Stability Region Estimation and Systme Strength Evaluation of MMC-HVDC Connected to a Weak AC Grid

Analyzing the stability of MMC-HVDC under large disturbances helps us to understand and improve the system’s operation under startup, load dynamics, and fault conditions. This paper analyzes the stability region of MMC-HVDC connected to a weak AC grid after large disturbances on the AC side. A direct method for estimating the stability domain and a system dynamic strength evaluation index based on critical energy are proposed, which achieves quantitative evaluation of the dynamic strength of MMC-HVDC connected to weak AC grid and compensates for the shortcomings of static indicators. The proposed approach and analysis results were verified by an MMC/AC simulation model built in PSCAD/EMTDC.