In this study, a four-port solid-state transformer (SST) with decoupled control scheme to control the power flow and the output voltage is proposed. The proposed decoupled control scheme controls all of the four ports' powers independently. In addition, the design of the four-port transformer including core material selection and winding placement is investigated. The designed transformer is modeled in ANSYS-Maxwell and also co-simulated with ANSYS-Simplorer. The operating frequency of the system is designed for 100 kHz; therefore, a very compact size is obtained for the entire multi-port converter. The performance of the proposed system is validated throughout MATLAB/Simulink simulation and experimental studies carried out for a 10kW/port SST prototype. The obtained results show that the four-port SST provides an interface for four-different power supplies or loads. It is seen that the proposed decoupled control scheme can control the output voltage at the desired value and track the reference power signals for each port. It provides as well a good steady state and dynamic performance.