A drive is embodied to drive a rotor at a variable rotational frequency; the rotor has a winding that is embodied to produce a rotary field magnetomotive force of a generator, with a rotor rotary field frequency which is variable in relation to the rotor; the frequency converter is electrically connected to the rotor winding; a regulating device comprises a recording element for measuring values of the generator, a calculating unit for a generator simulation, and a transmitter for transmitting a control signal to the frequency converter; and, on the basis of the control signal, an electrical excitation of the rotor winding can be triggered by the frequency converter in such a way that a pre-determined stator rotary field frequency is present in the event of a variable rotational frequency of the rotor and a variable rotor rotary field frequency.