A Multi-stage Control Strategy for Enhancing Low-voltage Ride-through Capability of Doubly-fed Induction Generator Units

When the grid experiences a major disturbance that results in a voltage drop, doubly-fed wind turbines need to coordinate with hardware-based modification measures to achieve low-voltage ride-through (LVRT) capability. To address the need for coordinated power control strategies throughout the entire LVRT process in DFIG-based wind farms to comply with grid codes, this paper proposes a multi-stage control strategy that enhances both the LVRT capability and reactive current injection capacity of DFIGs. This strategy includes three stages: voltage drop, transient voltage stability, and voltage swell. The voltage drop and transient voltage stability stages are responsible for the improved LVRT control, while the voltage swell stage ensures system recovery. This method utilizes the existing rotor string impedance protection circuit and improved transient voltage control to achieve LVRT. Simulation results demonstrate that the proposed approach not only effectively suppresses transient impacts on DFIGs under severe voltage sags but also ensures the injection of reactive power during faults, supports grid voltages, and enhances the fault ride-through capability of the units.