Double-ended fast protection system of LCC-VSC-MTDC independent on boundary component

Hybrid DC transmission technology is used in new energy transmission due to its advantages of large capacity and long distance. Line-commutated converter-Voltage source converter-Multi-terminal DC (LCC-VSC-MTDC) is one of the important development directions of the future power grid. But the Multi-terminal high voltage direct current system has the problems of inconsistent boundary characteristics, inconsistent control, and fault response characteristics, which puts forward higher requirements on the protection scheme. A protection scheme based on the undistorted factor is proposed to ensure the safe operation of the system. First, the inconsistent line mode voltage attenuation characteristics of different fault locations are used to construct undistorted factor. Subsequently, the undistorted factor is used to identify fault. The advantage of this scheme is that it is not affected by boundary elements, control strategies, and distributed capacitance. Finally, the LCC-VSC-MTDC model verifies the correctness and superiority of the proposed protection scheme.