模块化多电平换流器型直流输电系统的启停控制

Start/Stop Control of Modular Multilevel Converter Based HVDC Transmission System

介绍了模块化多电平换流器型直流输电系统(modularmultilevel converter based high voltage direct current system,MMC-HVDC)的起停控制策略。启动分为不控启动阶段和可控启动阶段,对不控启动阶段模块化多电平换流器(modularmultilevel converter,MMC)的等效电路进行数学建模,得出了限流电阻与最大充电电流之间的数学关系,为限流电阻的选取提供了理论基础。停机分为能量反馈阶段和放电阶段,能量反馈阶段将MMC各子模块电容存储的能量部分反馈回电网,充分利用了MMC子模块储能的优势,提高了能量的利用率。放电阶段,通过一定的触发方式,逐步将能量耗散掉,该方法有效地降低了放电电阻的功率、阻值和耐压水平。最后,对建立的两端有源网络的MMC-HVDC系统进行了数字仿真,仿真结果验证了该启停控制策略的有效性。

The start/stop control strategy for modular multilevel converter （MMC） based HVDC transmission system is proposed. The start-up is divided into uncontrollable stage and controllable stage, and the model of equivalent circuit of modular multilevel converter （MMC） during uncontrollable stage is built and the mathematical relation between current-limiting resistance and the maximum charging current is obtained to provide theoretical foundation for the selection of the value of current-limiting resistance. The stop stage is divided into energy-feedback step and capacitor-discharge step. In the energy-feedback step, the energy stored in the capacitor of each sub-module of MMC is partially fed back to power grid to give full play to the superiority of energy storage of MMC sub-modules, thus the energy utilization is improved; in the capacitor-discharge step, by means of connecting discharging capacitor at DC side and adopting a certain trigger-strategy, the residual energy in the capacitor of each sub-module of MMC is gradually dissipated, thus the rated power, resistance value and withstand voltage level of discharging resistor can be effectively reduced. Finally, a digital simulation system of MMC-HVDC based two terminal active network is established and the effectiveness of the proposed start/stop strategy is verified by simulation results.