An input end of a first power conversion circuit of the system is connected to a power supply, and an output end of the first power conversion circuit is connected to a stator winding of an electrical excitation motor. An input end of a second power conversion circuit is connected to the power supply, and an output end of the second power conversion circuit is connected to a primary side of an excitation transformer. The excitation transformer transmits energy required by an excitation winding of the electrical excitation motor from a stator to a rotor. A first controller controls the first power conversion circuit to inject a current excitation into the stator winding, so that a current is generated on the excitation winding. A detection circuit obtains a response signal of the primary side of the excitation transformer and sends the response signal to a second controller.