Vienna Rectifier-Fed Squirrel Cage Induction Generator Based Stand-Alone Wind Energy Conversion System

Back-to-back voltage source converters are normally preferred for interfacing squirrel cage induction generators (SCIG) with loads in stand-alone wind power generation applications as they allow for maximum power point tracking. However, the total converter losses tend to be very high, especially near the rated wind speed. Therefore, to reduce the power converter related losses, a Vienna rectifier is utilized as the machine-side converter in this article to interface the SCIG. Owing to the limited reactive power handling capability of the Vienna rectifier, a fixed capacitor bank is also required to provide the excitation VAR for the variable speed SCIG. In this article, a new computational method is proposed to calculate the value of this fixed capacitance based on maximizing the yearly energy output from the wind energy conversion system. A voltage sensorless vector control scheme for the Vienna rectifier-fed SCIG with the reference frame oriented along the machine terminal voltage is also proposed, which adheres to the operating limits of the Vienna rectifier and gives much better dynamic performance under load and wind speed transients compared to similar Vienna rectifier based variable speed constant frequency generating systems reported earlier in the literature.