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METHOD FOR POWERING UP MMC CONVERTERS AND AN HVDC LINK IN ORDER TO START-UP ELECTRIC POWER PLANTS
WO21209664
Researchers from the Universitat Jaume I and the Universitat Politècnica de València have developed a technological procedure that allows an offshore wind power plant to be black started, that is, to start up the plant without the support of an external power grid. Until now, this service, which is essential for restoring an electrical system in the event of a shutdown, has only been provided by conventional thermal or hydroelectric power stations. The invention relates to a method for supplying an external supply network (8) through a DC link (4), the external supply network (8) being connected to the DC link (4) by a DC/AC converter (3) and the power plant (1) being connected to the DC link (4) by means of an AC/DC converter (2), allowing start-up without an external power transmission network, comprising: increasing the voltage in the AC network (7); charging the AC/DC converter (2) and DC link (4); reducing the voltage in the AC network (7); synchronising the AC/DC converter (2) and the AC network (7); increasing the voltage of the DC/AC converter (3); charging the DC/AC converter to a nominal voltage; and starting-up the DC/AC converter (3).
Unlike the methods used or proposed to date, the procedure outlined here makes it possible to: - Energise the MMC converters and the HVDC link using only power provided by the plant itself, i.e. without the need for an external power source (blackstart). - Restore a power grid by an offshore wind farm or other type of plant connected by means of HVDC links. - Charge the capacitors of the MMC converters without any auxiliary equipment (rectifiers, thyristors, auxiliary DC sources, pre-charge resistors, diesel generators, etc.). - Control the charging currents at all times without the need for pre-charge resistors. - Charge the capacitors of the MMC converters which are HVDC-linked at constant current to the voltages of the capacitors under control. Sectors for commercial pplications: - The procedure is applicable to any power plant (wind or otherwise) that connects to the AC grid through an HVDC link using MMC converters in one of its converter stations or directly to HVDC grids.