Phase-locked oscillator control system for thyristor-controlled reactors

The thyristor-controlled reactor (TCR) is used for AC voltage control on transmission lines and industrial busbars. It has a relatively simple main circuit and its performance depends very much on its control system. The phase-locked oscillator type of control system is now universally used for HVDC convertors, and is being introduced for the TCR. The form of this control described is of the `zero-delay´ type, without control filters or other lags, and gives freedom from harmonic instability and a good combination of stability at other frequencies, with fast response. Examples of applications are described briefly