Role of the Reference Bus in Three-Phase State Estimation

As more and more renewable energy sources are being connected to the power grid at lower voltage levels, closer monitoring of distribution networks is becoming a necessity. This is accomplished by state estimation and deployment of Distribution Management Systems (DMS). Distribution feeders are typically untransposed with unbalance loads. Thus, their modeling and analysis show significant differences compared to those for transmission networks. This paper focuses on the state estimation problem and its formulation for unbalanced distribution systems. Specifically, it is concerned about the modeling and solution of three-phase networks without a fully balanced bus to be selected as the angle reference. It is shown that best results will be obtained via the use of a virtual symmetrical bus. Validation of the proposed formulation is carried out by simulations.