a rotor core having a plurality of metal parts and an inner hole for the motor rotor, the inner hole passing through the rotor core, and areas of all the metal parts forming a rotor metal total area ΣA_metal;

a plurality of reluctance parts surrounding the inner hole, each of the reluctance parts comprising a plurality of flux barriers penetrating through the rotor core, each flux barrier in a reluctance part having an area ratio which is a ratio of an area of the flux barrier to areas of all the flux barriers in the reluctance part, and the area ratios of the flux barriers in the reluctance part increasing sequentially as an arithmetic progression sequence along a direction from a periphery of the motor rotor to the inner hole for optimizing performance of the motor rotor;

wherein areas of the flux barriers in all of the reluctance parts form a flux barrier total area ΣA_air, and a flux barrier ratio K_A is expressed as