**6. Conclusions**

The method of identifying the sensitive and vulnerable transmission lines based on improved power flow exceeding risk index is proposed, and it can apply to AC/DC hybrid systems, weak power grids, and other power systems. And the proposed method can quickly identify the sensitive and vulnerable transmission lines in the shortest path and simplify the method of calculating the branch disconnection coefficient. The method would not have to repeatedly calculate the impedance matrix of the line disconnection and connection.

The optimal energy storage configuration can be obtained by the multi-objective optimal mathematical model, including minimizing the annual investment cost of BESS and maximizing the sum of the improved power flow exceeding the risk index of the sensitive and vulnerable transmission lines. The BESS for sensitive and fragile lines can quickly eliminate the impact of DC power transfer on AC lines, and the BESS can also suppress power fluctuations and greatly improve the transient stability operation ability of the power grid.

The proposed energy storage configuration method does not only improve the transient stability of the power grid. Simultaneously, during the stability power grid, the configured energy storage can actively supports voltage, frequency, etc. The configuration method proposed in this article enriches the application scenarios of energy storage. The safe and stable operation ability of the system is greatly improved.

In the future, we will study the HIL implementation of the proposed system along with the proposed optimal allocation method. After this, the fault disturbance, power system planning BESS resources will be explored through the robust optimization-based model.

**Author Contributions:** Conceptualization, L.J. and T.Z.; investigation, Y.T., L.J., B.Z., X.S. and Y.X.; resources, B.Z., X.S. and Y.X.; data curation, L.J. and T.Z.; writing—original draft preparation, L.J. and T.Z.; writing—review and editing, L.J., T.Z. and S.M.; supervision, T.Z. and S.M.; project administration, Y.T.; funding acquisition, Y.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Technology Project of State Grid Sichuan Electric Power Company (No. B1199721009N).

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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