A Flexible-AC-Port Solid-State Transformer-Based Enhanced Soft Normally Open Point for Interconnecting Distribution Networks

The enhanced soft normally-open point (e-SNOP) can integrate large-scale dc sources and loads into the ac grid, featuring flexible power flow control, reactive power compensation, and accommodation of new dc sources and loads. A novel e-SNOP based on the flexible-ac-port solid-state transformer (FACP-SST) is proposed in this article to alleviate the high cost and large volume of existing full-power counterparts. The adopted partial-power series-shunt structure in the FACP-SST enables the flexible active power exchange between the medium voltage (MV) side and the low-voltage dc port (LVdc) port. Decoupled active/reactive power of the connected medium-voltage ac port (MVac) feeders can also be well-regulated by the proposed device. Additionally, the MVac port expendability of the device will facilitate its advantages of the cost and volume over the conventional e-SNOPs. In this article, a 3 MVA/10 kV/750 V three-port system is constructed in MATLAB/Simulink to verify the feasibility and effectiveness of the proposed device, where the component count, die area, and total capacitance can be decreased by more than 20%. Moreover, a 2.5 kVA/240 V/60 V experimental prototype is built for the validation as well. Both simulation and experimental results prove that the FACP-SST can flexibly regulate the connected MVac feeders’ active and reactive power, and the LVdc bus active power under different operational conditions.