A framework for sizing of grid-forming batteries for primary frequency support in small isolated power systems with high penetration of PV

This paper proposes a framework to size battery energy storage systems (BESS) for primary frequency support in isolated power systems with high penetration of renewable energy sources (RES). The proposed method consists of two steps: (a) selection of representative scenarios using clustering techniques, instead of analyzing a large set of scenarios, and (b) sizing of the BESS in order to achieve frequency stability requirements in the set of representative scenarios. Frequency stability is assessed by means of time-domain simulation by using using a system frequency response (SFR) model. Rather than providing a single size of the BESS, curves of percentage of hours with the frequency outside security limits versus the size of the battery are provided. This aims to supporting making the final decision of sizing the BESS, which in practice should be determined by a trade-off between security, investment cost of the BESS and operating cost of the system. Simulations in a realistic small isolated power system with high penetration of PV generation are carried out in Matlab %2B Simulink, illustrating the effectiveness of the proposed framework. Finally, sensitivity analysis of how different ways of operating the system could affect the size of the BESS is also carried out, such as considering or not reserve on PV generators or considering or not under-frequency load-shedding (UFLS) schemes.