Continuation power flow is an important tool for assessing power system voltage stability. A continuation power flow calculation method for three-phase distribution networks is proposed for the unbalanced three-phase lines and loads existing in distribution networks with distributed generators (DGs). Composed of the tangent predictor and the Newton corrector

the proposed method uses local geometric parameterization technique for the characteristics of the PV curves of three-phase unbalanced systems. And a double-switching logic is proposed for handling the operation constraints of DGs modeled as PV and PQ nodes. A scheme for identifying the type of bifurcation is also given. Simulation results on an IEEE 33-bus distribution system show that the proposed method is effective in tracing the PV curves of three-phase distribution systems and calculating the voltage stability critical point as well as identifying the type of bifurcation. This work is supported by National Natural Science Foundation of China (No. 51077042)

National High Technology Research and Development Program of China (863 Program) (No. 2012AA050207) and Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP) of China (No. 20120094110008).