Time-Invariance of Distribution System Security Region Considering Flexible Resources

Distribution system security region (DSSR) has time-variant characteristics after considering flexible resources (FRs) such as energy storage systems and demand response. This paper conducts an in-depth study on the time-variance of DSSR for the first time, pointing out and addressing the problem it causes. Firstly, the existing DSSR model is introduced. The reason for the time-variance is analyzed: FR regulations are reflected in the region varying. The problem caused by the time-variance of DSSR is also analyzed, namely that the region-based method will lose its speed advantage in online security analysis. Secondly, a time-invariant DSSR model and its security analysis method are proposed, considering complete types of FRs and N-1 security. The key to addressing the time-variance of DSSR is to reflect FR regulations as the operating point movement. Finally, the proposed model and method are verified in a real case and a large case, and compared with the existing research. The comparison shows that the proposed model maintains the speed advantage of the region-based method in security analysis. This work establishes a link between time-variant DSSR and time-invariant DSSR, laying a key foundation for practical applications of DSSR in smart distribution networks.