Power flow models of unified power flow controllers in various operation modes

A comprehensive UPFC steady-state model for power flow analysis will be proposed. With considering resistances of coupling transformers and converter losses, this new model can implement any desired control actions, including any combinations of active/reactive power control and voltage magnitude control, within the same framework. The d-q axis decomposition of UPFC control variables will be considered as UPFC unknown variables in conventional Newton-Raphson power flow solvers. An IEEE 118 test system embedded with 2 UPFCs is studied to validate our new model. Performance comparisons between our new model and the voltage-source-based (VSB) model are also performed. Simulation results demonstrate that the quadratic convergence of the Newton-Raphson algorithm is still maintained in our model even under different operation modes. Influence of coupling transformers and converter loss are also studied in detail.