Abstract: An electric machine may include: an alternating current electric motor comprising a first semi-winding and a second semi-winding; an inverter comprising a first inverter branch electrically connected to the first semi-winding and a second inverter branch electrically connected to the second semi-winding; and a control unit configured to provide a first control signal to the first inverter branch, so as to induce a first alternating current in the first semi-winding, and a second control signal to the second inverter branch, so as to induce a second alternating current in the second semi-winding. The first and second alternating currents may have a first frequency. The first and second control signals may have a second frequency that is less than the first frequency. The first and second control signals may be reciprocally out of phase by substantially 180° relative to the second frequency.

Abstract: A method of manufacturing an electric-motor rotor may include providing a magnet of sintered magnetic material, the magnet having a first diameter; providing a sheath of composite material, the sheath having an inner diameter smaller than the first diameter; reducing the first diameter to a second diameter; fitting the sheath onto the magnet when the magnet has the second diameter; and letting the magnet with the sheath fitted thereon to interfere, allowing the sheath to exert inward pressure on the magnet. An electric-motor rotor may include a magnet of sintered magnetic material, the magnet having a first diameter; and a sheath of composite material, the sheath having an inner diameter smaller than the first diameter. The sheath may be associated with the magnet in such a way that the magnet with the sheath fitted thereon interfere so that the sheath exerts inward pressure on the magnet.

Abstract: A method for manufacturing a rotor with permanent magnets may include providing a central core with a desired cross-section; providing a plurality of ferromagnetic discs having a hole shaped in a complementary manner to the cross-section of the central core; stacking up the ferromagnetic discs around the central core to form a cylindrical structure with a longitudinal cavity, wherein the longitudinal cavity is formed by the holes of the stacked-up ferromagnetic discs; integrally blocking together the stacked-up ferromagnetic discs; and removing the central core. A rotor may be manufactured by the method. The rotor may be used in an electric motor.