Improved control of dynamic voltage restorer for compensation of unbalanced and harmonic-distorted grid voltage

Abstract

Doubly fed induction generator (DFIG) are vulnerable to unbalanced voltage and harmonic distortion, which will lead to the heating problem of stator/rotor windings and the damage of gearbox. This paper establishes the transient modeling of the DFIG under composite unbalanced voltage and harmonic distortion condition, and elaborates the dynamic response of DFIG from the perspectives of rotor voltage, active power and reactive power under voltage harmonics and unbalance. It also presents an improved control strategy for a dynamic voltage restorer (DVR) to accurately track the specific voltage harmonics, with targeted consideration of constraining unbalanced voltage and fifth- and seventh-order voltage harmonics. The extractions of each voltage signals are presented in this paper via multiple notch filter (MNF), which has a good low-pass characteristic and an excellent performance in trapping the specific AC signals. The presented notch-filter-based algorithm has the advantages of simper control structure and faster response speed, and is more accurate in harmonic extraction. A 1.5-MW DFIG has been employed to establish the object of protection in simulation analysis to verify the validity of the proposed control strategy. The results show that the proposed control strategy is effective which is consistent with the theoretical model, and the oscillations of each crucial parameter can be well-suppressed.