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Publisher Summary This chapter presents the basic operation principles of flexible ac transmission system (FACTS) devices. Self-commutated switches are adequate for use in converters where turn-off capability is necessary. The switching characteristics of thyristors are appropriate for using in line-commutated converters, such as in conventional high-voltage direct current (HVDC) transmission systems with a current source in the dc side. Thyristor-based FACTS devices use line or natural commutation together with large energy storage elements. On the other hand, devices based on self-commutating switches, such as GTOs, IGCTs, or IGBTs, use gate-controlled commutation. The VSC-based HVDC technology is a suitable solution for dc transmission systems through underground or undersea dc cables. The VSC-HVDC system can also be seen as an extension of the IPFC concept, keeping in mind that the main idea is to transfer active power from one bus to another through a dc link. The VSC-based dc transmission has an exactly dual configuration of the conventional HVDC transmission system, which is based on the thyristor-controlled CSC. |
