Fault ride‐through enhancement in DFIG with control of stator flux using minimised series voltage compensator

Abstract

Wind energy systems based on doubly fed induction generators (DFIG) are very sensitive to grid disturbances, mainly voltage sags, which can cause rotor and stator overcurrents and rotor overvoltage, resulting in turbines shutdown or even damage to the converter connected to the rotor. Besides, the transmission system operators have been issuing strict grid codes, which require the wind energy conversion system (WECS) to keep operating during grid disturbances and supplying reactive power to the system, if necessary. Due to difficulties to access the offshore DFIGs, avoiding damages and shutdowns in these WECS is paramount. In order to overcome this problem, this article proposes the control of the generator stator flux through a series voltage compensator (SVC) with minimised components. The proposed SVC draws power from the grid through a transformer with a single turn in the primary side (single turn primary transformer) and injects power in the system through an LC filter, without any series transformer. The control of the generator stator flux reduces considerably the stator and rotor current as well as the rotor voltage, allowing the generator to ride-through the grid disturbances.