Backstepping-Based DPC Strategy of a Wind Turbine-Driven DFIG Under Normal and Harmonic Grid Voltage

This paper presents a sort of nonlinear backstepping-based algorithm combining with direct power control (DPC) to a wind turbine-driven doubly fed induction generator (DFIG) under normal and especially harmonic grid voltage. First, the power control objectives are analyzed and designed under normal and harmonic grid voltage for the purpose of harmonic stator current suppression; second, a unified mathematic model of a DFIG under normal and harmonic grid voltage is founded, exploring its power model in detail; finally, the backstepping algorithm is introduced briefly and the backstepping-based DPC (BS-DPC) algorithm of the DFIG is developed under normal and harmonic grid voltage. The comparative simulation results between vector control (VC) with resonant controller, look-up table DPC (LUT-DPC) and BS-DPC under normal grid voltage verify that the proposed BS-DPC realizes the decoupling control of active and reactive power of DFIG, with better dynamic performance than VC, as well as with better steady performance than LUT-DPC. Under the harmonic grid voltage, further simulation results verify the effectiveness of BS-DPC for suppressing the harmonic stator current of the DFIG in contrast to VC with a resonant controller and LUT-DPC with improved control objectives proposed by this paper; meanwhile, the adaptability of BS-DPC to minute frequency derivation, harmonic component order and distorted degree of the grid voltage under harmonic conditions are verified as well.