Implementation of improved positive and negative sequences separation phase-locked loop under grid voltage sags

Detecting and locking the phase and frequency information of the voltage at point of common coupling (PCC) quickly and accurately under grid voltage sags is the premise of grid connected inverter which can ride through the fault successfully. In order to achieve grid voltage synchronize with phase and frequency information quickly under voltage sags, this paper proposed an improved Phase-Locked Loop (PLL), which is referred to as DSCαβ-PLL, based on the stationary references frame PLL. The DSCαβ-PLL can separate and track the positive-sequence voltage component of PCC in the stationary references frame. Then the proposed method is deduced in detail, and math expressions are presented next. According to above improvements, the relevant PLL simulation model is built in MATLAB/Simulink. The results show that the DSCαβ-PLL can not only be stable in different types of voltage sags, but also can track and lock the phase and frequency information of the voltage at PCC fast.