混合直流输电系统常会出现不同类型的故障，传统控制方法的故障处理时间过长，对此，研究基于换相换流器（LCC）和模块化多电平换流器（MMC）的混合直流输电系统优化控制方法。根据系统结构特征绘制拓扑结构图，建立LCC数学模型和MMC数学模型；利用三角星型接法和星型接法控制整流侧直流电压，实现整流侧LCC的优化控制；利用电压源逆变器（VSC）双闭环控制器对逆变侧MMC进行优化控制；通过从系统直流侧直接充电，减少中间电流转接过程，利用MMC数学模型计算电压调制波，实现均衡电压，控制系统稳定运行。仿真结果表明，应用所提方法可以在5 s内控制整流站交流故障，面对直流线路单极故障问题，所提方法在5 s内快速反应，将LCC和MMC的电流控制在稳定的区间内，同时对三组电流的控制均有较好的效果，能够实现混合直流输电系统优化控制，快速解决输电系统故障。

Hybrid DC transmission system often has different types of faults, and the traditional control method takes too long to deal with such faults, so the optimization control method of hybrid DC transmission system based on line-commutated converter (LCC) and modular multilevel converter (MMC) is studied. The topological diagram is drawn according to the system structure characteristics, and the LCC and MMC mathematical models are established. The rectifier side DC voltage is controlled by the triangle and star connection to realize the optimal control. The inverter side MMC is optimized by the voltage-sourced converter (VSC) double-closed-loop controller. By directly charging from the system DC side, the intermediate current transfer process is reduced, and the voltage modulation wave is calculated by the MMC mathematical model to achieve balanced voltage and stable operation of the control system. Simulation results show that the proposed method can control the AC fault of the rectifier station within 5 s. For the DC line unipole fault, the proposed method can quickly respond within 5 s, and the currents of LCC and MMC can be controlled in a stable range. All three currents are effectively controlled, proving that the optimal control of the hybrid DC transmission system is realized and the transmission system faults can be handled quickly.