Analytical Fault Modeling of Droop-Controlled IIDG and its Cluster

Fault modeling of inverter-interfaced distributed generators (IIDGs) is the basis of power system fault calculation and protection scheme design. Due to its inherent properties and flexible control strategy, analyzing the transient-state fault responses of droop-controlled IIDG is difficult, and an analytical fault model has yet to be proposed. This work establishes a controlled voltage source-based fault equivalent model of droop-controlled IIDG in synchronous reference frame to address this research gap. The impacts of droop characteristics, virtual impedance, double-closed-loop controller, current limiting, and low-voltage-ride-through requirements are all considered, and the obtained model can cover both the transient- and steady-state fault responses. An IIDG clustering method based on the equivalent admittance matrix of the grid is also proposed, which lays the groundwork for model reduction. A corresponding model aggregation method is then provided. With this, the complexity of fault analysis for peer-to-peer controlled distributed power systems can be significantly reduced. The scheme proposed in this paper is verified by simulation experiments in PSCAD/EMTDC software.