Dynamic Coupling and Cooperative Control for Multi-Paralleled Doubly Fed Induction Generator Wind Farms During Symmetrical Low Voltage Ride-Through in a Weak Grid

In multi-fed grid-connected systems, there are complex dynamic interactions between different pieces of equipment. Particularly in situations of weak-grid faults, the dynamic coupling between equipment becomes more pronounced. This may cause the system to experience small-signal instability during the fault steady-state. In this paper, multi-paralleled doubly fed induction generator (DFIG)-based wind farms (WFs) are taken as an example to study the dynamic coupling within a multi-fed system during fault steady-state of symmetrical low voltage ride-through (LVRT) in a weak grid. The analysis reveals that the dynamic coupling between WFs will introduce a damping shift to each WF. This inevitably affects the system's dynamic stability and brings the risk of small-signal instability during fault steady-state in LVRT scenarios. Increasing the distance to fault location and fault severity will exacerbate the dynamic coupling between WFs. Because of the dynamic coupling, adjusting the control state of one WF will affect the stability of the remaining WFs in the system. Hence, a cooperative control strategy for multi-paralleled DFIG WFs is proposed to improve dynamic stability during LVRT. The analysis and the effectiveness of the proposed control strategy are verified by modal analysis and simulation.