A Joint Sequential State Estimation Algorithm for VSC-MTDC Systems Using Virtual Connections

This paper proposes a joint sequential state estimation (JSSE) algorithm for power system planning and operation containing voltage source converter-based multi-terminal direct current (VSC-MTDC) networks. The conventional sequential SE method estimates the decoupled AC and DC grids separately, and the interface data at the point of common couplings (PCCs) are treated as constant injections. The connecting relationships between AC and DC grids are neglected or not fully calculated, leading to low accuracy and convergence speed. To address these challenges, the proposed algorithm considers the data and connections of interface and DC lines by using virtual connections to extend the decoupled AC grids. Both the PCCs and DC lines are equivalently modeled as virtual AC buses and branches, and subsequently integrated into AC estimation. The joint algorithm not only keeps the decoupling feature of conventional sequential SE methods, but also enhances the integrity of SE problems for better accuracy and convergence speed. Case studies on a modified IEEE 5-bus and the RTS-96 bus systems verify the feasibility and efficiency of the proposed JSEE method.