Active Power Transfer Capability Enhancement for DFIG-Based WT Under Asymmetrical Faults

The design of current commands under asymmetrical faults is crucial for enhancing the active power transfer capability (APTC) of doubly-fed induction generators (DFIG)- based wind turbines. However, it's significantly challenged by the inherent nonconvexity of model, which stems from the nonlinear transformation between stator and rotor quantities due to slip characteristics, and the multivariable coupling introduced by dual-sequence coupling effect. This letter establishes an optimal APTC enhancement model incorporating rotor current, rotor voltage, voltage unbalance factor (VUF) and transient stability constraints. With reconstruction of dual-sequence coordinate systems and semi-definite relaxation, the convexified problem is solvable with guaranteed global optimality. The power and current capacity of DFIG are fully utilized by adaptively coordinating APTC enhancement and VUF attenuation. The effectiveness of the proposed method is experimentally verified.