Fault protection scheme of flexible DC grid based on transient power instantaneous energy difference

The DC line protection is the key to the stable operation of the multi-terminal flexible DC grid, and the current limiting reactor (CLR) as the boundary condition provides great convenience for the design of the flexible DC grid fault protection scheme. Using the boundary condition characteristics of the CLR, the paper proposes a fault protection method for flexible DC grid based on transient power instantaneous energy (IE) difference. First, the equivalent circuit of the DC line of the flexible DC grid under different faults is established. On this basis, the conclusion that the transient power amplitude of internal fault is much larger than the external is deduced from the full-power in the time-domain. The Teager energy operator is used to calculate the maximum IE of the transient power, and then the internal and external faults are identified. Secondly, according to the difference of the transient power amplitude of the CLR on the fault pole and the healthy pole, the ratio of the IE of the positive and negative CLR transient power is used to construct the fault pole selection. The scheme is simple and easy to implement, and does not need to consider the synchronization problem of data at both sides. Finally, the simulation results show that the proposed method can better satisfy the speediness and selectivity requirements of DC grid protection. The scheme can accurately detect faults under different working conditions, and has strong fault resistances capability.