Magnification of Transients at the Voltage Dips Starting and its Impacts on DFIG-based Wind Power Plants

Abstract

This work shows that transients at voltage dips starting impact fault-ride-through of wind turbines. For fault-ride-through studies and manufacturer tests, it is therefore important to consider these transients and their magnification from the transmission grid through the collection grid to the wind turbines. Fault-ride-through studies in the literature do not consider the transient as a dip characteristic and employ overly-simplified models that do not consider the collection grid. This work studies in detail how the dip-starting transient changes during the propagation from the transmission grid to the wind-turbine terminals. It is also studied how this transient impacts the dynamic behaviour of the wind turbines in terms of the overvoltage on the DC-link of wind turbines based on doubly-fed induction generator (DFIG). The analyses are performed for several realistic configurations of a wind-power plant, all based on an existing installation. The results show that the magnitude of the transient is magnified when the resonant frequency of the collection grid is similar to the oscillation frequency of the transient. Moreover, the higher magnitude of the transient results in a significantly higher overvoltage on the DC-link. This work is the first in power quality literature to cover the collection and internal grid as a factor for the magnification of dip-staring transient. The main finding of this work is that the detailed models of the collection grid and the transients at the voltage dips starting must be not neglected when accessing the LVRT of wind turbines. It is strongly recommended to consider the details of the dip-starting transients and of the collection grid to assess the impact of dips on the wind turbines properly.