中文摘要：

多端柔性直流输电系统（voltage source converter multi-terminal DC system,VSC-MTDC）中各换流站的功率协调控制是至关重要的。采用传统的下垂控制时,电压功率只能按特定的斜率分配。然而,换流站功率实时变化,且根据电流方向变化不同换流站的功率裕度也不同。为了防止单个换流站功率裕量不足而影响系统功率分配,提高VSCMTDC的稳定性,文中提出一种适用于功率共享的自适应下垂控制方法。根据直流电压变化的大小及方向,实时调节下垂系数,使系统中采用下垂控制的换流站可根据自身功率分配能力灵活参与功率调节,达到功率的最优分配。同时结合定直流电压控制和所提自适应下垂控制,提出一种通用的VSC-MTDC功率协调控制策略。该方法考虑了各个换流站的动态功率裕度,无需站间通信,响应速度快,能在各个控制模式中平滑切换,对所有拓扑结构的多端系统均适用。基于PSCAD/EMTDC进行了仿真验证,同时,搭建了四端直流输电实验平台,通过仿真和实验结果验证了该方法的有效性。

英文摘要：

It is crucial for voltage source converter multi-terminal DC system（VSC-MTDC） to control the power allocation of converters. When it uses traditional droop control, the power will be shared according to specific droop coefficient. But the power may change in real-time, and each converter station has different power margin with the change of current direction. In order to avoid insufficient power margin of a converter to affect the power allocation of system and ensure a good stability for MTDC, this paper proposed an adaptive droop control method which was suitable for power sharing. According to the value and direction of DC voltage variation, it can adjust the droop coefficient of each converter to make the power of the droop control converters allocated flexibly based on their own power regulation ability to achieve optimal power sharing. Meanwhile, this paper proposed a general power coordination control strategy of VSC–MTDC by combining constant DC voltage control with adaptive droop control. This control method considers the dynamic power margin of each converter. It has fast response speed without communication, and it also can switch smoothly in each control mode. It is applicable to all multi-terminal topology structures. Simulations based on PSCAD/EMTDC were made and a four-terminal HVDC platform was built. The simulation and experimental results verify the effectiveness of the proposed methods.