Grid Impedance Measurement for Distribution Networks With Three-phase Untransposed Model Parameters

Electrical power supply systems worldwide are undergoing a major transformation due to the penetration of Distributed Generations (DGs) based on Renewable Energy Sources (RESs). These units are mainly installed at distribution network levels, causing significant changes in systems’ characteristics, including the dynamic response behavior down to the sub-transient period. At a Point of Common Coupling (PCC), the dynamic response can be represented by using an equivalent grid impedance. Knowing this impedance parameter gives an opportunity to enhance the dynamic control performance of connected DGs and thus contribute to the overall system stability.However, in three-phase distribution networks, the supply conditions are often asymmetrical, and the networks at this level are essentially untransposed. Considering these conditions, the three-phase equivalent impedances should therefore be independently parameterized for each individual phase, including independent coupling elements (untransposed model). Doing so results in a higher model complexity than a conventional single-phase equivalent circuit and makes parameter estimation a challenging task. In this paper, a novel method to estimate all of these independent impedance parameters is presented. It is based on Least Squares (LS) fitting for non-linear systems. The algorithm’s effectiveness was verified by an actual hardware experimental setup with a down-scaled circuit model.