Fault-Tolerant Control Strategy of Single-Phase Cascaded DVR under Different Voltage Sag Depth

Dynamic voltage restorer based on cascaded H-bridge converter is the main topology of 10kV voltage sag mitigation device. Due to the use of a large number of power switching devices in the cascaded H-bridge converter, the probability of its failure increases. This paper first proposes a module operation state optimization strategy that is adjusted according to the voltage sags depth, which dynamically matches the corresponding number of submodules to work according to different voltage sags depths. On this basis, for the common open-circuit fault of single power semiconductor device, under shallow voltage sag, this paper proposes a fault-tolerant control strategy based on n+1 redundancy to bypass the faulty H-bridge module and put the spare redundant module into operation when a fault occurs. Under deep voltage sag, this paper proposes a fault-tolerant control strategy based on DC bias compensation, which makes the faulty H-bridge module seamless switch from full-bridge mode to fault-tolerant mode and output half of the rated AC voltage. This paper builds a simulation model in PLECS software to verify the feasibility and effectiveness of the proposed control method.