Direct Torque Control of Doubly Fed Induction Generators Connected to Grids with Unbalanced Voltage

Abstract

This article describes a direct control method for doubly fed induction generators that are connected to networks with unbalanced grid voltage. As the proposed method employs direct feedback of the torque and reactive power of the doubly fed induction generators in the control of power generation, it requires less computational power than methods using cascaded control loops. In the proposed algorithm, the feedback and control variables are separated into symmetrical components; they are independently controlled to i) realize the minimization of the undesirable stator power ripples or torque ripples arising from the unbalanced voltages in the three-phase supply and ii) regulate the torque and reactive power independently at variable speeds. The proposed method is validated by computer simulation and experimental results.

Keywords:

• doubly fed induction generators
• variable-speed generation
• unbalanced operation
• negative sequence

Acknowledgment

The authors would like to thank the studentship support from the Department of Electrical Engineering of The Hong Kong Polytechnic University.