With the advancement of DC transmission,both LCC-HVDC and VSC-HVDC systems will inevitably inte-grate into the same regional grid.This integration has led to the formation of hybrid multi-infeed DC transmission systems in some areas of China.The layered access method for LCC at the receiving end can enhance the voltage support capabil-ity of these hybrid systems.However,in UHVDC transmission projects employing hierarchical connection modes at the receiving end,a commutation failure in the valve group of one layer may induce a commutation failure in the valve group of a non-faulted layer due to the coupling relationship between layers.To address this issue,a coordinated control strategy is proposed,which leverages MMC fast reactive power support and LCC non-fault layer over-trigger angle compensation.This strategy provides reactive power support to the LCC nonfault layer at the receiving end,depending on the levels of AC voltage drop.By considering the four-quadrant operation capability of the receiving-end MMC,reactive power sup-port is supplied solely by the MMC when the required reactive power support falls within its four-quadrant operation range.The MMC reactive power support command value is determined by the voltage drop value of the common cou-pling bus.When the required reactive power support exceeds the MMC's four-quadrant operation range,the MMC reactive power support command value is set to the maximum reactive power value at the four-quadrant operation active power threshold,and the over-trigger angle compensation control for the LCC non-fault layer is simultaneously activated.Extensive simulation tests demonstrate that the proposed coordinated control strategy effectively suppresses simultaneous commutation failures in both high and low-end inverters.
关键词
混合多馈入/LCC分层接入/MMC无功支援/换相失败/协调控制
Key words
hybrid multi-infeed/LCC hierarchical connection mode/MMC reactive support/commutation failure/coor-dinated control
维普
万方数据