A novel phase-control topology to improve characteristics of thyristor controlled series compensation in AC transmission systems

A novel phase-controlled series compensation scheme is presented which is dual to the thyristor controlled reactor (TCR). The proposed scheme is called a thyristor controlled capacitor (TCC). The advantages of the TCC scheme in comparison to the TCR one are as follows: the inductor is not needed in the TCC, the VA rating of the capacitor is reduced, semiconductor switches are turned on at low di/dt and turned off at zero voltage, voltage and current ratings of switches are reduced by 40%, low voltage and peak current stress allows for use of a conventional series capacitor, the control algorithm is simple and the reactance of the TCC segment can be controlled continuously, voltage harmonics are reduced by about 50%, response time is not longer than two periods of the fundamental frequency. A salient feature of the TCC scheme is its greater than TCR ability to mitigate subsynchronous resonance and power swing, and to control power flow. The disadvantages of the TCC are that GTOs must be used in place of SCRs and inductive reactance of the series segment cannot be obtained without additional series reactors. The novel TCC topology has been validated by Pspice simulations