Quantifying the impact of inverter-based distributed energy resource modeling on calculated fault current flow in microgrids

Abstract

Microgrid fault calculations are crucially important for setting the relay protection in both modes of operation – grid-connected and islanded. To obtain accurate results for this class of analysis, distributed energy resources within the microgrid must be accurately modeled. As most of distributed energy resources within the emerging microgrids are inverter-based, their precise models are of a significant importance. Thus, the aim of this research is to quantify the impact of the model accuracy on short circuit calculation results as well as quantifying the differences in the results obtained by models that are in a complete accordance with various Grid Code requirements, and simplified models proposed in the most commonly used International Standard for fault calculations – IEC 60909. To accomplish this goal, in this paper, various shares of inverter-based distributed energy resources’ penetration in the total generation power of a microgrid – from 50% to 90%, are thoroughly analyzed, and the differences between the results obtained by using standardized models relative to more accurate modeling that considers Grid Code requirements are presented. The obtained results suggest when the share of inverter-based resources in the total generation power of a microgrid is considerable, especially in the islanded operational mode, simplified models from the IEC 60909 standard become unreliable. According to these observations, we lay out cases in which the simplified and standardized models for inverter-based distributed energy resources are reliable to use. Additionally, we provide recommendations on improvement of the standardized models in critical cases of microgrids with high penetration of these resources, that operate in the islanded mode.