Distribution system security region with energy storage systems

The high penetration of distributed energy resources (DERs) in distribution systems calls for advanced security management techniques. Hence, this paper proposes the model of the distribution system security region with energy storage systems (DSSR-ESS). The N-1 secure operation range of distribution systems integrating ESS is characterized. Further research reveals the effect and mechanism of ESS on the DSSR properties. Firstly, the ESS in distribution systems is clarified from the perspective of security, and the security service time and real-time security service capability are defined. Secondly, the DSSR-ESS model is formulated by: 1) selecting load and distributed generation (DG) as the state variables, 2) identifying the normal operation security and N-1 security scenarios, and 3) determining the complete security constraints. Then, to solve the time-varying and nonlinear N-1 DSSR-ESS model, an algorithm is developed. The analytical expressions of the region boundaries considering voltage constraints, line loss, and ESS SOC are further obtained. Finally, a modified IEEE-RBTS-BUS4 system and its expanded 104-node test system are used to verify the proposed model. Comparing with the existing research, the proposed DSSR-ESS model considers ESS. This paper concludes that ESS bidirectionally adjusts the power flow of its upstream branches, thereby expanding the security region both in positive and negative directions. But limited by state space boundaries and security boundaries unaffected by ESS, increasing ESS capacity may not lead to DSSR-ESS expansion. Based on this discovery, a sitting strategy for ESS is developed to expand the security region, which demonstrates the practical application of DSSR-ESS in the security management of distribution systems.