Internal Fault Detection and Isolation for Paralleled Voltage Source Converters

This paper presented a systematic analysis of the protection methods for paralleled VSCs system especially with common DC bus from four types of internal faults, including short or open circuit faults of single switch or diode. The potential damages of such faults relating to circulating current were first explained. After that internal faults detection and isolation schemes based on de-saturation and circulating currents were shown in detail. The study confirmed that if the system can be shut down for a short period, SCRs can be used to recovery the system from internal faults with one redundant VSC. Otherwise, the topology with isolated DC buses for each VSC or other fast DC current breakers should be used. Finally, experimental results using a 2+1 VSCs system validated the analysis and protection schemes.