Specifying angular reference for three-phase distribution system state estimators

In power system state estimation, similar to power flow, an angular reference is required in order to solve the problem providing the most likely state of the system. For single-phase state estimators (SEs), the usual practice is to specify the angular reference at the substation bus, usually at 0 degrees. This study discusses and presents how to specify the angular reference for three-phase distribution systems SEs (DSSEs). As the main contributions, two different approaches for specifying the reference are presented and assessed. Additionally, the more general proposed approach is improved and a robust version, based on a reduced number of state variables, is presented. The proposed approaches are applied to three SEs commonly recommended for distribution systems. The results show that the approach based on a reduced number of state variables is a proper and general solution to specify the reference angles for three-phase DSSEs.