With the rapid development of voltage source converter based multi-terminal direct current(VSC-MTDC)technology

the existing state estimation algorithms need to be improved to support the application of dispatching systems. According to the structural features of a hybrid AC/DC with VSC-MTDC power system

a fast decoupling algorithm of state estimation for AC/DC system with VSC is proposed. The model of VSC-based DC system is extended on the basis of conventional AC state estimation. In this modified decoupling algorithm

the AC/DC current measurement and states are classified into active and reactive ones according to the steady-state physical characteristics of this unified AC/DC unit. A few minor factors in Jacobian matrix are neglected while the coupling relation between hybrid systems is preserved. The matrix elements are set with appropriate constant values to realize the fast decoupling estimation calculation of AC/DC system. Two cases are adopted for the validation of current algorithm

including a modified IEEE 14-bus and IEEE 118-bus AC/DC system with three-terminal VSC-HVDC. It is confirmed that the proposed algorithm is practical and effective with good convergence performance and estimation accuracy.