A Lightweight Cascaded Mutilevel Solid State Transformer Scheme Based on Ripple-Power Decoupling Channel

Cascaded H-bridge (CHB) has been the typical scheme in medium and low voltage AC/DC conversion applications, and large-size capacitance of submodules (SMs) is the inherent problem of CHB-based systems, which is caused by ripple-power on SMs during AC/DC conversion. This paper proposes a novel lightweight cascaded multilevel solid state transformer (CM-SST) based on series resonant push-pull (SRPP) decoupling channel for ripple-power. CM-SST can utilize the low impedance characteristic of SRPP and the three-phase symmetry of SMs ripple-power to realize the natural decoupling, which significantly reduces the size of SM capacitance. The CM-SST configuration, SRPP operation principle, CHB ripple characteristic, ripple-power decoupling process, system design and evaluation are discussed in detailed in this paper. Finally, the correctness and effectiveness of the proposed CM-SST are verified by simulation and experiment.