A Coordinated Control Scheme to Realize Frequency Support of PMSG-Based Wind Turbines in Weak Grids

Frequency droop control is widely used in permanent magnet synchronous generators (PMSGs) based wind turbines (WTs) for grid frequency support, in which a phase locked-loop (PLL) is commonly needed to realize grid synchronization of the WT. However, when connected to weak grids, the dynamics of the PLL can be deteriorated, which may even cause instability of the WT. To deal with this problem, this paper proposes a coordinated control scheme for PMSG-based WTs, which applies a virtual synchronous control in the grid-side converter to realize grid synchronization and a frequency droop control in the generator side converter for frequency support. It can ensure the desired stability of PMSG-based WTs when integrated into weak grids and simultaneously, provide frequency support to the grid. Simulations verify the rationality of the analysis and the effectiveness of the proposed control scheme.