Analysis of fulfillment of LVRT requirements under unbalanced operating conditions

As the wind power penetration continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability, thus new grid codes for wind turbines are established. Most grid codes provide the LVRT curve only for the connection to the transmission system. Only few of them include the distribution system and yet the measuring of the terminal voltage do not consider unbalanced operating conditions. This paper analyses the fulfillment of LVRT requirements under unbalanced voltage conditions for doubly-fed induction generator (DFIG) wind turbines connected to the distribution system. Three different terminal voltage measurement schemes are used and analyzed. The simulations are carried out in EMTP-RV software and the results indicate that for highly imbalanced systems all three phases must be independently analyzed.