A MERS type series FACTS controller for low voltage ride through of induction generators in wind farms

Low voltage ride through (LVRT) of squirrel cage induction generators in wind farms is challenging due to the large required reactive power after low voltage period. Reactive power compensation with shunt compensation can improve the LVRT capability, but requires a large rating. The alternative use of series compensation is studied. Series compensation is based on increasing the reactive power transfer from the grid, and can by this reduce the required rating of the compensator compared to shunt compensation. A series compensator called magnetic energy recovery switch (MERS) is found suitable due to large control range and good over-current capability. Simulations and experimental results demonstrate that MERS can improve the LVRT capability by injecting a series voltage during and/or after the low voltage period. Finally, evaluation of series compensation suggests cost reductions compared to shunt compensation; however, the influence on power system stability of increased reactive power transfer from the grid after low voltage period should be investigated in future works.