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Small Signal Model of VSC-HVDC Considering the Impact of Time Delay

The time delay of the control system is an important factor leading to the high-frequency resonance in VSC-HVDC. In this paper, a two-level VSC-HVDC electromagnetic transient (EMT) model is established for the research, and time delay links are added to the control system of the two-level VSC-HVDC EMT model to activate the high frequency resonance phenomenon. Then, the small signal model of the VSC-HVDC system considering the time delay is developed by adopting the Pade approximation to represent the time delay links. The dynamic response under power step change of the small signal model is compared with those of EMT, the correctness of the model is verified. Finally, the influence of time delay on the small signal stability of the VSC-HVDC system is analyzed by eigenvalue analysis.