STATCOM control with Instantaneous Phase-locked Loop for performance improvement under single-line to ground fault

The STATCOM (Synchronous Static Compensator) based on VSC (Voltage Source Converter) is used for voltage regulation in transmission and distribution systems. The STATCOM can rapidly generate or absorb dynamic reactive power during system faults for voltage regulation. Strict requirements of STATCOM loss and total system loss penalty preclude the use of PWM (Pulse-Width Modulation) for STATCOM applications. The commonly- implemented PLL (Phase-locked Loop) in the system, which is based on positive-sequence bus voltage, can not response to dynamical changing of negative-sequence bus voltage due to system faults. These constraints result in over-currents and trips of the STATCOM during system faults. In this paper, we propose and develop an “Instantaneous PLL” to prevent over-currents (and trips) in the VSC during single-line to ground system faults, and to ensure that the STATCOM supplies required reactive power.