Analysis of synchronous oscillation of MMC-HVDC in offshore wind farm

Abstract

Due to the special meteorological conditions of offshore wind power generation and the large wind turbines used, offshore doubly-fed wind turbines have larger shafting elastic coefficients than onshore doubly-fed wind turbines. When the offshore wind farm is connected to the grid through MMC-HVDC, two kinds of sub-synchronous oscillations are caused. One is the natural torsional vibration of the wind turbine shaft system, and the other is the sub-synchronous oscillation caused by the interaction between the wind turbine and the devices in the MMC-HVDC converter control system. In view of the above problems, the MMC-HVDC grid connection model of the offshore doubly-fed wind farm is established. The eigenvalue analysis method and participation factor are used to identify the oscillation mode of the interaction between the wind turbine shafting torsional vibration and the converter device, as well as the corresponding strong correlation state variables. According to the correlation of the state variables obtained, the parameter suppression strategy of the CCSC controller based on MMC valve optimization is proposed. The effectiveness of the proposed suppression strategy is verified by PSCAD/EMTDC electromagnetic transient simulation software.