A Novel Power Integrated Modular Multilevel Solid-state Transformer With Reduced Passive Filters

Solid-state transformer (SST) is a vital device in the electrical energy internet, but the factors such as multiple power conversion stages, huge volume, and low efficiency restricts SST from further application. To this end, this paper proposes a novel power integrated modular multilevel solid-state transformer (PI-MMSST) topology for improving its power density and thus promoting its practical application in the future power grid. The PI-MMSST is designed with four sub-arms per phase-leg, where the middle points of upper and lower arms are linked out as the medium-frequency voltage terminal that transmits high frequency power to the secondary side via a DC blocking capacitor and a medium-frequency transformer. With this arrangement, the passive filters required in such topology is reduced to only a blocking capacitor which further improves the system power density. The operation principle and the associated four-layer voltage balancing control strategy are presented, followed by simulation validations through an established PI-MMSST model with 10 submodules per sub-arm.