With the large-scale of renewable energy resources connected to the grid

strict grid codes are formulated to ensure grid safety. Of the grid codes

the low voltage ride through (LVRT) regulation requires that the new energy generation system be capable of LVRT so as to be able to provide the grid with support during grid fault. This paper proposes a fast voltage detecting method suitable for the new energy grid-connected system. The method consists of the traditional three-phase phase locked loop and two voltage detecting modules that can quickly detect the grid voltage sag in a short time according to the maximum voltage point and zero crossing point. And accurate detection of module makes it possible to obtain the precise voltage sag range in the case of a complex power grid

which provides a powerful support for grid-connected system to accurately and quickly respond to the grid demand. The validity and accuracy of the proposed method is verified by simulation and experimental results. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2011AA05A301).