New Images of Map for Distribution System Security Region

2D image is the most common way to visualize the distribution system security region (DSSR), and all possible images are summarized into the DSSR map. This paper discovers several new images that do not exist in the existing map and reveals their mechanism. First, the 2D image and existing map of DSSR are briefly introduced. Second, five new images are presented. Their characteristic is that the diagonal line boundary is divided into two parallel segments, and there are convex and concave at the same time. Third, the mechanism of new images is revealed: If the distribution network has multiple load transfer paths after N-1, its DSSR is a backup region formed by the union of multiple convex sub-regions, which is a simple concave region. The bulge on the region cape forms a ridge; The connecting part between two region capes forms a valley, leading to the sag of DSSR. If the power-lost load of the distribution network can also be distributed and transferred to multiple paths, its DSSR is a complex concave region formed by covering the distribution region on the backup region. The distribution region compensates for the sag of the backup region and translates its ridges and valleys. When the complex concave region is observed in 2D viewpoint, it is found that the translated ridges and valleys cause the diagonal line boundary to be segmented, and new convex and concave are also formed. Then, the new images are formed. Finally, IEEE RBTS-Bus4 expanded cases are used to verify the mechanism. This work is an important supplement to the complete DSSR map, which enables researchers to understand the shape characteristics and mechanism of DSSR much more closely and thoroughly.