一种基于模块化多电平换流器的多端高压直流输电系统协调控制方法

针对基于模块化多电平换流器的多端高压直流输电系统(modular multilevel converter based multi-terminal DC,MMC-MTDC)中，交流区域的负荷波动导致该区域功率短暂不平衡，造成区域内电网频率波动的问题，首先提出一种基于虚拟同步发电机(virtual synchronous generator, VSG)的换流器控制方法。其次，针对在应用VSG策略调频过程中会改变换流站的输出功率，打破直流侧的功率平衡，而导致直流电压偏差过大，当存在线路阻抗时影响尤为明显的问题，将VSG控制与改进下垂控制相结合，形成MMCMTDC系统多站综合协调控制策略。该控制方法不仅可以为交流区域提供频率支持，还能优化直流母线上不平衡功率的分配，提高系统直流电压的稳定性。最后，基于Matlab/Simulink构建5端MMC-MTDC系统进行仿真，仿真结果验证了所提控制策略的有效性。

A Coordination Control Method for Multi-terminal High Voltage DC System Based on Modular Multilevel Converter

In modular multilevel converter-based multi-terminal DC (abbr. MMC-MTDC) transmission system the load fluctuation in AC area leads to the transitory power imbalance in this area, thus it causes the grid frequency fluctuation in this area. To cope with this problem, firstly, a virtual synchronous generator (abbr. VSG) based converter control method was proposed. Secondly, in allusion to fact that when VSG strategy was applied to frequency regulation the output power of converter station might be changed and the power balance at DC side might be broken so that too large deviation of DC voltage might occur, and such an impact would be especially evident under the existence of line impedance, for this reason, combining VSG control with improved droop control to form a comprehensive coordinated control strategy of MMC-MTDC system with multi-stations. Such a control strategy not only could provide frequency support for AC area but also could optimize the distribution of the unbalance power of DC bus to improve the stability of system DC voltage. Finally, based on Matlab/Simulink platform, a five-terminal MMC-MTDC system was constructed for the simulation. Simulation results show that the proposed control strategy is effective.