Effective monitoring and management applications on modern distribution networks require a sound network model and the knowledge of line parameters. Network line impedances are used, among other things, for state estimation and protection relay setting. Phasor Measurement Units (PMUs) give synchronized voltage and current phasor measurements, referred to a common time reference (coordinated universal time). All synchrophasor measurements can thus be temporally aligned and coordinated across the network. This feature, along with high accuracy and reporting rates, could make PMUs useful for the evaluation of network parameters. However, instrument transformer behavior strongly affects parameter estimation accuracy. In this paper, a new PMU-based iterative line parameter estimation algorithm for distribution networks, which includes in the estimation model systematic measurement errors, is presented. This method exploits the simultaneous measurements given by PMUs on different nodes and branches of the network. A complete analysis of uncertainty sources is also performed, allowing the evaluation of estimation uncertainty. Issues related to operating conditions, topology and measurement uncertainty are thoroughly discussed and referenced to a realistic model of a distribution network to show how a full network estimator is possible.

Abstract-Optimization of distributed power assets is a powerful tool that has the potential to assist utility efforts to ensure customer voltages are within pre-defined tolerances and to improve distribution system operations. While convex relaxations of Optimal Power Flow (OPF) problems have been proposed for both balanced and unbalanced networks, these approaches do not provide universal convexity guarantees and scale inefficiently as network size and the number of constraints increase. In balanced networks, a linearized model of power flow, the LinDistFlow model, has been successfully employed to solve approximate OPF problems quickly and with high degrees of accuracy. In this work, an extension of the LinDistFlow model is proposed for unbalanced distribution systems, and is subsequently used to formulate an approximate unbalanced OPF problem that uses VAR assets for voltage balancing and regulation. Simulation results on the IEEE 13 node test feeder demonstrate the ability of the unbalanced LinDistFlow model to perform voltage regulation and balance system voltages.

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The availability of accurate measurements is the prerequisite for the actual implementation of many monitoring and management applications in smart distribution networks. Phasor Measurement Units (PMUs) can provide synchronized voltage and current measurements, referred to a common time reference (usually the Coordinated Universal Time, UTC). This feature, as well as the high accuracy and reporting rate of PMUs, can be exploited for an accurate network monitoring. At the same time, the smartness of the grid can include the possibility for the measurement system to self-detect its weak points and improve its performance. In this perspective, a technique for the estimation and the compensation of systematic errors existing in the components of a PMU-based distributed measurement system suitable for monitoring three-phase distribution networks is presented. The uncertainty induced by the components of the measurement system, mainly instrument transformers and PMUs, is included in the model, along with the uncertainty affecting the values of the network line parameters. The method exploits the possible constraints introduced by the grid topology (presence of multiple lines, injected currents, etc.) to improve the accuracy of the estimation, so that a proper compensation of the estimated errors can be allowed. The validity of the approach is verified though simulations performed on a small portion of a test medium voltage distribution grid.