Harmonic state estimation for distribution systems based on synchrophasors

This paper describes a harmonic state estimation technique for unbalanced three-phase distribution systems using Phasor Measurement Units (PMUs), considering the presence of non-linear loads connected to the system. In the proposed approach, the measured phasor values are harmonic voltages and branch currents in those buses continuously monitored by PMUs. For the non-monitored buses, their loads are represented by a set of bounded inequality constraints in a proposed constrained optimization problem. The state variables to be estimated by the methodology are harmonic branch currents in rectangular coordinates. The method is capable of estimating harmonic components in distribution feeders and power quality indicators such as THD (Total Harmonic Distortion). A modified IEEE 33-bus test system is used to validate the proposed methodology.