一种适用于交流线路改造成直流的扩展式双极直流输电结构

An Extended Bipole HVDC Structure With Three Wires for Conversion of AC Lines to HVDC

为提升现有交流输电线路的输送能力,提出了一种将交流线路改造成直流的拓扑结构,即扩展式双极直流输电结构。详细介绍了扩展式双极直流的运行原理以及相关辅助设备在过渡阶段的动作时序。同时,对电流调节控制器的运行范围进行了研究,并指出由全桥子模块级联构成的全桥模块化多电平换流器能够用作电流调节控制器。为使得系统能够稳定运行,给出了12脉动晶闸管换流器和全桥模块化多电平换流器的控制策略,尤其对直流电流调节和电容电压平衡控制进行了分析和设计。通过PSCAD/EMTDC时域仿真,验证了所提出的扩展式双极直流输电系统及其控制策略的可行性和有效性,表明了系统能够在过渡阶段跟随指令变化,同时还具有较好的暂态响应能力。

In order to increase the transmission capacity of the existing ac lines, a topology for conversion of AC lines to HVDC was proposed, which was named the extended bipole high voltage direct current（extended bipole HVDC）. The operation principle and action sequence of auxiliary equipment of this structure in the transition process were presented in detail. Meanwhile, the operating range of the current regulation controller, which could be realized by full-bridge modular multilevel converter（F-MMC） based on cascaded full bridge sub-modules, was introduced. Control strategies for the 12-pulses thyristor converter and F-MMC were designed, especially for DC current regulation and capacitor voltage balancing. Results from the time-domain simulation in PSCAD/EMTDC verify the feasibility and effectiveness of the proposed extended bipole HVDC and its control strategies, and present that the system could change with command values in the transition process and response well in the transient state.