Control contributions to the universal operation of wind turbines

Abstract

The continuously growth of the energy consumption is taking the current electric system close to certain limits where the power supply reliability is seriously affected by voltage interruptions. Besides, some factors like the downturn in the economy and the drive of developing countries (i.e. China and India) have forced the companies to extend their products to weaker power systems, where the power quality has not been treated with a strong regulation yet. This Thesis is framed in the improvement of the power supply reliability through the isolated operation of Wind Turbines. The concept of Universal Operation addresses the island operation of Wind Turbines when the connection to the grid is not longer required after a voltage interruption. In constrast with other tendencies, the peculiarity resides on avoiding the use of expensive external storage devices. This concept is just proposed in the low and medium power level scenarios of on-shore Wind Turbine to face power interruptions of minutes. With the general objective of extending the island operation to cover the most of the interruption, this work approaches the main challenges of the Universal Operation from the control point of view: regulation of the island power mismatch by means of the inherent storage and dissipation capacities, transition between the island and grid-connected modes, power sharing, etc. On the other hand, an important research line of this Thesis is focused on the optimization of the system response under unbalanced conditions. The proposed control enhancements deal with the oscillating power and the distortion of control references caused by unbalanced conditions.