Modeling For Thyristor Controlled Series Capacitor

The application of Flexible AC Transmission System (FACTS) is quite promising in power systems. It becomes one of the research emphases in recent years. The Thyristor Controlled Series Capacitor (TCSC) is an important member of FACTS family. It possesses not only simple configuration and cheaper cost; but also the superexcellent capability, such as enhancing the transmission faculty of lines and improving system stability. Thereby, it is of great value to investigate the theory and operation of TCSC. Some issues about TCSC are studied in this dissertation. The primary contents are as follows:TCSC impedance model at steady state has been constituted, and its impedance characteristic has been analyzed. If the ratio of inductance to capacitance is larger than 1/9, TCSC has one steady state resonance pint, and the operating region of TCSC is divided into two parts depending on the delay angle: one is inductive operating region, the other is capacitive operating region. If the ratio of inductance to capacitance is smaller than 1/9, the steady state resonance point will be more than one. And the harmonic voltage across TCSC has been derived through dynamic equation, and the harmonic characteristic about TCSC has been studied. The harmonic voltage will be very large when the two conditions are satisfied: one is the ratio of capacitance toinductance is 32, 52, 72......; the other is the product between the square root ofcapacitance to inductance's ratio and the half of conduction angle is odd times of π/2. In addition, an algorithm to calculate the subsynchronous voltage across TCSC by a subsynchronous current has been developed, and the theory of mitigating Subsynchronous Resonance (SSR) about TCSC has been analyzed. The results of simulation show that TCSC has positive effect on mitigating SSR.On the basis of characteristics analyzed above, the control model of TCSC has been developed using the relationship between the delay angle and the reactor current. In the capacitive impedance operating range, the gain of the proposed model changes as the delay angle varies from maximum delay angle to minimum delay angle. Thecapacitive impedance operating range may be divided into two sub ranges depending on the delay angle: the response is monotonous in one sub range and damped oscillatory in the other sub range. The simulation results show that outputs of the model are almost identical with the cotTesponding system responses for the same inputs.