Small Signal Modeling Method for VSC-MTDC System with Wind Farms

Multi-terminal high voltage direct current transmission system with wind farm connection is prone to instability, it is necessary to construct an accurate small-signal model to analyze the stability of small disturbances in the system. However, most of the existing literature does not considering wind farm models when establishing a small-signal model of an DC system with a wind farm. Accordingly, a small-signal model of the DC system including the wind farm was established based on the average model. In order to reflect the converter's power loss, the DC side equivalent bridge arm impedance will be considered, so that the dynamic response of the converter can be reflected more accurately. Moreover, a small-signal model of the full-powered wind farm is established to improve modeling efficiency, which can be constitute a single state space with wind farm side converter. The small-signal model of the four-terminal VSC-HVDC transmission system with wind farm is built in the case study, this model's step response and stability margin are compared with the PSCAD. The results indicate that the proposed small-signal model can accurately simulate the small disturbance dynamic response as well as system stability.