Electric motor, in particular induction motor, comprising a stator, a rotor and a control device which is arranged at the rotor. The three rotor windings are connected to a Rotor Control device with inverter and controller unit mounted on the rotor. A capacitor is placed in the DC link. The capacitor is supplied from the EMF induced in the rotor. The current in the rotor windings is advanced in order to achieve a 90 degree phase shift between rotor current and stator MMF vector. To achieve this the frequency and amplitude of the rotor current as well as the phase shift can be varied. Wherein the frequency of the rotor inverter is matching the slip frequency.