Differential Detection of Feeder and Mesh Impedances Through a Series–Parallel Direct-Injection Soft Open Point

The grid impedance is a crucial parameter for the operation of grid-tied converters and also maintaining voltage robustness of a grid segment. However, in meshed distribution grids, it is essential to separate the feeder impedance from the overall grid impedance for an accurate assessment of power transfer capabilities and overload risks. Traditional research in power flow often treats the grid impedance as one lumped value. Beyond that, they treat this one lumped value as a known constant, overlooking its time-varying nature, which needs regular updates. Furthermore, low-voltage grids, in particular, are still only poorly monitored in real time. Thus, any practical interventions and devices, e.g., power-flow controllers and soft open points (SOP), ideally characterize their grid autonomously without the need of many distributed sensors. This article introduces a novel differential detection method to distinguish feeder impedance from total grid impedance. Through exploitation of the asymmetry of the circuit, the method can even separate the impedances of each of the transformers if there is more than one and the bare feeders. The method leverages a series–parallel direct-injection SOP circuit for reactive current injection for a precise, real-time impedance detection without extra equipment. This approach contrasts with conventional methods that typically focus on a single grid's impedance, as it can estimate the impedance of both feeders in a two-bus system. It is particularly effective in differentiating medium-voltage/low-voltage transformers and cable impedance, thus offering significant insights for both stability and power transfer analysis.