Comparison of DC fault handling strategies for hybrid HVDC system

摘要

The hybrid high voltage direct current (Hybrid HVDC) system based on line commutated converter (LCC) and modular multilevel converter (MMC) is a feasible solution for long distance bulk power transmission. In order to handle the dc-side short-circuit fault, two kinds of methods can be adopted. The first one is to replace half-bridge sub-modules (HBSMs) with full-bridge SMs or clamp-double SMs which have the capability of dc fault clearance, and the second one is to arrange diodes at the dc port of MMC. In this paper, detailed processes of the dc fault solutions are described and discussed. The typical testing system is built in PSCAD/EMTDC, and the system performances under different strategies are compared. In addition, the non-block dc fault handling strategy based on full-bridge SMs is analyzed and tested. The results show that this kind of solution is not suitable for the bipolar HVDC system and the fault current cannot be blocked thoroughly.