模块化多电平柔性直流输电系统的启动策略

分析了阀侧接地与不接地两种模块化多电平柔性直流输电系统(MMC-HVDC)拓扑结构的充电过程,根据其不同的充电回路分析了直流电压以及桥臂子模块电压和的充电稳态值。提出了调制波预跟踪策略,即在解锁前实现调制波与阀侧电压的跟踪,为减少解锁时带来的冲击电流做好准备。针对定直流电压站与定功率站,分析了解锁时冲击电流的来源,设计了相应的解锁策略,通过主动充电方式以提高子模块在充电阶段的电容电压,有效地减少了在解锁时带来的冲击电流。最后,在PSCAD上搭建了两端MMC-HVDC模型,仿真结果验证了所述策略的有效性。

A Startup Strategy for Modular Multilevel Converter Based HVDC System

The charging procedure of a modular multilevel converter (MMC) based HVDC (MMC-HVDC) system with valve-side grounded and ungrounded is analyzed. According to their different charging circuits, the steady DC voltage and the total voltage of the sub-module belonging to one arm is calculated. A strategy for modulated wave pre-tracking is proposed, i.e., realizing tracking of the modulated wave and valve-side voltage prior to deblocking as a preparation for minimizing the inrush current. The mechanism of the inrush current is analyzed, and the corresponding deblocking strategy is designed for the DC voltage control station and the constant power control station. By the active charging mode, the voltage of sub-module is increased, which can remarkably reduce the inrush current brought about during deblocking. A digital model for the MMC-HVDC system with two terminals is finally realized by the PSCAD software, the simulation results showing that the proposed control strategies have satisfactory performance.