This paper shows an improvement of the WRSM (Wound Rotor Synchronous Motor) by satisfying the voltage limit condition at high speed. After that, it compares the performance of the improved WRSM to that of the IPMSM (Interior Permanent Magnet Synchronous Motor). The comparison has been made under the condition where the dimension of the motor is identical to that of the IPMSM, having the rotor switched to a wounded rotor form. Moreover, this paper compares the Basic Model of the two motor, and estimates the parameters of the WRSM, thereby proposing the method to improve high speed performance. Furthermore, this paper presents the feasibility of switching the conventional motor into rare-earth-free motors for traction purpose.