Instantaneous Phase-Locked Loop for performance improvement of power system with STATCOM under single-line to ground fault

Voltage-Sourced Converter (VSC) based STATCOM is used for voltage regulation in transmission and distribution systems. STATCOMs often tripped and shut down during power system faults such as Single-Line to Ground (SLG) fault, mainly due to over current protection when the voltage support is needed the most. For “angle-controlled” STATCOM, there are generally two possible control methods to improve the STATCOM performance. One is implementing separate conventional PLLs (Phase-Locked Loop) and multiple controllers for positive and negative sequences, and another is implementing single PLL, which is able to provide information of both positive and negative sequences, with a single controller. In this paper, the required PLL signal to improve the STATCOM performance under power system fault will be introduced without the need for sequence extraction control blocks. The proposed synchronization method is called Instantaneous PLL (or IPLL). As a result, over-currents (and trips) in the VSC during faults is prevented, and the STATCOM provides voltage support and required reactive power. The detailed analysis of the proposed IPLL signal effect on a 100 MVA angle-controlled STATCOM is presented.