Research On Modular Bi-directional DC/DC Converter In DC Microgrid

Environmental protection has been paid more attention by governments around the world. Distributed generation based on renewable energy has attracted considerable attention and is being expanded, which is clean, flexible and reliable. The stability of large-scale power grid caused concern widely, so the concept of microgrid is rising gradually and being studied. AC microgrid including distributed power is the important part of the smart grid. With the development of power electronics and the wide use of the power electronic load, DC microgrid has more advantages of simplicity of control, few power conversion stages, high efficiency over AC microgrid. In DC microgrid, DC/DC converter is one of the important devices connecting DC microgrid and the distributed power, the function of which is to meantain the DC bus voltage. So the DC/DC converter used for energy transfer and energy flow control has broad application prospects.This paper analyzes the basic principle of non-isolated bi-directional DC/DC converter, and compares the voltage stress and current stress of switch elements between different structures. Then the influence of the multiple converters on current ripple, current harmonic, and voltage ripple is analyzed deeply, and the circuit parameters are designed. For a single bi-directional DC/DC converter, the average current mode control strategy is adopted, and a digital sampling method of the average current is put forward. The PSCAD simulation software is used to prove the validity of the control strategy in the active mode and passive mode. For more paralleled bi-directional DC/DC converters, considering the diversity of battery in low voltage side and the automatic switch of bus voltage control, a new method of DC bus voltage margin control is proposed. The proposed method solved the problem of the automatic switch of bus voltage control between the paralleled bi-directional DC/DC converters and the AC/DC converter. Finally, simulations are made in PSCAD/EMTDC software to verify the effectiveness of the proposed control method.