A compound motor-generator system including a first motor-generator and a second motor-generator. The first motor generator includes a stator having a set of three-phase field windings and a first rotor disposed inside and coaxial with the stator and configured to rotate relative to the stator. The second motor-generator includes a rotational stator and a second rotor coupled to a common shaft with the rotor of the first motor-generator and disposed inside and coaxial to the rotational stator. The rotational stator is configured to rotate relative to the second rotor and at a higher rotational speed than the second rotor.