Fast Linear State Estimation for Unbalanced Distribution Systems Using Hybrid Measurements

Distribution system state estimation (DSSE) is traditionally solved iteratively using unsynchronized measurements provided by the SCADA system and/or smart meters. This article puts forward a decoupled linear state estimation (SE) method for unbalanced distribution systems. Contrary to conventional methods, the proposed linear DSSE (LDSSE) method can function with purely unsynchronized or hybrid synchronized/unsynchronized measurements. In the case of purely unsynchronized measurements, the voltage phase angles of the reference bus are acquired through local measurements. In the first stage, the proposed LDSSE method estimates the voltage phase angles in terms of network parameters and available measurements. These are referred to as pseudo-synchronized voltage phase angles, which establish a basis for deriving pseudo-synchronized voltage/current phasors. In the second stage, a set of linear equations are derived for each phase separately. Solving these equations results in estimates for voltage phasors. The linearity and decoupled nature of the proposed LDSSE method significantly reduces the computation time without impacting the accuracy of estimates. The superiority of the proposed LDSSE method over the existing methods is verified using extensive simulations conducted on several test feeders, delivering results 20 times faster than the nonlinear DSSE (NDSSE) on the 8500-bus test feeder.