Control of VSC-based STATCOM using conventional and direct-current vector control strategies

Abstract A STATCOM is a device that can compensate reactive power and provide voltage support to an ac system. Due to the advance of power electronic technology, VSC-based IGBT or IGCT converters have been increasingly used in modern STATCOM systems. A traditional VSC-based STATCOM consists of a voltage source converter, connected to an energy storage device on one side and to the ac power system on the other, and a control system based on the conventional standard d–q vector control technology. This paper studies and compares the conventional and a direct-current vector control schemes for a VSC-based STATCOM. A limitation of the conventional control mechanism is analyzed. An optimal control strategy is developed based on a direct-current vector control design. Close-loop control evaluation demonstrates that a D-STATCOM system works well using the proposed control mechanism both within and beyond the converter linear modulation limit while the conventional standard control technique could result in over voltage and system oscillations when the converter operates beyond its linear modulation limit.