Transformer inrush mitigation for dynamic voltage restorer using direct flux linkage control

Dynamic voltage restorer (DVR) based on transformer-coupled topology is the most cost-effective solution to protect consumer from voltage sags. However, an important issue about this topology is the transformer saturation. Magnetic saturation of the transformer will generate large inrush current which may greatly distort the compensation voltage or even trigger the over-current protection. To prevent the transformer from saturation, this study proposes a novel direct magnetising flux linkage control strategy. Distinguished from existing DVR models which ignored the transformer magnetising branch, this study establishes a comprehensive DVR model by adopting the magnetising flux linkage as a state-variable. Therefore, by adopting flux linkage feedback, the magnetising flux linkage would be directly controlled. Otherwise, to implement the flux linkage control, this study proposes a robust flux estimation method to carry out the proposed control scheme. Finally, the whole system is verified on a 380 V/10 kVA three-phase experimental DVR prototype.