Study on the grid supporting effects for GFM energy storage system in distribution networks under grid faults

The grid-forming energy storage system (GFM-ESS) plays a critical role in enhancing the reliability of power-electronic-based power systems by providing voltage support to the grid. In this paper, the grid-supporting function of GFM-ESS on different buses was studied under the different types of short-circuit faults. First, the mathematic models for control strategies of the grid-following (GFL) converter and grid-forming (GFM) converter as well as their duality relationships were studied and illustrated. Secondly, the response of the GFM inner control loop to different short-circuit fault types is analyzed using symmetrical component decomposition. An optimization algorithm is then proposed to improve the voltage-supporting capabilities of the GFM-ESS and to identify the optimal placement of energy storage systems (ESSs) within the distribution network. The relationship between the support capabilities of the GFM-ESS under different short-circuit faults was derived and represented. Finally, the results of case studies were presented, analyzed, and discussed. The optimal location for the GFM ESS in the distribution network can be determined with the proposed mathematic models and the method for the optimal placement.