LCC-MMC混合三端直流输电系统送端交流故障下的不间断运行协调控制策略

Coordinated control strategy for uninterrupted operation of LCC-MMC hybrid three-terminal DC transmission system under AC fault at sending end

为实现基于电网换相换流器与模块化多电平换流器(LCC-MMC)的混合三端直流输电系统送端交流故障下的直流低电压穿越,提出兼顾传输容量与响应速度的自适应电压协调控制策略及有功功率分配策略。在维持故障期间功率续传的前提下,定量分析了模块化多电平换流器(MMC)的降压值以减少传输功率的绝对值损失量,并设计MMC根据本地直流电流偏差快速减投子模块总数的降压方式;考虑到半桥型MMC的调制比约束,设计正极MMC定量吸收无功功率与负极MMC动态调整交流电压参考值的换流站极间协同控制策略;同时,为抑制从站的过电流及避免送端严重交流故障时主站的潮流反转,提出各受端换流站有功功率自适应调整的控制方式。最后通过对输电系统送端交流电压跌落不同幅度时的故障穿越效果进行仿真分析,验证了所提控制策略的有效性。

An adaptive voltage coordination control strategy and an active power allocation strategy considering both transmission capacity and response speed are proposed to realize DC low-voltage ride-through of line commutated converter-modular multilevel converter(LCC-MMC)hybrid three-terminal DC transmission system under sending end AC fault.Under the premise of maintaining the continuous power transmission during the fault,the step-down value of MMC is quantitatively analyzed to reduce the absolute value loss of transmission power,and the step-down method of MMC reducing the total number of sub-modules according to the local DC current deviation is designed.Considering the modulation ratio constraint of the half-bridge MMC,the inter-pole coordinated control strategy of the converter station is designed to quantitatively absorb the reactive power of the positive MMC and dynamically adjust the AC voltage reference value of the nega⁃tive MMC.At the same time,in order to suppress the overcurrent of the slave station and avoid the power flow reversal of the master station when the serious AC fault occurs at the sending end,a control method of active power adaptive adjustment of each receiving end converter station is proposed.Finally,the effective⁃ness of the proposed control strategy is verified by simulation analysis of the fault ride-through effect when the AC voltage at the sending end of the transmission system drops by different amplitudes.