Impedance Modeling and System Stability Analysis of Grid-Forming Direct-drive Wind Turbine

Considering that the grid-following permanent magnet direct-drive wind turbine is prone to instability under weak grid, the grid-forming direct-drive wind turbine with weak grid adaptability has attracted much attention. However, at present, most of the models established for the grid-forming direct-drive wind turbine are based on the state space model, which involves many state variables. In addition, if the control structure of the system is changed, the model reconstruction is difficult. Therefore, this paper will take the grid-forming direct-drive wind turbine with DC voltage control on the generator side and VSG control on the grid side as the research object. Firstly, the impedance model of grid-forming direct-drive wind turbine grid-connected system is established based on multi-harmonic linearization method. Then the damping characteristics and oscillation mechanism are studied. Finally, based on the Matlab/Simulink platform, the simulation is built to verify the established impedance model and the stability analysis results.