混合多馈入直流输电系统中LCC分层接入方式下后续换相失败抑制策略

Subsequent Commutation Failure Suppression Strategy for Hybrid DC Multi-infeed Transmission System in LCC Hierarchical Connection Mode

随着直流输电的发展,LCC-HVDC与VSC-HVDC将不可避免的馈入同一区域电网,我国部分地区已经形成了混合多馈入直流输电系统,而受端LCC分层接入方式能够提高混合多馈入直流输电系统的电压支撑能力。受端分层接入方式下特高压直流输电工程在本层阀组发生换相失败时,由于层间耦合关系,可能引发非故障层阀组同时发生换相失败。提出基于MMC快速无功支援与LCC非故障层超前触发角补偿的协调控制策略,根据不同交流电压跌落程度,考虑受端MMC四象限运行能力向受端LCC非故障层提供无功支援,需要的无功支援量在MMC四象限运行范围内时,仅由MMC进行无功支援,利用公共耦合母线的电压跌落值确定MMC无功支援指令值。需要的无功支援量超过MMC四象限运行范围内时,MMC无功支援指令值为四象限运行有功临界值时的无功最大值,同时启动LCC非故障层的超前触发角补偿控制。大量仿真测试表明所提协调控制策略对高低端逆变器同时发生换相失败的抑制效果明显。

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.