Modeling and Analysis of Sequence Impedance for Direct-Drive PMSG Considering Frequency Coupling

The broadband oscillation caused by the grid-connected direct-drive permanent magnet synchronous generator (PMSG) has received widespread attention. The impedance analysis method is currently one of effective measures to study this phenomenon. In the process of impedance modeling, it is generally believed that the system is the single-input single-output structure, but the single-input double-output phenomenon will occur when the system has frequency coupling effect. Thus, the original hypothesis is no longer applicable. This paper first analyzes the transfer relationship between the disturbance component and the coupling component in direct-drive PMSG. Then, based on the harmonic linearization theory and the frequency coupling, the sequence impedance model (SIM) considering the dynamics of the grid equivalent impedance, phase-locked loop (PLL), inner loop control, outer loop control, DC bus capacitance and port filtering is established. Finally, the accuracy of SIM under different working conditions of direct-drive PMSG is verified by MATLAB/Simulink.