A Fast and Sensitive Current Differential Protection for MMC-HVDC Lines

This article proposes a fast and sensitive current differential protection (CDP) for modular multilevel converter based high voltage direct current lines. This method utilizes the fully distributed and frequency dependent (FD) line model to compensate for the influence of FD parameters, thus achieving high sensitivity. The improved curve fitting scheme in the FD line model is provided to enable the formulation of the differential current. Then, a fast time domain convolution scheme is specially designed to achieve the capability of the real-time calculation with the FD line model, and therefore guarantee the high response speed. A comparative analysis between the proposed CDP and the existing Bergeron based CDP is utilized to demonstrate the superior sensitivity and faster response speed of the proposed method. Moreover, the proposed method only requires a relatively low sampling rate and can complete internal fault detection within 3 ms after the fault occurs. Hardware-in-the-loop experiments using real time digital simulator are also conducted to verify the proposed method.