EMTP Simulation of a Chain-Link STATCOM

A recent addition to the STATCOM family has been obtained by connecting a number of gate turn off (GTO) thyristor converters in series on the ac side of the system. Each GTO converter forms one ldquolinkrdquo of a one-phase, full-bridge voltage-source converter (VSC) and is referred to as a ldquochain link converterrdquo (CLC). Each GTO of the CLC is switched ldquoon/offrdquo only once per cycle of the fundamental frequency by employing a sinusoidal pulse width modulation (SPWM) technique. Approximate models of a three-phase chain link STATCOM (CLS) using dq-transformation are derived to design two controllers for controlling both reactive current and ac voltage to stabilize the system voltage at the point of common coupling. A novel technique, called the rotated gate signal pattern, is used for balancing the voltages of the link dc capacitors of the VSC. The performance investigation of the CLS system when used in a radial line transmission system is carried out under steady- and transient-state operating conditions by means of the simulation package electromagnetic transients program-restructured version.