Static VAr compensator (STATCOM) based on single-phase chain circuit converters

Voltage-sourced converter circuits using gate turn-off (GTO) thyristors have been proposed as an alternative means of providing static VAr compensation (SVC). Such 'advanced SVCs' are classified under the nomenclature STATCOM (STATic COMpensator), The published converter circuits suitable for power system application include the classical Graetz bridge and the multilevel converter. An alternative circuit arrangement has been developed with significant advantages in terms of cost and performance; this is in the form of a number of GTO converter links connected in series to form a chain and is referred to as a chain circuit converter. The paper discusses the chain circuit converter and its application to var compensation, followed by the design and simulated performance of a 3-phase STATCOM under both steady state and transient operating conditions. The technical advantages of the chain circuit converter compared with other known arrangements of STATCOM are given. These include good harmonic performance, fast response and improved output at low voltage compared with conventional SVCs. The paper includes comments on the successful testing of two prototype chain links for both leading and lagging reactive currents up to 2000 A peak and concludes with a description of the equipment now being designed for commercial service.