The invention relates to a power electronic transformer system, a transformer and a fault ride-through control method thereof, belonging to the technical field of bidirectional isolated DC voltage conversion. The power electronic transformer includes at least one module group. Each module group includes a high-voltage half-bridge module and a bidirectional DC conversion unit. Each high-voltage half-bridge module includes a high-voltage upper arm branch and a high-voltage lower arm branch. The power electronic transformer also includes a self-blocking module which is connected in parallel withthe low-voltage side of each module group. The self-blocking module includes low-voltage half-bridge modules. Each low-voltage half-bridge module includes a low-voltage upper arm branch and a low-voltage lower arm branch. The low-voltage lower arm branches are used to connect a DC power grid at the low-voltage side. The main branch formed by connecting the low-voltage upper arm branches and the low-voltage lower arm branches is connected in parallel with the low-voltage side of each module group. Through cooperative control of the half-bridge modules arranged at the high-voltage sides of the module groups and the half-bridge modules in the self-blocking module, the power electronic transformer of the invention has the fault ride-through ability, and the operation reliability and stabilityof the power grid are improved.