Estimation of Voltage Unbalance at the Reference Bus in Distribution System State Estimation

Distribution System State Estimation provides an accurate model to assess the real-time condition of the three-phase unbalanced distribution networks. However, the entire estimation is prone to the voltage unbalance at the reference bus (RB), typically assumed with balanced voltage phase angles at the substation. This work enhances the voltage unbalance estimation for traditional three-phase state estimators and demonstrates that many practical situations enable proper estimation of the RB voltage unbalance without the need for special substation models or Phasor Measurement Units (PMUs). A three-phase numerical observability analysis, based on the H ∆ matrix, assesses the feasibility of estimating the voltage phase angles at the RB through the coupling elements among different phases. Simulation results on the IEEE test feeders demonstrate the feasibility and the effects of a proper voltage unbalance estimation, showing an overall increased accuracy for the entire network.