Simultaneous Local Identification of Thévenin Equivalent Impedances in a Distribution System

Advances in grid analytics are enabling significant operation improvement by identification of Thévenin equivalent system. Thévenin impedance is particularly useful for stability analysis in systems facing influx of distributed energy resources (DERs) and control of inverters interfacing DERs. In this article, a connection point Thévenin impedance is identified by each customer, simultaneously across the feeder. First, the potential of existing power exchange of loads and DERs is explored towards this simultaneous identification and the limitation is shown based on data from a Queensland's suburban feeder consisting of overhead lines. Then, probabilistic and deterministic probing-based identification methods are proposed, drawing on the inverters’ programmability. The probabilistic methods are based on the normal and the uniform distributions. The deterministic method utilizes the Walsh codes. All proposed methods use a one-step change in the customer's current magnitude, voltage magnitude, and phase angle. Efficacy of the proposal is demonstrated through simulations on IEEE 33-bus system amended by the empirical data. Analysis of equally strong methods shows Walsh coded probing gives more accurate Thévenin estimate but potentially makes identification longer and more visible to the customers. Uniformly distributed probing offers the best balance on the preceding criteria. Practical insights into the proposal are further provided.