Schemes of simultaneous AC-DC distribution network used for grid-connection of distributed generation

Simultaneous AC-DC distribution network was proposed to achieve the connection of distributed generation into distribution power system, but one of the major problems of this system is core saturation of transformer caused by injected DC current generated by distributed generation which is usually random and fluctuant. This paper proposes two methods aimed to alleviate the effect of DC bias magnetic. The rationales and designs of the topology are described in this paper. The first method is based on the traditional inductive filtering, the proposed intelligent inductive filtering add the monitoring of various orders of harmonics in distribution power grid, and the filters in the inductive filtering device can be intelligently switched on/off based on the information provided by monitor. Simulation results reported in this paper demonstrate that this method can solve core saturation of transformer in the AC and DC distribution network and at the same time can reduce the effect of redundant induction filters on the operation of power system. The other way is that zig-zag transformer replaces the conventional transformer in power distribution network to draw DC power into the grid. DC power provided by the distributed generation connects to the distribution line along DC-DC converters and is injected into distribution line through neutral line of zig-zag transformer, zig-zag transformer is characteristic of inhibition for core saturation of transformer. Then construct AC and DC power distribution network topology based on this scheme. Modeling and computer simulation based on this method has verified feasibility and effectiveness of this topology.