Offline Reconfigurability Based Substation Converter Sizing for Hybrid AC-DC Distribution Links

Hybrid ac-dc distribution systems with multiple parallel operating ac and dc links are being developed to maximize system capacity during (n-1) contingencies. This paper shows that offline reconfigurability between such ac and dc links post-fault clearance allows an additional design flexibility of reducing the required substation converter rating to maintain the same required capacity by maximizing the utilization of healthy infrastructure. The associated variation of system capacity with power rating and number of substation converters is determined for different types of component faults. It is discussed that while converter downsizing is possible, as a consequence the parallel ac-dc link system is forced to operate at a sub-optimal efficiency during normal conditions. Using case studies, the economics of this trade-off is quantified for determining the optimal de-rating factor for varying grid voltage, link length, and conductor area.