Low Voltage Ride Through Capability Analysis of DFIG using Feed Forward Current Regulator

In recent years due to increase in the load demand a lot of emphasis is given on the use of nonconventional energy sources since fossil and atomic fuels will not last forever, and that their use contributes to environmental pollution [1]. Out of all non-conventional energy sources wind has been the fastest growing energy source over the last decade mainly due to very significant improvements in wind energy technology. Doubly fed induction generators have become the most popular type of wind turbine generators due to its excellent characteristics of control. But, these types of generators are susceptible to grid-side low voltage faults and short circuits. Power electronics converter connected on the rotor side affects badly under these conditions. When a short circuit or voltage sag occurs on the grid side, the rotor current of the generator tends to rise, which could cause damage to the rotor convert. To overcome this difficulty RSC is disconnected and crow bar is activated thus the DFIG now acts as the conventional induction machine. Grid codes suggest that these plants are required to remain connected to the grid in the event of voltage dip also they should contribute to the power system by feeding the active and reactive power safely [5]. The LVRT requirement is very important as far as grid stability is concern when a large wind farm is connected to the grid. But it is difficult to satisfy for wind plants using DFIG system since the DFIG stator is directly connected to the grid and the rotor is connected through RSC, hence complete DFIG system is much sensitive to grid disturbances [4]. This paper presents the feed forward current regulator for rotor side converter of DFIG and analyses its low voltage ride through capability. The results show that the LVRT capability of doubly fed induction generator has improved.