As shunt-connected controllers, series-connected FACTS controllers can also be divided into either impedance type or converter type. The former includes Thyristor-Switched Series Capacitor (TSSC), Thyristor-Controlled Series Capacitor (TCSC), Thyristor-Switched Series Reactor, and Thyristor-Controlled Series Reactor. The latter, based on VSI, is usually in the form of a Static Synchronous Series Compensator (SSSC). The composition and operation of different types are similar to the operation of the shunt connected peers.