This chapter is dedicated to DC Microgrid's application to provide ancillary services to weak AC grids. In particular, control algorithms are designed to provide inertial, frequency and voltage support for weak grids, such as AC Microgrids composed mainly by sources interfaced by power converters, with a small portion of diesel generators. A number of synthetic inertia approaches are introduced to improve the stability properties of an AC grid face to strong variations on loads and productions, brought by electric vehicles and possibly other renewable energy sources. The power electronic issues related to control interactions and poor inertial response are described, where suitable solution is addressed. The power converter is driven as a Virtual Synchronous Machine (VSM), where the control strategy follows classical swing equation, such that the converter emulates a synchronous generator, including inertial support. This strategy can be exploited in low inertia systems with high penetration of renewables. An application example illustrates the performance of the Microgrid in the context of virtual inertia control.