Rotor for electric motor

A rotor for electric motor, comprising:

• a rotor shaft, and
• a rotor core in which a plurality of poles each composed of a pair of first permanent magnets arranged in a V-shape open toward an outer peripheral side and a second permanent magnet arranged in parallel to a circumferential direction in an open part of the V-shape are arranged in the circumferential direction while alternately changing the polarities thereof,
• wherein a groove is formed which has a groove center in a range extending from a base point located at an electrical angle position shifted by ¼ cycle of a harmonic component of a torque ripple toward a d-axis from a dividing line located between a line connecting a rotor outer peripheral side corner portion of the second permanent magnet and the rotor shaft center and a q-axis out of a plurality of dividing lines connecting a plurality of dividing points set at an electrical angle interval corresponding to one cycle of the harmonic component from the d-axis to the q-axis on the rotor core outer periphery and the rotor shaft center up to an electrical angle position shifted by ⅛ cycle of the harmonic component toward the q-axis from the base point.