State estimation for distribution systems with zero-injection constraints

In this paper, a new fast decoupled state estimator with equality constraints is proposed for the three-phase distribution systems. The Lagrange multipliers were utilized to deal with the zero injections. The proposed method is based on the equivalent-current-measurement and rectangular coordinates. The method uses a compact constant-symmetric Gain matrix which can be decoupled into two 'identical' sub-Gain matrices. The update and factorization of the gain matrix needs to be done only once. Tests have shown that the proposed low-storage method is efficient, accurate and robust in solving the unbalanced three-phase distribution systems. Keywords - State Estimation, Distribution Automation System, Zero Injection, Equality Constraint, Observability Analysis.