The paper presents the optimization and comparison of different rotor design concepts of an Electrically Controlled Permanent Magnet Excited Synchronous Machine (ECPMSM) possessing a field control capability. The experimental results of a no-load back electromotive force (back-EMF) waveforms, cogging torque and electromagnetic torque values are presented in detail. Moreover, in order to compare the over-speed capability of the machine in the varying rotor designs, the predicted performances, i.e. range of speed and resulting torque of the machines, have been estimated.