Internal Voltage Frequency Response Model of Grid-Forming DFIG-Based Wind Turbine and Its Characteristics

Abstract

The system frequency response (SFR) of doubly-fed induction generator (DFIG) is different from synchronous generator (SG). A grid-forming DFIG via virtual synchronous control of inner voltage vector is proposed to mimic the characteristics of SFR of SG, which leads to an internal voltage SFR model with virtual incremental mechanical power model similar to SG. For clearly demonstrating the inertial dynamics of grid-forming DFIG, the expression of the inertial dynamics in the time domain is firstly derived by convolution, which has same inertial dynamics with SG at the beginning of disturbance. Moreover, the inertia difference between DFIG via synthetic inertia control and grid-forming DFIG is analysed, and the fast power response capability of grid-forming DFIG is demonstrated by comparison with synthetic inertia control. Furthermore, a multi-machine SFR model is established by the proposed SFR model to analyse the impacts of different control parameters on the system frequency dynamics, which is convenient to coordinate with load disturbance. Finally, numerical simulations are conducted to show the effectiveness and accurateness of the proposed SFR model.