To identify weak areas accurately and fast, within which ac system faults will adversely induce concurrent commutation failure among inverters, is of great significance to the safe and stable operation of power grid. Considering that the related study is mainly performed with simulation tools and its application can not cover the entire ac systems, a rapid identification method of weak areas in power grid based on commutation failure analysis in multi-infeed HVDC systems was put forward. With the ac line fa...