Power electronic transformer (PET) is being widely used in place of line frequency transformer (LFT) in modern power systems. Modular structure, such as cascaded H-bridge (CHB), is preferred solution for PET in high-power and high-voltage applications. For such topologies, the low-frequency ripple powers stored in dc-link capacitors pose passive effects on power density. To overcome this, a power channel based power electronic transformer (PC-PET) is proposed in this paper for three-phase AC/DC conversion. Based on cascaded architecture, the ripple powers introduced by each AC input are counteracted without flowing into dc link. Therefore, the dc capacitance can be reduced so as to achieve higher power density and lower cost. Modeling and control scheme including power decoupling of the PC-PET are introduced. Simulation results prove the validity of proposed topology and control system. It is expected to be applied in the inter-connection of three-phase AC and DC grid such as power supply of urban rail transportation.