Battery-less grid-forming type converter in an isolated AC microgrid

Abstract

Abstract Typically, in electrical microgrids (MG), the grid-forming type converter (GFRTC) includes a battery pack at its DC bus; thus, the GFRTC is modelled as a voltage source. In contrast with papers reported in recent literature, where the GFRTC with a battery pack is seen as a voltage source, this work proposes a GFRTC which can be used without a battery pack; with this, the GFRTC operates as a smart load to form the voltage at the point of common coupling (PCC); this is possible, as long as the smart load is supported by a grid-following type converter (GFLTC). This battery-less GFRTC proposal ensures a suitable operation of the isolated MG under linear and nonlinear load conditions. Also, this work proposes a control strategy for both GFRTC and GFLTC with a photovoltaic array. The test results showed that the control proposal allows to form a correct PCC voltage, ensuring a suitable operation of the isolated MG; this while the battery pack is: connected, disconnected, and reconnected to the GFRTC DC bus. This GFRTC proposal is very attractive for isolated MGs where the GFRTC battery pack must be replaced or reconfigured because of new demand profiles, without interrupting the isolated MG operation.