US Patent 7183686 Permanent magnet synchronous motor

A synchronous motor includes a stator, a rotor and permanent magnets. The rotor includes a rotor iron core that is rotatable relative to the stator, and a plurality of conductor bars accommodated within corresponding slots in the rotor iron core. The conductor bars have their opposite ends shortcircuited by respective shortcircuit rings to form a starter cage conductor. The rotor also has a plurality of magnet retaining slots defined therein at a location on an inner side of the conductor bars, in which hole permanent magnets are embedded.