The Magnetic Branch Snubber Channel and Magnetic Model Analysis for SM Capacitor Reduction of SST

For a cascaded H-bridge-based solid-state transformer where the isolation stage is a quad active bridge (QAB), this article proposes a magnetic branch snubber channel scheme with zero harmonic impedance/flux. This innovative scheme offers a low-impedance pathway specifically for second-order frequency ripple-current (SFRC), serving as an alternative to traditional large capacitor branch snubber channels. Through this approach, the SFRC is efficiently transmitted to the primary side of the QAB high-frequency transformer and subsequently filtered. A thorough analysis of the magnetic model reveals the fundamental principle of eliminating ripple current through equivalent filtering utilizing magnetic coupling, and the corresponding equivalent filtering transfer function is presented. The implementation of the magnetic branch snubber channel and the robustness of the solid-state transformer are examined through electromagnetic coupling analysis. Notably, the proposed solution enhances the system's tolerance to transformer parasitic parameters and enables fault ride-through capability under conditions of three-phase voltage unbalance. An application-oriented evaluation of the proposed solution was conducted, and the results demonstrated significant reductions in system size and weight, without hardware constraints and leveraging high-frequency and high-efficiency operation potential. This makes the solution advantageous in compact, enclosed carriers’ systems, such as ship power systems and medium-to-large hybrid electric aircraft applications.