LCC-MMC HVDC Line Pilot Protection Based on U-Q Characteristic Curve

Hybrid high-voltage DC systems are gradually becoming the main form of DC engineering. The distributed capacitance effect of long-distance DC lines is very obvious, which leads to the fact that the existing pilot protection schemes need a long enough rectification delay to avoid false operation. This article proposes a pilot protection principle based on U-Q transient characteristics. The U-Q characteristic of the line is a regular linear spiral characteristic under normal operation and external fault (EF) condition. For internal fault (IF), the transient U-Q characteristic of the transmission lines are nonlinear. Based on this difference in characteristics, A pilot protection scheme will be developed on the basis of transient U Q characteristics. The proposed scheme is less computationally intensive and is not constrained by system parameters. The model is constructed in PSCAD/EMTDC and a large number of simulations are carried out to test the speed and stability of the proposed scheme. The simulations under different conditions show that the proposed scheme can act quickly and reliably and has good robustness to high resistance faults.