基于最优功率分配的多端直流网络改进下垂控制策略

An Improved Droop Control Strategy for Multi-Terminal DC Grids Based on Optimal Active Power Allocation

由于多端直流系统各输电通道距离不一致以及直流线路本身电阻较大,导致远距离、大容量直流输电系统的铜耗较大。为了实现整个系统铜耗最小的站间协调控制,构建未考虑本地负荷与考虑本地负荷时直流电压下垂系数的计算方法,提出一种改进的直流电压下垂控制策略。引入换流站可调容量大小,使得各换流站"量力而行"地参与下垂控制功率调整。利用PSCAD/EMTDC建立该四端直流系统的详细模型,仿真验证了正常运行及故障工况下该系统的运行特性。结果表明,所提出的控制方法可有效减少直流系统铜耗,有效改善交流侧故障引起的直流侧功率振荡,实现紧急功率支援。

Due to various distances of transmission lines as well as higher resistance for the voltage source converter multi-terminal direct current（ VSC-MTDC） system,the copper loss for the whole system,especially the long distance and large capacity high voltage direct current（ HVDC） system,is larger. In order to realize the coordinated control between different stations achieving the minimum copper loss for the HVDC system, the calculation method of the voltage droop coefficient for the VSC-MTDC system without / with local load is built,and a DC voltage droop control strategy is proposed. By introducing the remaining capacity space,each converter station can participate in the power compensation according to its remaining capacity. The PSCAD / EMTDC is used to build the detailed models of the VSC-MTDC system. The simulation verifies operating characteristics in normal /fault conditions. Simulation results show that the proposed control can reduce the copper loss effectively,restrain the DC power oscillation caused by AC fault,and realize the emergency power support.