The large-scale access of new energy causes broadband oscillation

which poses a serious challenge to the safe and stable operation of synchronous motors in the power grid. Based on fully controlled power electronic devices

the flexible excitation system not only retains the traditional rotor side excitation voltage control channel

but also expands the stator side reactive power control channel

which can realize the stator/rotor dual damping channel control; It can effectively reduce the torsional vibration risk of synchronous machine shaft system and improve the stability of new energy access system. In order to analyze the oscillation suppression ability of flexible excitation system in the wide frequency band

the impedance analysis method is used to establish the wide frequency domain sequence impedance model of flexible excitation synchronous motor system considering the flexible excitation stator/rotor dual damping channel control

synchronous machine output characteristics and stator/rotor power control coupling. Based on the established impedance model

the influence of the control link and stator/rotor dual channel control parameters of the flexible excitation synchronous motor system on the system stability is analyzed. Finally

based on the MATLAB/Simulink simulation model

the correctness of the impedance model of the flexible excitation synchronous motor system and the effectiveness of the flexible excitation synchronous motor system in suppressing the sub-synchronous oscillation of the power grid are verified.