At present, there are two main HVDC technologies, one is the traditional thyristor-based phase-controlled converter's Line-Commutated Converter-HVDC (LCC-HVDC) technology; the other is a new type of voltage-based type. Lightweight High Voltage Direct Current (VSC-HVDC) technology for converters. ABB's recently introduced new version of HVDC technology is the second, achieving a doubling of transmission capacity. The choice of which method to connect offshore wind farms requires consideration of the characteristics of various wind power grid-connected modes. The AC transmission and connection mode is simple in structure and low in cost, but the transmission distance and capacity are limited. It is suitable for small-capacity, close-range offshore wind farms. The transmission and grid connection mode of LCC-HVDC is not limited by the transmission distance. The frequency of the wind farm can vary widely, but the cost of the converter station is relatively high. It is generally used for grid connection of extra-large offshore wind farms. VSC-HVDC has the most advantages in transmission and grid connection. It is very suitable for the grid connection of offshore wind farms and onshore power grids. However, due to the development level of high-power IGBTs, the maximum transmission capacity of VSC-HVDC transmission systems can only reach a few. One hundred megawatts, and the cost of the converter station is relatively high, so it is more suitable for grid connection of medium and large offshore wind farms. At present, the capacity of offshore wind farms is not too large, so the construction of offshore wind farms using traditional HVDC has not yet been completed. The practical engineering of VSC-based light-duty direct current transmission for the commercial operation of wind farms is: the Swedish Gotland project is used for on-grid wind farm integration; the Danish Tjaereborg project is used for offshore wind farm integration. . The smooth operation of these two projects and the benefits they obtained provide an application premise and feasibility verification for the use of flexible DC transmission in wind farms in China. Wind farm engineering using VSC-HVDC grid-connected Planar Non Tactile Membrane Switch
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At present, the offshore grid wind turbines are generally connected to the form of AC Var and Static Var Compensator (SVC), but for large offshore wind farms with a rated capacity of several hundred megawatts, the AC grid connection method must be The grid is kept in sync and the AC cable transmission capacity is limited, while the DC grid connection can operate asynchronously with the grid. Therefore, for long-distance, high-capacity transmission, high-voltage DC (HVDC) mode has advantages over high-voltage (HVAC) mode.
September 08, 2022