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A DC Line Protection Scheme Based on Current Traveling Wave for MMC-MTDC Grids

The multi-terminal high voltage direct current (MTDC) grids make it possible to connect large scale clean energy to the grid. However, the lack of effective methods minimizing the DC line faults impact limits the development of MTDC grids in some extent. This paper first analyses the propagation characteristics of the fault traveling wave in DC line. Then, the expressions of the initial line-mode fault current traveling wave (ILCTW) under typical internal and external fault are obtained. Moreover, a fast nonunit protection scheme is proposed based on the filtered fault transient current traveling wave. A modular multilevel converter (MMC)-based four-terminal high voltage direct current (HVDC) grid is established in PSCAD/MTDC, and extensive simulation results are conducted to validate that the protection scheme can not only identify the internal fault accurately and rapidly, but is also effective in detecting different fault locations and large fault resistance.