A novel protection scheme of wind farm access to flexible DC power grid based on high frequency measurement inductance difference

• A protection scheme based on high-frequency measurement inductance difference is proposed. • Frequency domain transient characteristics of MTDC system can be accurately described. • Establish a model considering switching of sub-modules and connection mode of bipolar lines. • Accurate discrimination based on inductance difference of inner and outer area is realized. • This method can accurately identify the high resistance fault at the end of the line. A protection scheme for the DC transmission line of the four-terminal flexible DC grid connected to the doubly-fed wind farm based on the high-frequency measurement inductance difference is proposed. Firstly, combined with the structure of MMC flexible DC converter, considering the switching of MMC converter sub-module, the high frequency model of MMC flexible DC converter is constructed. On this basis, combined with the DC side connection mode and system topology of the four-terminal MMC-HVDC grid connected to the doubly-fed wind farm, the high-frequency equivalent network of the four-terminal MMC-HVDC grid connected to the doubly-fed wind farm is constructed, and the high-frequency measured inductance difference measured by the DC transmission line protection is calculated. The difference between the measured high-frequency measurement inductance difference area is used to construct the protection criterion. Finally, the simulation results based on RT-LAB platform verify the effectiveness and superiority of the proposed method, which can reliably identify the fault of 300 Ω underground line within 3 ms.