Researches on DC modulation to damp low frequency oscillation in China Southern Power Grid

For China Southern Power Grid (CSG), which has the feature of long distance power transmission with strong DC system and weak AC interconnection, low-frequency oscillation is more serious than before for specific operating situations. Therefore, using DC modulation technique to suppress inter-area low-frequency oscillation becomes a very important topic. This paper investigates low-frequency oscillation problem of CSG, and carries out system modal analyses to find out dominant inter-area oscillation modes, and then applies HVDC modulation to damping system oscillations. Gain optimization of modulation controllers of Yunnan-Guangdong DC systems is carried out to improve system damping performance. Simulations with and without modulation controllers are performed in frequency-domain and time-domain to verify the effectiveness of controllers.