The invention discloses an alternating current excitation system based on a full control device. The alternating current excitation system comprises an excitation power unit and an excitation regulator, wherein the excitation regulator controls the excitation current output of the excitation power unit, the excitation power unit comprises an excitation machine excitation system, an excitation machine excitation winding, an excitation machine and a current converter, the output end of the excitation machine excitation system is connected with the excitation machine excitation winding, the input end of the current converter is connected with the machine end of the excitation machine, the excitation machine excitation system provides excitation current for the excitation machine, the excitation power unit also comprises a chopper, the current converter adopts a full control current converter, the output end of the full control current converter is connected with the input end of the chopper, and the output end of the chopper is used for being connected with an excitation winding of a power generator. The alternating current excitation system adopts the full control current converter, the phase shifting failure problem does not exist, the reliability is high, the excitation capability is good, the power generator capacity is improved, the deexcitation failure is effectively prevented, the system manufacturing cost is reduced, the equivalent time constant of a regulating system is reduced, and the response speed is improved.