Mechanism analysis of using thyristor controlled serious compensation to mitigate Subsynchronous Resonance

The small signal method is adopted to formulate the subsynchronous frequency equivalent impedance of thyristor controlled series compensation (TCSC), by adding a tiny subsynchronous frequency component to the fundamental current source. Based on the TCSC´s characteristic of equivalent zero resistance, the equivalent fundamental frequency resistance of TCSC is derived, which is utilized to analyze the numerical relationship between subsynchronous frequency equivalent resistance and fundamental frequency equivalent resistance. And then the mechanism of mitigating subsynchronous resonance (SSR) with TCSC is analyzed and the results show that TCSC can mitigate SSR upon the comprehensive effects of its resistance and reactance characteristics, while the reactance one plays a dominant role. According to the mechanism analysis, how to choose TCSC´s conduction angle to mitigate SSR is proposed. Results of time domain simulation on the IEEE First Benchmark system show the mechanism analysis is reasonable and feasible.