Frequency support of DFIG-based wind turbine via virtual synchronous control of inner voltage vector

With the increasing penetration of doubly-fed induction generator-based wind turbines (DFIG-WTs), the frequency support of DFIG-WTs based on virtual synchronous control is more and more important to system operational security. In this context, a novel virtual synchronous controller based on inner voltage vector synchronization (VSCIVVS) for grid-connected DFIG-WT without phase-locked loop is proposed for frequency support, which can lead to a simplified small signal model of grid-connected DFIG-WT controlled by virtual synchronous controller. Detailly, unlike the classical virtual control method, VSCIVVS adopts rotor current control loop to guarantee the good transient current response characteristics and realizes the synchronization and orientation of inner voltage vector. Moreover, DFIG-WT controlled by VSCIVVS is equivalent to a voltage source with an internal impedance, which can improve the active power transmission ability of DFIG-WT to guarantee the frequency support in weak ac grid. Then, the small signal stability and performance of VSCIVVS for DFIG-WT is analysed. Furthermore, the sustained frequency support ability of VSCIVVS for DFIG-WT is demonstrated by frequency estimation, and the rotor speed recovery of sustained frequency support control is acquired by adaptive VSCIVVS. Lastly, numerical simulations are performed to show the effectiveness of the proposed VSCIVVS control method.