A practical method to assess the potential of energy storage systems to mitigate voltage sags

Abstract Energy storage systems (ESS) have attracted significant interest and investments. Despite this interest, industry and utility engineers have not widely considered this technology as a potential solution to improve the power quality supplied for critical loads. This is in part because of the high cost and in part because of the high complexity to assess this type of solution. This paper, therefore, proposes a practical approach to determine whether shunt/series ESS can mitigate voltage sags assuming the availability of system information, as short-circuit impedance and historical voltage sags, and load information. This is done by analyzing a chart obtained analytically, which can be easily constructed based on simple information from the system and load, without resorting to computer simulations. By inspecting this chart, engineers can quickly determine not only the ESS capacity required to mitigate specific sags, but also which is the optimum power factor for operation. Sensitivity studies are provided to reveal key factors affecting ESS capability to mitigate voltage sags and to validate the proposed approach. Results outline that the requirements of shunt ESS depend on the system short-circuit level and X/R ratio, whereas requirements of series ESS depend on the load demand and power factor.