  The increasing distributed and renewable energy resources and controllable
devices in distribution systems make fast distribution system state estimation
(DSSE) crucial in system monitoring and control. We consider a large
multi-phase distribution system and formulate DSSE as a weighted least squares
(WLS) problem. We divide the large distribution system into smaller areas of
subtree structure, and by jointly exploring the linearized power flow model and
the network topology, we propose a gradient-based multi-area algorithm to
exactly and efficiently solve the WLS problem. The proposed algorithm enables
distributed and parallel computation of the state estimation problem without
compromising any performance. Numerical results on a 4,521-node test feeder
show that the designed algorithm features fast convergence and accurate
estimation results. Comparison with traditional Gauss-Newton method shows that
the proposed method has much better performance in distribution systems with a
limited amount of reliable measurement. The real-time implementation of the
algorithm tracks time-varying system states with high accuracy.
