A novel doubly-fed induction wind generator control scheme for reactive power control and torque pulsation compensation under unbalanced grid voltage

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, including overheating and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance (for example 6%), induction wind generators are switched out of the network. In doubly-fed induction generators, control of rotor currents allows for adjustable speed operation and reactive power control. In addition, it is possible to control the rotor currents to correct for the problems caused by unbalanced stator voltages. This paper presents a novel controller design for a doubly-fed induction generator that provides adjustable speed and reactive power control while greatly reducing torque pulsations.