A Protection Scheme for Multi-Terminal HVDC Grids Using Local Transient Voltage Characteristics

This paper proposes a novel single-end protection scheme to satisfy the operating speed, sensitivity, and selectivity required in the protection of HVDC grids based on the modular multilevel converter (MMC). In this regard, the fault voltage characteristics are analyzed at the early stage of internal and external faults to implement the protection scheme. It is shown that the existence of smoothing inductors at both sides of the MMC-HVDC transmission line causes the attenuation of the high-frequency components of the fault traveling wave head under external faults. Whereas, the generated fault traveling wave under internal faults contains plenty of high-frequency features. Putting this into perspective, an improved complementary ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) is used to extract the highest frequency oscillations of initial fault voltage. Afterward, the high-frequency energy of the initial fault voltage is calculated by adopting the Hilbert transform (HT). As a result, the high-frequency energy calculated via ICEEMDAN-HT forms the fault identification criterion. To assess the proposed protection scheme, a four-terminal half-bridge MMC-HVDC system is modeled in the PSCAD environment. According to simulation results, the proposed protection method is capable of detecting remote faults up to 300 Ω transition resistance within 1.1 ms only by acquiring local voltage data. Furthermore, the proposed method exhibits reliable performance under external faults and noise interferences.