A Single End Backup Protection Scheme for MMC-HVDC Line Using Reactor Power at High Frequency

One among the many challenges in the operation of the HVDC system is the fast identification and isolation of the DC faults in the line. Similar to the AC system, proper protection of HVDC requires both primary and backup protection. A single-end communication-free backup protection scheme for the MMC HVDC system has been proposed in the paper. Smoothing reactors placed on either side of the line serve as the boundary for the transmission line. The protection scheme utilizes the reactor power at a high frequency to identify the fault. Discrete Fourier Transform (DFT) is used to extract high-frequency current during fault which is further used to determine reactor power. The proposed algorithm initiates action on the detection of uncleared faults by primary protection. The method is proficient in differentiating between external and internal faults. Furthermore, the scheme neither requires data synchronization nor requires high sampling frequency. Thus, increasing the reliability of the protection system. A typical two-bus MMC HVDC system is designed in MATLAB to verify the performance of the scheme.