Analysis of Grid-Forming IIDG’s Transient- and Steady-State Fault Model

Abstract

Due to the inherent characteristics of inverterinterfaced distributed generators (IIDG), their fault responses are different from those of conventional synchronous generators. Investigating fault responses of IIDGs and establishing their fault models will benefit the fault calculation and protection scheme design for microgrids. This paper focuses on grid-forming IIDGs (GFGs) and hierarchically analyzes their fault characteristics under symmetrical and asymmetrical faults. A generic fault model of GFG, which covers both the transient-and steady-state, is proposed. Impacts of the transfer function of controllers, current limiting module, and fluctuation of DC-link voltage on GFG’s transient-and steady-state fault responses are respectively investigated. The influence of GFG’s topology is also considered, and both three-phase three-wire and three-phase four-wire GFGs are covered in the fault analysis. Model parameters calculation methods for all kinds of fault conditions are presente. It is found that the fault type, the fault severity, and the response speed of the DC power regulator all have significant impacts on GFG’s fault responses. The fault analysis and fault model are verified by simulation results in MATLAB /Simulink.