Abstract: With the development of high percentage of renewable energy power system, the equivalent rotational inertia of the system has decreased significantly, and the problem of system frequency stabilization is becoming more pronounced when grid faults occur. To address this problem, this paper proposes a grid-connected converter power supply system with open-winding wound field synchronous motor (OW-WFSM) as the interface. Based on the establishment of the mathematical model of OW-WFSM, the system power and voltage-current vector relations are analyzed. The converter power transfer control strategy with phase difference closed-loop control and the reactive power-voltage coordinated control strategy of the OW-WFSM excitation system are designed to realize the decoupled control and stable transmission of the converter and the OW-WFSM power. The control principle is analyzed and verified by using the Lyapunov stability theorem. By analyzing the transient frequency support capability, it is proved that the OW-WFSM in the proposed topology still has the inertia response capability. Meanwhile, the converter with motor rotor position orientation is able to naturally increase the active power, which realizes the further improvement of grid inertia and active power support capability. The simulation results verify the effectiveness of the proposed control strategy.