虚拟同步控制在MMC-HVDC无缝切换控制的应用

摘要

针对MMC（modular multilevel converter）型VSC-HVDC（voltage source converter-high voltage direct current）在并网运行模式与孤岛运行模式相互切换过程中易于发生切换失败、冲击电流大的难题，将虚拟同步控制运用到MMC的运行模式切换中。在虚拟同步控制和MMC基本原理的基础上，提出基于虚拟同步控制的MMC-HVDC（modular multilevel converter-high voltage direct current）无缝切换控制方法。引入的虚拟同步控制无需采用专门的同步控制电路，并网前可自动与电网同步；并网后能准确跟随电网频率，实现友好并网。当电网出现故障或需要检修时，MMC仍可孤岛运行，从而实现了运行模式的无缝切换。PSCAD/EMTDC平台下的仿真结果验证了所述控制策略的可行性和有效性。%Modular multilevel converter (MMC) based voltage source converter-high voltage direct current(VSC-HVDC)systems are susceptible to large inrush currents or system failure when switching between the grid-connected and islanded operation modes. This paper introduces a virtual synchronization control to realize a seamless mode switch control method for the MMC to solve this problem. The virtual synchronization control method allows automatic synchro⁃nization with the grid without requiring any dedicated physical synchronization control units,and it follows the grid fre⁃quency accurately after being connected to the grid,realizing a friendly connection. When the grid fails or needs offline maintenance,the MMC can continue to operate in an islanded mode to realize a seamless switch between operation modes. The validity and effectiveness of the proposed control strategy is verified by simulaticns on PSCAD/EMTDC plat⁃form.