Analysis of LCC-MMC DC Overvoltage Suppression Strategy Based on Energy Consumption Device

Hybrid HVDC transmission system takes both advantages of LCC and MMC, so it is one promising way to transmit power from large-scale renewable energy basis to city center through long distance overhead lines. However, once the AC system at the receiving end fails, the DC voltage of LCC-MMC system will rise, which will cause MMC blocking to shut down the whole system in serious cases. To solve this problem, this paper studies the adaptability of three energy dissipation devices, namely, DC chopper, discharge thyristor and controllable arrester, in suppressing the DC overvoltage of LCC-MMC. Firstly, the DC overvoltage mechanism of LCC-MMC is studied. Secondly, the working principles of three kinds of energy dissipation devices are introduced, and on this basis, the AC fault ride through strategies based on different energy dissipation devices are proposed. Finally, the effectiveness of the proposed AC fault ride through strategy at the receiving end is verified by simulations. It is found that all the three energy dissipation devices can suppress the DC overvoltage of LCC-MMC. Among them, controllable arrester takes into account the advantages of overvoltage suppression function and low cost and simple control, which is more suitable for LCC-MMC.