Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three-phase stator voltages cause a number of problems, such as overcurrent, unbalanced currents, reactive power pulsations, and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance, induction wind generators are switched out of the network. This can further weaken the grid. In doubly fed induction generators (DFIGs), control of the rotor currents allows for adjustable speed operation and reactive power control. This paper presents a DFIG control strategy that enhances the standard speed and reactive power control with controllers that can compensate for the problems caused by an unbalanced grid by balancing the stator currents and eliminating torque and reactive power pulsations.
Bibliographical noteFunding Information:
Manuscript received July 12, 2006; revised October 17, 2006. This work was supported in part by the National Science Foundation under Grant ECS-0245550 and in part by the Fulbright Program and the Norwegian University of Science and Technology. Paper no. TEC-00238-2006.
- AC generators
- Induction motors
- Power system dynamic stability
- Reactive power control
- Torque control
- Variable speed drives
- Wind energy