Analysis and experiments of improved 2L VSC with DC fault ride-through capability

Two-level voltage-source converter (2L VSC) is the key equipment in micro-grid. However, power electronic devices in VSC are vulnerable to surge current under DC faults. Up to now, existing methods to deal with DC faults cannot balance fault current elimination performance and investment. To solve this problem, by adding a unit with a thyristor anti-parallel with a diode in the up- or down-bridge-arm of each phase, an improved 2L VSC with DC fault ride-through capability is proposed in this paper. The topology and working principle of the improved VSC are presented. The parameter design method of the proposed 2L VSC is discussed in terms of current and voltage requirements during DC fault ride-through. The simulation and experiments are carried out for verification, and the results are consistent with the theoretical analysis, showing that the fault current inside the proposed VSC could be eliminated within 1ms, and there is no overcurrent or overvoltage issues. In the end, comparisons between the proposed method and the existing methods are presented to prove the superiority of the proposed 2L VSC.