Universal wind turbine working in grid-connected and island operating modes

In the future power system based on active distribution grid, allowing some portion to be disconnected, the concept of universal wind turbine systems may arise. This concept covers both grid-connected and island operations. This may happen if the voltage goes outside the range recommended by the standards. In such conditions, an island is constituted where the universal wind turbine is capable to manage the local voltage and frequency assuring the continuous supply to local loads. In this paper, a control loop based on droop and voltage controllers disposed in cascade is employed in both operation modes. Droop control offers power load sharing between the distributed generation sources connected in parallel in the island. The voltage controller is designed to provide smooth transitions between modes and power quality. A synchronization system is also introduced for assuring safe reconnections with the main utility. Simulation and experimental results are presented to verify the performance of the complete system.