Comparative Study of AC and DC Connection Schemes for Photovoltaic Integration in Yangshan Island

The 120MWp PV project in Yangshan of Shengsi needs to connect to the Zhoushan power grid. Currently, two connection schemes, AC connection and DC connection, are proposed for the power grid structure of Yangshan. This paper compares the characteristics of broadband oscillation in these two schemes under three conditions: grid-connected operation, islanded operation, and grid-connected to islanded transition, from both theoretical and simulation aspects. The analysis results indicate that the MMC converter station exhibits negatively resistive and inductive characteristics, while the PV farm shows negatively resistive capacitive characteristics in specific frequency ranges. When the AC connection scheme is adopted, resonance instability phenomena will occur, while there is no oscillation risk in the DC connection scheme. Therefore, it is recommended to adopt the DC connection scheme for the Yangshan PV system.