Improvement of Frequency Support for a DFIG Using a Virtual Synchronous Generator Strategy at Large Power Angles

The frequency regulation rate and operation stability of a doubly fed induction generator (DFIG) based on a virtual synchronous generator (VSG) strategy decreases under large-power-angle conditions, which reduces the grid frequency support capacity. This paper proposes the compound adaptive parameter (CAP) and coordinated primary frequency regulation (CPFR) strategies to improve the grid frequency support capacity in terms of multiple dimensions of the transient properties, operation condition range, and regulation duration. Mathematical and small signal models of the DFIG-VSG system are constructed. The effect of large-power-angle conditions on the transient properties under grid frequency perturbations is analyzed based on these models, and the CAP strategy for excitation control and virtual damping is formulated. The constraints of the rotor kinetic energy and the load increase capacity of the grid-side converter are analyzed, and the CPFR strategy is formulated based on this. Finally, the effectiveness of the proposed strategies is verified via simulations of single-machine and wind farm scenarios under grid frequency perturbation.