A New Control Method of Cascaded Brushless Doubly Fed Induction Generators Using Direct Power Control

Cascaded brushless doubly fed induction machines have attracted much attention because of the elimination of slip rings and brushes. However, only limited works have been reported on the control strategies due to the complex machine modeling. Further developments of these kinds of machines are still under investigation, especially for wind energy applications. This paper proposes a new control strategy for cascaded brushless doubly fed induction generators (CBDFIGs) based on direct power control. The effects of voltage vectors on the output active and reactive powers are first investigated. A vector selection strategy is then proposed to achieve flexible power regulation. In addition, the behaviors of the CBDFIG under unbalanced grid voltage conditions are studied and a power compensation scheme is developed to improve the power quality. The effectiveness of the proposed control strategy is validated experimentally on a laboratory prototype.