基于OPF的MMC-MTDC自适应下垂控制策略

传统下垂控制无法解决模块化多电平换流器多端直流MMC-MTDC(modular multilevel converter multiterminal DC)输电系统中换流站功率裕度和系统功率协调分配的问题,为此提出一种最优潮流下自适应下垂控制策略。首先根据电压变化方向与实时裕度设计MMC自适应下垂控制器;然后分析传统下垂控制无法解决MTDC中直流线路阻抗产生电压偏差的缺陷,针对影响直流网络潮流的因素,构建约束条件以及目标函数求解潮流优化分配下垂系数;最后通过直流电压差值实时计算权衡系数来分配两种下垂曲线所占比例。在PSCAD/EMTDC中建立5端MTDC模型,分别在稳态与暂态工况下对比两种控制方式,结果表明该控制策略可以避免换流站满载、减少线路损耗实现系统功率优化分配。

Adaptive Droop Control Strategy for MMC-MTDC Based on OPF

The traditional droop control cannot solve the coordinated allocation problem of power margin for a converter station and the system power in a modular multilevel converter multi-terminal DC(MMC-MTDC) transmission sys-tem. Accordingly, an adaptive droop control strategy based on optimal power flow is proposed in this paper. First, an adaptive droop controller is designed according to the change in voltage direction and real-time margin. Then, the defect of the traditional droop control, i.e., it cannot solve the voltage deviation resulting from the DC line impedance in MTDC, is analyzed. In consideration of factors that affect the power flow in the DC network, the constraint conditions and objective function are constructed to obtain the droop coefficient of power flow optimal allocation. Finally, the proportions of two kinds of droop curves are allocated by calculating the trade-off coefficient in real-time with DC voltage deviations. A five-terminal MMC model is established in PSCAD/EMTDC, and two control methods are compared in steady-and transient-state working conditions. Results show that the proposed control strategy can avoid full load on the converter station and reduce the line loss, thus achieving optimal power allocation of the system.