分析了基于箝位双子模块的MMC-HVDC正常自励起动过程，将起动过程分为两个基本阶段，即不控充电阶段和可控充电阶段。利用电路原理方法化简了不控充电阶段的系统等值电路，推导了最大充电电流与限流电阻之间的关系，并指出在该阶段由于二极管箝位作用电容无法充电至额定状态。设计了三种可控充电方法以对电容继续充电获取足够的能量，其中方法一利用直流电压控制器和调制均衡策略，而方法二和方法三则通过改变充电回路中等效内电势和等效电容实现电容完全充电。为充分发挥系统故障穿越能力，设计了直流侧暂时性和永久性故障后的系统自动再起动控制时序。在PSCAD/EMTDC中搭建两端有源的MMC-HVDC系统，仿真结果表明所提出的起动控制策略效果良好。%The self-start procedure of the modular multilevel converter (MMC) based HVDC system which adopts clamp double submodules (CDSM) is analyzed. This procedure is divided into two basic stages, i.e., uncontrolled charging stage and controlled charging stage. The equivalent circuit in uncontrolled stage is simplified according to theorem of electrical circuit and the relationship between the maximum charging current and current-limit resistor is derived. Furthermore, it is indicated that all capacitors could not be fully charged to the rated value, owing to clamping functionality of diodes. In order to continuously charge these capacitors, three controlled charging methods are proposed, enabling that each achieves enough stored energy. Among them, method No. 1 takes advantage of the DC voltage controller, which uses the modulation and balancing strategy; method No. 2 and method No. 3 are realized by changing the charging loop’s equivalent electric potential and equivalent capacitance. In fully implementing the faults ride-through ability, auto-restart control sequences under temporary and permanent DC faults are designed. Finally, a digital model of the MMC-HVDC system with two active terminals is realized in the PSCAD/EMTDC software. The simulation results show that the proposed control strategies have satisfactory performance. This work is supported by the National High Technology Research and Development Program of China (863 Program) (No. 2012AA050205).
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