Saddle-node bifurcation of voltage profiles of small integrated AC/DC power systems

Switch-mode converters are used for power transfer and load control in small integrated AC/DC power systems. In this paper, the authors develop a rectifier and inverter model for power flow analysis. These converters are operated in several control modes where rectifier and inverter may be either or both controlled. Depending on the control mode, they explore and compare different bus type models for the rectifier AC terminals. The developed models are integrated into an existing second-order power flow solver, which uses the Newton-Raphson-Seydel (N-R-S) technique to locate the saddle-node bifurcation point for multiple power flow solutions. They show in this paper that, depending on the control mode, a single DC link system may exhibit more than 2 power flow solutions. Based on stability analysis of the different branches of power flow solutions the feasible and controllable system operating points are determined. These studies yield estimates of maximum (steady state) loading points of small, integrated AC/DC power systems