Abstract: The key structure of an Ac excited grid frequency synchronized machine (AEGFSM) was presented. The simulation of AEGFSM, cyclo-converter, field-oriented vector control algorithm was done according to their discrete mathematical model. An AEGFSM sample drived was fabricated. Simulation results are in excellent agreement with the experimental under the typical working condition. It is concluded that AEGFSM drives have the high-quality dynamic performances as DC drives and provide an applicable solution of middle-voltage freqency-variable drives.