STATCOM Operation Strategy under Power System Faults

The STATCOM (synchronous static compensator) operation can be adversely affected due to voltage source converter (VSC) over-currents and trips, during power system faults when its dynamic VAR support functionality is most required strict requirements of STATCOM losses and total system loss penalty preclude the use of PWM (pulse-width modulation) for VSC based STATCOM applications. This constraint of implementing VSC without PWM functionality, results in over- currents and trips of the STATCOM during and after system faults. In this paper, we propose an "emergency PWM" strategy to prevent over-currents (and trips) in the VSC during and after system faults, with slightly different B-H characteristics (due to manufacturing tolerances) for series connected transformers. Simulation results are presented for a 48-pulse VSC based plusmn100 MVAr STATCOM connected to a 2-bus power system. Simulation results validate the "emergency PWM" strategy to prevent VSC over-currents and to supply reactive power under all power system faults - single-line to ground, line-line and three-phase system faults.