Location and Migration Laws of Out-of-Step Center under Multi-Frequency Oscillation Based on Voltage Phase Angle Trajectory

With the rapid development of ultra-high voltage AC/DC hybrid power grid projects and the large-scale of renewable energy integration, it puts high demand for safety and stability control of the power system. Splitting control (or islanding control) is the last resort to preserve the power system from severe blackouts. In China, the out-of-step center (i.e. the physical point of an oscillating system where the voltage is near to zero) is applied to determining the splitting locations. However, the increasingly complicated power system might oscillate in multi-frequency after large disturbance, which thus leads to dynamic migration of out-of-step centers. To address this issue, this paper derives the migration function of the out-of-step center in three equivalent machines system, based on which the migration laws are analyzed. Accordingly, the voltage angle trajectories method is employed to determine the time and location of splitting control in advance, which could guarantee the real-time implementation of islanding control. Finally, IEEE 9-bus and IEEE 39-bus test systems in PSS/E verify the effectiveness of the proposed method.