A Double-Ended Protection Principle for an LCC-VSC-MTDC System with Strong Anti-Interference Ability

The DC grid technology of multi-power supply and multi-drop-point power reception is an effective solution for large-scale renewable energy integration into the power grid. Line-commutated converter-Voltage source converter (LCC-VSC) power grids are one of the more important developmental directions of the future power grid that have occured in recent years. But the multi-terminal high voltage direct current system has the problems of inconsistent boundary characteristics, inconsistent control, and fault response characteristics, which puts higher requirements on the protection scheme. Thus, a completely new protection principle is proposed in this paper. Firstly, the fault characteristics of distributed capacitance current are analyzed. The reactive power calculated by the distribution parameters of different frequencies is different. Subsequently, the fault characteristics of DC reactive power are analyzed, and a DC reactive power extraction algorithm is proposed. The polarity of the multi-band DC reactive power is used to construct the protection scheme. Finally, the LCC-VSC power grid model verifies the correctness and superiority of the proposed protection scheme. The proposed scheme uses DC reactive power instead of fault current to solve the long delay problem caused by distributed capacitance. Compared with the prior art, the proposed solution is not affected by distributed capacitance and has a stronger anti-interference ability (600 + 10 dB + 1 ms).