DFIG-based wind turbines with virtual synchronous control: Inertia support in weak grid

Abstract

This paper presents virtual synchronous control (VSynC) for DFIG-based wind turbines (WTs) in particular when integrated into weak AC grid with low SCR. Different from the typical vector control (VC) based on the widely-used phase-locked loop (PLL) technique, VSynC synchronizes DFIG with the grid directly through active power control, which effectively avoids the difficulties associated with PLL in weak AC grid. Eigenvalue analysis shows that the VSynC-based DFIG displays pronounced superiority in stability when accessing low-SCR AC grid. In such case, the DFIG's power transfer capability is not limited, which means the maximum theoretical power transmittable, viz., 1.0 pu, can be achieved even when SCR is decreased to 1.0. More importantly, the VSynC also makes DFIG provide the desired inertial response naturally for dynamic frequency support. Comparisons between the VSynC and the typical VC-based inertia control are also performed, and simulation results demonstrate the superior performance of VSynC-based DFIG attached to weak AC grid.