向无源端网络供电的多端MMC-HVDC控制策略研究

中压直流配电网具有良好的发展前景，本文以贵州电网柔性直流配电示范工程为对象，研究向无源网络供电的多端MMC-HVDC控制策略。首先分析了无源网络的供电特性以及MMC-HVDC向无源网络供电的可行性，研究了基于混合子模块的MMC数学模型，然后搭建了一个向无源网络供电的四端柔性直流输电系统仿真模型并为其设计了相应的双环控制策略。常规的无源端控制器采用定交流电压和频率控制，介绍了虚拟同步发电机的控制原理，结合项目需求，文中同时还设计了采用虚拟同步发电机控制的无源端控制器。最后，利用PSCAD对搭建的多端柔性直流输电系统模型及其无源端控制器的设计进行了仿真验证，仿真结果表明两种控制策略都能实现向无源网络的灵活供电，但基于虚拟同步发电机控制的无源端控制器能减少负荷波动时的频率波动。

Research on Multi-terminal MMC-HVDC Control Strategy for Powering Passive Networks

The medium voltage DC distribution network has a good development prospect. In this paper, the multi-terminal MMC-HVDC control strategy for power supply to passive networks is studied for the flexible DC power distribution demonstration project of Guizhou Power Grid. Firstly, the power supply characteristics of the passive network and the feasibility of power supply from the MMC-HVDC to the passive network are analyzed. The MMC mathematical model based on hybrid submodules is studied. Then a simulation model of the four-terminal flexible DC transmission system for powering the passive network is built and the corresponding double loop control strategy is designed. Conventional passive-end controllers use constant AC voltage and frequency control. The control principle of virtual synchronous generator is introduced. Combined with project requirements, the paper also designs a passive-end controller that uses virtual synchronous generator control. Finally, PSCAD is used to simulate the multi-terminal flexible DC transmission system model and its passive-end controller design. The simulation results show that the two control strategies can realize flexible power supply to the passive network, however, passive end controllers based on virtual synchronous generator control can reduce frequency fluctuations during load fluctuations.