Rotor for electric motor, electric motor and compressor

A rotor for an electric motor, comprising:

• a rotor core having a circular cross section, wherein the circular cross section defines a central axis of the rotor, the rotor core comprising:
• a shaft hole, wherein the shaft hole is circular and has a center;
• and
• four magnet grooves equally-spaced around a circumference of the shaft hole, both ends of each magnet groove being provided with a magnetic isolation slot in communication with the magnet groove, a magnetic isolation bridge being defined between two adjacent magnetic isolation slots;
• and
• four permanent magnets each provided in a corresponding magnet groove, a shape of each magnet matching a shape of the corresponding permanent magnet groove, each permanent magnet comprising a first surface and a second surface arranged opposite each other in a radial direction of the rotor core, the second surface being radially approximate to the shaft hole,
• wherein, when viewed from a projection surface that is perpendicular to the central axis of the rotor, the first surface comprises an arc segment, when viewed from the projection surface, the second surface comprises a plurality of straight segments connected sequentially, with an angle between two adjacent straight segments,
• wherein a thickness H of each permanent magnet on a corresponding magnetic pole centerline, a length L of the second surface projected on the projection surface, and a radius R of the rotor core satisfy the following relationships:
• 0.24≤H/R≤0.26 and 1.07≤L/R≤1.11, wherein the magnetic pole centerline is a line connecting the center of the shaft hole and a center of an imaginary circle that contains the arc segment.