Solid-state transformer (SST) for onboard traction application is also addressed as power electronic traction transformer (PETT), which is used to replace the line frequency traction transformer (LFTT) and four-quadrant converter (4QC) to further improve efficiency, save installation space, and reduce weight of the onboard equipment. However, based on the conventional PETT configuration with the modular series-parallel structure, it is hard to guarantee the high efficiency and high power density at the same time due to the limitations caused by the switching characteristics of the semiconductor devices, transformer design, and high-voltage insulation design, etc. To deal with the mentioned problem, a PETT configuration and the parameters’ design method for onboard traction application are proposed in this paper to replace the conventional dc/dc stage with the low-voltage IGBTs. By using the proposed configuration, the high-voltage IGBTs can be replaced by the low-voltage IGBTs, which can help reduce switching loss. Meanwhile, zero-current switching (ZCS) or zero-voltage switching (ZVS) for all the IGBTs can be guaranteed, and the number of the medium-frequency transformers (MFTs) will not increase. Therefore, a multiple optimization of PETT, including switching losses, the number of MFTs and switches, and costs, can be finally achieved. Finally, an experimental prototype is built to verify the performance of the proposed PETT configuration. A Power Electronic Traction Transformer Configuration with Low-Voltage IGBTs for Onboard Traction Application