A Multiport AC–AC–DC Converter for Soft Normally Open Point
Dajun Ma, Wu Chen, Liangcai Shu, Xiaohui Qu, Shilong Gao, Kai Hou
Abstract
The soft normally open point (SNOP) is a critical apparatus in AC distribution grid to increase the distributed generation (DG) penetration. The existing converters for SNOP are limited by either the utilization of abundant switching devices and passive components or the voltage coupling between two AC systems. Therefore, a multiport AC–AC–DC converter for SNOP is proposed in this brief, where two cascaded H-bridge (CHB) converters with a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonant circuit in parallel connection with each phase-leg are adopted in back-to-back (BTB) structure. The two three-phase CHB converters are connected by three medium-frequency transformers (MFTs). Moreover, the mixed-frequency modulation method and voltage decoupling principle are introduced. Therefore, less switching devices and passive components are used for the multiport AC–AC–DC converter. In addition, the voltages between two AC systems are completely decoupled, and the electrical isolation is ensured. The operating principle, control strategy and parameter design of multiport AC–AC–DC converter are introduced in detail in this brief. Finally, the experimental results are provided to verify the feasibility of proposed multiport AC–AC–DC converter.