模块化多电平换流器型高压直流输电系统停运控制策略研究

Shut-down Control Scheme for Modular Multilevel Converter Based HVDC

针对模块化多电平换流器型高压直流输电系统(modular multilevel converter based high-voltage direct current,MMC-HVDC),为了确保停运过程中子模块电容能够可靠且快速地放电,提出一套完整的停运控制策略。根据作用机理的不同,停运过程被划分为能量反馈阶段、可控能量耗散阶段和不可控能量耗散阶段。在能量反馈阶段中,通过提高调制比m,三次谐波注入,调节换流变压器变比及冗余子模块的投入,降低子模块电容电压,最大程度地将电容中的储存能量反馈至电网。在可控能量耗散阶段,子模块电容通过直流线路或者启动电阻进行放电,避免了放电电阻的使用。在不可控能量耗散阶段,子模块电容仅通过子模块电阻进行放电。最后,基于时域仿真软件PSCAD/EMTDC下搭建的400 MW/±200 kV数字仿真模型,验证所提出方法的有效性。

In order to discharge the sub-module （SM） capacitor rapidly and reliably in the shut-down stage, this paper proposed a complete shut-down control scheme for modular multilevel converter based high-voltage direct current （MMC-HVDC） transmission systems. According to the discharge mechanism, the shut-down control scheme is divided into three parts：, the energy feedback stage, the controllable energy dissipation stage and the uncontrollable energy dissipation stage. In the energy feedback stage, the SM capacitor voltage is reduced ＂by increasing the modulation index m, activating the third harmonic injection, adjusting the converter transformer tap and inserting the redundant SMs. Therefore, some part of the SM capacitor energy can be fed back into the connected ac systems. In the controllable energy dissipation stage, the SM capacitor energy is consumed by the dc line or by the start-up resistor. In the uncontrollable energy dissipation stage, the SM capacitor is discharged through the SM internal resistor. The case studies were performed on a two-terminal 400 MW/q-200 kV MMC-HVDC system in PSCAD/EMTDC. The time domain simulation results validate the efficiency and effectiveness of the proposed shut-down control scheme.