New chaotic phenomena occurring during voltage sags in small wind turbine systems based on back-to-back converters

This paper deals with a small wind turbine system (WTS) constituted by a permanent magnet synchronous generator (PMSG) connected to the grid via a back-to-back converter. The Low Voltage Ride through (LVRT) requirements for the WTS are described and the nonlinear dynamics of a grid-side converter is analyzed in the presence of voltage sags. The study shows that new chaotic phenomena are generated when the size of the dc-link capacitor is reduced. The reported time waveforms and state-space attractors clearly highlight that the system becomes chaotic during the voltage sag, being stable before and after the occurrence of the disturbance. Finally, the chaotic behavior is validated via the 0-1 test for chaos, thus confirming the novel phenomenon described herein.