In this paper the control system of Power Electronic Transformer (PET) for the Smart Grid application is proposed.The structure of PET is based on two Cascaded H-bridge (CHB) converters. The electrical energy is transferred between converters using Dual-Active-Bridges (DAB) and high-frequency transformers. This type of coupling has been used to connect the DC-links of all H-bridges. The proposed control system for PET makes it possible for DC-link voltage stabilization and allows to reduce the total harmonic distortion (THD) of converter currents and voltages. The simulation and experimental researches of 600 kVA / 3.3kV PET are presented in the paper.