Transient Oscillation Analysis Method for DCPFC in Urban Distribution Systems based on State Space Modeling and Dynamic Partition

Flexible DC Transmission System (FDCT) plays a crucial role in facilitating the integration of large-scale renewable energy resources into power grids. The incorporation of DC Power Flow Controllers (DCPFC) into FDCT significantly enhances operational performance, owing to its superior power flow regulation capabilities compared to conventional interlinking converters. However, DCPFC controlled by proportional integral (PI) controller faces transient oscillation issues, as its optimization primarily improves the transient performance of regulatable state variables while remaining ineffective for autonomous state variables. This paper proposes a dynamic partition method, strategically decomposing DCPFC into regulatable and autonomous subsystems, which enables focused investigation of transient oscillation in DCPFC. Firstly, state space modeling and dynamic partition of DCPFC are carried out. Secondly, singular value decomposition analysis of the autonomous system is performed to characterize its transient oscillation. Thirdly, the impact of line resistance and current reference on transient oscillation in DCPFC is given. All theoretical analyses are validated through time-frequency domain simulations in MATLAB/Simulink.