Modular LLC Resonant-based Soft Open Points for Smart Distribution Networks: Design and Field Validation

This paper proposes a novel industrial design of soft open point (SOP) with various control modes for smart operation in hybrid AC/DC distribution networks (DNs). Core innovations include: (i) a full-bridge LLC resonant-based SOP with bi-directional energy conversion capability and power quality enhancement; (ii) modular design to improve the flexibility and expandability in different scenarios; (iii) quick maintenance or replacement of power modules to maximize system operation continuity; (iv) communication data bus design to monitor and control each power module. In field validation, a 500 kW SOP that consists of 25 modules interconnects two real-world low-voltage substations, establishing a small-scale hybrid AC/DC DN. The electrical stress of the components, phase balancing test, and protection test are examined to ensure the reliability of the SOP device. Power flow results and adjustable control modes are presented to validate the stable operation of smart hybrid AC/DC DNs.