In Nanjing western power grid

the series side of unified power flow controller(UPFC)device is installed on the 220 kV Tiebei-Xiaozhuang double-circuit transmission line

while the parallel side of UPFC is connected to the adjacent 35 kV Yanziji bus. The novel topology structure imposes higher demand for system-level modeling of UPFC: not only double-circuit line can be controlled by series converter

but also the impact of low voltage bus and neighboring lines should be analyzed. A UPFC five-terminal power injection model considering novel topology structure is proposed

in which series part can control the power flow of double-circuit line respectively and parallel node can be flexibly connected. Based on the power injection method

the mathematical expressions of this model are derived. The power flow calculation principle in PSASP and implementation method of this model are discussed. Based on this model

the double-circuit control strategy of UPFC is established. Finally

simulation is realized in Nanjing UPFC project both under normal steady state and N-1 contingency occurred on the line of UPFC series side. The control results reveal the validity

flexibility and comprehensiveness of this proposed model.