Delta-Type Serial Shunt Soft Normally-Open Points With Wide Power Flow Regulation Range in Distributed Network

The soft normally-open points (SNOP) have been proposed in response to challenges raised from renewable energy in the grid. Main scheme adopted in SNOP demonstration projects are back-to-back modular multilevel converter (BTB-MMC), which is costly in multifeeder scenarios. The series shunt multiport SNOP (S
²
-MSNOP) can reduce the cost and volume. But its energy balance faces difficulties under operating conditions where reactive power provided by the cascaded H-bridge of the device is too small, thus impeding its practical implementation. Accordingly, this article presents a novel delta-type serial shunt soft-normally open points (D-S
³
NOP) scheme, offering a practical multifeeder interconnection solution. D-S
³
NOP employs an internal circulating current mechanism to achieve energy balance among its constituent parts, thereby expanding the power flow regulation range. First, the topology feature and working principle of D-S
³
NOP are presented. Subsequently, a suitable control strategy is designed. Comparison of power flow regulation area and cost among S
²
-MSNOP, D-S
³
NOP, and BTB-MMC is made after. Finally, a simulation model and an experimental prototype are constructed for verifying the effectiveness of D-S
³
NOP.