The Study of Power Electronic Transformer on Power Flow Control and Voltage Regulation in DC Micro-grid

The AC and DC distribution grids between different voltage levels coexist in smart grids, and a reliable connector was needed between them. Power Electronic Transformer (PET) was suitable for being used as public interface to control power flowing between different electricity networks and regulated DC bus voltage, because of its abundant functions and electrical interfaces. In order to take advantage of PET served as a power balance junction, an improved droop control method for DC micro-grid was proposed. Power can flow bi-directionally between DC micro-grid and AC grids by using this method. Then the power distribution was achieved in DC micro-grid and the stability of the DC bus voltage was enhanced. The simulation studies were carried out in three cases: system load mutation, power fluctuation of distributed generation and voltage sag in high voltage distribution network. The simulation results showed that the DC micro-grid was still on stable operation in the cases above, and proved the good performance of the improved droop control method.