A Novel Backup Protection Scheme for LCC-VSC Based on Current Integral

The LCC-VSC hybrid DC transmission technology combines the advantages of the two converter technologies and has broad development prospects. The multi-terminal hybrid connection also causes its transmission line fault characteristics to be different from the traditional single DC system. Aiming at the fault characteristic analysis of LCC-VSC hybrid multi-terminal DC transmission line, it is found that there are problems of current imbalance on both sides when the transmission line fails, and the LCC branch and VSC branch have different backup protection time requirements. Traditional current differential protection has the problem of long delay due to distributed capacitive current. In view of this problem, this paper proposes a protection scheme based on current integral as a fast backup protection for traveling wave protection. The paper uses integration to eliminate current oscillation and distributed capacitance current, and solves the long delay problem of traditional current differential protection. Simulation results show that the protection principle has a strong capacity to withstand transition resistance, distributed capacitance and noise interference. It can be used as backup protection for LCC-VSC system.