Transient energy storage systems for fast frequency response: Power-train considerations

Renewable energy sources generate power intermittently, which poses challenges in meeting power demand. The use of transient energy storage systems (TESSs) has proven to be an effective solution to this issue. Hence, it is crucial to understand the impact of TESS components design on sizing the power-train system during fast frequency response. While power-train systems have been extensively discussed, the impact of dc-link voltage on the TESS power-* train and associated power electronics specification requirements has not been evaluated. This study uses a sodium-nickel chloride (NaNiCl₂) battery-based TESS to assess different power-train options. Specifically, the research investigates the impact of variations in dc-link voltage due to battery regulation and state-of-charge (SoC) on the design of the TESS-connected power-train system, since these will be the major contributions to the power-train system performance envelope. This paper also compares the performance of TESS power-train systems with four different schemes. The power-train models include the detailed modelling of energy sources, power electronic converters, and transformers based on published parameters and testing data. Additionally, the study proposes a performance index to evaluate the superiority of the four schemes in terms of voltage and current rating, efficiency and battery size.