A simple method for analytical evaluation of LVRT in wind energy for induction generators with STATCOM or SVC

Low voltage ride through (LVRT) has emerged as a new requirement that system operators demand to wind turbines. E-ON Netz, the major German transmission operator has introduced a LVRT grid code that is receiving wide acceptance and being used as a template for similar requirements from nearly every country with wind generation. STATCOM and SVC are both good candidates for providing LVRT for wind turbines with induction generators. This paper provides a new analytical approach that allows using torque-slip curves to evaluate induction generator stability limits when having shunt reactive compensation such as STATCOM or SVC as the LVRT solution for the wind generation. This analytical approach is proposed as screening method to assess stability and/or to estimate the required rating of the reactive compensation that will ensure stability in a given system. Analytical and simulation results compared are in good agreement and both indicate the advantage in using a STATCOM since it gives an increased transient stability margin and consequently enhanced LVRT capability compared to SVC. The proposed method can easily and reliably be implemented by wind farm developers and the utilities after the validation by simulations presented in this paper.