【摘要】 针对整流侧采用LCC结构，逆变侧采用高压阀组LCC换流器与低压阀组MMC换流器相串联结构的混合级联直流输电系统。为了解决当一个MMC受端交流系统发生故障时，多个MMC及其受端交流系统发生潮流转移，可能引起正常运行的受端交流系统过负荷，并导致距离后备保护误动作，进而可能发展为连锁故障这一问题，提出一种自适应距离Ⅲ段保护原理。首先，分析了在受端级联型结构中，逆变侧多个MMC共同承担功率传输任务；其次，研究了系统正常运行时受端出口测量阻抗与MMC功率指令值之间的关系，然后提出一种适用于并联MMC的距离Ⅲ段保护原理。该原理可以随MMC输出功率指令值的变化而自适应调节距离Ⅲ段整定值，并且可以主动识别故障与过负荷，防止距离Ⅲ段保护因过负荷而误动作；最后，基于仿真平台搭建混合级联直流输电系统模型，验证了所提保护原理的有效性。更多还原

【Abstract】 Hybrid cascaded high voltage direct current transmission system was adopted with LCC structure on the rectifier side and series connection structure of high voltage valve group LCC converter and low voltage valve group MMC converter on the inverter side. In order to solve the problem of multiple MMCs and their receiving AC systems experiencing power flow transfer when a fault occurs in one MMC receiving AC system, which may cause overload of the normally operating receiving AC system and lead to misoperation of the distance backup protection, which may further develop into a chain malfunction, an adaptive distance Ⅲ protection principle was proposed. Firstly, the power transmission task was jointly undertaken by multiple MMCs on the inverter side in a cascaded structure at the receiving end. Then, the relationship between the measured impedance at the receiving end outlet and the MMCs power command value during normal system operation was studied. Afterwards, a distance Ⅲ protection principle suitable for parallel MMCs was proposed. This principle can adaptively adjust the setting value of distance Ⅲ according to the change of MMC output power command value, and can actively identify faults and overloads to prevent misoperation of distance Ⅲ protection due to overload. Finally, a hybrid cascaded HVDC transmission system model was built based on a simulation platform and verify effectiveness of the proposed protection principle.更多还原