A three-phase state estimation in active distribution networks

•WLS-based three-phase state estimation algorithm for active distribution networks.•Different models of three-phase transformers, lines, loads and DG units.•Simulation studies are illustrated on 13- and 322-bus test examples. This paper presents the improved Weighted Least Square (WLS) based three-phase state estimation algorithm for active distribution networks. The three-phase component models are developed for characteristic types of transformers (respecting their winding connections), lines (three and four wires), loads (voltage dependent grounded-Y, ungrounded-Y and ungrounded-Δ) and distributed generation (DG) units (synchronous generator, induction generator and three-phase (three- and four-wire) electronically-coupled based DG units). The unmonitored (or partially monitored) powers of loads and DG units are initially estimated from normalized daily load profiles, or from external inputs (historical database/weather forecast), such as wind, sun and water inflow forecasts, respectively. These measurements are introduced with lower weights (treated as the pseudo-measurements in the proposed state estimation algorithm). The results and practical aspects of the proposed methodology are demonstrated on two characteristic examples: modified IEEE 13-bus test system and 322-bus real-world distribution network.