLVED: To reduce torque ripples by a simple construction by making the pole center angles formed in a rotor unequal, and providing center angles corrected in the peripheral direction for the uniform pole center angle of the stator.

SOLUTION: The magnetically insulating parts 4 of a motor are so arranged that a real d-axis 21 may be shifted from an imaginary d-axis 6' being the original pole center by a shift angle s 22, and this shift angle s 22 is an angle for correcting the equal central angle t of poles formed on the stator and has been confirmed experimentally. And when the number of poles P equals four, and the number of slots of the stator Ns equals twelve, and m=2, a fundamental central angle t becomes 90 degrees, and a correction angle s becomes 15 degrees, and the pole central angles r become 105 and 75 degrees. This is a correction angle for aiming the reduction of a ripple component called a slot ripple mainly by the teeth of the stator 1. As the result, torque ripples are canceled by each rotor pole pair mutually and reduced, and a synchronous motor having good controllability is obtained.

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