Battery-Less Grid-Forming Power Converter as a Smart Load for Microgrid Operating Mode Transition

Both the transition from grid-tied mode (GTM) to islanded mode (ISM), denoted as GTM-ISM transition, and the transition from ISM to GTM, denoted as ISM-GTM transition, are one of the main topics in AC electrical microgrid (MG) research. Within the MG, the grid-forming power converter (GFRC) is responsible to carry out both the GTM-ISM and ISMGTM transitions. Usually, the GFRC includes a power supply source at the DC bus; in most cases, this DC source is a battery pack. In abnormal mains conditions, the MG must operate in ISM, then, the GFRC uses the battery power to generate the voltage at the point of common coupling (PCC) during the GTM-ISM transition; in the same way, the GFRC uses the power from the battery pack to sustain the PCC voltage during ISM and for synchronizing it when the nominal conditions of the mains are recovered. The transition of MG operating modes with a battery-less GFRC in the literature has not been reported. Thus, this paper presents a control scheme proposal to perform both GTM-ISM and ISM-GTM transitions with a battery-less GFRC. The results showed the capacity of the battery-less GFRC to operate as smart load during both GTM-ISM and ISM-GTM transitions. This battery-less GFRC proposal highlights a contribution within the research of GFRC units, since the GFRC operation has always been reported using a power supply source at the DC bus, mainly battery packs, but not using a battery-less GFRC working as a smart load for the generation of the PCC voltage.