A Research of Grounding Mode and Protection Configuration for DC Microgrids

With the rapid development of distributed energy, DC load, variable frequency load and voltage sensitive load, DC microgrid will be widely used in the future power grid. The DC microgrid have various wiring modes, such as unipolar wiring, symmetrical unipolar wiring, and symmetrical bipolar wiring, etc. So, there are many grounding methods for DC microgrid, and no unified specification has been formed at present. The fault current characteristics are quite different under various grounding methods, and the protection configuration and setting are quite different. This paper compares the pole-to-ground voltage characteristics of DC microgrid under various typical grounding modes, and presents a recommended grounding scheme of DC microgrid. Then a simple and practical protection configuration scheme is proposed, which meets the economic requirements of DC microgrid. Simulation results show that the scheme has good selectivity for various fault situations. The research results will provide an important theoretical basis for promoting the formation of a unified design specification for DC microgrids.